GGG's KOT Presence Control Does Nothing for Me. Ideas? Schematic link included.

[Guitarist1983]

I built this circuit using GGG's PCB for the BluesBreaker:
http://www.generalguitargadgets.com/pdf/ggg_mbb_kt_sc.pdf

However, the Presence knob 0-to-max makes no audible difference.  In order of likelihood:  A) I messed up the build, B) My hearing doesn't go that high, C) a component should be changed.    I am a lowly hobbyist and am easily befuddled; could someone kindly tell me what frequencies are being filtered out by GGG's presence control (R12 --> R20 --> C12)?  Any recommendations to increase the cut control of the presence path?   Thanks in advance.

[Mark Hammer]

The Presence control comes more or less "after" the Tone control, and can only alter (or more specifically, take away from) what remains after the Tone control has done its business.  If you have the Tone control up full (and it is behaving properly), then one might hear an effect of adjusting the Presence.  If the Tone is turned down, however, then there may be little or no upper treble for the Presence control to affect.  Does your circuit behave like that?

[Guitarist1983]

Strangely, the Presence control has no effect, except when the Tone control is fully counterclockwise (as in on "0").  Then I hear the Presence roll off just the barest of highs.  In fact the Tone control doesn't ever give a dark tone--even on 0.  I may try removing the Presence circuit to see what happens, then breadboard around with different caps in the tone path.  Any suggestions?  The current Tone path uses a 0.01 uF cap as does the Presence path.

[Mark Hammer]

It seems your Tone control isn't wired up right.

[Slowpoke101]

Having checked several KOT clone circuits there appears to be a slight difference with the GGG circuit. It may be worth trying just to see if the presence control has more effect.



You may find that changing R12 to 15K may produce a more pronounced change as well.

[PRR]

Agree: Tone full-up, Pres wired as GGG drawing, Pres has hardly any effect. Even mid-Tone, not much effect.

Ian's re-draw is more likely.

But at the extremes, Tone and Pres may be tamping-down the same frequency zone, close enough.

[Guitarist1983]

Having checked several KOT clone circuits there appears to be a slight difference with the GGG circuit. It may be worth trying just to see if the presence control has more effect.



You may find that changing R12 to 15K may produce a more pronounced change as well.

Thanks.  I rerouted the circuit as you suggested, but I kept the 6.8K resister.  I can hear the Presence control working now and the overall tone is less brittle.  Much appreciated.  Basically I cut the Tone#2--Vol#3 jumper and moved it to Presence#2--Vol#3.  Easy-peasy. 

[Guitarist1983]

Agree: Tone full-up, Pres wired as GGG drawing, Pres has hardly any effect. Even mid-Tone, not much effect.

Ian's re-draw is more likely.

But at the extremes, Tone and Pres may be tamping-down the same frequency zone, close enough.

Yep, this is what I experienced.

[Rob Strand]

Ian's re-draw is more likely.

The original Blues-Breaker had a fixed filter with 6k8 in series and 10n to ground, which further supports Ian's drawing.