Sunday, November 6, 2016

Fix Ground Loops Quickly, Safely and Easily

What is a Ground Loop?

It is video noise or audible hum that plays through your speakers that occurs when multiple ground points with slightly different potentials are connected together through your equipment. More on this is available from Jensen Transformer's web site. It's called a loop because it's actually that, a closed circuit.  All we have to do is either connect everything to the same ground, or break the loop in the safest and most convenient location.

A clue to a ground loop is that the hum stays constant whether you play music or video or not. Sometimes equipment such as a TV doesn't even have to be on to help cause in the loop.

Note that this is not mechanical hum. If you hear the chassis or transformers vibrating and making more of a buzzing sound your problem is more likely DC on the line. I'll cover that in another post, but this is often caused by PCs, light dimmers, and modern compact florescent bulbs.

Ground Loops and Digital Signals

The usual "scientific" belief is that digital signals are immune or at least very resistant to noise. While it is true that digital circuits are resistant to many types of noise these circuits, including digital video, can participate in a ground loop which can cause enough jitter to be audible or visible. This includes HDMI, coaxial and USB circuits. Optical digital connections however are completely immune to all external noise, including ground loops.

Ground loops will not occur in Ethernet cabling unless there was a fault in the switches / routers. In other words, almost never since preventing ground loops was part of the design of the entire Ethernet eco-system.

Diagnosing the Cause

There are a few common culprits:
  • Cable TV or Satellite Dishes
  • External antennas like FM or television
  • Audio or video cables from a Personal Computer
  • Laptops! (Problem goes away when you disconnect USB or charger) See USB fixes, below.
The best way to find the root cause is to disconnect each suspect and listen for the problem to go away. Sometimes the problem is related to two devices interacting, which gives you a choice of where to break the loop. This process also works for finding noise sources in general. Turning lights off and disconnecting wall-wart supplies may solve other symptoms.

Lethal Fixes and Myths

One type of fix can be lethal to you and your neighbors. That's a "cheater plug like this one. Any attempt to defeat the ground pins in equipment that has them may be lethal. Do not do it. Do not rely on signal grounds to work the same way. They don't.

Pangea originally sold "high end" IEC cables with removable ground pins. Don't buy them, don't let your friends buy them. They appear to be discontinued, probably due to safety concerns. There is now a 2 conductor C7 version with a removable pin, but that's perfectly safe, and the feature is kind of useless.

I recently heard this argument:
I've been removing ground pins for years and never had a problem.
The problem is these pins are like safety belts. So imagine me telling you this:
I've not had a car accident in 20 years, so I no longer wear a seat belt.
That should sound dangerous to anyone who drives a car. That's how we electrically minded people think when we hear of audiophiles removing ground pins for that last bit of audio nirvana. There are better and safer ways. Another myth, spread by audiophiles who do not understand the safety ground or the life safety issues involved in UL certification and the National Electric Code:
Your system will be grounded by your RCA cables. No problem!
If no problem means dead and on fire, they're right. 

Free Fixes

If your problem is caused by a piece of audio/video gear, try connecting it all to the same power strip or conditioner. This ensures all the ground wires are at the same potential.

Another free fix may be to use XLR cables. XLR cables are not usually quieter in homes than balanced, BUT! there is a difference. XLR cables don't mix the ground and signal together. You avoid this contamination and XLR inputs often have a safe "Ground Lift" switch. It prevents the grounds loop from occurring at all.

Not A Ground Loop

Some issues have nothing to do with ground loops but are caused by induced noise from other sources. This noise can come through the power lines OR be induced by proximity to interconnects and electronics. Things to try turning off, disconnecting, or removing from the environment:
  • Compact Flourescent bulbs - VERY noisy! 
  • Wall warts - These tricky bastards stay on, and polluting even if the device they are feeding is off.
  • Wall dimmer switches
  • PC and laptop power supplies (yes, again!). Disconnect your PC or laptop cables to your stereo, TV, etc. If the problem comes and goes with the PC/laptop being plugged in, then you have a noise problem and will need to relocate it.
  • WiFi devices, including routers, streamers, receivers, modems, etc. If your Wifi device is part of your stereo, try moving the antenna or putting it on a different power strip/conditioner. 

Noiseless Cables

Sometimes the problem is noise our cables pick up. Especially problematic in apartments with a heavy concentration of WiFI signals or near transmission or cellular towers. Some electronics will help pick this up more than others.

Make sure your interconnects are 100% shielded. Most cheap and a lot of expensive RCA cables use a braided ground, which is more of a pick-up antenna than anything else. Regardless of whether you use RCA or XLR cables, the best use 2 conductors plus a foil shield. In essence they are built of conductors:
  • Positive conductor
  • Negative conductor
  • A super thin and delicate foil shield
  • The drain wire which is used to attach the foil to a ground conductor on the RCA or XLR jack
On RCA cables the drain wire should be attached to the negative conductor at the source. The destination end does not use it but instead uses the positive and negative wires. With an XLR cable all 3 wires are attached at both ends, unless the destination does not have a ground lift pin in which case the ground may go unattached at the destination.

My favorite brands for non-esoteric cables:

  • DH Labs
  • Connex
  • Mogami
  • Belden
I personally use Connex solid silver cables for everything, but they are delicate. Get the more expensive DH Labs varieties if you need rugged.

Cable TV & Antenna Problems

This problem can also cause Internet access issues. I use a dedicated Cable TV isolator like this one. You put it immediately inside the RF plug, unless you have a satellite dish.  More on that, below.

Satellite Dishes

Make sure the satellite dish cable is grounded before entering your home. Even though it is required by code, installers often fail to do this, and ends up in having your receiver or antenna getting fried by heavy wind causing static as it blows across the dish.

Unlike Cable TV and overhead local antennas, satellite dishes require DC power to operate the RF amps built into the little head. For this reason isolating them is a little trickier. Normal isolators block DC in all forms.

The trick is to buy a separate DC power supply for your antenna. Place the ground loop eliminator closest to your receiver, and your antenna power supply closer to the antenna.


Your best / cheapest way to eliminate issues from your television over HDMI are to fix any connections going to it such as cable tv, satellite, a PC, etc.


Early in the history of external DACs ground loops could occur through coaxial cables. Most good DAC's today provide what is called "galvanic isolation" meaning that there is no DC or ground loop path between the input plugs and the rest of the circuits in a DAC. This can be done by purpose built transformers or modern monolythic IC's. Unfortunately no magazine or agency I know of tests for this so there is no way to 100% guarantee a DAC's isolation. Of course, the way to test this is to disconnect your USB input and see if your hum goes away. There are also cases where you have very little ground loop noise. To fix either use a USB isolator like this inexpensive model designed for medical professionals, but works just as well with USB 2.0 DACs.

Another fix is to use a purely optical cable between your source and DAC such as the Audioquest Forest or Monoprice both of which come in a variety of lengths.  Check the size of the plugs, some may interfere with other sockets on your equipment. Optical cables are also a very good choice for going from PC to a DAC or receiver if the PC supports it since PC's are such noisy environments.

Of course, since the entire point is to avoid a current path, gold plated optical cables are kind of silly.

Audio Signal Isolators

Audiophiles hate putting anything in the signal path, and some fussy recording engineers may also, but pro's also know that it's far better to put in a transformer than delaying a show, so here are a couple of isolation products from Ebtech that are reasonably inexpensive.

I'm currently working on Cable Mittens, a new concept to warm up the sound of an amplifier while breaking ground loops and reducing noise.  Until then, the choices below are the best available!

The Hum Eliminator takes 1/4" jacks, but adapters are easily found. For a little more you can get the XLR version shown here.

The EbTech models, especially at their prices, are very good, but audiophiles who only want the very best turn to Jensen Transformers for the gold standard in high quality audio isolation. If that's what you need, I present the RCA Jensen Iso-Max for your approval. It's usually the best solution for PC audio problems.

The XLR Iso-Max, below, is also available for around $250.

Last Ditch Efforts

If your problem is your electronics and the single power strip idea doesn't work, the only remaining almost safe way to prevent the problem I know of is the Ebtech Hum X. The Hum X is only rated for 6A which limits it to line  level electronics. You cannot use it on power amps, which is not really a problem because we can prevent the ground loop at either end. You will find it just as effective by putting this on a preamp, TV or source as on the amps. It should also be effective on PCs, but I'm not sure if it could cause other problems.

I say it's "almost safe" because it has not yet been UL approved. The 6A rating is probably why, as there's no way to guarantee users will only plug-in 6A devices.

Iffy Solutions

If you are an audiophile you might have gotten to the end of this article wondering why the real "power conditioners" weren't mentioned. The truth is that the solutions provided above are the most effective in solving ground-loops than almost any high-end power conditioner.   Balanced power conditioners, which are often touted as the best solution for this, may or may not fix actually fix a ground loop problem.  Bill Whitlock and Jamie Fox of Jensen wrote a great paper for the Audio Engineering Society on the matter. Balanced conditioners ARE completely effective at removing DC from an AC line however, and very effective at reducing other types of incoming AC line noise.

