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Author Topic:  Hum when using two Amps?
Greg Lambert

 

From:
Illinois, USA
Post  Posted 4 Aug 2019 2:03 pm    
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I use a Boss DD5 to split the outputs to two separate amps. this produces a hum in the amps. so I connected a Direct box on the second amp and lifted the ground. Hum is still there.

then I used the pre out on NV400 to go to the direct box. Hum still there. Any suggestions?

Both amps when used alone are quiet.
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Bill Burch

 

From:
California, USA
Post  Posted 4 Aug 2019 2:24 pm    
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Is everything plugged into the same circuit? Powered from the same line conditioner or outlet strip. Sometimes different circuits could have different characteristics, noisy devices sharing the circuit, etc.

Bill
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Jack Goodson

 

From:
new brockton,alabama (home of me and don helms
Post  Posted 4 Aug 2019 2:33 pm     hum?
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try bypassing the direct box....thanks jack
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Greg Lambert

 

From:
Illinois, USA
Post  Posted 4 Aug 2019 5:31 pm    
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Bill Burch wrote:
Is everything plugged into the same circuit? Powered from the same line conditioner or outlet strip. Sometimes different circuits could have different characteristics, noisy devices sharing the circuit, etc.

Bill


Same circuit.
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Greg Lambert

 

From:
Illinois, USA
Post  Posted 4 Aug 2019 5:31 pm     Re: hum?
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Jack Goodson wrote:
try bypassing the direct box....thanks jack


IT was hummin before I installed the direct box.
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Arvis Moore

 

From:
Brandon, Ms.
Post  Posted 4 Aug 2019 5:38 pm    
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Try a two pole adaper on one of the amps electric cord.
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Roger Dillingham


From:
Kentucky, USA
Post  Posted 4 Aug 2019 5:41 pm     Hum in amps
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No guarantee that this will fix your problem, but any time this occurs with me I plug one of the amps in to a HUM-X and then proceed. That normally takes care of any unusual hum I may have. Good luck! Roger Smile
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Jack Goodson

 

From:
new brockton,alabama (home of me and don helms
Post  Posted 4 Aug 2019 5:42 pm     black box?
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it might not not be the box, but it has a ground and it is still the same signal as before. you might want to try it just plugged from the effects pedal to each amp with the ground lift on the amp.
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Lee Baucum


From:
McAllen, Texas (Extreme South) The Final Frontier
Post  Posted 4 Aug 2019 6:17 pm    
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I've always used a HUM-X to correct ground loop issues when using two amps.


Click Here
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Michael Brebes

 

From:
Northridge CA
Post  Posted 5 Aug 2019 6:22 am    
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You still haven't told us which two amps you are using. I can infer by one of your statements that one of the amps is a NV400.
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Jerry Overstreet


From:
Louisville Ky
Post  Posted 5 Aug 2019 6:25 am    
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Yes, you have to lift a ground on one of the amps per Arvis' and Lee's replies.
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Fred Treece


From:
California, USA
Post  Posted 5 Aug 2019 8:14 am    
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Is the hum there when you take the DD5 out of the chain (stereo w/o delay)? Or switch the cabling?
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Michael Butler


From:
California, USA
Post  Posted 5 Aug 2019 8:51 am    
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i'll third the humx. works great for me.

play music!
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Greg Cutshaw


From:
Corry, PA, USA
Post  Posted 5 Aug 2019 10:20 am    
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This ABY switcher is not perfect but I've been able to make it work for my needs and it does eliminate the 2 amp hum if set to the proper mode:

https://www.amazon.com/gp/product/B000FKIO6M/ref=ppx_yo_dt_b_asin_title_o09_s00?ie=UTF8&psc=1

It only uses a battery or power supply for the LED's. No power is needed for the ABY or ground lift functions.
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Steve Lipsey


From:
Portland, Oregon, USA
Post  Posted 5 Aug 2019 10:52 am    
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A couple of bucks, keep one in your gig kit, never know when you will hit a two-wire socket or have hum from whatever source..this always does the job, I've used it for the two-amp problem.. only needed for one of the amps to kill the ground loop ..and the most useful ones don't have one wider plug tab, but just a little wider thing at the end, that you can file off, so they will fit into the really old two-wire outlets with only narrow slots (available cheaper elsewhere)
https://www.amazon.com/Grounding-Wire-Polarized-Electrical-Grounded/dp/B00VX615QS

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Greg Lambert

 

From:
Illinois, USA
Post  Posted 5 Aug 2019 6:18 pm    
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Michael Brebes wrote:
You still haven't told us which two amps you are using. I can infer by one of your statements that one of the amps is a NV400.


