If the buzzing stops when you disconnect safety earth you have got a ground loop. 99.99% of the time such kind of ground loop is introduced by the input connections (RCA cables), that's why I asked you if the amp still buzzes, when inputs are not connected to anything - to rule out a ground loop.
What I said was the switching power supply of the PC causes the buzzing. You must have to have the RCA cables connected so whether the noise is present with or without them is pretty close to irrelevant as you can't use the amp with the input cables unplugged.
What does stop the buzzing is if you use everything identical in the setup but you change the PC to a laptop and you run the laptop from the internal laptop battery. Then the buzzing stops as there's no switched power supply on the circuit.
With the setup as it is now in the photo, if you disconnect the earth lead by cutting the cable (which I've just tested) then the buzzing goes away.
I suspect that would be the case with or without the filter.
Other two amps I have don't buzz with the rest of the setup identical.
What does stop the buzzing is if you use everything identical in the setup but you change the PC to a laptop and you run the laptop from the internal laptop battery. Then the buzzing stops as there's no switched power supply on the circuit.
With the setup as it is now in the photo, if you disconnect the earth lead by cutting the cable (which I've just tested) then the buzzing goes away.
I suspect that would be the case with or without the filter.
Other two amps I have don't buzz with the rest of the setup identical.
Well, as you see - my question was not irrelevant because if you had answered that question I would have known in advance that the problem is not conducted EMI via the mains cable of the amp but it is a ground loop, which is a whole different thing.
Why is it better with the laptop instead of the PC connected - might be for example that the laptop has a two wire mains cable and thus no earth connection => no ground loop. Might also be that the laptop simply produces less leakage currents in the earth wire than the PC PSU.
Now you have three options:
1) Give your amp a proper balanced input stage with an instrumentation amplifier that has a high CMRR.
2) Completely redo the grounding inside the amp - it obviously is done badly.
I highly recommend reading this article by Bruno Putzeys. Or better read it several times until you understood every bit of it as it is a complicated subject. At least it took me several readings to grasp everything.
3) less complicated but involves audio transformers which introduce some THD: get a ground loop breaker for your RCA input cables. Something like this here:
PAC SNI-1 Noise Filter Ground Loop Cinch Entstorfilter Isolator Premium : Amazon.de: Elektronik & Foto - Just did a quick google search, these are available in any price and quality range.
PS: I suppose you switch your tone to a less arrogant one and try to answer my questions even if they seem irrelevant to you. otherwise I will stop answering here.
EDIT: I just read that you use your laptop with battery and without PSU. That also breaks the ground loop as the audio source (latop soundcard) has no connection to mains earth.
Why is it better with the laptop instead of the PC connected - might be for example that the laptop has a two wire mains cable and thus no earth connection => no ground loop. Might also be that the laptop simply produces less leakage currents in the earth wire than the PC PSU.
Now you have three options:
1) Give your amp a proper balanced input stage with an instrumentation amplifier that has a high CMRR.
2) Completely redo the grounding inside the amp - it obviously is done badly.
I highly recommend reading this article by Bruno Putzeys. Or better read it several times until you understood every bit of it as it is a complicated subject. At least it took me several readings to grasp everything.
3) less complicated but involves audio transformers which introduce some THD: get a ground loop breaker for your RCA input cables. Something like this here:
PAC SNI-1 Noise Filter Ground Loop Cinch Entstorfilter Isolator Premium : Amazon.de: Elektronik & Foto - Just did a quick google search, these are available in any price and quality range.
PS: I suppose you switch your tone to a less arrogant one and try to answer my questions even if they seem irrelevant to you. otherwise I will stop answering here.
EDIT: I just read that you use your laptop with battery and without PSU. That also breaks the ground loop as the audio source (latop soundcard) has no connection to mains earth.
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Okay, I've ordered a ground loop suppressor. Again, not an expensive gamble so we'll see if that does it.
I'm not sure if you are reading everything I'm writing as I explained the laptop works without a mains cable connected. If you run it from the battery and not from a plugged in laptop charger then the buzzing goes away. If you connect the laptop battery charger it is almost as noisy as the PC. The laptop battery charge / power supply is a bit smaller than the one in a PC so the buzzing is only 75%.
Is there any other use for the filter I've bought?