Other types of power conditioners will have no effect at all on ground loops but may reduce other types of noise or provide surge protection and, as mentioned, connecting all your electronics to a single strip or conditioner may also eliminate the problem but don't go spending big bucks on them trying to fix ground loop issues, or ignore the solutions above because they don't seem high-tech or expensive enough.

Saturday, July 16, 2016

Wyred4Sound Remedy - First Listening Impressions

I have hooked up the Remedy between my Logitech Squeezebox and my Audio Research DAC 8.  The only true jitter measurements I could find were for it's slightly newer cousin, the DSPre.  It seems that the DSPre is wildly sensitive to jitter, at least the measurements are, so I'm just going to assume the DAC 8 is the same or worse.

Most of my listening these days is to Internet radio, including Toronto Jazz FM 91, which in addition to having great programming also streams at 24/96.   The other station was KDFC 90.1, Bay Area Classical.

In the middle of this my power regulator has started to hum, so I can't do the remedy justice until I move it to a quieter location.

Still, here's what I think so far.

The remedy works much more noticeably with low-resolution stations, but it IS better. The sense of space inside the sound stage and the treble decay. Sometimes it feels worse though. During mass string crescendos the sound gets too complicated.  With Jazz 91 the improvements seem much less pronounced, but still there.

However this is really hard to gauge with radio.  I'll give this a better listen soon, when my biggest noise sources have been fixed.

Update August 28, 2016
So I had thought my impressions might greatly change, but they did not. I think this is a good tool but only for more source sensitive DAC's like I had (just sold it), the ARC DAC 8. That DAC played brilliantly when driven by an Ayre CD player, but when I brought it home it was much fussier.

With high resolution music (96k and above) I could honestly not tell if it was working or not, which I guess is a good thing. So, overall I would recommend this to clean up the sound of a mid-Fi CD player or Internet radio or inexpensive streamer like my Squeezebox Touch. 

I have however switched over to a Mytek Brooklyn DAC which sounds as good as the Wyred4Sound + ARC DAC 8 without the remedy in place, regardless of how it was driven.

I'm now driving the Brooklyn with a 2TB Linux streamer I built myself ($650) and it's very happy to play PCM, MQA and DSD from it.

Monday, July 11, 2016

Digital Audio - Upsampling and Oversampling Explained

Many types of digital sources, accessories and Digital to Analog Converters (DACs) provide some sort of sample data magic called oversampling or upsampling.  Put simply it means you end up with more digital data than you started with.

There are some benefits, but none of these methods truly gets you closer to the original music. They are all just ways of trying to make the experience more pleasant. Think of it as looking out your window with a screen. You may take a picture and find that you can see the screen itself in the image, or you can do some editing with Gimp or PhotoShop and remove it. The new image can't possibly contain more true to life data than you started with, but the picture should be much more pleasant to look at.

Many audiophiles have been led to believe that this kind of digital math can do things like you might see on the TV shows CSI or NCIS. Somehow four pixels on a grainy satellite image can be processed over and over again until the criminal's face is clearly visible. It's just not true.

Looking at it another way, the frequency response of up and oversampling does not change. A 44.1 kHz file is not going to have 30kHz created after 4x upsampling.  The frequency range and content density is unchanged. What may happen is that digital filtering becomes smoother and easier on the ears, or that jitter is improved somewhat by the use of higher data rates.

Differences Explained

Let's take original data.  Since digital music is always integer, I'll imagine two consecutive samples with convenient values of 24 and 28. Now lets see what happens at 4x up or oversampling. If the original data was 44kHz/16 bits the DAC will now see a sample rate of 176.4 kHz but the bit depth may or may not. So, just to be thorough, here is our original data:

  • 24
  • 28

at a sample rate of 44.1 kHz these two samples represent:

  • 2 samples / 44,100  = 45 microseconds of music. 
 Remember that we are adding samples in between the time slots, so we don't want to stretch out our time, that would result in pitch changes. Instead we increase the rate (samples / second) at which we feed the DAC, keeping the pitch constant.
So, instead of 2 samples, we have 8, but with a new sample rate.  Lets redo the math:

  • 8 samples / 176.4kHz = 45 microseconds of music.
Thhat's great, because if that didn't work the sound would be 4 times slower. :)


This is the oldest trick in the book. Almost immediately after CD players became commercially available oversampling became a buzz-word. I am no longer sure, but this may have only worked with so-called Delta-Sigma or 1-bit DAC's.

It's so simple you don't think it should work. Take a sample, and repeat it several times. It's that simple. It does not attempt to provide any more data but may shift some noise far above the Nyquist frequency.  No math is involved, just counting.  With 4x oversampling the DAC our orignal two samples become:

  • 24
  • 24
  • 24
  • 24
  • 28
  • 28
  • 28
  • 28
It's weird it helps, but it does. In fact, with oversampling, only 1 sample really matters at a time.


Bit Perfection

One of the objections to upsampling, is that the signal is no longer bit-perfect.  The DAC no longer gets the original facts, but the original facts, plus a lot more. That "lots more" is pure mathematical conjecture. However, there are some real benefits to be had.

Things get even more muddled when upsampling is used for ASRC, Asynchronous Sample Rate Conversion, but also more beneficial, as it's one of the best ways to reduce jitter.  More on that in a future post.

Technically and mathematically more challenging, there are two general approaches. To take the best advantage of this it's better if the bit depth increases beyond the original. So if the original was 16 bits, 24 or 32 bits will provide better resolution.  However remember that this doesn't really make it more true to life. It just makes some things easier to do and helps us keep more of our results. There are some VERY nice 32 bit DAC chips out there though, so taking full advantage of them may also get us much closer to true 24 bit resolution. That's a topic for someone else.

Linear Interpolation

Imagine two points on a chart. Draw a straight line between them. That's simple interpolation. It's no more complicated than simple algebra. Calculate the rise, divide it by the number of intervening samples, and add that much for each "new" sample. For linear interpolation, the sample rate converter needs to know two samples at a time in order to figure out the rate at which the intermediate samples should change.

Again, consider our original two samples, 24 and 28. The rate of change is 4/sample.  4/4 = 1. Now the DAC gets:

  • 24 +1 =
  • 25 +1 =
  • 26 +1 =
  • 27 +1 =
  • 28
We'll just assume there's no bit-depth changes, or that in this case no extra resolution was required. Of course, I chose 24 and 28 to make the math here easy.


A much more advanced way to create more samples is by using what are called splines. Remember the "French Curve" tools you may have used in drawing school?

Technically you only need 2 samples for a spline, but the result is the same as linear interpolation, so we'll ignore that case. With spline math we take a number of samples, usually under 20,  to draw a much softer curve. Wadia was the first company I know of who introduced this concept. In this case it really helps to have more bits, as the extra bits help with more fine grained results. As you might imagine, the math and CPU power required is greatest for this example.

If this was floating point math our working data set would be:

  • (nine samples before)
  • 24.000
  • 25.185
  • 26.355
  • 27.888
  • 28.000
  • (nine  samples after)
Remember that what's really going on is that the algorithm is taking more samples into account than our original two in order to fit the curve properly.  So why the third sample is 27.888 instead of 27.978 or 26.500 has to do with the nine samples in the original file before the first (24) and after the last (28) shown here. It is believed, without a lot of proof, that this method may provide the most natural resulting sound.

Are Splines Really Better?

Splines are very cool, but it may be argued, convincingly, that we are not doing much more than you could achieve with a capacitor and resistor with the proper time constants. In other words, it's a lot of math and hardware for what could be done with $2 or less in parts. The real potential benefit of this advanced though is in custom algorithms. You can be as creative as you want to in your algorithms.

What About Sound Quality? 

Personally I have come to believe that the analog output stages matter much more than interpolating algorithms and sample rates or bit depth but the devil is in the implementation details. As always, buy what you like, and what is most pleasant to your ears. Don't buy algorithms or chips. Buy results, and spend no money that isn't pleasing to you.

Wyred4Sound Remedy - Snake Oil or a True Panacea?

I've just ordered a Wyred4Sound Remedy.  I had been drinking and needed a pick-me-up and based on Digital Audio Review's positive impressions I ordered it.

What I have just realized however is that the Remedy is not the product I thought it was in a couple of ways.

Mind you, it's clear that for some kinds of low-grade digital audio sources the Remedy is probably a very good solution. I'm thinking of Sonos, Apple TV and Chromecast specifically. However, it is a terribly over-hyped product which smells of snake oil.

What Kind of Product is the Remedy? 

Of course, marketing people, being devoid of souls at birth, are free to call a tomato a vacuum cleaner and there's rarely any legal consequences. In my world however the Remedy should properly be called a sample rate converter (SRC) or Asynchronous Sample Rate Converter, a feature built into many of the top DAC chips today.  SRCs always includes re-clocking, so calling it an SRC with reclocker is redundant.