Nv400 and a DV Mark 50 watt head.
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Greg Lambert

 

From:
Illinois, USA
Post  Posted 5 Aug 2019 6:20 pm    
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Fred Treece wrote:
Is the hum there when you take the DD5 out of the chain (stereo w/o delay)? Or switch the cabling?


yes
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Garry Vanderlinde


From:
Southern California
Post  Posted 5 Aug 2019 8:44 pm    
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Here's another vote for lifting the ground on ONE of the amps.
been there, done that...
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Fred Treece


From:
California, USA
Post  Posted 5 Aug 2019 10:27 pm     Re: Hum when using two Amps?
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As for everyone suggesting lifting the ground on one of the amps...
Greg Lambert wrote:
I use a Boss DD5 to split the outputs to two separate amps. this produces a hum in the amps. so I connected a Direct box on the second amp and lifted the ground. Hum is still there.

Obviously, lifting the ground is not the answer, nor was removing the DD5 from the signal path. Whatever device he is using to split the signal from his instrument is causing one path to interfere with the other. I don’t have experience with the HumX, but apparently it and other similar devices address ground lift, phasing, and signal isolation issues that can cause hum and other noise in stereo amp configurations.

.
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Danny Letz

 

From:
Old Glory,Texas, USA 79540
Post  Posted 6 Aug 2019 4:00 am    
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In one of Jeff Newman’s pedal rod newsletters in the earlier days of running stereo, like running 2 amps with an effects device one dry one with effects, he stated that only one of the powered devices could be grounded at the male plug. You were to use a three prong adapters to lift the rest. He also stated that all of them would be grounded thru the connecting cables which made the whole thing not make sense to me but I did run that way & don’t remember having a hum.
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Lee Baucum


From:
McAllen, Texas (Extreme South) The Final Frontier
Post  Posted 6 Aug 2019 9:26 am    
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Quote:
so I connected a Direct box on the second amp and lifted the ground


Was the ground lifted on the direct box or on the second amplifier?
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Greg Lambert

 

From:
Illinois, USA
Post  Posted 6 Aug 2019 1:47 pm    
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Lee Baucum wrote:
Quote:
so I connected a Direct box on the second amp and lifted the ground


Was the ground lifted on the direct box or on the second amplifier?


Yes , Also I isolated the ground on the DV Mark and problem seemed worse. all cables are good. Guess Ill have to go with the HumX.
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Michael Hill

 

From:
Arizona, USA
Post  Posted 6 Aug 2019 7:33 pm    
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How are you using the direct box? A typical direct box has 1 input and 2 outputs. 1 output to feed the amp and a balanced output to go to a mixer or PA or whatever. The output to feed the amp is almost always not effected by the ground lift setting.
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Georg Sørtun


From:
Mandal, VA, Norway & Weeki Wachee, FL, USA
Post  Posted 7 Aug 2019 1:41 am    
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For such situations I always use "direct box" with galvanic separation - audio transformers - and no GND-connection. Then it doesn't matter if the amps are grounded or not since no loops exist. Only thing is that such a "direct box" must be kept away from electric noise-fields, as audio transformers will pick up the noise from such fields.
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Greg Lambert

 

From:
Illinois, USA
Post  Posted 7 Aug 2019 6:03 pm    
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Michael Hill wrote:
How are you using the direct box? A typical direct box has 1 input and 2 outputs. 1 output to feed the amp and a balanced output to go to a mixer or PA or whatever. The output to feed the amp is almost always not effected by the ground lift setting.





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