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Wiring a reverse phase jumper cable

11/17/2005 2:47 PM
starfish Wiring a reverse phase jumper cable
What is the proper way to reverse phase on a TS 1/4" guitar cable. This will be used for jumpering two out of phase guitar amp channels. (brilliant and normal channels of a rear panel Top Boosted JMI AC30).
Rick Erickson

Perhaps with an inverting buffer circuit or a 1:1 transformer. There's no way to simply reverse the signal wires since one is directly connected to ground.  
Don Symes

Yeah, you'd need to go to balanced, reverse the phase and then back to unbalanced. A good DI box would do that, I think.  
Any single-transistor fuzzbox or wah pedal will do what you're after - but may not be the sound you want.  
What about wiring a reverse-phase speaker cable for one of the amps - or swapping the speaker leads of it's a combo?  
Oh, this is two out-of-phase inputs on the same amp?
11/17/2005 8:17 PM
Yes, this is two out of phase inputs on the same amp.
11/18/2005 12:12 PM
Rick Erickson

You could rewire the amp so that both channels sum before the tone stack driver - like a Marshall preamp, or you could have the normal channel sum with the Vib. Channel on the other side of the phase inverter. Then you could use a normal Y cord to join the channels.  
11/21/2005 12:35 AM
Steve A.

    Have you heard of the new AC30CC? It evidently has a switch to allow you to jumper the two channels together:  
    Looks pretty slick and the price is better than the reissues.  
Steve Ahola
11/21/2005 5:18 PM
Rick Erickson

"It evidently has a switch to allow you to jumper the two channels together:"
Funny - it doesn't mention solving the phasing issue, just says that many people have jumpered the channels with a Y cord and that they added an internal switch to do the job. I know of one customer of mine that uses a standard Y between the Normal and Brilliant (TB) channel and likes the way it sounds. There is going to be some additional phase shift through the tone stack of the TB channel, so the two channels will never be perfectly in-phase anyway.  
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