Using an ASRC is a very good way (and a little lazy by itself) to ensure minimal jitter with possibly very jittery sources, such as Internet radio.  The reason I'm kind of on the fence about this is that an ASRC is no longer bit perfect, but time-perfect. To ensure that every x picoseconds a new sample is processed, regardless of how the input signal may vary in the short and long term an ASRC resorts to a mathematical brute-force method, the details of which are beyond the scope of this posting.  Suffice it to say you can kiss bit-perfection goodbye, and not just for the interpolated samples either.

One major annoyance, that relegates the Remedy to mid-fi sources is that the input signal is ALWAYS recreated. What's worse is that if you have music with a higher sample rate, such as  24/192kHz, the Remedy will actually DOWN-sample it to 24/96kHz. This, plus having no input switching makes his solution seem kind of dopey.

For about three times more a more robust option is the Mytek Stereo 192 SRC. It gives you much better control over what you want to do with the signal, up, down or no change with equivalent or better jitter reduction, as well as being able to convert up to 24/192kHz

Of course, this is all spec-manship. Listening is the true arbiter of what you should buy.

Is it really a femto-clock?

Having examined one, it seems W4S has used one of the best commonly available Crystek oscillators, the CCHD-957 series, which does in fact have very good phase noise characteristics, among those affordable to mere mortals.  I'm still confused though. Based on W4S's own measurements this does not appear to be a femto-clock grade solution but a pico clock. What's the difference? About 1,000 times worse performance. It is possible that the internal clock device inside the case is a femto-clock class part, but that the other circuitry used can't take full advantage of it, or that it can only do so much in one pass. It would be very interesting to see measured comparisons using a standard Mac Mini or Apple TV to see how it measures to Mytek, M2Tech or Auralic with and without.

Consider this. The Auralic Vega with a true femto clock (and 10x more expensive) has jitter around 80 femto seconds. The image on W4S's own Remedy page shows jitter around 87 pico seconds. That's about 1,000 times worse performance. Of course, many would argue that you can't hear 80 pico seconds of jitter, but the point is the marketing hype. I don't like being lied to or misled.

Another similar device with a price point kind of in between is the M2Tech HiFace Evo 2. It is intended as a USB to SPDIF interface, but it will also take a coaxial SPDIF as an iput and allow you to select sample rate conversion.  Price is around $700 USD.

Why does this matter? 

My point to all of this is that the Remedy is doing more than just jitter reduction, and I would really have liked to know this before I ordered. Hiding major behavior is not a sign of a trustworthy vendor. Remedy is playing with the bits and I should have known that first. For more on why this is different, see my post on Upsampling and Oversampling.

It's a little odd as many DAC's make upsampling a key feature. They charge more for it and often tout their proprietary algorithms as being better one way or another.

In the end though I'll have to listen to it to evaluate the Remedy as having any sort of meaningful benefit. More on that in the next several weeks. One of my sources however will be Toronto Jazz 91 which streams at 24/96kHz already, this will let me do direct comparison to see if the jitter reduction is worthwhile, in addition to a small selection of 24/96kHz FLAC recordings I have.

Many listeners are easily swayed by "different." Even John Coltrane suffered this, always thinking his next performance was better. If jitter or SRC at these levels is audible it's quite possible many will be swayed by a different sound, but not necessarily a better sound.  I can imagine many will get worse jitter than they started with, and then proclaim how audible and beneficent the differences are!

Friday, July 8, 2016

So your CPAP treatment isn't working?

I've gone through seven or eight sleep studies. I've lost count of exactly how many, but the last three at the same sleep lab, without my symptoms being fully improved. I would estimate that at the beginning they were about 20-30% better, but years later seemed to fail completely.

What I eventually discovered is that exercise actually made my sleep quality much worse. If this sounds like  you, it might, then it is possible we share an odd, and previously unreported condition. The only other two conditions which I've read that can cause this is Cushing's Syndrome and Chronic Fatigue.  However, sleep apnea that is not fully treated can mimic both of these, including elevated cortisol levels. So if you have noticed, or are able to determine if exercise is bad for you, then we may share a condition, which is treatable!

The problem in my case only was that I have two modes of sleeping. The lazy day, fully rested mode, and the "I've worked out" mode.

Why didn't the previous sleep studies help?

The previous sleep studies did find a partial solution.

I didn't notice the problem at the time, but looking back it seems that since I slept poorly after exercising I learned not to exercise, even a little. I stopped taking the stairs and always chose an elvator, had groceries and food delivered, anything I could do to avoid physical labor. That is, my symptoms conditioned me not to exercise, so I would go get a study done after a couple of days of being fully rested, and as a result my full symptoms did not occur. I only know this after-the-fact because of the use of a Jawbone UP (lasted 3 months, but did the job) which allowed me to discover exactly when I had good and bad days of sleep.

After using the Jawbone for several months looking for clues to my problem I was able to completely correlate exercise with poor sleep the next several nights. This is the exact opposite of what should happen for most people but for me was the wall I could not overcome.


Moderate exercise (5,000 steps / day) would not cause this problem to occur immediately.  It would sneak up on me.  I needed it to be vigorous, or weight bearing to cause the symptoms to show up faster.

Another thing that seems to trigger this effect is calcium channel blocking medications, or medications which are related. These can be prescribed for a range of issues from depression to high blood pressure.  The good news is that if this is you then your sleep studies should show up without having to go through the exercise portion of this experiment. 

Further, the post-exercise crashes would last for days, sometimes even a week.

How can I tell if this fits me?

If you have a Jawbone, FitBit or ResMed S+ you may see your deep sleep very disturbed, or lots of wakings, despite the CPAP measuring otherwise low AHI numbers and tolerable leaks.

In the picture on the left I share an image from the Jawbone UP application showing my very worst night of sleep.  See how many different periods I have of deep and light sleep?  There should be about 8 of them.  Instead I have about 17.  Also notice the time I slept. Over 11 hours! That's because the sleep quality was so poor.

You should have big chunks, around 6-9 of deep sleep/light sleep cycles with no awakenings. 

Be Your Own Guinea Pig

If you want to investigate on your own first, try to correlate it over a couple of weekends.  One weekend take it completely easy. Do no physical labor for two days, see how well you sleep Sunday night. If weekends are your housework days, hire a cleaning service this once. If you are already in a disturbed sleep cycle though you may need to do this for several days until your symptoms clear.  Only after you are in a "good" cycle should you attempt to disturb your sleep with exercise.

The next weekend, attempt to exercise normally both days. I don't mean do your normal routine, I mean work out 30-45 minutes each day, see how much of a difference this makes to your sleep Sunday night. If you find that your first Monday was great, and your second Monday terrible, you fit this profile.  However, there are many unanswered questions that remain, and I've noticed in addition to exercise a secondary, cyclical pattern which I have yet to pin down.

Notice that the ResMed S+ was less sensitive for me than the Jawbone for this particular issue.

How can I get better?

Schedule another sleep study, but this time make sure you exercise normally the day of the study, if not two days before the study. In my case this was really a challenge, since my symptoms had been getting worse, my energy levels and moods had been suffering, causing me to exercise less and less.

It really helps to hire house keepers and have friends to support you.  Let them know what you are up to and that you'll need extra help while you try this. Take time off from work if needed. If you are like me, you'll crash for 3-5 days and be completely unproductive after the exercise portions.

It's also important to stress that immediately after exercising I felt great. My lungs felt clear, I felt light on my feet, it was such a great thing. It was only after I slept and failed to recover that symptoms appear.


Remember that exercise IS recommended as part of almost every sleep improvement regimen, so you aren't breaking any rules by following the advice here. In all cases follow the advice of your doctors and personal trainers, but the guidelines here should be in compliance with them.

Right now as far as I know, there is no guidance on exercise before a sleep study/titration, however it's generally recommended not to exercise in the late afternoon evening as it can wake you up and prevent you from sleeping fully. 

The day before the sleep study:
  • Have no alcohol.  Zero.
  • Stop caffeine and chocolate after noon. 
  • Have a couple of bananas.  
The bananas and stretching do nothing for sleep, they are to help prevent leg cramps, skewing your study, and possibly disconnecting your wires. If you aren't used to exercising, a little extra potassium will help.  Any other potassium-rich food will do of course, if you are allergic, or just don't like them.

The day of the sleep study:
  • Have no alcohol, Zero, nada, zilch. 
  • Exercise as much as you should be able to do if you had no sleep issues.
  • Exercise vigorously 30-45 minutes in the morning if possible, but no later than early afternoon. Get into your aerobic zone for most of it. Again, be an adult and follow the advice of your doctors and qualified exercise instructors. For me, it seems that weight bearing causes the symptoms faster than aerobic exercise, so a few squats to tire your legs out may be all you need. Climb stairs with a couple of gallons of water in each hand should do the trick as well if a gym is out of your reach.
  • Make sure to cool down and stretch your legs.
  • Have a couple of bananas after your workout.
You may be desperate for an answer, but if you are like me, this doesn't take THAT much effort to tip your body over, so don't give yourself a heart attack before your sleep lab!

