How to get the tone-rolled-off low-mid bump without a tone pot

[gdvsbp]

Hi, folks. I’m a guitarist, and I have a circuitry problem that evades my electrical understanding.




When a standard tone control is turned all the way down, it created a low-mid frequency bump in addition to the expected high-frequency roll-off. See the teal T0 line here:









Why is that? At 0 the tone pot should just have no resistance in the circuit, so at that point it’s just a fancy junction for a voltage divider. Is it a capacitance thing? If so, how much capacitance is added by a tone pot?




And, more to my point, how can I recreate the effect of a rolled-off tone pot — expected low-pass plus the low-mid frequency bump — with a switch?




I ask because I play most of my lead stuff on the neck with the tone rolled off, kind of a “woman tone” thing. Part of that sound is that low-mid bump. However, most of the rest of my playing is with the tone turned up and some bass rolled off (PTB-style circuit). It’s… a lot of hand-dancing to turn the bass back up and roll the tone off (and switch to the neck sometimes) when it’s solo time. I have an unused switch on my guitar at the moment, and it occurs to me that I could really streamline things for myself if that switch could easily pop me right into that special tone spot I love so dearly.




So, please, help me understand why this is happening! I know an EQ pedal or something could get me there in a much more straightforward fashion, but I’ve got a very particular itch and I’ve resolved to scratch it with a soldering iron.




For reference, I play an H/H with 50s wiring. Master volume, post-volume master tone, and pre-volume master bass cut.




Thanks for any input, folks!

[Helmholtz]

With tone pot at zero the tone cap is directly wired in parallel with the PU and shifts the resonance to a lower frequency.

So you just need a switch and a tone cap to ground to get the same effect.
In other words you replace the tone pot with a switch.

[Chuck H]

What this guy said^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

And... Just to mention it, the component interaction that creates the resonant peak in the low mids with the tone pot at zero is broken by even a little resistance on the tone pot. Which is why there is only a treble cut when the tone is anywhere besides zero or ten and the mid bump only happens at zero.

Below is a simplified diagram of a basic guitar circuit. The additional circuit that Helmholtz mentioned is wired in red. If you want the exact effect you get with your tone pot at zero then use the same value capacitor as your tone circuit. But also know that you can experiment with the capacitor value to move the frequency of the mid bump.

NOTE: If the switch is noisy or makes any sort of pop sound you should install a 10meg resistor across the switch terminals.


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[gdvsbp]

Thanks, folks! I don’t know why I always assumed it was some interaction with the pot that created that hump… knowing any bit of resistance cancels it out makes a lot more sense. I appreciate you humoring my silly question with responses haha.

[Chuck H]

Since this next thing is a circuit based on similar principals I thought I might go ahead and share it here...

I used this on a guitar when I played gigs. It added simplicity and versatility. Wired to a push/pull pot on the tone control. With the switch on the volume and tone controls are bypassed which increases the resonant peak. Then a comparably small value capacitor to ground lowers the resonant frequency about 2k. So this is a big mid boost that sounds sort of like a cocked Wah pedal. Not the low mid boost of a tone control rolled down but a real kick in the actual mid range frequencies. Great for solos. My favorite trick was to have the volume rolled down for a clean-ish tone and be able to switch between that and full mid boost with the switch.

[Chuck H]

Thanks, folks! I don’t know why I always assumed it was some interaction with the pot that created that hump… knowing any bit of resistance cancels it out makes a lot more sense. I appreciate you humoring my silly question with responses haha.

There are NO silly questions. Certainly we all had to learn about resonant peaks at some time in our own paths. FWIW the impedance of the pickups is relatively low compared to the resistance of the tone pot. The resonant peak is a result of the pickups construction being an inductor. And inductors have "impedance" Impedance is basically AC resistance. So, resistance at a given frequency. When you put an inductor in series with a capacitor you will get a resonant peak. More so than the pickups own capacitance it's the capacitance of the guitar cable you use that determines the resonant characteristics of this inductor/capacitor resonance interaction. Since the pickup has the much lower resistance at the resonant frequency (impedance) the tone pot can fault the interaction that forms the resonant peak between the pickup and the guitar cable capacitance with very little rotational travel introducing a comparably huge resistance, which, in this case, acts as an AC impedance.

You've probably noticed that your guitar sounds different when using a 10' cable compared to a 20' cable. A 10' cable will have around 300pf+ capacitance while a 20' cable has 600pf+. This is changes the frequency of the resonant peak and this is why they sound different.

