Tone Control Mod

Hi everyone,

I'd like present a very simple little circuit modification on the typical tone control of a guitar, as seen for example in ASATs. I use this circuit in virtually all my guitars which have a standard treble-dim tone control (that is, other than G&L's PTB, for Strat-style guitars).



The only change (expect some values) is the capacitor C_bleed in the dashed box, top right. Normally, this connection would be open. Note that in many guitars the tone circuit may not wired exactly this way but it does not matter -- for the original function -- where the capacitor is or how the pot is oriented as long as it is in a series connection and the same solder lugs are used.

What does it do?
0) Technically, it is a large additional treble bleeder (C_bleed) accross the volume pot which can be adjusted in effectiveness by the tone pot top end of travel.
1) When tone pot is fully rolled back, things works like normal, muting the treble. When turning it up, still like normal operation, gradually adding treble content.
2) Once you get somewhere near of 80%...90% rotation, things start to change -- but only when the volume pot is backed off a little (otherwise no change from standard function).
3) With the volume backed off a little and the tone put fully open most of the frequencies except bass / lower notes are bypassed accross the the volume pot, effectively the bass gets rolled off.

Seen in an other way, with the volume at around 80% rotation the treble pot goes from treble cut (0% rot.) to flat (80%) to treble/middle boost (100%), referenced to tha 80% volume postion.


What's the use of this?
Additionally to you normal operation functions of volume and tone pots, you can get a thinner sound with weaker bass which is not possible otherwise with a standard circuit. Of course it's not a fully indepedent bass control (like with PTB) but extremely useful for eg dimming the bass on ASAT Specials.

Back off volume, with tone fully up, for crunchy rhythm sounds on the neck pup without mud, switch to bridge for solo and crank volume... or vice versa if you play leads on the neck pup and need a thinner rhythm sound on the bridge pup.

For normal volume operation set tone to 80...90%. Besides for the conventional feel of the control action, this is really needed eg when you want to make volume swells, with the tone fully up that would result in treble/mid increasing in volume much too early.

You can play with the capacitor and pot values, of course. Shown here is what I actually use in my ASAT Special. C_bleed may be usefull from about 2.2nF (mostly treble bleeding through) to 10nF (lots of mids bleeding through, but making volume pot action a bit difficult/unbalanced).
Because both pots might now be used more often at about 80% rotation (50% of track resistance) you could use 500kA pots to reduce loading, resulting in more treble and sparke, if needed that is.


In the circuit we also see the standard treble bleeder cap accross the volume (200pF typically), which may or may not be present. Its job is to reduce loss of SC sparkle when rolling back the volume and using longer runs of guitar cable. Hence its name C_cablecomp.

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A personal preference of mine is to drastically reduce the value of the tone capacitor C_peak, I don't like the muffled tone with the standard values (22nF to 100nF, typically). Rather, I prefer values that make SC sound like humbuckers, only cutting off the sparkle and giving slightly peaking response at somewhat lower frequencies than where a SC pup would normally have its seld-resonance. Useful values depend much on the pup but within the 1nF to 10nF range there will be good effect.

You can test the basic effect of both caps before any soldering by simple adding C_bleed accross the volume pot (parallel to the existing bleeder, if present), or adding C_peak from vol pot input to GND, using short leads with small alligator clips.

Skill level is easy, you should be able to make good solder joints, that's it. Or test values as described and then have someone do the change (as the tone pot and original tone cap may need a physical rearrangement of how exactly they are connected).

Looks like this in my Tribute ASAT Special:



You can see it pretty much looks like the schematic (except for being rotated).
The top capacitor is the (changed) tone cap (C_peak).
The bottom capacitor is the new bleeder cap (C_bleed), note the added brown wire to make it to the volume pot wiper on the right.
The center lug of the tone pot goes to the top (input) of the vol pot (green cable, as is from factory).
Note the brown original treble bleeder / cable compensation cap (C_cablecomp).

The wiring on the tone pot had to be swapped as noted in previous post. Center and top lug connections had to be flipped (the tone cap was originally mounted between wiper lug and shell and the green cable went to top lug).

Great thread, thanks!