In my case, it was like magic, symptoms that had never shown up before became clearly and consistently visible during the lab work. The CPAP machine that was fine for the first 6 studies was completely inadequate now.

By challenging your body, and your CPAP machine you'll have the best study possible.

If you are a sleep specialist, or researcher, and would like detailed information I would be willing to make that available privately.  Please leave me a comment with information about your publicly visible contact information and I'll reach out to you.

Saturday, May 21, 2016

Furman PL-PLUS DMC Power Conditioner - Dead Eye Mod

The Furman PL-PLUS DMC is a power conditioner featuring Furman's serial, non-sacrificial power conditioning technology. It's a very nifty unit I'd recommend to anyone.

One issue that may drive some to modifications however is the voltage meter. It's easily off by about 2-4%. due to the use of a low-tolerance part.  This may sound pretty good, but consider if you are in an environment with slightly elevated voltages, around 125VAC.  You'll see 130 which is a cause for real concern.  This is exactly why I hacked this unit to be within 1%. Though less frequent in residential areas it's quite common in commercial locations (auditoriums, office buildings, parks).

Of course, any time that you work in a device like this you take your fate and that of your unborn children into your own hands, so this is not for the inexperienced stupid, or squeamish. If you don't know that you must disconnect the unit from the wall before working on it, just stop, stop right here.

Open up the unit and look at the meter board.   You will see resistor R10 that is nominally 2.2k. The voltage reading is proportional to the resistor value here, so if, hypothetically, the meter was reading high by two percentage points, adding a high value resistor (around 180k) in parallel would correct the problem.  If the voltage is too low though you'll have to replace R10. These are all low voltage parts, so you don't need to go crazy with high voltage, fusible, yadda yadda but something thermally stable would ensure correct readings even in warm road cases. $1 tops. You could replace R10 with a 1%, thermally stable resistor, this will give you the best reliability regardless of your environment. Not needed for me. :)

So if you are a traveling roadie and need a dead-accurate voltage reading, you know what to do.

Thursday, May 5, 2016

Fiio X5II and E12A - Mont Blanc Edition

The E12A headphone amplifier is specially marketed for the low impedance and low sensitivity of in ear monitors.  While usable with any portable device that uses a 3.5mm stereo jack, the special X5II stacking kit makes it a breeze to attach your X5II semi-permanently. The amp itself comes with a number of Livestrong-like bands that help attach it to most portable devices.

As noted elsewhere, the biggest failing of the X5II seems to be the built in headphone amplifier. If it was just weak across the board it would still be useful.  Unfortunately by itself it sounds hard and gutless. As if only a tweeter was playing.  This is a little bit of an exaggeration, but it helps illustrate the problem with sound quality. Neither of my headphones played nicely with it despite having a broad (20 and 60 Ohm) variation in impedance.

The E12A, like the K5, really opens up the sound. You get much more spacious and neutral sounding playback. Also, and one other reviewer mentioned this, the X5II seems to break in.  Yes, I know it's nuts, but if you absolutely can't stand it at first, put it in a drawer and let it play for 4-5 hours before you listen again, then tell me I'm nuts.

Anyway, with either add-on amplifier the X5II is a much much better sounding DAP. However, even at sales prices I'm now out $471  ($299 + $160 + $16) in total and I don't have the slim profile of the iPod classic, and I dare say the Tobleron shaped Pono may actually fit my pockets better.


Oddly, the dual SD cards in the X5II are seen as 2 separate cards by my Windows 7 PC and Media Monkey. To keep from going completely crazy I ended up moving all of my classical collection to SD 2, and keeping all the Pop, modern and world on SD1.  I guess that's fine, but in the 21st century it's surprising to find a digital device that doesn't take care of stuff like this for you.

Another issue is that each device charges independently.

Lastly, un-strapping the X5II to place in the K5 is kind of a bother. It seems you need to commit to using the X5 as either your commuter player, or your desktop player with easy to drive headphones. This combination is not going to be able to do all things for you. Not that any other solution would either.


Overall, the X5II/E12A is a much better sounding solution than the X5II alone. It's much clearer and warmer than my 160 GBbyte iPod classic (currently snuggled into the glove box of my car) but it's still not as good as the $399 Pono. The Pono still sounds warmer and sweeter without any loss of detail, but the X5II/E12A is a really good combination and credible good sounding alternative.

Wednesday, May 4, 2016

Headphone Impedance

We often see speaker impedance charts from reviews, but rarely do we see them in headphones, so I thought it might be fun to do so for my two reference headphones.

One nice exception are reviews from InnerFideility which do include this information.  Why should we care about headphone impedance? The lower the impedance at a given frequency, the more current an amplifier must provide. Portable headphone amplifiers are especially limited in current drive. This causes the sound to track the impedance curve instead of the music. So, in general, a headphone with a higher impedance and low phase angle will be easier to drive to the same high quality sound. They will tend to sound more consistent across different headphone amplifiers.

To do this I used my trusted Dayton Audio Test System v. 2. Of course most use this for speaker testing, but what are headphones but speakers you can wear?

I have two completely different headphones I have been using as my standards. They're probably now considered quite old.  The headphones I turn to most often are the AKG K712.

The impedance plot was a solid 60 Ohms or more.

My other set of references are Shure E4c in ear monitors. I'm not even sure they used that term when I purchased them. They are definitely the most "discerning" or "demanding" of the two. While they have fantastic noise isolation, the bass doesn't open up except with the best headphone amps.  All others need not bother. This should not be a good thing! What buyers really should look for are headphones that play great with cheap amps. The minimum impedance here is a punishing (for portable amps) 24 Ohms.

The only portable player so far that I have heard play this very well is the Pono. I just wish the Pono had more features that would make it a no brainer.  The amplifier part of the player is just simply outstanding. I need to get either easier IEM's or bite the bullet and get a Pono. The other sub-$1k player that played these well was the UFO DSD DAC, until it died. 

Sunday, May 1, 2016

Affordable Headphone Solutions From Pono, Fiio, Oppo and others

I have been in the market for a headphone listening solution for a couple of years. I'm not quite sure what it is exactly, but my thoughts were something like a portable player and/or headphone amplifier/DAC.  This all started since the Apple iPod Classic was discontinued and I got a great deal on an AKG K712. I still have the iPod, but it's married to my car which is iPod only. The iPod Classic sounds fine, but not the best I've heard, and it's limited and fixed storage size has been an issue.

In the mean time my search for solutions continues. 

So, what IS ideal?  That varies from person to person, but they are, from most important:
  • Sounds great
  • $500 or less. 
  • Battery operated (i.e. portable)
  • Supports 128 GBytes or more
  • Support for Tidal music streaming
  • Nice if it can double as desktop DAC/amp
I've also been struck by how completely off some reviews have been compared to my ears. They tend to be universally positive with colorful and nuanced critiques regardless of the source. I really have to wonder about the reviewers. In any event, I present my own list:

Pono PMPOppo HA-1Fiio X5IIFiio X7EchoBox ExplorerUFO
Approx. Cost$399$1,200$299$650$449$430
Maximum Storage192N/A2561921 Micro SD Slot??N/A
Sound QualityExcellentSadisticSadistic-ish??????Very very good
Wi Fi TidalNoN/ANoYesYesN/A
DACESSESSBurr BrownESSBurr Brown???


As I have written before, the sound of the Pono Portable Music Player, regardless of headphones, is always excellent, musical and enjoyable. It handled both my AKG and Shure IEM's so convincingly and smoothly that is has been my reference standard for what a portable Digital Audio Player (DAP) should be. However it is hampered by a few things which have kept me from pulling the plug on one for myself: Size, features and storage.

The size is too chunky, the apps are non-existant and storage is limited to about 192 GBytes. There's no way to stream music from a NAS or online service.  If it had BluTooth connectivity (and BluTooth could do high resolution music) so I can play from my phone it would be hands down unbeatable.


I purchased a UFO DSD DAC from Blue Coast Records at a show and it worked for about 2 months before it died from what I believe were power supply  and overheating issues. Among the USB DAC's I've listened to under $1,000 the sound quality was simply outstanding, and almost as good as the Pono player. If mine had not died so quickly it would be an easy recommendation.  If you buy, make sure it's from a reputable vendor (such as Blue Coast Records) and save your receipt.  In a sense, it IS portable in that it can be driven from the USB out of a phone or tablet, which works surprisingly well given the limited power a phone could supply but it is far too chunky for a pocket.

Oppo HA-1

This is a beautiful looking headphone amplifier and DAC from Oppo that I really wanted to like. The Oppo 103 BluRay player with it's 7.1 analog outputs makes my home theater life so simple and beautiful and easy to integrate with my music listening that I could not be happier or conceive of buying another brand of BluRay player, ever.

