Are pots ever matched?

[MattAnonymous]

I read on hear that a 500k pot can range between 400k and 600k.  So I was wondering if having matched sets (like transistors) wood make a difference in certain situations.

[Bluesgeetar]

I don't know there.  If it eases your mind just measure them and match them.  Their values are all over the place.  About 3 weeks ago I measured a little over three thousand pots and values were everywhere.  I still got more to measure!  You know how to measure them right?  The majority I measured where A/B, Clarostat, and CTS.  All over the place.  Not that many dead on values.

[Paul Perry (Frostwave)]

It depends entirely on the circuit. If pots are being used as voltage dividers, it hardly matters. But in some filter applications, it would make all the difference in the world. For FX in general, it shouldn't matter.
I expect most pairs of pots (from the same lot) are matched at least as well as your ears!

[Mark Abbott]

The only time that I've seen people really get worried about pots being matched is when they are used as volume controls in Hifi.

I suppose it makes sense that you would want each channel increasing in volume by the same amount.

To get even further off topic, I've seen some guys buy switches with A LOT of positions and wire it up with their favourite and most trusted resistors. Each to their own madness!

Yours Sincerely

Mark Abbott.

[Mike Burgundy]

yup, volume controls in all their forms - with more than 1 channel.
A balance pot is usually a dual - wouldn't it be annoying if the center mark has one speaker louder than the other?
It only really matters when it's really important response is *equal* to another pot, wether it's on the same shaft or not.
Even when you match the total resistance, the resistance curve doesn't necessarily match either.
I wouldn't worry about it unless you plan to build hi-end stereos or lab equipment that needs pots with reliable scale read-out.

[Mark Hammer]

Uh-huh to all of what has been said.

Pots need to be matched when the capacity of something to perform as predicted depends on the joint action of two or more pots.  Multi-pole filters are one example, balance controls are another, ganged (stereo) tone controls are a third, and stereo volume controls would be a fourth.

Of course, remember that matching for absolute maximum value (i.e., knowing that two pots labelled 500K are both 482k and not one of them 473k and the other 512k) is not the same as two pots or identical absolute value having the identical resistance at each point along their rotation.  That's one reason why audiophiles use multi-position rotary switches and 1% resistors for volume control.  That way, when you move from 60% attenuation to 30% or 75% attenuation, you'll know you don't have to change the relative channel balance to compensate for mismatching of pot taper.

[Nasse]

There is interesting info bout new Texas audio level control chip, ookey dookey just copied this from Elektor Electronics 4/2004:

Tracking error of some vol/level controls:

carbon film pot: more than 3 dB
quality carbon film pot: 0,5...3 dB
conductive plastic pot: 0,1...3 dB
rotary switch & resitors: 0,1 dB
Texas Instruments PGA2311 digital chip: 0,1 dB

I quess low quality pots and with my bad luck the error is sometimes more

Maybe a simple diode volume control is quite easy to match, compared to led/ldr and fet thingies, but has poor distortion and level handling properties

[TheBigMan]

I try to get a good match for guitar pots, especially tone controls.  You could gp insane if you take it to extremes though.

[Peter Snowberg]

The phrase "close enough for Rock n' Roll" comes to mind here.

Take care,
-Peter

[Paul Marossy]

"The phrase "close enough for Rock n' Roll" comes to mind here."

What about "close enough for government work"?  :lol:

I have measured pots ocassionally, I have noticed that they are rarely close to what they are labeled. There really ought to say "approx. 500K"...

[Peter Snowberg]

What about "close enough for government work"?  :lol:

I can tell you as a former Federal employee that it doesn't have to be anywhere near close in that case. In fact, the farther from close... the more typical there.

I like your "truth in labeling" of "approx. 500K". :lol:

Take care,
-Peter

[Nasse]

500 k pots are labelled 470 k here, they are just same stuff

[Paul Marossy]

Or maybe 500K, +/- 30%...  :wink:

[R.G.]

Pots are substantially never matched unless you pay extra for hand-selection. But then, if you use them as voltage dividers (three terminal pots) you don't need matched, only good mechanical tracking from one to the next. When hooked up as two terminal variable resistors, the absolute resistance does matter. It's a problem.

The classical EE way is to design circuits that don't need matched pots, whatever that costs.