Opinions About Boost Design

[GibsonGM]

Interesting question commandant, one I have not encountered   Does it have to be DEAD quiet with everything rolled back?  I've never had a need for that...but I put my volume pots on the output, so my stuff COULD go to zero.   The way of doing volume above is actually 'better' tho, doesn't affect output impedance.   

The formula for the gain of a noninverting opamp gain stage like that is 1+Rf/Ri, or 1+ Gain/Volume pot resistances.  The resistance in those pots will be tiny, but not absolute zero (no division by zero!); but we can discard that for now.  That leaves the "1".   This says that the stage won't ever be less than gain of "1", or unity gain.

I'm sure there's a trick to change the volume or gain pot to go to Zero signal, just eluding me now as I'm about to go do some recording.  Let's see what Antonis or others might suggest!  But the "1" is "why". 

[spacecommandant]

Interesting question commandant, one I have not encountered   Does it have to be DEAD quiet with everything rolled back?  I've never had a need for that...but I put my volume pots on the output, so my stuff COULD go to zero.   The way of doing volume above is actually 'better' tho, doesn't affect output impedance.   

The formula for the gain of a noninverting opamp gain stage like that is 1+Rf/Ri, or 1+ Gain/Volume pot resistances.  The resistance in those pots will be tiny, but not absolute zero (no division by zero!); but we can discard that for now.  That leaves the "1".   This says that the stage won't ever be less than gain of "1", or unity gain.

I'm sure there's a trick to change the volume or gain pot to go to Zero signal, just eluding me now as I'm about to go do some recording.  Let's see what Antonis or others might suggest!  But the "1" is "why".

I ended up changing the 10uF cap (C11) to 220uF and it's now totally silent when the Volume pot is at zero.

[antonis]

Can't get the reason for a dead silent effect, but let it be..

For MAX pot set fully CCW, IC1_A turns into unity gain buffer (signal on pin 7 is in phase with pin 5 and of equal amplitude)..
(meaning whatever comes into pin 5 comes out of pin 7 identical..)

250k pot, C11, R11, R10 and C10 form a rather complex LPF with 250k pot serving as the "upper" element..
Any non-zero resistance between pot wiper and lug 1 is added on filter's "lower" part, hence raising its corner frequency..
(which frequency is drastically lowered again by making C11 bigger..)

IMHO, hot humbuckers might upset VR, dominating op-amp's power supply rejection, hence passing AC into pin 5..
(interpreted as a faint input signal..)