Measuring potentiometer resistance in situ

jaymenon

My rear routed strat sounds a little less bright than I sould expect - and I wonder if the volume potentiometer might possibly be a bit lower than 250K...

Is there a way to measure the value of my volume pot without doing any major de-soldering? Or perhaps minimal de-soldering?

Also does the presence of a Kinman type treble bleed cap/resistor affect the procedure (or readings)?

Expert opinions most appreciated...

 

ICBM

It doesn’t make a significant difference. It would need to be low by about 25% to be audible. I did some testing and found that it was much less important than I expected.

If you do want to measure it, it’s fairly easy - turn the volume to zero, select one pickup only, plug a cable in and measure the resistance from tip to sleeve at the other end. It should read 0 ohms. Now turn the volume up slowly, watching the resistance - it will peak when the control is at about 7 (with a Log pot) and then go back down to the DC resistance of the pickup when the knob is at 10.

Take the peak value, multiply by 4 and subtract the pickup resistance - that gives the pot resistance.

The treble pass network complicates things slightly if the resistor is in parallel with the cap, but I think it just moves the position of the peak rather than changing the value. (I would need to draw it out and do some calculations, but I think that’s right.)

But - and you aren’t going to like this - the most common cause of dull tone on a Fender-type guitar is too much shielding...

jaymenon

Thanks John -  my treble bypass involves a capacitor and a resistor in series.

Re: shielding, on my guitar it involves only one coat of graphite paint. Is that too much?

ICBM

jaymenon said:

my treble bypass involves a capacitor and a resistor in series.

In that case it won’t affect the DC resistance measurement at all.

jaymenon said:

Re: shielding, on my guitar it involves only one coat of graphite paint. Is that too much?

It’s not the thickness of it, it’s how close it is to the pickups and wiring. It could also be the shielded cables to the pickups, I think I remember you said it has those.

Capacitance is a function of area and separation - the larger the area and the closer it is, the higher the capacitance.

Try temporarily disconnecting the cavity shielding and see if it improves - that will at least help to identify where the problem is.

jaymenon

Thanks John.  Measured accordingly, my volume pot value is 257K

Now to disconnect the shielding and see what happens (the bright switch on my amp pretty much solves the problem though),

Thanks very much...

jaymenon

How about measuring tone pot values in situ? Is that possible please?

Dave_Mc

Can I piggyback on this great thread slightly and ask if it works if you've used a resistor to make a 500k volume pot into 250k for an HSS guitar?

That's code for saying I tried it and I don't think it worked, it still just read 500k. Is there any way to test if the resistor has worked for the correct selector switch setting? I have an awful habit of wiring blade selector switches backwards for some reason and I don't want the humbucker to be seeing 250k while the neck single coil will be seeing 500k... and it's a subtle enough difference that I don't want to trust my ears!  

SteveRobinson

jaymenon said:

How about measuring tone pot values in situ? Is that possible please?

Easy @jaymenon it's only connected at one end so it's a simple measurement across the outer lugs

jaymenon

Thanks Steve - that makes sense :-)

jaymenon

...and done.