XLR Bypass w/ 4DPT

[Gregory Kollins]

A ways back I started a topic about building a distortion for vocals. The project is now built, but I'm having some issues with it...

The idea was this:
I would have a 4DPT switch so that I could true-bypass the XLR leads. While engaged, the second negative lead (pin 3) would be grounded. The positive lead (pin 2) would go into a gate, and the output from this would go straight into the distortion circuit. Now I have found out that this idea must have had some holes, because it's not quite 100%...

To make things a bit more fun, I also have a switch wired in so that while the effect is on, the now one + one - lead signal can be patched out through a 1/4in jack instead of through the XLR.

To make things more-more fun, there is a bypass switch for the gate, to induce feedback.

To clarify - While bypassed all of the leads from the XLR cable are connected. Only while engaged, pin 3 is grounded.

Symptoms:
While bypassed and sent to the XLR output, there is no signal (I've checked my wiring and it is as described above).
There is noticeable background noise and occasionally some AM radio.
When the GATE is engaged, the signal drops out and all you hear is a hollow static sound, like pink-noise inside a tunnel.


I know I'm doing something wrong. Help?

[GibsonGM]

How 'bout drawing a schematic and posting it, Greg? That might help us along...sounds like a  pretty cool idea, I'd like to see it!

[Minion]

Well when you Unballance a Mic signal like when you are grounding pin 3 you also loose 6db of signal , you also loose the noise rejection that ballancing provides , also if the Mic uses an output transformer then there is the issue of transformers no likeing there output grounded .....

I suggest maybe building a ballanced line reciever to unballance the Mic signal then put the switch after that , this way you are only switching one unballanced signal without haveing to unballance the mic and not dropping signal or injecting more noise ...

you can build a ballanced line reciever with a single opamp like figure 2 on this page ...

http://sound.westhost.com/project51.htm


Cheers