Then I come to this "thing" released by Oppo as the HA-1. Are they serious, or just being cynical? I can't tell really. What a hard, strident and difficult to listen to treble and limp sounding bass. I heard it at the 2015 California Audio Show, the same show where I heard the UFO DSD DAC, driven by a Macbook Air. It was literally the worst sound at the entire show, of any kind, and I heard some really bad rooms and bad music at that show. I thought perhaps it was me but I mentioned this to a fellow audiophile who owned one for about two months who described it as "fingernails on a chalkboard." It's a real shame because it's beefy, sexy and comes from a company I really appreciate for it's high quality products and connection to consumers. Perhaps it performs much better with their own headphones? I never found out. For about a third of the price, the UFO DSD DAC easily sounds better and takes up less space.

Fiio X5II (2nd Generation)

The Fiio X5II is an extremely well reviewed player that is now in it's second generation, as well as heavily discounted from it's original $500 to around $300. With the glowing and numerous consumer reviews, and Fiio, like Oppo, showing very good customer engagement, I was certain this would be a good player for my commute. Unfortunately, cold and alone it's barely listenable. The treble is such an ear drill it literally makes them feel hot after twenty to thirty minutes of listening. It's like when you've been out in the sun too long and your eyes ache? Imagine that in my ears. It's not hyperbole, it's exactly what it feels like. By itself I really can't recommend this player. The closest experience I've had to this is the Oppo HD-1, or speakers from Triangle.  Ouch. Not all is lost however for with an outboard amplifier this is a very good source.

Fiio X5II/K5 Combination

As an article at EnjoyTheMusic points out that the Fiio K5 headphone amplifier really improved the sound of the X7.  I have not heard the X7 at all, but It seems from my listening to the X5II/K5 combination that the K5 does in fact improve the sound quality of the player. Using the K5 the listening experience is much more balanced. The midrange and bass are no longer shy, the treble softens up, channel separation (or something like it) gets really good. Thanks to the K5 I'm not as ready to throw in the towel than if I had purchased the X5II by itself. Also, while I usually review with the AKG K712 my outdoor headphones are Shure in-ear-monitors, so I need to give them a good long listen in the streets to see if that is a reasonable arrangement.

I have also recently reviewed the Fiio E12A Mont Blanc Edition portable amplifier, which also does an admirable job of driving difficult headphones from the X5II.  If you are only looking for a portable solution, that may be your dream ticket. 

EchoBox Explorer

The $449 Explorer is an indy Android / Wifi DAP in a dapper looking whiskey flask design. It will constantly remind you to drink, so probably not good for those dealing with addiction issues, and what audiophile isn't? Still, it looks promising at a reasonable price. Like the X7, it aims to be an Android answer to the iPod Touch challenge. For those not familiar with the iPod Touch, they are essentially iPhones without calling abilities and as a result can run the full suite of iOS apps that don't require calling. To my knowledge only the X7 and Explorer are reasonably good Android equivalents.

Sadly I've never seen one in real life so cannot comment except to say they look very interesting!

Lessons Learned

I. The resolution of the playback files is much less important than the sound of the player.
 I'm not saying crappy MP3 files sound as good as everything else.  What I am saying is that the sound quality and balance of the player is a much bigger factor to my enjoyment of the music than the file resolution. This may not be true in my home system, but  it is here. I would much rather have the Pono sound at 44.1kHz/16 bit FLAC than the Oppo at any file quality.

II. Online audio reviews, even when apparently independent, are often completely off the mark.

III. DAC chip makers don't matter as much as the amplifiers.
Some audiophiles ascribe to the idea that DAC chips from manufacturer X are always better than Y, but putting together this report and going over my past experiences I can't agree with that at all. I've listened to ESS and Burr Brown devices and have found great and bad examples of both. My current and previous home DAC's had Burr Brown chips in them. The Pono uses an ESS chip.  The X5 uses Burr Brown. The Oppo 103 uses Cirrus Logic. There's no correlation in my experience that either chip is inherently better or worse.

I'll write more on this as I gain more experience. As always, please for the sake of the Dark Goddess of Coffee and Chocolate I worship, use your own ears to spend your own money. Buy what you like, always.

Wednesday, April 20, 2016

Focal Beryllium Tweeter Upgrade

Good news for all of you Focal owners out there! If you own a Focal Profile or Chorus from the late 90's you may be able to easily upgrade the tweeter to the latest Beryllium tweeter from ScanSpeak for a parts cost starting around $300 per speaker. 

I have a new campaign to bring this upgrade to the Focal Mezzo Utopia! Stay tuned here.


The Focal Profile and Chorus line shared a design that mounted the tweeter on an L shaped bracket at the top.  It's fairly easy to remove it and then route a slightly larger hole for the ScanSpeak tweeter to replace it.

Unfortunately I only have really good measurements from the Focal Profile 918 speakers so I can only offer you exact advice on the crossover modifications needed for them.  However given how much Focal likes to re-use ideas and designs it's quite likely you can use most of this other Profile as well as the Chorus range of speakers as well.If you have speakers besides the Profile 918's you may need to take some measurements to select the correct crossover parts.

After a long search and then analysis I have found that the ScanSpeak Illuminator D3004/6040-00 is a pretty good physical, acoustical and electrical upgrade tweeter for all of the Focal Profile speakers and a relative bargain at $270 each.  Since the Focal tweeters are all severely under-damped, we are using the less damped of the two low-profile ScanSpeak Illuminator tweeters we could choose from. If you use this tweeter's larger sibling the 6040-10 the crossover parts will not work and you won't gain much in this application except a more difficult crossover design.

Sadly I no longer own the Focal Profile 918's.  I wish I did because if I had thought a little more about it I would have done this upgrade instead of all the others. Except pulling out the bass caps, which is still a good thing to do (see previous posting).

The chart shows the frequency response of a Focal Profile 918 before (red) and after (blue) the modifications. The raggedness you see in the Focal Profile tweeters is common to almost all Focal tweeters since they sharing a similar underlying motor structure. Tweaks to the back of the tweeter have been done in the Sopra line to unknown benefit. The infinite horn loading used in the Sopra is an idea Focal may have borrowed from Wilson Audio Specialties who did some work on improving the tweeter chamber in the previous speaker line, or from B&W's Nautilus. Sadly, the measured improvements seem modest and fail to overcome the shortcomings of the motor/dome combination in my opinion. 

Focal Profile, original vs. Be Tweeter
Using the ScanSpeak Be tweeter results in an unbelievably flat and smooth frequency response, and is not shamed by any mid-range Focal ever made. This sounds like the ravings of a madman until you realize one thing:

Focal Aria 936
ScanSpeak tweeters have a much better motor structures than Focal uses in their mid-range speakers, and possibly even the Utopia's as well.

Focal's tweeter motors have improved since the Profile range and as a result the Aria range has a much smoother treble than the Profile could achieve, as you can see in this chart from the Stereophile review of the Focal Aria 936, but in the end it is still pretty ragged. 
This upgrade is designed with two requirements:

  • The tweeter will be flush mounted to the face of the baffle.
  • The tweeter will be used without the grill cloth. 

The Profile range required the grill to extend the tweeter range at the expense of the overall smoothness of the response.  The superior construction and motor used by ScanSpeak makes those requirements unnecessary and the grill will actually be in the way. Chorus owners could probably go either way. However I have found the rickety plastic used tends to vibrate and create secondary sound sources.  The speakers are really much better off without the grills after this upgrade.

Modifications Required

You will need to make some simple part replacements to the crossover, and you will need to expand the tweeter hole by a few millimeters to fit the larger tweeter motor. The original tweeter and bracket won't be re-used. 


To make the modifications you'll need:

  • Plunge router
  • Circle cutting jig
  • 1/4" Spiral upcut bit (as recommended by jig make)
  • High power, preferably temperature controlled soldering iron with wide tips 
  • 3/4" wooden scraps. 
  • Long handled phillips head screwdriver to pull out crossover
  • Torx T25 to pull out midrange and woofer.  
  • Drill with 1/8" drill bit for tweeter pilot holes.
You really need the router and jig for this project. In addition to enlarging the hole you'll need to route a recess for the tweeter flange. It's not something you should freehand if you have any dreams of impressing your friends with your modifications.


A full schematic is provided below, this is just for reference:

Crossover Changes

The original tweeter filter, top left, uses a single resistor followed by a fourth order crossover. This will make these changes a breeze to make on the original circuit board since we are in fact removing parts. Note that the schematic part names don't correspond to the circuit board. You'll have to examine the traces yourself to be sure of what's what. Also notice that in the original design the tweeter polarity has to be inverted for the better phase matching.  Actually the original Profile 918's phase matching is rather crappy in either polarity. It's just slightly better inverted.

