Hum free ABY causing distortion?

[stallik]

Just built this and while it mostly works well, I'm getting distortion if I either:
Whack the bottom E or play anything with a wah pedal up front. Strangely, it doesn't appear to be caused by the input of the aby being overdriven as I can boost the signal using a booster without the effect changing. If I play normally, everything's fine with absolutely no hum     thought about lowering the gain of the TL072's by changing the feedback resistors but thought I'd ask if anyone else has experienced this? I modified the layout as described and had to connect input earth to output 1 earth to keep it quiet. Output 2 has an isolated earth

Layout

[/Guts

Guts

[wavley]

It sounds like your transformers may be saturating, I had the same problem when I was playing around with gain.  I ended up using bigger Edcor transformers because I also play a bass VI.  The first thing I would do is make sure you don't have any DC offset, too much DC going through a transformer and it will saturate.  If that's not the problem I would down the gain of the op amps.  When I was messing around with this I got it to where is suited most any guitar playing need by lowering the gain, but my bass VI (actually a Jaguar Custom Baritone, it tunes like a Bass VI) drove it crazy so I switched to the Edcors, problem solved.   Problem is that they're easily 4 or 5 times the size.

[stallik]

@Waveley Thanks for that -seems logical. I'm not playing bass and I only get the issue on the bridge pickup on my Strat ( JB Junior ) and I really have to whack it so I'm on a knife edge. Will check for DC offset then lower the gain a little. If that doesn't work then I'll just play softer while considering the bigger trannys

[stallik]

Today the distortion I was getting, suddenly got worse - Much worse. Whipped of the back, noticed that the cap at bottom left had ballooned up, looking fit to burst. Some idiot had fitted it the wrong way round! Seemed logical at the time - negative to the negative rail etc. Popped on a new one... Quiet as a  mouse....... Playing rock
Suprised it ballooned though, it was rated at 63v

[PRR]

> Suprised it ballooned though, it was rated at 63v

63V "forward".

The reverse voltage on an electrolytic is always 1V-2V max.

Think of a rope foot-bridge. Or even a plank across two rocks. It may safely carry 63KG down-force. But UP-force will upset it very easy.

[roseblood11]

A bufferless splitter:
http://forum.musikding.de/vb/showthread.php?33565-Trafoloser-Parallel-Buffer-Spliiter-mit-quot-galvanischer-quot-Trennung

[stallik]

Thanks Paul, yet another great analogy. I wasn't aware of the low level of reverse voltage but it makes sense

[R.G.]

A bufferless splitter:
http://forum.musikding.de/vb/showthread.php?33565-Trafoloser-Parallel-Buffer-Spliiter-mit-quot-galvanischer-quot-Trennung

I can't see the schemo, but my dim understanding of German plus help from Google translate makes me think it is a variant of this:

http://geofex.com/FX_images/oaspltr.gif

No transformer needed as the opamps drive "ground" with the differential ground voltage.

As I said, my German is poor to nonexistant.