Mismatched vol/tone pot resistances

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BarnyardCoral
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Mismatched vol/tone pot resistances

Post by BarnyardCoral » Thu Jul 28, 2022 7:19 pm

Hey all,
So a while back I did the Rothstein Super PTB mod on my CPJM, but I installed 500k vol pots and kept the treble/bass roll-off pots at 1M. While I have no issues with this setup, I'm curious as to what this technically does to my signal. I'm no electrical engineer but what effect does mismatched resistances have on the overall signal? What would happen if it was reversed, with a 1M vol pot and 500k tone pot?
And I will be the one to hold Larry Csonka down, kiss him so hard, I'll take Larry Csonka's breath away...
*Scheckenbacker on TGP

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Lost In Autumn
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Re: Mismatched vol/tone pot resistances

Post by Lost In Autumn » Fri Jul 29, 2022 1:15 am

my standard setup these days is a 1meg volume and 500K tone, with a 0.033µ orange drop cap on the tone and a treble bleed circuit on the volume. 1meg is typically regarded as "wide open," similar to going straight to the output jack. The tones can be overly bright and harsh sounding, but it will give a very wide range of sounds when using the tine pot. a 500K pot rolls off some of the treble automatically, making the tone a little warmer and less bright.

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JackFawkes
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Re: Mismatched vol/tone pot resistances

Post by JackFawkes » Fri Jul 29, 2022 11:18 am

If I'm not mistaken, I think BarnyardCoral was specifically asking about the effect of using pot values of 500K/1M/1M in a Passive Treble Bass circuit, rather than the 250K/500K/1M values that are commonly used in PTB; and then also about what effect swapping the Volume and Treble pot values might have.

Personally, I really like PTB with the right pickups. Everything that I think I know about how PTB works comes from the GuitarNutz thread Bass-cut and the G&L PTB system; it's been a while since I read it, but I'll give it a shot based on what I recall... apologies in advance if anything I say turns out to be inaccurate :squint:

First off, compared to G&L's typical values (and assuming you have all the controls set to "10"), your higher value Vol and Treb pots will raise the resonant peak of your pickups a bit, making them sound a bit "brighter" compared to lower value pots (just like they would with more traditional control wiring schemes).
If I remember correctly, someone in the Guitar Nuts thread said that the effectiveness of the bass-cut is related to the difference between the Vol and Bass pots... a 250K Vol with a 1M Bass makes a good amount of cut available, a 500K Vol with a 1M Bass will have less total cut available, and pairing a 1M Vol with a 1M Bass will make the bass control cut even less when turned all the way down.

So to answer your question... if you swapped your Vol and Treb pot values and used a PTB wiring scheme with 1M Volume, 500K Treble, and 1M Bass:
Your Vol+Treb resistance total would stay the same, so the resonance peak of your pickups would remain the same when everything is at "10".
But since your Vol versus Bass values would be so close, your Bass pot would cut less bass when turned down.

Hope that helps!

Jack

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BarnyardCoral
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Re: Mismatched vol/tone pot resistances

Post by BarnyardCoral » Fri Jul 29, 2022 5:59 pm

JackFawkes wrote:
Fri Jul 29, 2022 11:18 am
If I'm not mistaken, I think BarnyardCoral was specifically asking about the effect of using pot values of 500K/1M/1M in a Passive Treble Bass circuit, rather than the 250K/500K/1M values that are commonly used in PTB; and then also about what effect swapping the Volume and Treble pot values might have.

Personally, I really like PTB with the right pickups. Everything that I think I know about how PTB works comes from the GuitarNutz thread Bass-cut and the G&L PTB system; it's been a while since I read it, but I'll give it a shot based on what I recall... apologies in advance if anything I say turns out to be inaccurate :squint:

First off, compared to G&L's typical values (and assuming you have all the controls set to "10"), your higher value Vol and Treb pots will raise the resonant peak of your pickups a bit, making them sound a bit "brighter" compared to lower value pots (just like they would with more traditional control wiring schemes).
If I remember correctly, someone in the Guitar Nuts thread said that the effectiveness of the bass-cut is related to the difference between the Vol and Bass pots... a 250K Vol with a 1M Bass makes a good amount of cut available, a 500K Vol with a 1M Bass will have less total cut available, and pairing a 1M Vol with a 1M Bass will make the bass control cut even less when turned all the way down.

So to answer your question... if you swapped your Vol and Treb pot values and used a PTB wiring scheme with 1M Volume, 500K Treble, and 1M Bass:
Your Vol+Treb resistance total would stay the same, so the resonance peak of your pickups would remain the same when everything is at "10".
But since your Vol versus Bass values would be so close, your Bass pot would cut less bass when turned down.

Hope that helps!

Jack
That was a fantastic and helpful reply. That's exactly what I was looking for. Thanks!
And I will be the one to hold Larry Csonka down, kiss him so hard, I'll take Larry Csonka's breath away...
*Scheckenbacker on TGP

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jorri
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Re: Mismatched vol/tone pot resistances

Post by jorri » Mon Aug 01, 2022 7:51 am

Another thing is the parallel resistance determining impedance even when the pots/caps are 'out the circuit' as much as they can efectively be on 'full'.

So, mentioned was the effect of different values of volume pot (that resonant peak and high rolloff). Well, also the tone pot adds to this effect as well, and its calculated in parallel.

e.g. if you have 1meg --> 1meg
2 * 1meg pots --> 500k
4 * 1 meg pots --> 250k
or different pots?: 1meg, 1meg, 500k --> 250k
1meg, 500k, 500k --> 200k

anyway, who knows how much effect that has with 50k difference.

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Re: Mismatched vol/tone pot resistances

Post by JackFawkes » Mon Aug 01, 2022 8:44 am

jorri wrote:
Mon Aug 01, 2022 7:51 am
anyway, who knows how much effect that has with 50k difference.
On average? Mathematically, a 50K difference in pickup loading will translate into about a 0.4dB difference in response at the frequency peak, so... much too small a difference for any human to hear ;D

Jack

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Re: Mismatched vol/tone pot resistances

Post by jorri » Tue Aug 02, 2022 7:15 am

JackFawkes wrote:
Mon Aug 01, 2022 8:44 am
jorri wrote:
Mon Aug 01, 2022 7:51 am
anyway, who knows how much effect that has with 50k difference.
On average? Mathematically, a 50K difference in pickup loading will translate into about a 0.4dB difference in response at the frequency peak, so... much too small a difference for any human to hear ;D

Jack
True! It will make other differences when using mismatched pots though, and i didn't read the OP properly until half of it was written :whistle:

Applying this to certain guitars it begins to make sense why guitars with 4 pots started on this convention of 500k...but they happened to also use humbuckers, so it got associated with specific values for humbuckers (my theory i suppose...of course, only when both pickups engaged). I applied this to my jazz bass though, basically just the change in sound when i removed a volume and added a pickup switch, plus 1meg tone control. the thing with Jazz Basses is perhaps that impedance ends up very low when its 250k/3=~80k and i felt I am never in a situation where there is too much treble!

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