Here's a picture of the original crossover board from a previous blog entry. The resistor and caps you are interested in are in rectangles. The two inductors that you'll need to remove are the air core (i.e. donut) shaped coils at the bottom of the picture.

You'll replace the "Tweeter Resistor" with a new one. Discard both of the tweeter caps and place the replacement 10uF cap so it jumpers around both of them (C4 and C5 in the schematic).

Remove both of the donut-like coils.  Replace the last one with the new 0.27mH coil and you are done!

Here's the revised schematic.  The important part is on the top.  The new high pass filter is much simpler than the original due to better physical matching.  The end result is good, but not excellent, phase matching. It's certainly much better than in the original Profile, but could be improved upon with many more parts which I think are not worth it.

Also note that the ScanSpeak Be tweeter is in phase with the midrange.

There's nothing wrong Focal inverting the tweeter to improve phase matching. Given the location of the tweeter and overall crossover design, Focal's best choice was to invert the tweeter, but it did not end with idela phase matching except at the crossover point. I suspect part of the problems Focal's designers had was with the demands of matching the original tweeter to the woofer. It was a much bigger challenge than we have.

As noted in another posting, another quick mod  you can make is to eliminate C2. It's a waste of amplifier power.

Tweeter Mounting

Flush mounting the tweeter is the hardest part. What I may recommend is that you create a jig to help you use a router jig.  Use a scrap of wood about 6" by 2" and in the center add a wooden disk about the same radius and depth as the existing tweeter hole. The Focal tweeters are terribly small, around 36mm, but the replacement is only about 12 mm larger. You can make the disk using the same jig which you need to route the tweeter flange and cavity. Use hot glue to attach the wooden jig to the inside of the speaker cabinet so that the disk fills in the original tweeter hole. The disk does NOT have to be a tight fit. Just so long as you can eyeball it and have even clearance all around before the hot glue sets.


Before routing anything on the speaker baffle double check that the new tweeter will have plenty of clearance after routing! Don't forget to check that you have internal clearance as well! You are going to be routing very close to the top panel. Make sure after routing that the body of the tweeter won't be blocked by the top cabinet panel. This will vary greatly by model.

If In doubt, put the new center 25mm below the top of the original hole. That should ensure you have the same clearance to the top as the original tweeters.   On the Focal Profile 918, this is going to be about 6mm below the original center, give or take.

Once you are sure of the center location for the new tweeter, route the flange and then the main hole.  Hopefully you can then pop off the strip of wood and reuse it for the next speaker.

Be sure to drill pilot holes before attaching the screws.  The MDF Focal uses is pretty soft. Attach with 3 Cap head screws per tweeter.

You may need to attach new quick-disconnects to the leads from the crossover to ensure proper polarity and sizing.  If the sizes are right, but polarity is wrong you can also switch the cables at the crossover end.

Tweeter Tweak

Add your favorite color of Pressure Sensitive Adhesive (PSA) backed felt around the tweeter and all the way to the edges. It will really help increase the sense of spaciousness and smoothness. There's a reason why Wilson and Vandersteen use this approach, it works.  Fortunately for us you don't have to do much to reap the rewards.  A couple of $1 felt sheets from your craft store will do great things.


It's really easy to go crazy with capacitors. My recommendation on the cheap but worthy side is a 10uF Mundorf MKP bypassed by an Audyn 0.1uF TrueCopper capacitor. That should be around $30/speaker. On the high end I suggest the Jupiter Copper Foil capacitor by itself for $399 at Sonicraft.

Somewhere in the middle of the range are the ginormously sized Clarity MR caps.  I strongly suggest you use multiple caps here though, it has slightly high ESR. It's a great cap, but you are better off with a pair of 4.7uF and adding an 0.68uF cap than buying the 10uF cap by itself. You could save a little money with the single 10uF cap, and maybe some sspace too but then I strongly suggest the Audyn 0.1uF TrueCopper bypass or Jupiter Copper as bypass caps.

What about the high-end Mundorfs?  Sure, you can go that route, but I find they add a Disneyland-like sheen to the music that draws my attention away. If on the other hand you find it magically enchanting, that's the way you should go. That approach certainly works for Magico and their fans, so you have plenty of good company. The Mundorf EVO Silver in Oil are among the best exemplars of this. I'm not really criticizing you at all. Just letting you know what the differences are. I find the Mundorf MKP under-appreciated and more musically honest. However buy what you like, damnit, and don't let my personal ideals get in the way of your good time.


The inductor recommended here is a high-value but very good air coil core from Jantzen which runs $6 each, but you may also want to try the copper foil version, also from Jantzen for around $18 each.  Either way Jantzen makes very very good inductors. Given a choice though, the midrange coil is a much better upgrade to make to copper foil. The combination of new tweeter and midrange coil will enhance the overall velvety smoothness of the response. Make sure your coil axis are at right angles to any nearby coils.


I always recommend Mills for being fabulously accurate, transparent, low noise and virtually immune to changes due to temperature.

What's Next?

If you want to really take your speaker to the next level, I'd suggest returning to the older post and doing the major woofer mods at the bottom. Increasing the minimum impedance of these speakers will make most amplifiers sing for joy. You'll gain dynamic range and bass depth that will embarrass any other Focal's short of the EM woofer Utopias.

Friday, January 22, 2016

Duelund Precision Bypass Capacitor Review

Labelled: 0.047uF
Measured: 0.0476uF and 0.0475 uF

Max deviation from Spec: 1.2%.

Note that my own test tools may be off more than this!

Tuesday, January 19, 2016

Focal Profile 918 The Ultimate Upgrade Guide

Update - April 2016

This article takes each driver and discusses separate upgrades for each.

The information is correct, but there is a much better Beryllium tweeter mod now. The link to the new tweeter upgrade page is here.  It is a much more cost effective and incredible upgrade to replace the tweeter and install a brand new high pass filter than to do the tweeter modes in the article below.

However, the midrange and woofer upgrades discussed here still apply and are in fact pretty incredible. If you take the Be tweeter mod and do the woofer mod in this page you will end up with speakers far better than the Focal 928/938 series. 

 Original Article

If you follow up on the felt and crossover modifications below you will end up with a speaker that has a much smoother and open treble as well as stiffer and more enjoyable and realistic bass. The amount of information you'll gain in the decay of notes and sense of acoustic spaces will really surprise you.

The Focal Profile line was the spiritual, if not material predesessor to the Focal Sopra. As such, it's
got a lot of people wondering how to improve it to reach the Sopra.  Truth is you can probably reach if not exceed the performance of the stock Sopra with the Focal 918's and a little careful attention.

The Profile was the first un-boxy, MDF constructed Focal speaker, while the Sopra uses much of the lessons learned in the construction of the profile, with a central tweeter section to separate the upper and lower MDF sections.  I'll tell you a secret. The main reason Focal put the tweeter section is was to make the MDF manufacturing as cheap as possible. This MDF wedge makes it possible to glue the two MDF tubes together at an angle. Sound quality has nothing to do with the open back tweeter and "infinite horn loading."  Yeah, I know, Beryllium, blah blah.  Sorry but looking at the pictures, and measurements I can tell it has a very similar motor structure to the Profile. 

If you have or can lay your hands on a set of 918's here I'll show you how to make your Sopra drooling friends jealous. The SCR caps in the Sopra's just can't do the microdynamic detail the Mudorf caps can give you. It's not so much in the loud parts, but as signals decay that the Mundorf's will really shine. Pay close attention to this before modifying so you can hear what I'm talking about.  The effects are sometimes spooky too.

In the bass the increased impedance will add a new strength to the speakers.  You've probably unconsciously settled on using these speakers with a subwoofer or at least for movies you have them crossed over fairly high.  This will be gone.  You'll be able to run the Focal's full range without fear, and you'll probably forego a subwoofer at all for music. No joke, take a look at the original vs. final impedance measurements.  The green line is the measured impedance from my  Focal Profile 918.  The blue line is the impedance after making the final woofer modifications discussed below. That's really outstandingly better impedance with no downside but cost for the listener.

If you want to use tube amps with these speakers the complete woofer mods are a must-do upgrade! 

For a pair of speakers the total cost of these upgrades will be around $25 for the exterior felt mods alone, plus $160- $290 for the crossover mods depending on how frugal you want to be. One of the biggest improvements this article will show you won't even cost you a penny. You can try it before you commit to the final woofer modifications.

If you are only interested in the woofer modifications, that will only set you back around $70 and is probably going to be the single most dramatic change you can make. You can definitely do those and come back to the tweeter and midrange modifications, but to place the mid-range caps you'll need the woofer resistors out of the way first. That's the only real restriction.

You can do all three sections or just one, but in order of importance and convenience in terms of access to the PCB:
  1. Tweeter
  2. Woofer
  3. Midrange


Putting together guides like this takes a lot of expertise, time and tools.  If I have helped you please become a supporting member of the DIY community by securely donating $2 to the cause of independent reviews and advice.

