Blues Breaker oscillating...

[GibsonGM]

Hey all,

I put 2 perfboarded marshall Blues Breakers in 1 box, I added a bypass switch and a second switch to bounce between the 2 boards...this way I can dial in crunch for rhythm and boost the vol and dist for solos. 

Trouble is, I'm getting an oscillation (dog whistle) somewhere...probably of the parasitic variety.  I have both PCB's running to the input jack ground separately, and each has its own +9V line from the wall wart jack (no battery option here). 
Any suggestions how to maybe ground the opposite input when in bypass, or something like that, to kill the damn squeel?  I'm pretty sure its the circuit not in use at the time that is doing it.
Thanks,

~Mike )

[petemoore]

http://www.generalguitargadgets.com/index.php?option=com_content&task=view&id=33&Itemid=27
  ...More specifically...
     http://www.generalguitargadgets.com/diagrams/switch_lo_dpdt_input_grd.gif
  But I'd jumper a ground to the relevant input [the 'other' one]for pre-testing instead of rewiring the entire front end.
  At a glancing read I don't see how 'one side is signal path // other side input Gnd'd.' is going to happen for both sides..perhaps it's just the one side oscillating which needs input grounded though [?], I'd use testclip-wire and see first what could be the result with just grounding one side or the other.

[GibsonGM]

Hey, how'd you guess that, pete? I played w/a jumper, and yes, one side needs to be grounded when not in use...the other doesn't act up when bypassed.   This is the only way it seems I can get anything good out of my Hot Rod Deluxe, using a pedal on the clean channel.   

Does the GGG 2 in 1 box make both ckts independently bypassed? I think I've used that before.   What I'm trying to do is flip between 1 board or the other in 1 stomp, with the other switch bypassing the whole box rather than having to do a "#1 on, #2 off double move", if you know what I mean...I need a 3PDT scheme for that.   Problem is getting that 1 side grounded when not in use.    Do you see any way to do that?
Thanks! 
~M

[petemoore]

  Nope, not that I remember seeing...
  And I kind of figure 'it' has been done, but the only real way to find out for sure is to take a 3pdt on paper and try a bunch of wirings on it.
  I think a 4PDT 'could maybe' do it, haven't drawn it out, haven't tried it...

[dxm1]

How about this, using two 3PDTs?