Thursday, December 21, 2006

Tandberg 3001 2.0

Ok, just in time for Christmas I am announcing that I plan to do a run of the 2.0 Output boards.

They will include all of the fixes noted in the manual, the biggest being:

  • Crossed resistors in fixed outputs
  • Multipath jack being ever so slightly off
  • One resistor trace being on the wrong side of the board.
Enhancements include:
  • Silver plating instead of tin/lead
  • Fully soldermased and silk screened
  • Thickest available copper thicknesses
Order yours now for $75. Purchasers of the 1.0 boards receive $15 off. Sorry it can't be more, but these things are expensive when you are doing small runs.


Tuesday, December 5, 2006

What DID I get into?

Well, folks, the power supply is fully operational. I wish I could say the same for the tuner.

So long as I'm holding onto the tuning dial, it works great. As soon as I release it, it forgets what station it was last on, and tunes to the highest frequency on the dial.

Also, the presets seem to be broken.

On the plus side, it sounds really great, when I can hold on. :)

So, based on this, I'm going to take it to my favorite Cambridge repair place, Audio Lab to see what Derek can do for me.

Maybe for Christmas.

Sunday, December 3, 2006


Man, if only I had Read the Freaking Manual (R.T.F.M.) a couple of weeks ago I would be listening to the Tandberg instead of griping about upgrading it's power supply.

In the schematic for the Tuning System 2, which is where P801 goes to, pin 1 is clearly an OUTPUT to the power supply. That is, the 5.2 Volts gets generated elsewhere.

I could blame Tandberg, but honestly, had I remembered correctly how a PNP transistor worked, it would have been pretty obvious to me that it was. Fortunately on page 26 there is actually an arrow showing which direction the signal here is going.

What this means is that I really am done with the Power Supply rebuild! Yeay!

With a little luck, next weekend I'll actually be listening to this tuner for the first time!

A fully re-worked power supply with Mills wirewound resistors, and Panasonic FM caps, a slew of upgraded transistors, and a brand new output board with Cardas connectors and Vishay/Dale metal film resistors, this truly is going to be a pretty good piece of gear to own for a few years more. :)

The TDA 3001: Where are all the Parts?

The power supply is back together, and seems to be working. The 5V supply seems to have some sort of remote sense feedback circuit built in. I don't quite get it, but it was driving me mad until I spent some time with a breadboard and tried out different options.

I've finally decided that rather than assume it's broken, I'm just going to put it back into the tuner and see what it does. I need to check the voltages at the 15V and 25V supplies anyway. While cleaning the header pins which connect to the output board I noticed they had ALL come loose. That is, the solder connections were broken on all of the pins. It wasn't falling out, but it would have made a terrible connection. A few minutes with my 100W solder gun and everything was back where it was. I then took out the alcohol and toothbrush and scrubbed the board to get rid of excess flux and any other dirt which might have accumulated while it was waiting in a box.

The one thing I need before I can re-assemble the tuner is a package of insulated quick-disconnect, crimp on spades. A quick trip to Radio Shack, and the tuner should come back in a snap.

Then I'll probably have to worry about the backup battery and the preselect buttons.

You know, I'm almost ready to begin thinking about my next project. After taking apart the Rega EAR headphone amp, I'm thinking I should consider making my own. The one thing the EAR did well was provide discrete output transistors. Unfortunately, their potential was mired by the use of an aging op-amp design, and single ended supply. I am sure making the product as inexpensive as possible played a major part in these decisions. In order to get rid of the output caps you need a double ended supply, and your biasing solution gets more complicated in order to keep the DC offset as low as possible.

So, maybe next I'll make a headphone amp with high quality op-amp front end, with a Class-A discrete output section. I think I may take apart the InnerSound Electrostatic amplifier I have (manuractured by CODA) and try to use their transistors in my design. Yes, it's ridiculous. but that amp sounds soooo good and it's sooo efficient, that at the voltages we need for headphones they may work really well. Instead of 30 devices per output channel I'll use 2 though. But for this semester, this tuner really is all I'm going to be doing. I have a GPA to maintain. :)

Pics will be coming as I begin the re-assmbly process.