ashamed to admit i'm an EE...

drbakker

New member
..cause i can't exactly explain what's happening with this circuit...

my only excuse is that i've been out of college 20+ yrs and haven't used my eng skills much at work.

I installed 2 pearly gates PU's into my Les Paul (took out the burstbucker pro's) and installed 2 long shaft pots with DPDT switches. To keep things simple, I just wired the pot/switches simply to keep the red & white wires connected and floating when pushed in, or shunt them to ground when pulled out.

The rest of the les paul wiring I left identical.

Everything works great, and sounds great, HOWEVER, with the pickup selector in the middle position and the bridge PU split (neck pickup not split), when I turn down the bridge PU volume slightly the volume of the guitar goes up slightly and then back down as you turn it down and then eventually off as expected. As the volume goes up, the tone changes to the deeper bridge PU tone. When the neck PU is split and bridge not, same thing though less pronounced.

So, I stared at the circuit a while, and the only thing I can come up with is, well... nothing. It shouldn't be a phase problem, both bridge and neck PU's should be in phase regardless of single/double coil configuration - although it sounds like it would be a phase problem, e.g., as you turn down the out of phase PU, the combined signal sounds larger. It doesn't look like the tone circuits should affect anything, they have the 500K resistance between the cap and ground and are effectively not doing anything when fully open. It could be a loading effect on the PU's which are directly in parallel with both volume controls all the way up - perhaps when you turn one down, the resistance between the PU's isolates them and they no longer present as high a load on each other - this would explain the increase in volume, but my math is way too rusty to verify this.

Can anyone offer an explanation?? (and a cure...)

Thx in advance! Dave.


PS while making PU choices for my les paul, I read alot of threads on this forum and they were EXTREMELY helpful - they led me to the choice of the PG's and they really sound GREAT - you folks saved me alot of time and money goofing around with pickups with all the helpful posts here.
 
Re: ashamed to admit i'm an EE...

I believe that you are correct with your loading theory. Both pickups are wired in parallel with no resistance between them when both volume pots are on ‘10’. As soon as you turn one volume pot down, you start to isolate the pickups from each other.

A tip I saw on Guitarnuts.com recommends adding a 47k resistor between each pickup and the switch (provides 100k total between the two).
 
Re: ashamed to admit i'm an EE...

Excellent! Thanks.
That make perfect sense, it will be like the pot is turned down a small bit all the time, and ideally at the peak of the sound output with 47K. It's not like it will lose any signal because as noted, the output is louder with the pot turned down a little.
If I have time this weekend, I'll pop some resistors in and report back.
Seems like Seymour Duncan may want to include this on their split wiring diagrams...
Dave.
 
Re: ashamed to admit i'm an EE...

yeah, and it's even worse than that... i got a burn mark in my desk from the solder iron... what a noob.
 
Re: ashamed to admit i'm an EE...

I think it will be down to the pickups loading each other down

you could try adding a resister in series between the pickup and switch to isolate them from each other a bit, 20k or somehting should work fine

I had a related problem when I was rewiring a strat - I did it with a separate volume control for each pickup (sounds cool, too much faffing aorund in practise) and found when i wound down one volume, it took down the volume of all the other pickups - adding in a resister to each pickup sorted it

David
 
Re: ashamed to admit i'm an EE...

brisk, you're an EE? i never knew!

im doing chemical + process.. first year though!

tom
 
Re: ashamed to admit i'm an EE...

I am an BEH ( beginner electronics hobbyist)

I now feel much better about burning things...apart from my skin ( other than solder) with the iron.

Thanks for being so encouraging ! :-)
 
Re: ashamed to admit i'm an EE...

Well, to close out the story, I soldered in 2 22K ohm resistors one each in series with the pick-up. This fixed the problem, and the whole thing sounds great! Thx for the help.
Dave.
 
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