How much of a difference will a small-ish variation in pot values make?

[GabenFreeman]

I bought a few 500k pots, a couple of them are around 485k while a couple of them are around 515k. How much of a difference will there be between them or will it be completely imperceptible? Would it even be worth worrying about or should I just slap them in and call it good?

 

[freefrog]

If one single pot goes from 485k to 515k, the differenre at resonant peak should be of 0.12dB. Normal human ears shouldn't detect that...

Incidentally, 485k is not bad: I often test supposed 500k pots whose actual resistance is of 420k or less (the highest that I've ever measured clocking at 650k, for the record).

 

[Artie]

Incidentally, 485k is not bad: I often test supposed 500k pots whose actual resistance is of 420k or less (the highest that I've ever measured clocking at 650k, for the record).

I've mentioned before, I've got a 500k CTS pot here that reads 384K. Unusual, but every once in awhile, even the good one's miss the boat, so to speak.

 

[GuitarStv]

There probably won't be a huge audible difference between the 515 and 485k pots.

I had a 250k pot that measured 310k . . . and it when running it as the volume pot with single coils it made the guitar extremely bright. With humbuckers, I've found that a 500k pot that reads around 450 or lower will be a bit darker.

My guess is that when you start going beyond 10% of the value the pot should be that's when it makes a difference. Once you get to 20% it's going to be very noticeable.

 

[jeremy]

i always test pots before i put em in. if i have four 500k pots im putting in a lp, ill put the highest rated in neck volume, then next highest in neck tone, then bridge volume, then bridge tone. if one is way out of spec or something, ill keep it and make a note of the value. a 375k pot might be perfect for some thing down the road

 

[Artie]

A 375k pot might be perfect for some thing down the road

I was thinking that might be perfect for the Jazz set in my Cort, to tame the brightness a smidge.

 

[beaubrummels]

It can make a difference. Typically it will be in the very top end brightness. When people cite technical specifications as reasons you won't hear it are not considering that after the sound goes from the guitar, through effects, into an amp and hits a speaker then your ears, there are a number of points of compression, distortion, leveling that will make those differences audible in the end.

 

[switchman]

I was going to jokingly respond "small-ish?" but I get your question. I'm glad freefrog has a quantifiable answer.

An explanation that helped me is this. Take a 500K Audio taper pot and turn it down from 10 to to 9. That's about 475K across lugs 1 and 2 input from the pickups/switch and output to switch/jack. I just pulled a few CTS pots out which measure 500-505K and tried this. Do you notice a difference from 10 to 9?

Maybe with an amp really cranked I might but at studio non-drummer/stack volumes I don't. This may ignore other electrical factors I'm just going by my ears.


A while ago I bought a batch of CTS 500K from Stew-Mac with the default +/-20% tolerance. I got some near 400 and 600K. If you had four 400K controls on an LP vs four 600K, yeah that's a compounding difference ears can hear (more so the switch middle position).

After that I started paying more for CTS higher tolerance audio taper pots from The Art of Tone 525K +/-5% or Mojotone 500K -1/+5%. The latter I think were discontinued. The idea was either guaranteed no less than 495K. Since then I decided its pointless.

More recently I bought a bulk package of 500K +/-10% CTS from Mojotone. Oddly about 1 out of 10 were out of spec under 450K or over 550K. They sent me free replacements for those. The rest all measure in +/-5% between 480K and 525K. Maybe I just got lucky I don't know but based on that I see no economic reason either to pay extra.​

 

[GuitarStv]

i always test pots before i put em in. if i have four 500k pots im putting in a lp, ill put the highest rated in neck volume, then next highest in neck tone, then bridge volume, then bridge tone. if one is way out of spec or something, ill keep it and make a note of the value. a 375k pot might be perfect for some thing down the road

I do the same thing. Always use the higher values on the neck and lower on the bridge . . . usually I want more highs out of the one and a touch less from the other. It just makes sense.

 

[Artie]

Here's a super simple test anyone can do, to answer this question definitively for their own ears. The value of the resistor is simply the lowest value you'd ever anticipate using. It could be 25k or 50k if you desire. For added usefulness, make a dial, just with paper, and while outside the guitar, attach a meter to the "top" of the pot and the other end of the resistor. Now mark, with a pen, a few spots you want to hear, like 1 meg, 500k, 300k, 250k, etc.

Use your best junk-yard-dog guitar, and any pickup. (I used my Peavey Rockmaster.)

 

[freefrog]

To put things in perspective...

-When Frank Falbo was evoking small differences becoming noticeable at really high volume, I agreed with him but he was talking about deviations of 1dB, not ten times less.

-Usual tolerance with pots is of +/- 10%. A supposed 250k measuring 310k exhibits a difference of +24%. The values evoked by the OP differ respectively of -3% and +3% relatively to the 500k mentioned...

-pots resistance hasn't necessarily the same meaning relatively to sensorial floor in different circuits. For instance, a same 250k tone control might react differently to the ears of the player , even full up, when connected to ground through an inductor, various tone caps or a mere jumper (I've already shared here a few experimental results showing changes in harmonics with different tone shaping components while a tone pot was set @ 166k, albeit the resonant peak remained at the same level and frequency).

So, ultimately, inviting people to test "for their own ears" is an advice with which I fully agree.

+1 too on the idea to use highest resistance pots with neck pickups... ;-)

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[Teleplayer]

If the pot value varies by 15%, then it is likely to be a noticeable difference IMO. Eg. a 250k pot that measured 285k, or 500k pot that measures around 430k. I think that is the approximate threshold where pot differences become noticeable. I always measure the pots when I assemble a guitar. I try to match pots, for example I would try to install a low-reading 450k volume pot matched with a high reading 550k tone pot. That basically avoids the issue. If both volume and tone pots measured either low or high it would be very likely to cause a significant shift in tone.