Pot question

[daz]

For the record, i'm not a noob by any means, having been doing lots of guitar work and building since the 70's. But i just bought a little squier duo sonic on a whim. Gotta tell you, this is a amazing little axe. But it's 24" scale, and while i would expect it to be somewhat wooly undefined in the low end, (and it is, but not in a bad way) what i did NOT expect is the sound i'm getting when i clean up, IE: turning the guitar volume down to make a dirty amp clean up. First thing i did was put a .001 cap across the volume in/out lugs. It seemed not only to not work much, but almost does the opposite ! It gets slightly brighter in the plain strings, but believe it or not (took me a while to believe what i was hearing) as i turn down and get cleaner the low strings actually get muddier ! So i tried another .001 to make sure i did have a bad one and same results. The pot is indeed 250k also.

That said, heres my question. I have used plenty of cheap pots, (this one is really small and cheap) and while some had tapers i hated and made me change them, this issue never existed. And theoretically i cannot see how the pot could cause this no matter how cheesy. I will likely change it, but before i go to that trouble i'd like some opinions as to whether it's possible for the pot to cause this, and also if anyone has other ideas what could cause this. By the way, i don't have the tone connected and i have different known good pickups in it now, but it did this stock with only the cap added and still does it now with the new pickups and tone control removed.

[Mark Hammer]

Assuming it's done right, there is only one good reason I can think of why the result you describe for the low strings is to be expected.

Note that the compensation cap is to offset the loading down of thepickup when the volume is reduced. Remember that if the pot is 250k and you have it up full, the amp "sees" three basic things at its input: the input resistor to ground in the amp, the 250k resistance to ground from the pot, and the impedance of the pickup (usually <10k). Under those conditions it "prefers" the signal from the pickup. Turn down the volume, so that some of the 250k resistance (let's say 50k for argument's sake) is now placed in series with the pickup, and the amp is looking at the input resistor, 200k to ground (pot) and around 55-60k (pickup+pot fraction) to ground. Now, the pickup doesn't "look" so good to the amp and treble is lost.

The way we have traditionally addressed the effects of that loading is to do exactly what you did: add a compensation cap. Why does this help? Because it acts like a zero-ohm resistance for content above a certain minimum frequency. While you're busy adding pot resistance to the pickup by turning down, high frequencies are going "None for me, thanks!" , such that the consequences of loading are not evident.

But now ask yourself "Which high frequencies are being conserved?". The secret to that question is to remember that not all strings have the same sequence of harmonics generated, and even if they did, the 4th, 5th, 6th harmonic of your wound E are going to be lower than the same harmonics of your unwound E, simply because the fundamental starts out lower.

So, in a great many instances, most I would say, the compensation provided by the cap is really restricted to the upper strings. certainly the cap lets high content from the lower strings pass, but there isn't really all that much of it to start with, so you notice the treble preservation for the upper strings much moreso than the lower ones.

All of that is the long way of saying that a bypass cap counteracts the effects of loading more for the unwound strings than it does for the wound ones. Which is why when you increase the loading by turning down, the lower strings DO sound duller - they're being loaded down.

A second reason is, of course, because the bypass cap not only conserves top end, but can also make it appear to constitute a more significant portion of the overall signal. That impact will be felt moreso in the thin strings than the thick ones. On some of my guitars, I've put in a larger value bypass cap, and in those instances, it lets through so much midrange and treble, that it makes the volume pot act as if it were a bass-cut control. I mention that to illustrate that the act of bypassing can be tactically used as a means of adjusting overall tonal balance.

make sense?

[daz]

make sense?

Some did, but you lost me to some degree. I think what you may have been saying is that on this particular guitar because it has the shorter scale, there is less high content in the low strings to be passed freely via the cap, and so i need a different value with this guitar than my strats? i guess i'll have to experiment. I'll solder a couple wires from the pot and let them hand out of the guitar with the guitar re-assembled so i can try different values without taking it apart each time. Thanks.

[Mark Hammer]

Not quite. What I'm saying is that the effects of turning down the volume pot will always load the pickup down. Compensation caps help, but in a way that generally helps the high strings more than the low strings. Has very little to do with scale length. I'm sure that a compensated pot on an electric mandoli

Also has very little to do with the pot value, too. Remember that higher value pots have a beneficial effect on tone and treble preservation only when they are turned up full (or close to it). Once the pot wiper starts to move from the far end, and some of that pot resistance is placed in series with the pickup, you WILL experience loading.

[daz]

Well, at the risk of a red face, i found the problem....one leg wasn't soldered to the lug. This would be the end of the story, but what i don't get is this was the SECOND .001 i tried and the first one did the same thing, and it was soldered solidly. The only thing i can figure is the first cap didn't have the value on it, just the code.I have a app that deciphers codes, but maybe i just went by memory and got it wrong, who knows.....i can't recall. But the fact that it happened with both caps is why i dismissed the possibility of a loose connection or mis-wired. anyways, thanks for the help and sorry i put you thru this waste of time.

[Mark Hammer]

Not at all. I think it was an interesting challenge, and I suspect my reasoning will hold to some extent.

These days, I have taken to gently scraping the surfaces of component leads and solder lugs on pots and switches, for precisely the reasons you ran into. Hate those cold solder joints!

[daz]

I'm guilty of being hasty sometimes. But the guitar had a ground rail from the tone pot to the volume that was right in the way and taunt. Instead of unsoldering it to so i could do a clean job on the cap.....well, just stupid. Tell you what tho....this is the first 24" scale fender style guitar i've owned, and those clean sounds that get dirty when you dig in that come with a dirty amp and the guitar volume turned down are spectacular. I didn't know how nice till i fixed this issue, but for $230 OTD this little squier duo sonic is a killer bargain. Everyone should have one !