Below is the response I got directly from Soundcraft.
Hi Bill,
Why would you want to upgrade these pre-amps? (OK, that was a rhetorical question..!)
Seriously - This pre-amp design was developed especially for this console, and was quite innovative in it's day. The only things I can see that would be useful would be to:
a) beef up the electrolytic DC decoupling capactitors (higher value and working voltage, if you can find a suitable replacement with the same lead pitch). This may improve the frequency response. If the console is fairly old, and has been used well, this process of 're-capping' can sometimes make a significant difference (as with all audio equipment) because the electrolyte in these devices can dry out, affecting their frequency response.
b) use a higher spec op-amp in the mic-pre stage (IC1). The TL072 used is a very popular low-noise choice for practically all mixer manufacturers, but, as with anything there will be a higher spec device which may provide a 'perceived' improvement in audio quality. You could try using NE5532 or MC33078 devices, but I don't think you'll hear a significant improvement. (In fact, you may even cause more problems, like high-frequency instability by using a different device)
So, this is all just my opinion of course, and I can't stress enough that any change to the design cannot be sanctioned by myself should anything untoward happen due to this type of tinkering!
Hope this helps.
Best regards,
Ben Libby
Customer Services Engineer
Soundcraft
T. +44(0)1707 668 169
F. +44(0)1707 663 114
