Strange Resistance Measurements at my LP Output Jack

janalex

New member
Hi all,

I'm not very technically minded. Please help me out.

When measured outside the guitar at 70F my PAFs measure 7.35k and 8.58k

When measured from the tip of a short guitar cord inside the guitar they measure. ~7.67k and 8.47k

Typically I've seen the values decrease in circuit as in all my other guitars with this meter. Makes sense since the pot is in parallel with the pickup decreasing total resistance. My concern is that something is adding resistance to the neck pickup only.

The circuit follows the 50's wiring. I measured bridge lug 1 to ground and bridge wiper to ground and got the same value, 8.47K. I measured neck lug 1 to ground and got 7.25K which I would expect given the pickup measures around 7.35K out of the guitar. Neck wiper to ground measures 7.67K though (same as output jack). Also it seems the elevated resistance at the output jack neck position varies. Over the last week have seen it as low as 7.47K and as high as 7.8k.

I have plenty of worn pots on hand and I haven't found one where the resistance across the pot differs from the resistance to the wiper in open position. Pot has no audible issues with intermittent signal or scratchiness. This I presume leaves the switch neck side only as the culprit or maybe the soldering or tone cap?? Maybe oxidation on the switch? Has anyone experienced something similar? What if any effect on the tone could this have? In a perfect circuit there should be no added resistance (like in by bridge position) so I feel I need to correct this but would like to get some input on how to go about it.
 
Re: Strange Resistance Measurements at my LP Output Jack

When measured outside the guitar at 70F my PAFs measure 7.35k and 8.58k

When measured from the tip of a short guitar cord inside the guitar they measure. ~7.67k and 8.47k

Typically I've seen the values decrease in circuit as in all my other guitars with this meter. Makes sense since the pot is in parallel with the pickup decreasing total resistance. My concern is that something is adding resistance to the neck pickup only.

That added amount of resistance is too small to effect the signal at all. If I had to guess at the cause, I'd suspect maybe the volume pot or pots are adding some resistance, even at 10, since the wiper only as a mechanical connection to the resistive strip and isn't soldered. Maybe you could try measuring the resistance across the volume pot and see if it really reaches 0 ohms at 10.
 
Re: Strange Resistance Measurements at my LP Output Jack

+1 Pots don't go all the way to 10, unless you get a no-load pot.
 
Re: Strange Resistance Measurements at my LP Output Jack

Anyone care to explain why the bridge pickup has a higher DCR outside of the guitar?
 
Re: Strange Resistance Measurements at my LP Output Jack

The volume pot is in parallel with the pickup. Total resistance decreases when wired in parallel.
 
Re: Strange Resistance Measurements at my LP Output Jack

In that case, why is the neck lower when outside the guitar?
 
Re: Strange Resistance Measurements at my LP Output Jack

It shouldn’t. This is my original question

Ah, my bad I lost my train of thought in my head and forgot your question. Given that you have ~0.3k of variance in your readings, there is always the chance the numbers were off. I do not think that oxidation on the switch would be the cause because switch oxidation usually causes major losses of output rather than a small change in DCR.

So long as it sounds okay, there should be nothing to worry about.
 
Re: Strange Resistance Measurements at my LP Output Jack

Turns out that the wiper on the neck volume pot is damaged. Simply pushing on it lightly by way of the capacitor drops the output resistance to its expected value around 7.3K. Gonna either fix the pot or get a new Centralab because I'd rather not be playing with the equivalent of a 1K resistor between by volume pot and the output jack even if it's just psychological.
 
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