Where to source pots with a specific value?

whitedogbanana

Is there a shop that would be willing to find and test pot values before selling them? My goal is to find the lowest value 500k pot and the highest value 300k pot. 

I have a bright LP currently with 550k pots and I am looking to tame the brightness a bit. I also want to experiment myself how different pot value would change the sound. Given there is generally 10% tolerance on pots for a 500k pot it could be anywhere between 450-550k and 270-330k for a 300k pot, it is a bit of a blind shot.

Any recommendation is appreciated!

SteveRobinson

You can experiment with different values by putting a resistor across the outside legs of the pot to change the overall value. The taper may well be different but if you just want to hear what it's like at 10, you can.

E.g. to "convert" your 550KΩ pot to 450KΩ, put a 2.5MΩ resistor across it.

https://www.allaboutcircuits.com/tools/parallel-resistance-calculator/

ICBM

Contrary to popular myth, you will not hear any significant difference in tone between pots within the standard tolerance range.

I’ve done some direct-switching experiments with extra resistors as SteveRobinson describes, and there was no audible difference until the drop was more than about 25% of the original value. (Or higher by about 33% of the value.)

There is a very good reason why the standard 20% tolerance on pots was chosen.

Funkfingers

A few years ago, some bloke made a You Tube demonstration video, using a test rig, to enable direct comparison of capacitors in guitar control circuitry.

The video upset a few punters.

By now, there ought to be a similar video comparing pots for volume and simple treble roll off applications.

Jimbro66

Funkfingers said:

A few years ago, some bloke made a You Tube demonstration video, using a test rig, to enable direct comparison of capacitors in guitar control circuitry.

There is a YouTube video of that by Lindy Fralin that is quite interesting. He talks about the capacitor values he likes for neck and bridge pickups and demos the differences. For single tone control guitars (Tele example) he briefly mentions push/pull tone control with different value caps depending on which pickup is in use. In practice not particularly practical to change pickups and switch cap but overall a fairly informative video.

There is also an American guy (can't remember his name) who talks about how pots work and the pros and cons of different values but it's really aimed at novices 

ICBM

Cap *values* do make a difference - again with the qualification that you need at least a 20% difference to be able to hear it, which is also the standard tolerance - but types and brands don’t.

There’s also some evidence that the quality and physical size of the pots can affect the tone - because pots have ‘stray capacitance’ which is related to their construction and dimensions - but that’s harder to test with switching.

Jimbro66

Found it

https://youtu.be/8t_eqST1pWQ

springhead

There's a series of videos here where exciter coils are placed over the pickups and then a switching box is used to demonstrate the effect of various changes to the electrics.  First one is to do with pot value.

https://www.youtube.com/watch?v=W8dp9clGe-I

Jimbro66

That’s an excellent series of videos @springhead.

Coincidentally I was experimenting with pot, capacitor and resistor values only yesterday evening. The Tele I recently put together with Filtertron pickups was wired with the component values recommended by TV Jones but I was not altogether happy with the results. Bear in mind that TV Classics have fairly low coil resistance. After playing around with a bag of caps and several pot types/values I arrived at something more pleasing to my ear. Likewise, without a treble bleed circuit on the vol control the pickups quickly became muddy as the volume control was backed off. TV Jones recommended a .001 cap in parallel with a 150k resistor but I found that made the sound too thin at lower volumes so, retaining the .001 cap, I increased resistor values until the backed-off sound was reasonably close to the full volume sound and settled for 330k. All done by ear, but seeing results on screen as in those videos adds interest.