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Old 10th May 2005, 08:16 AM   #1
diyAudio Member
Join Date: Oct 2004
Question Multi amplifier connections

Guys, you have helped me in the past and I know one or more of you will this time.

I have been experimenting with using three or four guitar amplifiers at the same time. One takes the LR Baggs acoustic signal, the other three are fed from the magnetic pickups. I use a Boss LS-2 with the setting A+B to supply one amplifier and the second output goes to a Boss chorus pedal which has two outputs. The proverbial 'wall of sound' is what I want.

My question is could I wire a few jack sockets in parallel in a box to send a 'dry' signal to more than one amp? Physically it is no problem but what are the problems electrically?
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Old 11th May 2005, 12:33 AM   #2
Enzo is offline Enzo  United States
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Join Date: Sep 2004
Location: Lansing, Michigan
Two concerns come to mind. One is that as you parallel the various amp inputs, it lowers the impedance the guitar faces. It may potentially load down the guitar signal somewhat.

But my major concern is for ground loops. SOme amps may not agree with other amps when connected together. Here is the test. Line up the amps you would connect together via this multi box. Take a guitar cord and plug into amp A, then the other end into the input of amp B. Yes, I realize no signal is being sent to either amp this way. If a hum results, you have a ground loop..

Now pull the plug from B and connect it to input of amp C. and so on. Now try from B to C, B to D, etc. Try all the combinations. It won't take long really, it either hums or it doesn't.

If any combination hums, it has a ground loop, if not, no problem.

Ground loops do not mean there is anything wrong with either amp, they simply have different ground potentials.

It may work fine, but if loops occur, it is because the grounds are connected together. We cure loops by breaking the ground path between the two disagreeing amps. One way is to lift the third prong on the power cord, but I don't like that unsafe aproach. I make transformer signal isolators for the purpose, but that is beyond the scope of your box.
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Old 11th May 2005, 08:28 AM   #3
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Join Date: Oct 2004
The three amps work together fine, one from the LS-2 and the other 2 from the Boss Chorus pedal. Hum in my setup is not an issue, it is the loading of the guitar and/or the inputs that I was thinking of. Ideally I would like a clean feed to the third amp so that I can use delay on that channel, one with drive, two with chorus and three with delay. The hand built AXE JUICE pedal has a clean output but I already have a Sparkle Drive which I like and I prefer to keep it.

So if you can follow all that, is there a pedal or box that splits the guitar signal three or four ways without undue loading of the guitar signal.

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Old 11th May 2005, 08:58 PM   #4
Optical is offline Optical  New Zealand
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Join Date: Nov 2002
Location: Auckland, New Zealand
you could build an active buffer pretty easily out of an opamp to drive each channel. a single noninverting opamp configuration would do it i think
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Old 12th May 2005, 08:04 AM   #5
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Join Date: Oct 2004
Yeah, I was afraid of that. Simply put I have no idea of how to use or build such devices even if they are 'simple'.
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