Question About Pots...

[Strat Avenger]

'Probably a stupid question, but what's the difference between a 500k Volume pot and a 500k Tone pot? I used to think they were the same, with with a added capacitor on the Tone pot, but now I see that there are specific designations for each.

 

[line6man]

It's marketing nonsense.

There is absolutely no difference whatsoever between the components required to perform the tasks mentioned, unless you have the functionality-related preference of taper for each control. Some like linear for one and audio for the other.

When it comes to wiring up a guitar, where you are dealing with relatively low frequencies, extremely low current, voltage and thermal dissipation, not a whole lot of the manufacturing specifications of potentiometers are important. You don't need to pay attention to much more than tolerance and taper.

 

[line6man]

I used to think they were the same, with with a added capacitor on the Tone pot

Tone controls are wired differently than volume pots.
Remember that, while a tone pot varies the impedance parallel to the signal, with the capacitor there to block the low frequencies, a volume pot varies the parallel impedance across the entire signal, while also introducing a series resistance between the pickups and output.

 

[Cagey]

Tone pots in guitars don't block low frequencies; they provide a low impedance path to ground for high frequencies. In other words, they filter out high frequencies and only allow low frequency signals to pass by. That's why it's called a "low-pass" filter. It's not necessarily the best setup, but it's very inexpensive. High-pass filters are slightly more complicated in that they often require inductors. They cost a lot more than capacitors, relatively speaking, so OEMs are loathe to use them. Wouldn't want to add $.10 cents to the cost of a guitar that costs hundreds of dollars. Ruins the bottom line. Or, to be more charitable, it's rare that anyone wants to diminish the low-end response.

 

[line6man]

Tone pots in guitars don't block low frequencies; they provide a low impedance path to ground for high frequencies.

Reread what I said.
I said the capacitor is there to block low frequencies, not the pot. With a pot running parallel to the signal, the impedance varies over the entire signal, but when you put a capacitor in series with that pot, the capacitor blocks the low frequencies, so that only the high frequencies follow a low impedance path to ground.

 

[B3Guy]

earthenware all the way, man  :rock-on:

 

[Strat Avenger]

Okay guys, so are Tone pots typically linear taper?

 

[Cagey]

Tone pots in guitars don't block low frequencies; they provide a low impedance path to ground for high frequencies.

Reread what I said.
I said the capacitor is there to block low frequencies, not the pot. With a pot running parallel to the signal, the impedance varies over the entire signal, but when you put a capacitor in series with that pot, the capacitor blocks the low frequencies, so that only the high frequencies follow a low impedance path to ground.

Ok. I shouldn't have named the pot when I meant the "tone control" circuit.

I tend to follow physical circuit behavior rather than performance dynamics, which is probably just semantics but it's the way I think. I don't think of it as blocking low frequencies, which is essentially a non-event, I think of what the circuit is actually doing, which in this case is providing a path to ground for high frequencies. Maybe it's an opportunistic vs. inexpedient point of view.

 

[Cagey]

Okay guys, so are Tone pots typically linear taper?

Typically, they're not. But, they can be and it doesn't hurt anything. It's a response curve thing, and sort of a matter of taste/desire. With volume pots, you never want a linear response because your ear doesn't work that way with respect to sound pressure levels. But, frequency response is different, and sensitivity to it varies widely amongst people, and even with the same person as they age.

 

[line6man]

Okay guys, so are Tone pots typically linear taper?

Most people find that linear taper pots, when used as tone controls, with typical pickup impedances, tend to act as on/off switches.
Remember that a linear taper pot has to be rolled halfway down to get to the same resistance as an audio taper rolled down around a fifth of the way. Most find that a linear pot will not have much of an effect until you roll it way down, and then it suddenly kicks in.

These sort of things are often up for debate, however, and people will fight to the death over what taper they like. But that's usually for volume controls. It's relatively uncommon to hear someone prefer linear taper pots for their tone controls.

 

[line6man]

Tone pots in guitars don't block low frequencies; they provide a low impedance path to ground for high frequencies.

Reread what I said.
I said the capacitor is there to block low frequencies, not the pot. With a pot running parallel to the signal, the impedance varies over the entire signal, but when you put a capacitor in series with that pot, the capacitor blocks the low frequencies, so that only the high frequencies follow a low impedance path to ground.

Ok. I shouldn't have named the pot when I meant the "tone control" circuit.

I tend to follow physical circuit behavior rather than performance dynamics, which is probably just semantics but it's the way I think. I don't think of it as blocking low frequencies, which is essentially a non-event, I think of what the circuit is actually doing, which in this case is providing a path to ground for high frequencies. Maybe it's an opportunistic vs. inexpedient point of view.

A charge builds up on one plate that cannot be equaled on the other plate in time to allow low frequencies to pass.  Therefore, it blocks the passage of low frequencies. That IS what the circuit is actually doing. The capacitor varies it's impedance with the frequency of the signal, such that high frequencies pass through with a lower impedance the higher the frequency rises, while low frequencies encounter a higher impedance, the lower the frequency drops.

 

[Strat Avenger]

Okay guys, so are Tone pots typically linear taper?

Typically, they're not. But, they can be and it doesn't hurt anything. It's a response curve thing, and sort of a matter of taste/desire. With volume pots, you never want a linear response because your ear doesn't work that way with respect to sound pressure levels. But, frequency response is different, and sensitivity to it varies widely amongst people, and even with the same person as they age.

Yeah, I already knew that about Volume pots (found out the hard way -- I couldn't do volume swells with it. Anything above absolute zero was like "instant on". Really sucked).

 

[Cagey]

Yeah, I already knew that about Volume pots (found out the hard way -- I couldn't do volume swells with it. Anything above absolute zero was like "instant on". Really sucked).

That's how I found out, too.

A long time ago I worked for an industrial controls manufacturer who'd been in business since before dirt was invented, and they had tons of stuff out in factories that was still in use after 40+ years (actually, it would 70+ years now). We still serviced that stuff and had the ability to restore it to factory original. Cost a pretty penny, but maintenance budgets are different than capital expenditure budgets, so we'd get in stuff that was absolutely destroyed and get many thousands of dollars to repair when much better equipment was available new at a fraction of the cost.

Anyway, a great deal of that old gear was built to military specifications because that led to stuff that could withstand incredible abuse. One of the common parts was pots and caps that could live in really bad environments and continue working with a smile. So, early on in my guitar and amp modifying days, I'd "liberate" some of those parts to improve my gear <grin>

Problem was, they were often designed not only for the ability to live through hell, but for high precision in timing/sequencing operations. No good at all for most audio applications, but I didn't know that then. You'd put one of these pots in, and it behaved like a switch. Use one of those beastie caps, and you almost couldn't fit it into the space allowed. It was just overkill in the extreme.

You can actually still buy some of those parts, but they're unsuitable in many cases. Plus, they're expensive as sin. A sealed milspec Clarostat pot will run you $15 or so. Oil over paper caps can cost more than that, and neither is necessary.

 

[stubhead]

Or maybe the glass is just twice as big as it needs to be.