# 2 different hum problems with FBQ1000 (DSP1124)



## THX-UltraII (Nov 19, 2008)

Hi guys,

I just bought a FBQ1000 (the 'new' DSP1124) and I have 2 different humming/distortion problems (at least I think it are 2 different problems)

*problem 1:*
As soon as I turn on the volume knob of my AVR I get a humming noise on my speakers. It is NOT there when I FULLY turn down the volume knob of my AVR but comes in as soon as I give 'one click' volume up on my AVR. The thing I should mention is that this problem is ONLY with my R, L and C channel. For these (R, L and C) channels I use a separate amplifier that is unbalanced (RCA) connected with the R, L and C rca pre-outs of my AVR. The hum is NOT present at my SR and SL channels (which are directly connected to the speaker outputs of my AVR). The hum from the R, L and C channels DOES NOT go away when I turn off the FBQ1000. The hum is the same, wether the fbq1000 is on of off. The hum only is not present when I unplug the cable going from my AVR sub pre-out to the FBQ1000 1/4 jack input. 

*problem 2:*
The subwoofer is humming like with the FBQ1000 turned on. It is very noticable when scrolling and clicking with my mouse :scratch:

*My setup:*
Marantz SR5005: SR and SL are amplified directly by my SR5005 and my R, L and C channels are amplified by my NuForce MCH-2-C5
NuForce MCH-2-C5: connected with my Marantz SR5005 with unbalanced monster rca cables. Only R, L and C are amplified my my NuForce
Behringer FBQ1000: connected between AVR and subwoofer as follows: rca subwoofer pre-out avr => 1/4'' jack input 1 of fbq1000 with rca/jack plug => fbq1000 output 1 to rca input of subwoofer, also a rca/jack plug for fbq1000 output.


Could you guys tell me if they are both different problems and if I can eliminate one or maybe both of the problems with a cheater plug?


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## hjones4841 (Jan 21, 2009)

This sounds like a ground loop problem. First thing to try is to lift the ground connection on the Behringer with a 3-2 plug adapter. The Behringers are known for having ground loop problems in HT systems, maybe caused by HT not being balanced.

Are you sure that your balanced to unbalanced connections are done right? That could also be the problem.


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## THX-UltraII (Nov 19, 2008)

hjones4841 said:


> This sounds like a ground loop problem. First thing to try is to lift the ground connection on the Behringer with a 3-2 plug adapter. The Behringers are known for having ground loop problems in HT systems, maybe caused by HT not being balanced.
> 
> Are you sure that your balanced to unbalanced connections are done right? That could also be the problem.


Can I also make a home made powercable without connecting the ground in the plug?

And what do you mean with 'if my balanced to unbalanced connections are done right'? I am using 2 1/4"jack>rca plugs connecting to the in and output of the Behringer and I ve connected rca cables to these plugs running to my subwoofer and processor.


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## hjones4841 (Jan 21, 2009)

Homemade power cord will be fine.

In a balanced to unbalanced connection, one of the balanced wires has to go to "ground" on the RCA plug. Sometimes it can make a difference which one is grounded. That is what I meant. There is a diagram - I think on the REW forum here at HTS - that shows how do make up the adapter cables.


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## THX-UltraII (Nov 19, 2008)

> Homemade power cord will be fine.


ok



> In a balanced to unbalanced connection, one of the balanced wires has to go to "ground" on the RCA plug. Sometimes it can make a difference which one is grounded. That is what I meant. There is a diagram - I think on the REW forum here at HTS - that shows how do make up the adapter cables.


I m afraid I still don t understand what you mean here m8 (noob here :coocoo. In another thread Wayne answered that I could start if I can solve the problem by using XLR/RCA plugs that has the ground (pin 1) disconnected. Is that what you mean also?


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## THX-UltraII (Nov 19, 2008)

UPDATE:
I m using a cheater plug now and the hum is completely gone :T


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## hjones4841 (Jan 21, 2009)

Glad it worked - it did for me.


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