Metropoulos Forum

Not sure if anyone can help out here.... Think i need to re-wire my el-cheapo a/b box to switch between or combine two separate amps (100w 1972 Super Lead + Danelectro 30 watt w/ 8" speaker). At the moment its creating a ground loop hum with any of my guitars in any combination --- I've been through all the usual ground check things, guitar cables - and dont subscribe to the 'just lift the ground wire' routine.....

I'm sure its a simple operation, maybe it needs additional components, etc.... looked around the web, but can find a suitable circuit plan... anyone got any clues??

....oh yeah George, the shirts look cool!

thanks in advance,

zeeb.

It's hard to tell what's going on in your pedal, looks like some relays obviously.

The thing to remember is to ground the inputs of the amp that isn't active. So when you switch to the Marshall ground the feed going to the Dano.
And vice versa.

George

thanks for the reply, George ----

....nope. no relays - its just a passive circuit, with a 9v battery for 'added red light effects' ....! one line/guitar in, two switches & two outs -- plus and additional aux in/out for a tuner,etc...

maybe a relay thing IS needed to switch the ground between the two sends to the amps ??? not sure how i'd switch the amp input grounds...

hmmm.....

i'll post a clearer pic or diagram later...

zeeb.

OK, since you have individual On/Off control of each channel (A and B), that would be kind of hard to use to toggle between A and B.

Here's a little schematic that would work well in that box. Granted it doesn't provide LED status, but that wouldn't be to hard to add with either a relay or using 3PDT switches for the footswitches.

This circuit uses 2 DPDT Carling style footswitches. It grounds the channel not being used, therefore grounding the input to the unused amp.

Hope this helps.

Jon

Hey Jon ---

Thanks loads for that -- will go check a local store for Carling switches -- and brush up on my limited schematic reading! -- seemed a simple thing but i wasnt sure where to start ....

Thanks again -- will let you know how i get on...

Just finished buliding a new guitar - an old 60s' italian (eko? vox?) jazz body & neck w/ two firebird pick-ups... tried it today though the Marshall, and jeezus - it sounds amazing.

speak soon,

John Lee.

Most likely you won't get rid of the hum with a passive AB box. You will need one with isolated outputs.

hhhmm... isolated so that the box doesnt act as a ground? -- i.e. using plastic jack sockets, etc...

maybe that would work okay with the Carling switches then....

or maybe this means a new unit all together?

...thanks for your help -- i'm not too up on this....

cheers,

john.