ART MPA Gold Gain pots issue + noise?

dickiefunk said:
Hi,

I have an ART MPA GOLD and am wondering if there is any DIY I can do about the jump in gain in the last 15% of the pot travel?

Here is the MPA GOLD Schemo :-

http://www.harmoniccycle.com/hc/images/sound/ART_MPA/ART-MPA-Gold-schematic.pdf

Would I be able to put in new better quality pots?

Also, is there anything I could do about lowering the noise levels apart from swapping tubes?

Thanks
Click to expand...

You could change R214/R245 to larger values; that will reduce maximum gain but generally make the gain control more linear. 30 ohms would give up the last 6dB of gain, but the ART has a stupid amount of gain available anyway (+75dB), so no big loss. A change in R206/R236 might also be called for, but I don't have a recommendation, I'd have to experiment.

The pot itself is a dual reverse log pot; those aren't too easy to find. It's possible to make one by hacking a dual audio taper pot though. Basically, you drill out the back of the shaft a little, just enough to loosen the parts, and swap the front and back pieces.

The ART is already a fairly low noise preamp. The tube is a minor contribution to noise, because there are gain stages before it. If you need lower input noise, the easiest way would be to add a 1:4 transformer (keep the ART's input impedance set high if you do that).
 
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