Negative feedback mod for Carvin VT50 / Belair / Nomad

[xtian]

I'm testing this negative feedback mod for a Carvin Nomad (see attached, called Attitude Control by author Hasse). The idea is to add variable resistance at R71, which feeds the negative feedback loop. Higher resistance means less negative feedback, which results in more gain and more distortion. The stock R71 is 10K.

First I put in Hasse's recommended 100K pot. But any dirt in the pot is very loud in the output when you turn the shaft. Then I tried a on-off-on spdt with two resistors (820ohms and 10K). This gives me the choices of stock 10K, nice quiet 820ohms (my favorite so far) and infinite resistance (Hasse notes the VOX runs with no negative feedback--however it's just too much gain without messing with other values in the chain). As you'd imagine, the switching noise is terrifying. I have to turn the amp off and wait 30 seconds before switching, and I wouldn't want to leave it in this state for resale.

Is there something I can do with a capacitor to prevent this switching noise without affecting the tone?

BTW, Hasse's other mods worked out great: clipping diode removal, tone stack, and cathode bypass. Cleaned up the "mud" as advertised, and the Channel 2 "Soak" distortion sounds much less hard-clipped and more tubelike.