I have posted in the miniDSP forum...and some of the fellas there have made some good suggestions...mostly focused on gain staging. However, I have continued to get an audible white noise-like sound from the passive subwoofers I built in my thread. I have 4 identical, passive sealed 18" DA subwoofers being driven by two Behringer EP4000 amplifiers which are receiving a balanced signal from each of the four miniDSP 2x4 Balanced outputs. I am using a 2-Way Advanced Plug-In if it matters in this case.
The two gain knobs on each amplifier are at maximum. The amplifiers are looking for input of 1.23Vrms @ 8ohms to achieve max. The amplifiers have a voltage gain of 50x (34dB). They are rated at -100dB from 20 to 20.
The sound is present even when I disconnect all input wires feeding the DSP. Sound is also present and unchanged if I hook everything up to DSP inputs.
Here are some things I have tried with no input wires feeding the DSP. (keep in mind I have tried all of the below with the DSP using three different, and new, power supplies from different manufacturers on same and separate circuits, both through an isolator and without. The power supply changes did not seem to affect the white noise in any way.)
If I disconnect the DSP from the amplifiers, the subs go perfectly quiet.
If I reduce the amplifier front panel gain knobs by half, the volume of the white noise gets reduced by half.
Why is this sound present when I hook up the miniDSP? Is this a DSP board grounding issue? Any ideas for a solution or steps I could follow to isolate the issue?
I tried many different hook-ups with combinations of a Matchbox HD , miniDSP and some without one or the other as well as none and both.
Messed around with DSP jumpers in all combinations as well as trim levels, and gain levels in the plug-in. There were times when I experienced the same white noise as originally and times when I did not and there was hum introduced instead...which might have been masking the white noise?
All in all, the only definitive times the white noise was completely gone was when the DSP was out of the signal path.
The only assured way I could reduce the white noise with the DSP in the chain was by lowering gain knobs on the amps.
Behringer confirmed that the EP4000 amps look for a 1.23Vrms signal to function at max.
I had a Denon rep call me back Friday and he said the the sub pre-out voltage on the 2810 was not 2.1V as originally thought, but 1.75Vrms.
I can't imagine this makes a difference seeing that I get the same white noise even when there is no signal at the DSP inputs.
Of course, it made me question where the DSP jumper SHOULD be with that input level...I am assuming .9V position???
Something interesting I did note through all of this...
I had no hum to speak of when the receiver was hooked up to DSP, just white noise.
When I connected PC to DSP via USB cable, a low-volume electronic-like hum was introduced and audible through the subwoofers.
Gone as soon as USB was disconnected at either side of connection.
I am not sure what to do next....????????
I've had enough beers trying to work this out the last several days, so I have that part covered for sure.
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