A/B Box Circuit - Help Please!

Everything between your guitar and amp.

Moderators: VelvetGeorge, BUG

Post Reply
User avatar
zeeb
Senior Member
Posts: 202
Joined: Wed Sep 08, 2004 6:46 pm
Just the numbers in order: 7

A/B Box Circuit - Help Please!

Post by zeeb » Fri Dec 10, 2004 5:41 pm

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.

User avatar
VelvetGeorge
Site Owner
Posts: 7233
Joined: Tue Oct 14, 2003 5:12 pm
Just the numbers in order: 13492
Location: The Murder Mitten
Contact:

Post by VelvetGeorge » Fri Dec 10, 2004 6:26 pm

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
Check out Plexi Replicas for my personal amp builds...
Image

User avatar
zeeb
Senior Member
Posts: 202
Joined: Wed Sep 08, 2004 6:46 pm
Just the numbers in order: 7

Post by zeeb » Sat Dec 11, 2004 4:10 am

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.

User avatar
flemingmras
Senior Member
Posts: 2532
Joined: Fri Mar 19, 2004 1:39 am
Just the numbers in order: 7
Location: Rohnert Park, CA
Contact:

Post by flemingmras » Sat Dec 11, 2004 11:51 am

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
There's just that fine line between stupid and clever - Nigel Tufnel

User avatar
zeeb
Senior Member
Posts: 202
Joined: Wed Sep 08, 2004 6:46 pm
Just the numbers in order: 7

Post by zeeb » Sat Dec 11, 2004 2:31 pm

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.

User avatar
dosmun
Senior Member
Posts: 242
Joined: Wed Oct 22, 2003 4:51 pm
Location: Midland, MI
Contact:

Post by dosmun » Sat Dec 11, 2004 6:18 pm

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

User avatar
zeeb
Senior Member
Posts: 202
Joined: Wed Sep 08, 2004 6:46 pm
Just the numbers in order: 7

Post by zeeb » Sun Dec 12, 2004 11:45 am

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.

Post Reply