Thank you!

External Modifications

Externally there's a number of things you can do, which apply to the Focal 918, 908 and maybe even the CC 908. If you dont' feel comfortable with a soldering iron, or are afraid, you can make some improvements for cheap without ever opening up your speaker.

Feeling, er, Felting Around

The grill is important to the dispersion pattern, but the plastic adds it's own coloration. The edges on the tweeter add coloration thanks to the diffraction when the sound wave hits the edge. This all ads an edge (pun intended) to the treble which can easily be smoothed over by adding craft felt in the right places.

Felt Tools and Supplies

 Most of these supplies can be purchased via Amazon via my store here. 
Make sure you have a large, clear work surface.  If you prop the grills up they will tip over easily while you are working on them. A clean floor works too. I used 2 pieces of felt per speaker. Using the back of the grill as a general guide, fold  the black felt horizontally and cut it to the width and height of  one of the solid grill wings then make a cut out for the 'V' of the tweeter. You'll use the fold to push the felt behind the grill cloth. Carefully and patiently stuff each folded felt sheet it behind the grill cloth using a narrow piece of cardboard, or some other gentle but stiff tool. A little Zen and deep breathing helps here. Once that's in place, use your fingers to pull out any wrinkles from the bottom and smooth it out from the front. Don't obsess over the looks until you sit down.  No one will notice the "bra padding " effect, just the bodacious sound.  Hahaha, I kill myself.

The felt on the tweeter housing is about 20% of the overall effect. If you are worried about it making your speakers look like stand-ins for Monsters, Inc. don't be, no one will notice. You'll need to use pressure sensitive adhesive (PSA) backed felt.  Pick a color, and trim it roughly to the rectangular size of the tweeter.  I used white and covered both the front and the top with mine.  Use the felt punch to punch a 1 1/2" hole in one end to match the tweeter opening.  Remove the backing and place firmly on tweeter, being very careful not to touch the tweeter dome itself.  Just the V shaped housing.  After you've carefully adhered the felt using your finger tips use a sawing motion with a brand new razor blade and carefully trim the excess. I found it easiest to do this with the tweeter in place, but the big grill off. Just be gentle and remember to saw, not push the razor throught he felt. use about a 45 degree angle on the razor blade and try to keep as much of it flat to the tweeter housing as you can.  This will give you very clean results.

Done!! Sit back and enjoy, you've just smoothed out your Focal's treble.


The normal feet that come with the Focals are a joke.  Impossible to set properly, impossible to lock in place, and what's worse is they put your speakers, pets and children in more danger by making the footprint far too narrow.

I use these speaker stands from Soundocity and they work great! The benefit for me was being able to point my speakers exactly the right place, but I don't think they made the sound any better.  My floors are not flat, and these stands took care of that problem perfectly.

Crossover Modifications

I am serious when I tell you you may end up with a speaker better than the Sopra's.  It's not for the lazy but it's a fun and relatively quick project. You'll need some soldering skills, the right tools, and patience.  That't it.

You'll make improvements to all sections of the crossover to end up with a whole that is going to sound like much more expensive speakers than before, unless expensive means you must have a big amp.  That we don't do here.

My suggestions are based on thoroughly measuring every driver, and every inductor and trying a number of different approaches as well as spending at least a week of time in crossover simulation design. I also spent a ridiculous amount of money on high end parts I eventually changed my mind about, so please keep in mind that there's a lot of forethought that went into what you read below.
In order to do it you'll need to pull out the crossover and replace 3 parts with 4 parts.  Once you are done no one will be any wiser though. In fact, it may be a better idea if you plan on reselling than adding felt to the tweeter.

Necessary Tools

All of the tools recommended here are conveniently available through my web store. 

If you attempt to do this with a cheesy $10 soldering iron and the original tip you'll be really frustrated.  Any desoldering/soldering work should take 10 seconds or less to pull a component off. You'll need more than average output because the PCB has so much copper it will sink the heat off the connection.  This is also where the broad tip comes in.  It will transfer 10x more heat to the board per second than the standard pencil tip will.

Strictly speaking, you don't need a drill or cordless screwdriver, but it will greatly shorten your time to make the crossover mods.


The part counts are for a pair of loudspeakers.

Please note that all of the tweeter parts are available through Parts Connexion but sadly not through Amazon:

All of the midrange and woofer supplies are available through my on-line store via Amazon.


    At about half the prices of the Solen's are Axon's, available through Parts Connexion.  As far as I know they are the same cap with a different brand. If the idea of mixing capacitor brands to you is like having steak knives made up of 3 Wufshof and 1 Henkells then you can certainly substitute Mundorf MKP's for all the caps.  You may need to double up on the 10uFs though, not all makers include 20uF in their wares.

    An alternate, physically smaller but much harder to mount inductor:

    Tweeter Parts

    In a way, the Focal tweeter here forces you to stay away from more expensive boutique caps, most of them will end up sounding worse in the long run in this speaker. I picked the Mundorf MKP caps due to the synergy with the tweeter.  Mundorf MKPs are warm and smooth with tons of air.  This is a good match for a metal tweeter that's a little ragged but has lots of potential for detail, imaging and depth.  Nothing else in the $5/capacitor price range I know of has this combination.  If money is no object then a good alternate is the Clarity ESA line.  Even more clarity and depth, but about as warm but still affordable at $15/capacitor.

    If price is no object the Clarity ESA's should be your only choice.  If price matters, the Mundorf MKP are the best alternative, but both are very well suited to this upgrade. Caps in higher brackcet can be too neutral or bright by comparison which is not what we really want here. Then there is the issue of physical size.  The MKP's are perfect, and the ESA's just a little chubbier for the location, but completely adaptable.

    The Mills are just excellent all around resistors. Unless you are going for a vintage sound I just can't recommend any other brand in a crossover. Terribly natural, and invisible sounding, small for the power ratings, non-inductive, thermally stable, mil-spec and always spot on the rated values.  It is also helpful that in terms of price they are the bottom rung of "high end" power resistors.

    Mid-range Parts

    Lets start with a picture of the midrange filter.  Being a 2.5 way system, there's no high pass filter here. By the way, I used measured values here.  Obviously buy the closest parts you can. Focal probably wanted a 1.0mH inductor.  1.03mH is just what I happened to measure.

    The caps are in parallel to the driver so not as critical as the tweeter caps. Also, they are the largest in terms of Farads, so staying with high value, and relatively small parts is important.  For this reason the Solen / SCR parts are ideal. If you want to stay "high-end" substitute Mundorf MKP's of the same uF.  More expensive parts in these values are going to be too physically large for the spaces.

    I have selected Jantzen air-core inductors here. Spot on spec and great performers. 

    Woofer Parts

    For the woofer, I picked an inductor that is higher-tech and therefore shorter than a lot of alternatives: the ERSE Super Q series.  The DCR of the ERSE is a good match for the circuit as well.  Being  purely in the woofer, we don't need to worry so much about keeping an air core, plus at 15mH, finding a 12 AWG air core inductor gets expensive fast. This replacement will do wonders for you all by itself.

    You should be able to salvage the existing capacitor, but if you are worried of breaking it, or just want new for the sake of having new here get the non-polarized electrolytic.

      Speaker Disassembly 

      We'll need to pull the crossover out so you can work on it.  Take notes as you go to remember which color goes to which connector! 
      1. Unscrew and unplug the woofer and mid-range. Remove any stuffing that's in the way, but no more than that. Should be just two pads.
      2. Unscrew and remove the rear terminal plate.  Careful! The screw looks the same as the others but it's not.  Mark it or keep it separate.
      3. Unplug the tweeter. 
      4. Optionally remove the tweeter. There's a thumbscrew behind it you can undo with your fingers. This will make it easier to connect the crossover when you are done
      5. There's a white nylon ganglia that holds the cables going from the crossover to the mid-range section.  Unscrew with your fingers. 
      6. The crossover has 2 large Phillips head wood screws at the top.  Unscrew them.
      7. Pull all the cables out through the woofer opening. 
      8. The crossover sits in a slot via friction and a rubber boot.  Rock it to lift it up, then pull it out.
      The entire crossover will come out with wiring in tact. There is no need to cut or de-solder anything but you may need small pliers to grip contacts if a connector won't easily come off.

      Crossover Modifications


      There are three important sections in the picture below.  In red on the left you'll see two rectangles. These are the tweeter components we'll want to replace.  To the right, in a circle, is a part you'll remove and possibly save.

      Choices, Choices

      If you are going to do all of the modifications here, do them in the order suggested.  However, if you are only going to do the woofer mods you can do it by itself you can.

      Step By Step

       Tweeter ResistorOn the top in white the tweeter says "7W2.4 (Omega)JF" That stands for 7 Watts, 2.4 Ohms.  Replace the single tweeter resistor with 2 Mills resistors of 4.7 Ohms in parallel.  This will be equivalent to a 10Watt, 2.35 Ohm Resistor.  Sadly Mills makes nothing closer, but it's quality makes up for the 2% difference in resistor values. Having more watts in a resistor is a good thing, so 10 is better than 7.

