Since upgrade of my Class D power amp with NewClassD Singularity 3 modules (formerly Singularity2, wiring and case exactly like before), I have significant 50Hz-ish hum in my subwoofer. It only kicks in when the power amp is on and speakers engaged, turning down the volume on the sub does not stop it. I had NO problems using the exact same setup prior to the upgrade nor with several other Class D amplifiers.
The hum is arising in the subwoofer only, and goes away if subwoofer is turned off (obviously) or power amp is turned off. Other electronics nearby (including player/DAC, class A/B amplifier, miniDSP, phono amp, headphone amp) do not seem disturbed. There is absolutely no hum coming from the class D amp, so I figure the sub is picking up RFI which is overwhelming it's noise filter and letting in hum from mains or elsewhere (the high switching speed of Singularity3 may be why it doesn't happen with the other amps).
I have tried a number of things including adding clip-on ferrites to cables and so on. Initially I found that proximity of the subwoofer power cable to the speaker cables (unavoidable in my setup) was causing hum, so I installed a shielded and grounded power cable on the sub, and with addition of a ferrite internally and further two just outside the plate amp, the power cable no longer seems at issue. BUT I still get hum if I connect a signal cable. It doesn't make a difference if it's straight from the DAC/Player LFE output, or from the miniDSP. I have a voltmeter that can measure frequency (no oscilloscope unfortunately), however I can't seem to measure any electrical signal causing the hum (e.g. not between signal cables and disconnected sub). I don't hear hum when connecting the headphone amp directly to the sub end of the cables. A different an much cheaper subwoofer is also unaffected.
The Class D build is pretty much by the book in a grounded aluminum cabinet, dual mono wired up exactly as described in the v.300 instructions https://lctechs.dk/newclassd/index.php?page=15&hv=1 on page 28, but with the addition of an extra wire connecting input ground to one end of the ground cable at the power supply end of the modules - this connection was present in the Singularity2 build and wasn't causing problems so I decided to keep it.
I did install ferrites on the power supply cables to the modules, but due to cable length and thickness I couldn't run them through twice as shown on page 19 of the instructions, also I have ferrites on the speaker cables as shown on page 25, although I don't have the RFI caps installed (but neither did the Singularity2 build, or for that matter an older build which is not causing hum).
Sorry for the long writeup, but I am at a loss on what to try next? RFI caps? Ground loop breaker? further changes to subwoofer amp power supply?
Ideally I guess would be to stop the RFI at the source - but it'd also be great if I could stop it from entering the subwoofer amplifier...
Any experiences and ideas much appreciated!!!!
The hum is arising in the subwoofer only, and goes away if subwoofer is turned off (obviously) or power amp is turned off. Other electronics nearby (including player/DAC, class A/B amplifier, miniDSP, phono amp, headphone amp) do not seem disturbed. There is absolutely no hum coming from the class D amp, so I figure the sub is picking up RFI which is overwhelming it's noise filter and letting in hum from mains or elsewhere (the high switching speed of Singularity3 may be why it doesn't happen with the other amps).
I have tried a number of things including adding clip-on ferrites to cables and so on. Initially I found that proximity of the subwoofer power cable to the speaker cables (unavoidable in my setup) was causing hum, so I installed a shielded and grounded power cable on the sub, and with addition of a ferrite internally and further two just outside the plate amp, the power cable no longer seems at issue. BUT I still get hum if I connect a signal cable. It doesn't make a difference if it's straight from the DAC/Player LFE output, or from the miniDSP. I have a voltmeter that can measure frequency (no oscilloscope unfortunately), however I can't seem to measure any electrical signal causing the hum (e.g. not between signal cables and disconnected sub). I don't hear hum when connecting the headphone amp directly to the sub end of the cables. A different an much cheaper subwoofer is also unaffected.
The Class D build is pretty much by the book in a grounded aluminum cabinet, dual mono wired up exactly as described in the v.300 instructions https://lctechs.dk/newclassd/index.php?page=15&hv=1 on page 28, but with the addition of an extra wire connecting input ground to one end of the ground cable at the power supply end of the modules - this connection was present in the Singularity2 build and wasn't causing problems so I decided to keep it.
I did install ferrites on the power supply cables to the modules, but due to cable length and thickness I couldn't run them through twice as shown on page 19 of the instructions, also I have ferrites on the speaker cables as shown on page 25, although I don't have the RFI caps installed (but neither did the Singularity2 build, or for that matter an older build which is not causing hum).
Sorry for the long writeup, but I am at a loss on what to try next? RFI caps? Ground loop breaker? further changes to subwoofer amp power supply?
Ideally I guess would be to stop the RFI at the source - but it'd also be great if I could stop it from entering the subwoofer amplifier...
Any experiences and ideas much appreciated!!!!
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