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Re: Wiring a reverse phase jumper cable


 
11/21/2005 1:01 PM
starfish Re: Wiring a reverse phase jumper cable
Assuming I want to keep all modifications external to the amp, is there a way to build a reverse phase project box? What parts are needed and how would it wire up? Thanks for all the help so far. The amp in question is a vintage JMI Vox AC-30 so I don't want to modify anything internally if it can be avoided.
 
11/21/2005 5:11 PM
Rick Erickson
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quote:
"The amp in question is a vintage JMI Vox AC-30 so I don't want to modify anything internally if it can be avoided."
 
 
Well, you're no fun at all... ;)  
 
quote:
"What parts are needed and how would it wire up?"
 
 
Depends on what type of circuit you choose. This is a DIY forum so I assume you are willing to do the necessary research and try some designs on your own.  
 
Here are some links for an IC op-amp inverter that might help.  
 
http://ourworld.compuserve.com/homepages/Bill_Bowden/opamp.htm  
 
http://sound.westhost.com/dwopa.htm  
 
 
 
RE
 
 
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11/22/2005 9:02 AM
anonymous
Good info thanks! This is a bit like killing a fly with a stick of dynamite!  
 
Maybe it's my tech naivete but it seems like there's a simple way. Isn't a guitar's onbaord phase switch just a toggle with 2 conductors? I dunno but it seems like an external box should work the same. Opamps are only going to add noise, IMO.
 
11/22/2005 9:03 AM
starfish
Good info thanks! This is a bit like killing a fly with a stick of dynamite!  
 
Maybe it's my tech naivete but it seems like there's a simple way. Isn't a guitar's onbaord phase switch just a toggle with 2 conductors? I dunno but it seems like an external box should work the same. Opamps are only going to add noise, IMO.
 
11/22/2005 12:16 PM
Rick Erickson
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quote:
"Maybe it's my tech naivete"
 
 
That would be my guess! Your guitar pickup is a coil of wire with no ground reference until you assign it one. It is "ballanced" or more accurately "floating" with respect to ground. This makes it easy to reverse phase with a simple switch. Your amp is an unballanced signal line with one signal conductor and a ground. No way to invert phase unless you ballance the line (transformer or fancy electronics) or use a signal inverter. (IC/FET/Bi-Polar Transistor) I have already given you the options. Personally I wouldn't (read don't) jumper the channels in my JMI AC30's. They sound just fine the way they are. If I was going to do it on a regular basis though I would internally modify the amp one of the ways I already described to you. From the sound of your lack of technical experience I would recommend finding a good tech in your area who could do this for you. I would read the rest of my posts carefully first though. There's no guarantee that you will like what you get after spending the money for mods. What exactly are you trying to get out of this amp that you're not getting from one channel?  
 
RE
 
11/23/2005 10:52 AM
MBSetzer
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A vintage or homemade Electroharmonix LPB-2 pedal inverts the signal and adds no gain when its single knob is set for about 9 o'clock.  
Of course you can crank the boost fairly high if you want to but for simple phase inversion a unity-gain setting seems like it could fit the bill.  
 
I've used it in between different amps before, should be no reason you can't use it in between different channels.  
 
Mike
 
12/9/2005 1:13 PM
starfish
Thanks. Yeah, I found another option too, in a pedal I actually want to own - a BJFE Baby Pink Booster.
 
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