EDIT: And FWIW Helmholtz likes to use a cable capacitance around 2000pf+ for some of his strat playing. This would be similar to what Jimi Hendrix did with his coiled guitar cable. And it's worth noting that a vintage strat bridge pickup does not have a tone control in circuit. This increases the resonant peak in amplitude, but not frequency. When the higher (2000pf+) capacitance is used the strat bridge resonant peak frequency gets much closer to what you might expect from a typical humbucker in most cases. Usually preferred for higher gain tones. It's no surprise then that a genius like Jimi heard and exploited this phenomenon in his work. When Jimi recorded cleaner sounds he would often switch to a lower capacitance cable. This is very observant on Helmholtz part and you could do worse than to take a tip from Jimi Hendrix regarding tone

There are a lot of myths and hyperbole on line regarding tone but at this point it's really a known science for the most part. For example, there are many metal guys that have a guitar with active pickups and still invest in ultra low capacitance cables. The thing is that active pickups have a low enough output impedance that the guitar cable no longer has much affect on the sound. But guys that don't know better buy them anyway and swear to the improvement.

If you want to know anything about how to get your guitar to sound right you can come here and ask any "silly" questions you like. The answers will be accurate and considered with no lore, mojo hype, BS or hyperbole. Far from "silly" there will be calculations relative complicated circuit interactions that make important, if sometimes subtle differences that can take you from common tones to great tones. We're always here.

[Helmholtz]

For those who don't want to modify their guitar, Neutrik has a plug with 3 built-in switchable caps:
https://www.thomann.de/gb/neutrik_np2rxtimbre.htm

[Helmholtz]

EDIT: And FWIW Helmholtz likes to use a cable capacitance around 2000pf+ for some of his strat playing.

Not quite.
My favorite cables measure around 1100pF (+/-100pF). I.e.before the TS.
2000pF would kill the sparkle.
I use vintage style guitars and PUs, so rel. low inductance.

In the 60s players like Hendrix or Clapton used coiled cables (just check the videos). Still have a few but don't use them.
They looked cool but were not very reliable and had large capacitance at stage lenghts.
Something like 2000pF wasn't unusual then.

This said, I much prefer Hendrix' studio sounds to his stage sounds.

[Chuck H]

Ah. Ok. I thought you had said you used the higher capacitance but I think you must have been referring to Jimi's cable and perhaps mentioned that you prefer a higher capacitance. I misinterpreted things.

I just use a plain ol guitar store brand 20' cable. 600pf+. I don't like a 10' near as well and I haven't tried 1000pf (33-ish feet?) I think I should though since it's a move in the same direction I already prefer.

[gdvsbp]

Since this next thing is a circuit based on similar principals I thought I might go ahead and share it here...

I used this on a guitar when I played gigs. It added simplicity and versatility. Wired to a push/pull pot on the tone control. With the switch on the volume and tone controls are bypassed which increases the resonant peak. Then a comparably small value capacitor to ground lowers the resonant frequency about 2k. So this is a big mid boost that sounds sort of like a cocked Wah pedal. Not the low mid boost of a tone control rolled down but a real kick in the actual mid range frequencies. Great for solos. My favorite trick was to have the volume rolled down for a clean-ish tone and be able to switch between that and full mid boost with the switch.


image widget

I’m afraid I can’t see the image you attached, but from the sound of it that’s basically exactly what I’m doing (just with a much larger cap, and only on the neck pickup). Glad I’m not the only one with the idea!

I wired it up last weekend, and when I flipped the tone-cut switch… big fat nothing, total signal loss. And on top of it, the volume doesn’t roll all the way off now when I have the circuit disengaged. Clearly I made a mistake in my wiring (or original circuit plan)! I’ll have to draw it out and post it here… maybe there’s something obvious I’m missing. There’s a lot going on in that tiny little control cavity now… making me thing that investing in a few colors of wire other than black and white could be helpful for distinguishing portions of the circuit.

Anyway, thanks very much to all here for the discussion; it’s been very helpful! As a home-studio-only player, I never really change the cable (or length of cable) that I’m using. So, I’ve got a loop switcher pedal I’m going to put different lengths of cable in to do some A/B experiments with that capacitance effect.

[pdf64]

A buffer between guitar and the cable under test is going to void the result.
And I expect the pedal will have buffered outputs.

[Helmholtz]

A loop switcher doesn't need to be active.
If it doesn't need a battery or power supply, it's passive and should work as intended.

[gdvsbp]

Yup, this one’s just a little 2-channel passive rig. I don’t use any buffered effects in front of the amp.

[Chuck H]

I'm afraid I can't see the image you attached

That was strange. I'm sure I put it in and looking just now it was replaced by the term "image widget" Anyway, I put it back in and hopefully you'll see it and it will stay there.

[John_H]

With tone pot at zero the tone cap is directly wired in parallel with the PU and shifts the resonance to a lower frequency.

So you just need a switch and a tone cap to ground to get the same effect.
In other words you replace the tone pot with a switch.

I've done a tone circuit similar but added treble bleed cap to it.