mihaelbele
Member
Hi,
stereo amp I'm using with PC is missbehaving, and instead of fixing it, I decided I'll replace it with small D class amp (10w, one pot, powered from 12V PC PSU rail). Instead of building one, I found "perfect" ~$2 thing on aliexpres (PAM8610 board). Amp works OK, but I'm having a problem with induced noise (static like crackling influenced by CPU load and mouse movement, pulsing in ~4 pulses per second). This noise is present with the original amp also, maybe little less loud, and was one of the reasons why I wanted to power the new amp from PC PSU to avoid (longer) ground loop. PC is brand new and I think it has high quality components.
Here's what I've tried:
1. stereo cable with ferite beads on both ends - no audible difference compared to plain cable
2. ferite bead on 12V amp power line near the plug - no audible difference
3. ground lift on stereo cable (amp shorts DC 0V with audio GND, and it's shorted on motherboard side too) - didn't fix it, maybe the noise is a bit louder
4. analog audio output from monitor DAC (digital via DP) - no audible difference compared to PC analog output (stereo cable is far away from any power cables, but near DP and USB)
5. front vs rear analog output from PC - no audible difference
6. different analog source (smartphone) - acceptable noise level (almost none)
7. headphones instead of amp on PC front panel connector and monitor analog audio output - there's no noise! (or I can't hear it)
8. turning of both monitors (and unplugging HDMI/DP/USB cables), so no USB hub/wireless mouse/HDMI/DP - no audible difference
9. unplugging audio cable from PC - no noise, hums when I touch connector's hot terminals
Using optical output from PC and feeding the amp from external DAC solves the problem when using separate isolated 5V (phone charger) power supply for DAC (noise levels very low), while switching to power supply via PC USB noise level raises (but it's acceptable).
I don't have 12V/3A isolated (DC 0V not connected to protecive earth) PSU for the amp, so I used 12V/1A just to test the noise with PC analog output, and it's acceptable as long as I don't touch the metal pot (whole amp should be isolated and pot should have plastic knob) - just some low level buzz and hum. With non-isolated power supply, the noise is the same as when using PC PSU.
Can someone explain what is happening?
stereo amp I'm using with PC is missbehaving, and instead of fixing it, I decided I'll replace it with small D class amp (10w, one pot, powered from 12V PC PSU rail). Instead of building one, I found "perfect" ~$2 thing on aliexpres (PAM8610 board). Amp works OK, but I'm having a problem with induced noise (static like crackling influenced by CPU load and mouse movement, pulsing in ~4 pulses per second). This noise is present with the original amp also, maybe little less loud, and was one of the reasons why I wanted to power the new amp from PC PSU to avoid (longer) ground loop. PC is brand new and I think it has high quality components.
Here's what I've tried:
1. stereo cable with ferite beads on both ends - no audible difference compared to plain cable
2. ferite bead on 12V amp power line near the plug - no audible difference
3. ground lift on stereo cable (amp shorts DC 0V with audio GND, and it's shorted on motherboard side too) - didn't fix it, maybe the noise is a bit louder
4. analog audio output from monitor DAC (digital via DP) - no audible difference compared to PC analog output (stereo cable is far away from any power cables, but near DP and USB)
5. front vs rear analog output from PC - no audible difference
6. different analog source (smartphone) - acceptable noise level (almost none)
7. headphones instead of amp on PC front panel connector and monitor analog audio output - there's no noise! (or I can't hear it)
8. turning of both monitors (and unplugging HDMI/DP/USB cables), so no USB hub/wireless mouse/HDMI/DP - no audible difference
9. unplugging audio cable from PC - no noise, hums when I touch connector's hot terminals
Using optical output from PC and feeding the amp from external DAC solves the problem when using separate isolated 5V (phone charger) power supply for DAC (noise levels very low), while switching to power supply via PC USB noise level raises (but it's acceptable).
I don't have 12V/3A isolated (DC 0V not connected to protecive earth) PSU for the amp, so I used 12V/1A just to test the noise with PC analog output, and it's acceptable as long as I don't touch the metal pot (whole amp should be isolated and pot should have plastic knob) - just some low level buzz and hum. With non-isolated power supply, the noise is the same as when using PC PSU.
Can someone explain what is happening?
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