The Upgraded Pro-Ject Head Box Mk II

This morning the Pro-Ject underwent a major upgrade. All the electrolytic caps were replaced with Panasonic FM Caps, and the op-amp was socketed and replaced with an NE5532.

First impressions are WOW! :) The treble response is a lot better, the midrange has opened up and sounds absolutely spacious with deep bass, and a very extended treble. The Head Box Mk II plus this upgrade is highly recommended.

There were a few changes from the standard values which were made, here is what you need to do to replicate:

• 1000uF caps were upgraded from 16V to 25V. This is more of a longevity issue than sound.
  
• Input caps C13, 14, 16 and 17 were upgraded from 4.7uF to 22uF. For two reasons. First, they are almost the smallest FM caps I could find. Second, I wanted to beef up the bass response.
  
• Output caps C8 and C10 were upgraded from 470uF to 1,000uF. Again, to improve the bass response at the headphones.
  
• Op-Amp replaced with an NE5532. I know I dissed it as old, but it was a good old op-amp and I have them lying around.
  

If you wanted to do this yourself, you could probably do it for around $20 or less, including shipping from Digikey, making the total amount of time, and money well worth the quality of the head phone amp you are left with. This little amp already sounded better than the Rega EAR when I got it, it now sounds absolutely outstanding. The one minor issue that I'm having is that the case is getting a lot warmer than it did with the previous Op-Amp. I may have to put in some vent holes in the case to ventilate the voltage regulator. Especially since I'm still waiting on the pair of OPA617's from Futurelec. They will most likely warm up the regulator a little more.

The one problem is that it's picking up all the noise coming from my PC, which it masked before. I guess the next step is going to be an outboard DAC for it. :)

One tip, make sure you put the 1,000uF caps as close to the board as you possibly can. It's going to be a tight squeeze.