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Topic: Volume pedal pots |
Leo Grassl
From:
Madison TN
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Posted 27 Jul 2019 8:41 am |
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I was curious if anyone has any technical info on volume pedal pots. I used to use an old Goodrich pedal and I moved to an active pedal years ago because I preferred the brighter tone. I have since tried a number of pot pedals that didn't sound as dark as my old Goodrich. I'm guessing this difference in tone has to do largely with the choice of pot. Any thoughts on this?
Thanks!
Leo G |
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Donny Hinson
From:
Glen Burnie, Md. U.S.A.
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Posted 27 Jul 2019 9:48 am
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Two things will make a pot-pedal sound "dark" . The first (and least obvious) is that it's hooked up backwards, with the amp being plugged in where the guitar should go, and vice-versa. The second is a lower-than-optimal value of pot being used. Standard for straight guitars is 250k, while standard for pedal steel is 500k. The difference is because the pickups on a straight guitar are small (of lower impedance), and are therefore affected less by the parallel loading of a pot.
Pot pedals reduce, somewhat, the highs going to the amp. And in many cases, those reduced highs are welcome because of the "bridge pickup only" highs normally attendant on a PSG. |
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Georg Sørtun
From:
Mandal, Agder, Norway
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Posted 27 Jul 2019 10:04 am
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Tonewise a pot is a pot is a pot, etc = a variable signal divider with no effect of its own on tone. How long any brand/type of pot will last and its tolerance for DC is of course another matter, totally unrelated to "tone".
The pot – and what comes after it – will load the PU, and that is what determines the "tone". So the pot's value, cable capacitance, and first amp-stage's input impedance, is part of the PU load that varies with the pot's position. Thus, as PU load isn't a constant, "tone" will vary over the pot's travel. Variations between pots can be "blamed" on various pots imperfections in their resistance curves, but identical resistances measured over the pots for a given PU and amp setup will always result in the same PU load and "tone". |
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Donny Hinson
From:
Glen Burnie, Md. U.S.A.
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Posted 27 Jul 2019 10:58 am
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| Georg Sørtun wrote: |
| Tonewise a pot is a pot is a pot, etc = a variable signal divider with no effect of its own on tone... |
In theory of course, that's true. But in the real world, when one changes the value of a pot in a passive volume circuit, it does indeed change the tone. This isn't due to just the resistance of the pot, of course, but rather to it's interaction with the other (inductive and capacitative) elements of the circuit. So while it's perfectly logical for one to assume that the pot is what's changing the tone, it's important to know that that's not really what's happening.
But try telling that to someone who eschews pot pedals.  |
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Georg Sørtun
From:
Mandal, Agder, Norway
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Posted 27 Jul 2019 12:33 pm
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| Donny Hinson wrote: |
| […] But try telling that to someone who eschews pot pedals. |
Except when asked 
But you're right; many prefer "magic tales" and fiction over dry facts. Sells better too. |
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Tucker Jackson
From:
Portland, Oregon, USA
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Posted 28 Jul 2019 3:12 pm Re: Volume pedal pots
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| Leo Grassl wrote: |
| I have since tried a number of pot pedals that didn't sound as dark as my old Goodrich. I'm guessing this difference in tone has to do largely with the choice of pot. Any thoughts on this? |
If, back in the day, your signal went from the steel directly into the pot pedal... but now, you have some sort of powered unit in line before the pot pedal, that can cause the brighter tone you're hearing. For the science, see Georg and Donny's post about pick up load. |
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Leo Grassl
From:
Madison TN
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Posted 12 Aug 2019 4:44 pm
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I'm sorry for such a late reply. I forgot I had posted this question. Thanks to all who answered me. This is exactly the info I wanted to know! I appreciate it guys.
Leo G |
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Keith Hilton
From:
248 Laurel Road Ozark, Missouri 65721
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Posted 13 Aug 2019 1:59 pm
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Georg, you are so correct when you said, "Many prefer magic tales and fiction, rather than dry facts." Dry facts does not sell as good as tales of magic. Reminds me of a story about a guy who had several successful steak houses. The guy was asked why his steak houses were such a big success. The steak house owner replied--"I sell the sizzle, not the steak." You can not change human nature Georg---magic tales always sells better than dry facts!  |
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Georg Sørtun
From:
Mandal, Agder, Norway
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Posted 13 Aug 2019 5:04 pm
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| Well Keith, good thing I'm not interested in changing human nature. Observing it does it for me, especially now that I'm no longer selling anything and can focus entirely on facts. |
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Keith Hilton
From:
248 Laurel Road Ozark, Missouri 65721
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Posted 14 Aug 2019 9:22 am
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Georg, I consider you one of the most electronically educated-experienced people on this forum. But don't let my bragging on your knowledge go to your head.
Georg, remember back when we had the many posts here on the Forum about the distortion circuit you presented. I built that circuit and it worked as you described, when put first in the signal chain coming out of the guitar. In working with several different types of distortion circuits, I have discovered they all seem to have the same problem. The problem is the location in the signal chain. All distortion circuits I have encountered operate differently if they are first in the signal chain, or located after several pedals on a pedal board. Meaning the distortion circuit is dependent on the force driving the signal. Too much or not enough signal totally alters how the distortion circuit works. This seems to be true, even if you put a unity gain preamp before and after the distortion part of the circuit.
I know this is changing the subject, but maybe you can comment on this subject Georg. |
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Keith Hilton
From:
248 Laurel Road Ozark, Missouri 65721
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Posted 14 Aug 2019 9:26 am
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Georg, I consider you one of the most electronically educated-experienced people on this forum. But don't let my bragging on your knowledge go to your head.
Georg, remember back when we had the many posts here on the Forum about the distortion circuit you presented. I built that circuit and it worked as you described. In working with several different types of distortion circuits, I have discovered they all seem to have the same problem. The problem is the location in the signal chain. All distortion circuits I have encountered operate differently if they are first in the signal chain, or located after several pedals on a pedal board. Meaning the distortion circuit is dependent on the force driving the signal. Too much or not enough signal totally alters how the distortion circuit works. This seems to be true, even if you put a unity gain preamp before and after the distortion part of the circuit.
I know this is changing the subject, but maybe you can comment on this subject Georg. |
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Georg Sørtun
From:
Mandal, Agder, Norway
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Posted 14 Aug 2019 10:16 am
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Keith, others have written and demo'ed so much that I don't have to actually know much about anything electronic these days. Only have to remember where to look for whatever info I need 
Lots of variations, but nearly all distortion circuits are based on signal-clipping – in the signal-way or feedback circuit (or both), and to clip the signal it has to be high no matter what components that handle the actual clipping. If the clipping-components come first there is also the impedance factor, which of course is far from constant in a clipper. That is what a unity gain preamp circuit should solve, but unity means there is no level adjustment to optimise the signal for the clipper. Such an adjustment is most often needed – and other distortion points be kept under control, so I used to put a regulable preamp circuit consisting of single or dual inverters before the actual distortion circuit.
Apart from these basics I cannot add much without studying an actual sound-chain in depth. |
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