BSIAB2 "CONTOUR" AMZ versus GGG (schems inside)

[ataro]

I noticed that some people complains about "Contour" knob being very subtle, and some other people loving it.

I thought this is probably due to the place they added the pot and how. I made this layout to see the implementation differences between GGG, AMZ-style, and others, based on several builders reports that I have been researching.

The question is, which one is the better way to implement it, and why?

http://postimg.org/image/qz49x137n

[GGBB]

"Better" is always subjective. 

They are all variations of the same theme.  I've simmed them and others and the main problem I find with all of them is that they aren't really "contour" controls, if by contour one means essentially mid scoop.  They are more of a mid-high shelf cut.  That's probably why AMZ calls it "body" or "presence" rather than contour.  There is some scooping going on but only a little and only at extreme settings - the dominating effect is mid-high shelf cut.  #2 and #5 don't do much at all, #3 and #4 are just giving different curves due to different values.

The AMZ Presence version 2 is yet another variation that appears to work better, at least from the perspective of being able to obtain flat response, boost bass or treble, and boost or scoop mids.  What more could you want?  But that's based on their graphs - in-circuit performance may vary.

My feeling is that if you are going to add a second knob to a big muff style tone control, you'd be better off with a different tone stack entirely.  If you are trying to mod an existing BSIAB2 PCB, you'd probably have to do that via a daughter board so you'd need to be able to vero, perf, or etch.  Otherwise, the best suggestion is, as always, to try various things out via breadboard or at least sim software.