very strange multiplex echo machine problem ?!?!

[1878]

Hello Everyone...

I've recently built a Multiplex Echo Machine from 1776 Effects. Fired up first time with no problems whatsoever. 'Lovely.' I thought. Left it on the bench for 3 days whilst I waited for a new momentary footswitch to be delivered. Plugged it in again before fitting the new switch & it doesn't work when bypassed ?!?! The effect works perfectly when engaged, but as soon as you switch it off there's silence, with an infinite repeats thing going on in the background. When you engage the effect again, there's a very loud & non-musical blast of feedback before the effect works perfectly again.

I tried leaving the effect engaged & running it through a true bypass box, but this has the same outcome.

I fitted a new 3pdt, but this didn't help either.

Any ideas ??

[davent]

Did you use a 3pdt/2pdt bypass switch intending to ground the fx input in bypass and instead  wire it to ground the guitar input in bypass?

[1878]

Thanks for the reply.

It wouldn't matter because I left it engaged & ran it through a TB loop & had the same problem. I had thought my 3pdt was at fault for a while, so I swapped it for a new one but the problem remained. I always wire my effects like this before boxing them up...

3pdt viewed from bottom.

1 2 3
4 5 6
7 8 9

7 connected to 8
4 - guitar in
5 - guitar out
1 - effect in
2 - effect out

I do this to see if everything's working then wire it up properly with grounded input & a status led when I box it up.

I'm finding this really confusing because there doesn't seem to be any logical reason as to why this would happen. Bypass always works !!