Singing MXR Phase 100

[bilo01]

A friend brought me a vintage Phase 100 pedal to adjust it's DC which worked out fine. Another thing is that it keeps singing when both knobs are turned down all the way. Does anyone have a solution for this?
Thnx, Will

[Mark Hammer]

"Singing" meaning oscillating?

The feedback in a phaser - ANY phaser - assumes that that is no gain to be added in the phase-shift stages, or the feedback path.  Even if the total gain over 10 stages is only 1.01x, it is still gain, and feeding it back will produce oscillation.

When you consider that all the 5% resistors in all those ostensibly unity-gain stages can result in the teensiest bit of cumulative gain, that's why so many phasers have trimpots in the feedback loop, so that maximum feedback can be set to occur just below the point of oscillation.

[bilo01]

Thnx Mark, I don't know the exact translation of "oscilating". I'm a Dutch guy you know. But your explination is pretty clear to me. I'll have a go with that and let you know.

[Mark Hammer]

Oscillating = howling like a dog at the moon.

[bluebunny]

Yeah, this:



Wooo-ooooo-oooo-ooo-ooooo-ooo-ooooo-ooo-oo-oooo-oooooo-ooo-oooooo-ooo!!!   

[bilo01]

Grrrrrrr 
Didn't get the chance to tweak the trim yet. I do have a problem with the DC. It seemed so simple that i thought it had to work, but it doesn't!!

Here's the situation. It's a vintage 70's Phase 100. Somebody messed with the DC earlier, (don't know if they had a DC input originally ). The rectangular DC which was too small for the hole so somebody filled the left spaces with some kind of yellow glue and that's how it stuck in the enclosure.

My friend asked me if i could replace the DC with a round one. I did some changes to the hole and soldered it together like it was at the rectangular DC. No sound at all...
This morning i tried it buy placing a battery. When i hooked it up on my amp one of the vactrols started smoking!!

I hooked it off and couldn't resist to try it again. Now there was no smoke and there was sound, but no phaser effect....
I've read somewhere that the vactrols are impossible to find.. What can i do now?

It started as a simple job but now i wished i didn't begin on this. Can this be fixed??