Guitar Volume Treble Bleed Tester

[stallik]

Guitar volume pots shave off a little treble when turned down. We know this. The common remedy is to run a small cap between lugs 1 & 2 of the volume pot. A resistor is usually placed in parallel with the cap though sometimes in series and everyone has a favorite set of values for both components.

Whilst playing with DeadAstro's idea of a switched volume pot in a stompbox, the instant change of sound highlighted the effect of the treble roll off so I started playing with values and noticed the following:

• Treble bypass seriously effects the way a distortion pedal cleans up when you roll off guitar volume. The choice of values can alter the effect from dirty > clean or dirty > dirty at lower volume
• The values will also alter the clean sound when rolling off the volume and the ideal values for this may not match those for dirty sounds
• The above effects are different on different guitars, PU's, effects chains & amps
• Guitars with 2 volume pots can have different combinations

I've been using a favorite combination for years but had no idea how effective this could be at improving the sound of a poor guitar and ruining the sound of a good one.
Trouble is, rewiring a strat is a pain and even leaving trailing leads from under the scratchplate and breadboarding different components didn't allow me to accurately compare sounds so I put together a little test box with a few values on rotary switches. I've added switchable volume pots (250k & 500k) and also parallel/series switching for the cap & resistor. Position 1 on each rotary is bypass

Plug the guitar directly into the box then the output into the pedal chain or amp. Keep guitar volume on full then audition the various combinations using the volume pot in the tester. To compare with your current guitar, max the testers volume pot and use the guitar's. Don't use combinations of both! When you find something you like, wire those values into the guitar.

I've tested it in anger for a friend and the nice thing is that he did all the work auditioning and I got all the credit

Hardly elegant and there's probably a better way to do it. One word of warning though, with so many choices available, it can take some time to do the auditioning and if your friend playing is really bad......

No circuit diagram, just this - sorry

[karbomusic]

Totally off topic - I ended up removing mine not long ago. Way back in the 90s, I was sorely disappointed to lose treble when turning down the volume, now I like it because if I'm turning down, it tucks the guitar in better which is what I wanted from turning down to begin with. Total personal satisfaction and a little off topic but thought I'd ad. Back on topic...

[stallik]

Agreed Kary. There's some times you really want to loose the treble (my tele for example). This thing just allows you to test different setting without rewiring the guitar

[karbomusic]

Yep, didn't want to stray from your great topic, just happened to catch my attention. Interested to see where it goes!

[Mark Hammer]

Some time back, I suggested adapting the style of Tone control found on older Fender 2-knob amps, as below.  In one direction it reduces the resistance in series with a 500pf bypass cap across the Volume pot, while in the other direction it increases that resistance and reduces the resistance in series with a 5000pf cap to ground on the input of the Volume pot.  So, a reciprocal action.  Of course, if one has such an amplifier, you notice that the brightening function pretty much disappears at full volume, just as it does on guitars, whereas the dulling action of the Tone control rotated the other way has an impact no matter what the volume setting.

I tried implementing it on a guitar and it worked as expected.  The caveat is that one tends to need an additional parallel resistor on the leg of the pot in series with the bypass cap; the reason being that smaller values of series resistance make a bigger difference on that side.  So, if one was using a 1meg Volume pot, you probably want the brightening function to consist of resistance variations of less than 100k in series with the bypass cap.

[Ripdivot]

I do it like this in all of my guitars. Use what ever treble bleed values you like. What I like about this is by connecting to the tone control as shown it allows you to have full treble bleed or remove as much as you need depending on the amp or pedal you are feeding in to. With the tone control fully up (clockwise) the bleed works normal. When you turn the tone control from 10 to 8 you basically remove the treble bleed circuit and then from 8 down to 0 the tone control works normal. Adjusting the tone control between 10 and 8 lets you add or remove as much of the treble bleed as you want. This circuit seems to work equally well with 250K or 500K pots. The treble bleed values shown are the ones I like.

[dsayanp]

Can this tester be used as a standalone pedal? (Before a varitone stompbox for example). I've been looking for a way to have multiple treble bleeds in my tele without compromising the structural integrity of the body and this looks like an awesome solution.

Cheers

[stallik]

It's a bit impractical to use it as a Stompbox because you have to use the volume control on the test box instead of on the guitar. This is fine when testing but the idea is to make a choice and then wire those values into the guitar.

[Rob Strand]

You have to watch out about comparing apples with apples.
The cable capacitance has a lot to do with the loss in treble.
And the amount of cable capacitance has a lot to do with the length (and the type of cable).

Guitar  ->    Cable capacitance ->  Amp/pedal

Isn't the same as:

Guitar  ->    Cable1 capacitance ->  Treble bleeder ->  Cable2 capacitance -> Amp/pedal

It will be close if Cable1 is very short and Cable2 is a "normal" length lead.

[stallik]

Good point Rob. As it happens I had a very short cable 1 for convenience. Happy accident.
There is a tiny difference anyhow but small enough not to notice by the time everything's wired up

[Mark Hammer]

For dual-volume guitars, I like to use a higher-than-normal treble-bleed cap on the bridge pickup volume.  So something like 1200-1500pf.  It has the effect of acting like a bass rolloff until you get down to around 5 or 6 (after which it acts like a volume pot).  Great for bridge humbuckers where you want a thinner tone, and similar impact to the Contour control used on Reverend and some G&L guitars.

[dsayanp]

So the volume knob in the pedal would completely bypass the volume from the guitar? No way to keep the volume from the pedal at max and fiddle with it with the guitar...?

[deadastronaut]

funny, i only just added a cap/resistor to my guitar back off vol pedal

yesterday..

went with 1nf/150k para..seems ok.

[stallik]

So the volume knob in the pedal would completely bypass the volume from the guitar? No way to keep the volume from the pedal at max and fiddle with it with the guitar...?

Sorry no. the cap and resistor has to be attached to the pot you're turning in order to gauge the effect. Leave the guitar volume on full when testing and use the one on the test box. When happy, wire those values into the guitar and the effect should be pretty much the same.