      When you replace the resistor, make sure to leave about 1/4" to 1/2" of clearance between it and the board as well as the other components.  This will ensure the best air circulation.

      Tweeter Caps

      Below the  resistor are two black cylinders, labeled "6.8J and 7.5J." That's the capacitance.  They're probably made by SCR for Focal.  They're pretty much crap. Pull them off.  The 6.8uF cap is a straight replacement from Mundorf.

      You'll need to parallel a 6.8uF and an 0.68uF capacitor to get the equivalent of the 7.5uF capacitor. In reality we'll get 7.48uF, within 0.3% of the original.  More accurate than the originals, I promise.

      Be aware that the Mundorf MKPs need a little break in time and are subject to a pendulum effect.  At first they sound good but bright. Then after a day of playing they get grainy.  Finally after about 2-3 days they really mellow and relax.

      Bogus Woofer Cap

      There are kind of two ways to approach the woofer. You can remove one part which will have big benefits or you can do the optional coil replacement and part swap which is going to be even better, but also more expensive due to the $35 coil involved.

      So long as you stay within high-value coils I think this is a totally worth-while modification.  If you try to get fancy the value drops off quickly. See below for the frequency and impedance differences.

      In either event, you'll need to do these modifications before you do the mid-range modifications to create more space on the board.

      The only part in the crossover picture that has a circle is the "Bogus Woofer Cap."  Double check that it is labelled "195uF."  Carefully remove the 195uf capacitor just in case if you intend on doing the optional woofer mods, but leave it's sibling a 440uF cap in place.  Let me show you the woofer low pass filter schematic so you can understand what's going on.

      It turns out that the 195uF cap and the four 10W8.8(Ohm) resistors are all sales props with no redeeming value for the buyer.  They drop the impedance of the woofer to around 2.6 Ohms (very low!) at around 100 Hz. I might even argue that the entire woofer crossover is one giant sales prop.

      Dropping the impedance this low makes the speakers seem more demanding and, by implication, more exclusive, or maybe it convinces buyers to buy bigger amps.  Removing this cap add a tiny amount of bass (almost none) but more importantly, raises the minimum impedance up to 3.6 Ohms, a much easier load for most amplifiers, though still low. Any bass control and slam you notice is not due to the frequency response changing but just how much easier you just made it on your amp.

      By removing the 195uF capacitor you are also breaking the circuit to the 4 resistors it's connected to. You can leave the 8.8 Ohm resistors in place UNLESS you want to do the full mid-range cap mods, below, then you'll need the board space. Make sure you only remove the 8.8 Ohm resistors though.  The remaining electrolytic cap and 40 Ohm resistors are an important part of the low pass function of the filter. Don't bother being too neat. Just clip the resistors off, and de-solder the remaining leads.

      While you have the crossover out you should take a moment to check that the big red coils are actually working. Pay close attention to the biggest  two which straddle the capacitor you have just removed. The leads sometimes get installed too tightly and break after soldering, and perhaps during shipping.  If the leads are in fact broken, you'll need to sand off the red laminate and solder on a jumper wire to complete the intended circuit.

      Final Woofer Mods

      This part is a little complicated, so I'll share the final schematic so we can discuss it:

      Optional Woofer Filter Design

      This change involves replacing the 5mH inductor at the top of the board with a 15mH coil and swapping the location of the 195uF capacitor with it's sibling, the 440uF cap so we can re-use the 40 Ohm resistors. The inductor to the right is the 12mH coil. That one we'll leave in place unless you are just adamant about trying something new.

      Erse Super Q 15mH

      The ERSE Super Q inductor has 3x the inductance of the original so it's going to be about an inch longer than the original.  As a result you'll need to mount it to the back of the board, using the same tie locations as the original inductor. Fortunately there's plenty of space. 

      What does all this extra iron buy you? Quite a bit.  Comparing the original to this modification:

      As you can see above, the impedance no longer goes below 4 Ohms until around 180 Hz, and remains noticeably higher between 20 and 300Hz.  That's a huge win!  If you decide to go absolutely nuts and use film caps, I'll tell you a secret.  Anywhere from 120uF to 200uF will work in this circuit, so if you end up buying a bunch of 20uF film caps you can save some money. This solution is technically better in that it cuts the woofer off sooner than merely removing the bogus cap.

      Woofer Resistors - Optional Changes

      There is an optional change you can make here. You can replace the 4 resistors with Mills 12 Watt equivalents. In addition to cutting the impedance, we are also cutting the peak power through these resistors by half, so we have a lot more safety headroom here than with the original design. However, at 150 Watts that I simulate, the resistors are still a little small and if you want to play with large amps and loud volumes the Mills will give you 20% more safety margin, and degrade less quickly.  Is it worth $40?  I wouldn't do it, but my readers might.

      The Proof of the Pudding

      Now you might say to me "Sure, you can improve the impedance, and you have reduced wasted heat in the woofer resistors but come on, Focal designers are experts! This must ruin the frequency response, right?  Well, not so much. Here we can see the difference between the original modification and the advanced mod.  Original is in blue, mod in red.

      There's almost no difference at all, except for getting rid of that hump around 75 Hz.  If anything, this will make the bass sound tighter and less boomy.  Of course, these measurements are in my room, so a lot of this is room response, but the relative differences are real.

      Why didn't Focal design the crossover this way?  It could just have been cost.  A good 15 mH coil is more expensive than a couple of bi-polar caps and some power resistors. For a $4,000 MSRP speaker you would not have thought this was an issue though.  I think at the end of the day it was the realization that the market does not reward efficient and easy to drive speakers plus the $30 in part savings.  Why spend more money if no one will thank you in the end?

      What makes me sad is that the Sopra measurements I've seen indicate they've taken exactly the same approach there.  Oh, well, maybe I can sell entire crossover upgrades for those owners. :) 

      Mid-range Capacitors

      Make sure you've done the woofer mods, above first.

      If you look at the crossover picture around the tweeter caps, you'll see 2 small cans.  One to the right and one below. The one below should be a 20uF cap and to the right is 47uF.


      The 47uF capacitor that's left is part of a notch-filter, a type of equalizing circuit to make up for a driver's foibles.  Replacing it is purely optional, but why disassemble your speaker more than once? Make sure you've removed the 8.8 Ohm resistors, as described above.  There's one additional supply you'll need for this:

      •  About 6" of 16-20 gauge insulated wire.  Finely stranded is easiest to work with.

      Solder 1 of the capacitor leads into the location, and the jumper wire to the other.  Add hot glue to the board and set the capacitor down.  Bend the far lead towards the jumper, and solder the two together. 


      This it is the second pole of the high pass filter. Replace it after you've done the 47uF cap replacement. You might need to stand it up, or move it so you may need some jumper wires too. I went a little nuts and used a separate PCB for the mid-range modifications, so I'm a little unsure. Again, space matters, so for extra points replacing this with a pair of 10uF Mundorf MKPs is an option but not sure they'll fit.  Worthwhile?  A little.

      Mid-Range Coils

      The part to the left of the tweeter resistor is a 1.0mH coil.  It's at the very top and left of the PCB. This is the first pole of the mid-range low pass filter.  Iron core coils really should be reserved for woofers, so this makes me sad.  At the very least it should be an air coil.

      The coil replacement IS worth doing, but there's just not a lot room on the board.  I cheated and ended up making an entirely new circuit board for the midrange, before I decided it was complete overkill.

      Use plastic wire ties to secure the air-coil in place. Make sure the axis is aligned the same way as the original.  If you turn it around you'll risk magnetic coupling with the first woofer coil.  It's OK if it overhangs the top of the board so long as it's secure and not going to rattle against the board. Be careful not to get near the rubber boot due to the partition that's there.  For this reason you may have an easier time mounting it on the backside of the PCB.

      Wire ties are your best bet here, but hot glue can also help.  You will probably have to adjust the orientation of the wire tie 90 degrees to the original so the tie goes through the center of the coil, and crosses on the top of the board. This will keep everything out of the way of the partition the crossover rests on.

      There is also a 0.6mH coil in the schematic is part of a notch filter. I do not recommend replacing it due to being in parallel and of relatively low value. It's fitted between the two plastic donuts at the bottom of the board. If you must spend money though, this is a good replacement.

      Reassembly Tips

      Reassembly proceeds pretty much like you'd expect it.

      Rear connector

      To make threading the wires from the crossover to the rear connector easiest, I used masking tape and attached the ends to the end of an extensible magnetic holder.  The kind you can use to grab a loose screw in an unreachable place.  A wire hangar or similar would do the trick too.

      Thank You for Reading

      It's been a pleasure having others with similar interest stop by. If you've enjoyed this exercise it and benefited from the recommendations, please drop me a note and say hello or thank you in the comments.