I have assembled a Frankenstein setup in my home office that is very close to having excellent sound, but I can't quite figure out how to finally vanquish the noise in a convenient way. Apologies in advance for the long-winded post, but if I simply listed out my current gear it might not give context for why I have/need this setup and why "get something with a better USB implementation" isn't an option.
The heart of the system is a Dayton Audio DSP-408 that I use for EQ, room correction, and crossover. This DSP has 4 RCA inputs and 8 RCA outputs. Two output channels feed a Crown XLS-1002 that powers a pair of DIY SEAS Idunn speakers (not built for this purpose - they used to be in my living room). One output channel feeds a Behringer iNuke NU3000 that powers 4x JBL CS-1214 subwoofers in a pair of 2x12" prefab enclosures. My concept with this system was to be able to do both critical "audiophile" listening and to be able to crank up the subwoofers to provide club-quality sound for listening to and DJing electronic music. Mission accomplished.
Initially, my source was exclusively a Denon MC4000 USB DJ controller. My old NuForce uDAC-2 had died and my FiiO E18 has no preamp functionality, so I figured for the time being - not needing headphones for critical listening in this environment - the Denon would be just fine as a source since it reportedly has a decent soundcard and can be used with WASAPI/ASIO by Windows. It is not bus-powered - there is a separate 5V/3A power supply.
Unfortunately the Denon is horribly noisy. It has a high noise floor to begin with, and there is a ton of noise that comes over the USB cable from my PC chassis - buzzes, noise when I scroll the mouse, etc.. It's fine when music is playing, but it's not tolerable when idle and it's especially bad for gaming when the GPU spins up. Adequate for DJing, not adequate as an all-purpose source. I know that it's the USB because this noise goes away when I disconnect it. I've tried other cables and ports and it doesn't help.
Months later (now), I purchased a Schiit Modi 3 and Sys for passive volume control (this was dumb - I should have just bought a headphone amp with preamp outs and now have a JDS Atom on order) both to troubleshoot and see if it was a sound upgrade for non-DJ listening. I have the output from the Modi 3/Sys running to the other two input channels on the DSP (NB: I am well aware that the ADC/DSP/DAC part of my signal chain is a bottleneck on fidelity, but I think the signal going in still matters). One cool thing is that I can easily do a level-matched A/B between the two sources. The Modi 3 blows the Denon away - clearly a good DAC is an excellent addition to my system. But the Denon is a great piece of DJ gear and it needs to stay in my system.
And this brings me to the problem: troubleshooting the noise when this is all connected.
- With both fully connected, there is tons of PC noise coming through the speakers. No ground loop hum.
- With the Denon disconnected entirely and the Modi 3 on USB -> PC noise + ground loop hum.
- With the Denon disconnected and the Modi 3 on optical + external power -> no PC noise whatsoever, but ground loop hum.
- With the Denon connected and the Modi 3 on optical + external power -> PC noise, but no hum.
- With the Denon's USB disconnected and the RCAs connected -> no PC noise, no ground loop hum but only when the Denon is powered on.
Now, I am totally fine with only connecting the Denon's USB and accepting the attendant noise when I actually want to use it to DJ. But leaving it powered on with the USB disconnected to eliminate the ground loop hum is really annoying because all of the LED-lit buttons on the controller flash nonstop. I am also troubled by the fact that if the Denon vanished, I'd be left with a ground loop hum that I couldn't solve.
Two questions then:
- How do I eliminate the USB noise from the Denon given that it's already got an external power supply? Do those $40-50 USB isolators/filters actually work?
- Where might the ground loop hum be coming from in the rest of the setup, and why would the Denon eliminate it when powered on?
- Would hum eliminators or DI boxes or some other pro audio gizmo between the DSP and the amps (probably converting the unbalanced RCA to balanced XLR in the process) - which presumably would eliminate the hum - audibly degrade the signal?
Thanks!
The heart of the system is a Dayton Audio DSP-408 that I use for EQ, room correction, and crossover. This DSP has 4 RCA inputs and 8 RCA outputs. Two output channels feed a Crown XLS-1002 that powers a pair of DIY SEAS Idunn speakers (not built for this purpose - they used to be in my living room). One output channel feeds a Behringer iNuke NU3000 that powers 4x JBL CS-1214 subwoofers in a pair of 2x12" prefab enclosures. My concept with this system was to be able to do both critical "audiophile" listening and to be able to crank up the subwoofers to provide club-quality sound for listening to and DJing electronic music. Mission accomplished.
Initially, my source was exclusively a Denon MC4000 USB DJ controller. My old NuForce uDAC-2 had died and my FiiO E18 has no preamp functionality, so I figured for the time being - not needing headphones for critical listening in this environment - the Denon would be just fine as a source since it reportedly has a decent soundcard and can be used with WASAPI/ASIO by Windows. It is not bus-powered - there is a separate 5V/3A power supply.
Unfortunately the Denon is horribly noisy. It has a high noise floor to begin with, and there is a ton of noise that comes over the USB cable from my PC chassis - buzzes, noise when I scroll the mouse, etc.. It's fine when music is playing, but it's not tolerable when idle and it's especially bad for gaming when the GPU spins up. Adequate for DJing, not adequate as an all-purpose source. I know that it's the USB because this noise goes away when I disconnect it. I've tried other cables and ports and it doesn't help.
Months later (now), I purchased a Schiit Modi 3 and Sys for passive volume control (this was dumb - I should have just bought a headphone amp with preamp outs and now have a JDS Atom on order) both to troubleshoot and see if it was a sound upgrade for non-DJ listening. I have the output from the Modi 3/Sys running to the other two input channels on the DSP (NB: I am well aware that the ADC/DSP/DAC part of my signal chain is a bottleneck on fidelity, but I think the signal going in still matters). One cool thing is that I can easily do a level-matched A/B between the two sources. The Modi 3 blows the Denon away - clearly a good DAC is an excellent addition to my system. But the Denon is a great piece of DJ gear and it needs to stay in my system.
And this brings me to the problem: troubleshooting the noise when this is all connected.
- With both fully connected, there is tons of PC noise coming through the speakers. No ground loop hum.
- With the Denon disconnected entirely and the Modi 3 on USB -> PC noise + ground loop hum.
- With the Denon disconnected and the Modi 3 on optical + external power -> no PC noise whatsoever, but ground loop hum.
- With the Denon connected and the Modi 3 on optical + external power -> PC noise, but no hum.
- With the Denon's USB disconnected and the RCAs connected -> no PC noise, no ground loop hum but only when the Denon is powered on.
Now, I am totally fine with only connecting the Denon's USB and accepting the attendant noise when I actually want to use it to DJ. But leaving it powered on with the USB disconnected to eliminate the ground loop hum is really annoying because all of the LED-lit buttons on the controller flash nonstop. I am also troubled by the fact that if the Denon vanished, I'd be left with a ground loop hum that I couldn't solve.
Two questions then:
- How do I eliminate the USB noise from the Denon given that it's already got an external power supply? Do those $40-50 USB isolators/filters actually work?
- Where might the ground loop hum be coming from in the rest of the setup, and why would the Denon eliminate it when powered on?
- Would hum eliminators or DI boxes or some other pro audio gizmo between the DSP and the amps (probably converting the unbalanced RCA to balanced XLR in the process) - which presumably would eliminate the hum - audibly degrade the signal?
Thanks!