Should I leave bypass caps in my console master ?

[jnashguitar]

I'm in the midst of recapping my Soundcraft 800B. It's going well--upgrading to larger Panasonic FM caps is not only flattening out the low end, it's reducing 2nd and 3rd harmonic distortion--great!

I'm moving to the 8015 master module, and it has been modified. Someone added a PFL level, involving an additional DG308. Seems to work fine.

There are also bypass caps and what I think are snubber resistors and phase compensation caps--none of these appear on the schematic. I'd assume these were added to stabilize faster op-amps, but all the op-amps are stock as per original schematic. So, I'm guessing someone tried out different ICs, added all the additional parts, then went back to the originals.

What I know for sure is that those extra discs and wires are going to make replacing the original electrolytics kinda tedious--I'm figuring I'll need to remove at least half of those parts to get to the holes without making a mess. So, I'm tempted just to remove all the stuff on the bottom of the board and start from scratch.

Given I'm using the stock op-amps, are those bypass caps and snubber resistors doing any good, or am I best off cleaning things up and removing them ? I'm probably just going to stick with the stock ICs, and if I ever decide to upgrade, I could always replace.

But I don't want to remove that stuff and immediately run into oscillation or noise problems... advice ?

Thanks so much!

-James

[Ike Zimbel]

I would proceed with caution. It looks to me like the two chips in the middle had their power leads cut and these were replaced with the red and white wires, via series resistors. The discs are decoupling caps and you can see that the chip on the right got just those without the series resistors. I looked for a service bulletin on this but I don't have one in my files. So, you can't take all of this off and still have it work, and, it may have been a factory mod, or factory recommended mod to cure some stability issue with that module.
best,
Ike

[jnashguitar]

Wow, great catch, Ike! And thanks for checking through your files!

Sounds like the best bet is to remove what I need to do the recap, then put back the way it is now. Would be nice to know exactly WHY those traces were ever cut and re-routed, but I'll heed your advice: best to assume the mod was done for a reason, not to try to return to stock.

Thanks again!

-James

[Matt Syson]

Hi
What function is the 'repowered' chip doing? I would suspect it is something 'unpleasant' like oscillator or headphone out which was putting noise or distortion onto the remainder of the module, possibly corrected on a later board revision if it was done in factory.
I would simply recap as it is and put all the bits back as they are now, on the basis it works at the moment.
At a later date if you work out what that chip is doing, you could assess any other possibilities for improvement.
Matt S