# multiple amp setup hums



## studiodog (Sep 10, 2010)

Hi folks,

I'm troubleshooting a multiple amp setup with my Fishman Powerchip/Piezo bridge equipped hollowbody electric, and need some advice. 

The output from my guitar runs out a TRS cable, with mag pickups on tip, piezo on ring. The TRS hits a splitter/y-adapter, with respective TS outputs running to an acoustic amp on one side for the piezo sounds and an electric amp on the other for the mag pups. Terrible hum/buzz from both amps (worse on the electric amp) which goes away immediately if I disconnect the input from either amp. Both amps are plugged into the same power bar. 

I'm assuming a ground loop here? 

Any suggested course of action here? I thought of an isolation transformer between the input and amp on one (both?) signals - something like the ART DTI, perhaps? Or myabe an EBTech HumX on the AC line? 

Any thoughts/advice is much appreciated!


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## jimihendrix (Jun 27, 2009)

would one of these help...???...hums may be caused by plugging both amps into the same outlet...you could try plugging amps into separate outlets...

Radial BigShot AB-Y true bypass switcher


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## studiodog (Sep 10, 2010)

Hey jimi. Thanks for the reply. I don't think the Big Shot does what I need. I'm not trying to switch between amps, but rather send separate signals to both at once (piezo to acoustic amp, mag to electric amp). 

What I THINK I need is a way to isolate the grounds of the amps. I'll try your suggestion of plugging into different outlets, but that's backwards to the common practice of using the same outlet for all your gear. My home studio, for instance has everything on the same circuit - no hum there.


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## jimihendrix (Jun 27, 2009)

check these out...

[video=youtube;4YM1iwC6vhg]http://www.youtube.com/watch?v=4YM1iwC6vhg&feature=related[/video]

[video=youtube;qBEvnSmXc84]http://www.youtube.com/watch?v=qBEvnSmXc84[/video]


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## studiodog (Sep 10, 2010)

Sorry, man. That is exactly my problem, but those 3-prong to 2-prong ac adapters are not legal in Canada. If you find someone around here selling them, grab a few for me, but I've checked Home Depot, Crappy Tire, etc. No go.


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## 4345567 (Jun 26, 2008)

__________


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## washburned (Oct 13, 2006)

is that y adapter mono by chance? it should be female trs to male tsx2.


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## overdriven1 (May 6, 2007)

Yes the Radial Bigshot! There is a ground lift for just your problem, don't dismiss this, put it on one line after your y connection right before the amp and switch the ground lift and voila, no hum anymore, had the same problem, just have to use it differently than advertised, works perfect.


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## ronmac (Sep 22, 2006)

Removing the ground lug from the AC line has good potential to add a light show to your set. Don't do it.


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## studiodog (Sep 10, 2010)

Thanks to all the replies, everyone. overdriven1 - great tip on non-traditional use of the Bigshot! washburned - it's a TRS- F to 2 x TS-M. I'm sure cuz I wired it myself! 

On the advice of the clerk at my local shop, I tried inserting a Behringer HD400 Hum Destroyer - I know, I can hear the eyebrows going up - Behringer?!?1 But yes, Behringer..... Anyway, I had my doubts but took one on loan to try it out before plunking down all $28 of the asking price. Dropped it in right after the Y-splitter, and voila! Hum is gone! Yay for cheap fixes! 

The HD400 is a transformer isolatior, 2 channel,. So I guess I'll have an extra channel for the next thing to go wrong! We'll see if it lasts longer than it takes for the $28 to go from my bank account to the store's, but at least if it dies quickly I have an excuse to buy the Radial (the Spouse Approval Factor of a $28 guitar gizmo is very high!).


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## studiodog (Sep 10, 2010)

Hey ronmac - that's exactly why those adapters aren't sold north of Detroit!


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## Chito (Feb 17, 2006)

Hey thanks for the tip. I"ve been having a hum problem at the place where we rehearse and I've never had that problem in my house with all the gear that's plugged in there. And I thought initially it was the flourescent lights but it wasn't. So now I'm thiniking a ground loop must be causing the problem. Like you said it's a "cheap" fix so I can try it out and not having to bother returning it if it doesn't work for me. It's also small enough to carry around and would be good to have during gigs in bars in the middle of nowhere, where some electrical wirings produce AC ground loop hum.


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## studiodog (Sep 10, 2010)

No charge for that one - I'll getcha next time! LOL

I hear you on the AC wiring in most venues - that's why I also now always carry an outlet circuit tester in the kit bag. $8 at Home depot is a cheap way to make sure you're plugging into a decent outlet. Learned that the hard way when some genius in a past venue wired up a 110V outlet at 220V - instantly blew up every electrical device plugged in, including a powered speaker. NOT PRETTY! <shudder>


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