Strange Buzz, scary volume oscillation

[yakkmeister]

G'Day Nuts!

I have been working on my dano in another tread here and decided I should clean up the rats-nest I made in a different guitar while that issue got nutted out ...

Here I have a Yamaha Pacifica 112. She's been fitted with 2x DiMarzio ProTracks (N & M) with a PAF-Pro in the bridge.

I have wired it up as per this:
www.dimarzio.com/sites/default/files/diagrams/3h5w1v1t.pdf
I have noticed one difference - the input to the tone pot comes from a split off the switch, not the volume pot.

I have gone over the thing with a DMM and I can't find any soldering faults. The pickups have output and the bridge gets 1 Ohm resistance to the output jack.

The problem is that, when plugged into the little VOX Mini 3 amp I have, she does nothing but hum. The other, scarier, thing is that she has a slow oscillation in volume. This only happened with new, stainless steel strings on. Testing was carried out with a screwdriver for switch function - no hum was detected at that time.

I suspect that taking the tone pot input from the switch instead of off the volume pot may be the problem (I am going to go change that now and 'll report back if it changes anything)

[yakkmeister]

Resolved!

It would seem that with the tone input soldered to the switch, the tone was acting like a second volume and the cap was making the oscillations.

This leads me to an interesting conclusion ...

What if this behaviour were made to work for the forces of good and help mankind ...
What if a circuit were built that used a cap and a pot (I dunno, maybe also wire and other bits ...) to build a simple, adjustable oscillator, like an onboard trem...?

[newey]

yakky-

It would seem that with the tone input soldered to the switch, the tone was acting like a second volume and the cap was making the oscillations.

I don't know what you did to resolve the problem, or even what the problem was, but that wasn't it.

Standard Strat wiring has both tone controls wired off of the second pole of the 5-way switch. You don't have a need to do that, since yours only has the single tone control. But wiring it that way wouldn't cause either hum, or oscillations. I suspect that one of your other connections was marginal, and that you corrected it by simply rooting around in there. Checking connections with a DMM will show if there's no connection at all, but won't always tell you if a connection is made poorly (i.e., high resistance).

A bad connection to the tone pot might result in a non-functional tone pot, but you would still have output at some level if the volume pot is properly connected at all three terminals (and assuming pups are properly connected to the switch, jack is connected, etc.)

[yakkmeister]

Mar 7, 2012 7:05:03 GMT -5 newey said:

I don't know what you did to resolve the problem, or even what the problem was, but that wasn't it.

Standard Strat wiring has both tone controls wired off of the second pole of the 5-way switch. You don't have a need to do that, since yours only has the single tone control. But wiring it that way wouldn't cause either hum, or oscillations. I suspect that one of your other connections was marginal, and that you corrected it by simply rooting around in there. Checking connections with a DMM will show if there's no connection at all, but won't always tell you if a connection is made poorly (i.e., high resistance).

A bad connection to the tone pot might result in a non-functional tone pot, but you would still have output at some level if the volume pot is properly connected at all three terminals (and assuming pups are properly connected to the switch, jack is connected, etc.)

I moved the connection from the switch to the volume pot. This resolved the oscillation but not the hum. I then re-soldered the earth points on the backs of the pots, this eliminated most of the hum.

Any idea what the oscillations could have been from? It was a fairly long cycle, the change in volume was not from silence to full-noise but more like ~1/4 of the full range. The tone control has a 0.1 mF cap on it while the pot itself is a 1 MOhm jobby. The volume pot is a different taper - you turn it down a little and the volume drops a lot (I use it for a violin-like effect). Aside from that ... the p/ups are wired in parallel and the amp has a decoupled transformer (plug-pack style). Dunno if that helps ... It's quite weird though.