# Potentiometers?



## Jocko (May 17, 2010)

Can anyone tell me, are the tone and volume pots logarithmic or linear? Thanks.


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## mhammer (Nov 30, 2007)

Volume is always *logarithmic*, because of how human hearing works. Tone pot taper is often a question of taste and individual preference in how you use it. If you're one of those players who leave it on max treble all the time, then it really doesn't matter what taper it is. If you alternate between full on and full off, and tend not to futz around with the in-between, again it doesn't matter what the taper is.

How do you generally use your tone control/s?

There is considerable discussion of pot taper over the years in the Guitar Tech forum here: Guitar Tech


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## Jocko (May 17, 2010)

Thought volume pots were logarithmic as decibels are a logarithmic scale. I tend to use tone controls either full on or full off. Still undecided whether to go for 250K, 500K or even 1Meg. I am going to try a treble bleed capacitor, a la Telecaster. These are for a crappy Stagg M350 I am playing about with. Thanks mhammer for your input. I will give your link a good read.


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## keeperofthegood (Apr 30, 2008)

Logarithm is a math formula. Hearing is not a perfect log. Most makers use modified log tapers (we had a good long talk on this not long ago and yes the makers web sites will say they use a modification of the hearing logarithms and not a true log or wording to this effect) and these are 'audio', if you wanted a proper log taper for a piece of science equipment that would not be an audio taper but based on whatever the formula is that you supply to the maker.

As to full on/off, why use a pot? Use a switch ('bout a buck) and put a resistor across it, then you would be able to quickly cut it in and out, and you could just put in values until you have what you like at 10 cents a resistor rather than 5 dollars plus for what is essentially being used as a switch.


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## J-75 (Jul 29, 2010)

keeperofthegood said:


> Logarithm is a math formula. Hearing is not a perfect log. Most makers use modified log tapers (we had a good long talk on this not long ago and yes the makers web sites will say they use a modification of the hearing logarithms and not a true log or wording to this effect) and these are 'audio', if you wanted a proper log taper for a piece of science equipment that would not be an audio taper but based on whatever the formula is that you supply to the maker.


This is true. The audio world has for years relied on "audio taper" pots for critical equipment. They loosely fall into the category of log taper pots, but are a special variety.
First, it is correct that various log taper pots have been manufactured, based on specific client orders, eg. natural log versus base-10, and in-between. Medical electronics represents one of those critical markets.
Audio taper pots have an 'S'-shape curve where the _middle_ portion of its turning range has a finer (smaller) change in resistance per degree of rotation, as compared to the ends. This allows a more critically fine level of tuning in the normal (middle) operating range of the control.

Bill


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## Jocko (May 17, 2010)

Had heard about "Audio taper". Thanks for explaining it to me. The switch for tone is a great idea. May try a 3 or 5 position rotary switch with a selection of resistor values. Change tone like changing gear on a bike! Thanks for the inspiration.


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## Spellcaster (Jan 7, 2008)

" May try a 3 or 5 position rotary switch with a selection of resistor values. Change tone like changing gear on a bike! "

Isn't that basically what a Varitone is?


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## Phlegethon (Dec 18, 2009)

Alexplorer's Axe Hacks: Varitone

varitone circuits are notch filters with several options for cutting various frequencies if you build your own. they can make LP's sound like strats, and the other way around. they're quite handy IMO


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## Spellcaster (Jan 7, 2008)

"varitone circuits are notch filters....."

Thanks Phlegethon, I see what you're getting at. So, what's the deal with the resistors? Is that a way of siphoning off high frequency by using resistors to simulate different value pots?


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## mhammer (Nov 30, 2007)

The "deal with resistors" refers to the loading effects of different value volume pots. There is some truth and some bunkum in that particular soup.

Treble loss through the cable, and with respect to the input impedance of whatever you're plugging into, depends partly on the resistance from the "hot" to ground. When that resistance is lower, you tend to lose more top end. As a consequence, it has become tradition to use lower-value volume pots for single-coil pickups (to tame the "brittleness"), and higher-value pots with PAF-style humbuckers to hang onto as much of their limited treble as you can. Lord only knows what sounds "best" for things like dual rails, P90s, stacked humbuckers, etc. The general principle, though, is that if you want a little less treble, use a lower value, and if you want a little more, use a higher value.

But here's the thing, the resistance to ground is only equal to the value of the pot when the volume is maxed. Turn the volume down even a bit, such that the wiper moves away from max resistance to ground, and most of the utility of having this or that value volume pot is lost. Indeed, this is why, despite using lower-value volume pots to "tame" the treble in their guitars, Fender is the one that introduced the compensating bypass cap in volume controls so that one wouldn't lose too *much* treble as volume was reduced. Keep in mind that if you have a 500k volume pot and back off the volume a bit, you'll have, say, 50k in series with the pickup, and the remaining 450k to ground. Back off some more, and you may have 200k in series with the pickup, and the remaining 300k to ground. Obviously, at that point any tonal advantage you may have introduced by means of a higher-value pot has been pretty much lost. Some folks, like Jeff Beck and others, can use this loading to their benefit, by diming the amp and using the passive treble loss as a sort of adjustment. The rest of us are pretty much leave-it-up-full and turn it down when requested to.

The "resistor thing" is an attempt to mimic the effects of having this or that value volume pot *when it's up full*. So, if you used a 1M volume pot (which I kinda like), and strapped a 1M resistor in parallel with it (i.e., from one outside lug to the other), you would have the electronic equivalent of a 500k pot. Stick a 390k across the pot instead, and you have the equivalent of a 280k volume pot. Some years back, Craig Anderton published a little project in Guitar Player, that proposed using a rotary switch to select between values of parallel resistors, so that folks could experiment with the loading effect. If you have a SC-equipped guitar with 1M pickups, this may be of great use.

All of this works like a charm...provided you have the volume up full. So, the key question here is how you use your volume pot. If you're the sort that plays distorted all the time, then I can pretty much assure you that no one will notice the difference. If you play clean most of the time, with the volume up full, and let a compressor/limiter keep your wilder strums and pick attack under control so you don't overwhelm the singer, then it may have some limited benefit for you. If you're the type that constantly fiddles with the volume pot, then it may not hold any great advantage whatsoever.

I've built myself some Varitone boxes. They CAN have a nice honk-taming effect, but the thing to remember about those passive mid-cut units is that a LOT of signal lives in that zone, so they introduce very noticeable passive loss (enough that I felt it necessary to build in a FET booster to compensate). It you're relying on hot pickups to overdrive your amp, a Varitone may change the tone in useful ways, but it *will* "unheat" your pickup signal. Again, if you prefer to play clean, such a circuit can provide some nice tonal flexibility.


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