Choosing where to boost volume

[mark2]

Looking at the PedalPCB Arachnid schematic (also attached), I'm curious if anyone can share their thoughts on the pros/cons of different methods for boosting its volume.

e.g.

• add gain to the output buffer: increase R10 or reduce R9 on IC1.4
• Increase the volume pot size on IC1.1
• reduce the 15k resistors on the mixer (R4, R20, R19, R21)

Second, though less important, is there a good reason to have that output buffer IC1.4 in addition to IC1.1? Or was it probably a case of using the 4th opamp in a quad package because we can?

Thanks in advance!

[antonis]

No 1 should be more convenient..

IC1.4 is there for signal phase correction 'cause IC1.1 inverts..

[mark2]

IC1.4 is there for signal phase correction 'cause IC1.1 inverts..

Ahh, of course. Thanks!

No 1 should be more convenient..

I'll do more research on active filters (still don't have my head wrapped around them yet)... so sorry if this is a dumb question, but will changing R10 on IC1.4 require a change to the 470p C2 to get a similar frequency response?

I suspect the answer is no because the affected frequencies should be unchanged

[antonis]

It depends on the new R10 value..
As it is, it has corner frequency at 33.8kHz so you can double R10 value without significant audible outcome..
(most of op-amp NFB loop LPFs have corner frequency at about 15-16 kHz..)

P.S.
You can, of course, reduce R9 value as well without worry about C2 value..

[mark2]

If adding a jfet bypass, and now wanting to keep an always-on input and output buffer, is there any reason to choose one of these options over the other?

A. Keep the input buffer IC1.2 always-on.   Add a new, always-on non-inverting buffer to the end.

B. Switch both IC1.1 and IC1.4 to non-inverting.

C. Leave it as-is with IC1.2 and IC1.4 always-on, and just accept that it'll invert phase in bypass. This doesn't seem very user-friendly, though.