I'm not sure if you are reading everything I'm writing as I explained the laptop works without a mains cable connected. If you run it from the battery and not from a plugged in laptop charger then the buzzing goes away. If you connect the laptop battery charger it is almost as noisy as the PC. The laptop battery charge / power supply is a bit smaller than the one in a PC so the buzzing is only 75%.
Is there any other use for the filter I've bought?
It doesn't hurt to have a mains filter on any amp. Might clean up low level noise from a nearby switching power supply even after you fixed your ground loop problem.
You can do a listening test after you fixed the ground loop problem with and without the mains filter.
I personally add dual stage line filters to all my audio equipment just for good measure. But I worked at an EMI lab as my first job and I might be called biased 🙂 I also always add an RC low pass on all audio inputs to keep away radiated EMI...
You can do a listening test after you fixed the ground loop problem with and without the mains filter.
I personally add dual stage line filters to all my audio equipment just for good measure. But I worked at an EMI lab as my first job and I might be called biased 🙂 I also always add an RC low pass on all audio inputs to keep away radiated EMI...
I think there's an acceptable level of noise or buzzing but it has to be quiet enough not to be irritating. That isn't the case with this amp, the buzzing is loud and very annoying when sitting in a quiet room.
You might be amazed how much deeper you can listen into a mix if all the "acceptable/low level noise" is cleaned up as well. Especially for quiet late night listening...
PS: it would be best to put the mains filter inside the amp enclosure with solid ground connection to the chassis. Or at least keep the leads from filter to amp very short.
PS: it would be best to put the mains filter inside the amp enclosure with solid ground connection to the chassis. Or at least keep the leads from filter to amp very short.
I'll look into that. It had crossed my mind but it depends how much space there is inside the box.
>Other two amps I have don't buzz with the rest of the setup identical.
You might - as a learning experience - look into how those amps are wired internally regarding the AC, the power supply, how the "shell" of the RCA inputs go to ground. Compare with this class A unit.
Example, earth ground goes to a chassis stud. How does the RCA "signal grounds" make it to ground? Jacks hard bolted to the chassis? Isolated (floating), grounds to the circuit board, then through the circuit board to the ground stud?
Some difference between the two amps that work well and the one that doesnt is going to show up in the analysis. Line level isolation transformers are for those needing a quick-fix; they work, but the solution is pedestrian, vs "audiophile".
Unless of course you get some high end ($2500) stuff, like the Sophia Electric Magik Box. I think it isolates too. Of course I somewhat jest with that; there's other more reasonable priced devices from well known audio maker Lundahl Audio Transformers • Problem solvers • Lundahl Transformers.
You might - as a learning experience - look into how those amps are wired internally regarding the AC, the power supply, how the "shell" of the RCA inputs go to ground. Compare with this class A unit.
Example, earth ground goes to a chassis stud. How does the RCA "signal grounds" make it to ground? Jacks hard bolted to the chassis? Isolated (floating), grounds to the circuit board, then through the circuit board to the ground stud?
Some difference between the two amps that work well and the one that doesnt is going to show up in the analysis. Line level isolation transformers are for those needing a quick-fix; they work, but the solution is pedestrian, vs "audiophile".
Unless of course you get some high end ($2500) stuff, like the Sophia Electric Magik Box. I think it isolates too. Of course I somewhat jest with that; there's other more reasonable priced devices from well known audio maker Lundahl Audio Transformers • Problem solvers • Lundahl Transformers.
You know what might be happening is simply the difference between class-A and class-B. My other two amps are class-b so usually idling unless asked to amplify. So the noise / buzzing isn't picked up. I'm sure if you could idle the class-B amps at full power like the class-A it would probably pick up the noise, just never get to hear it as the music you're playing will always be far louder than the buzzing.
The class-A amp has a volume knob on it. If you turn it down to about 40% the noise can't be heard any longer. I've not tested it but I think if I were to measure the electrical consumption with the amp on 40% you'd probably see lower figures.
The class-A amp has a volume knob on it. If you turn it down to about 40% the noise can't be heard any longer. I've not tested it but I think if I were to measure the electrical consumption with the amp on 40% you'd probably see lower figures.
Hmm, that just shows that significant load currents flow through the audio grounds resulting in significant voltage drops along these audio ground lines. This will lead to ground bounce, that's why all "unbalanced" schemes are flawed right from the start.
Good news, with both the RCA filter AND the power filter connected at the same time this amp can be turned up to 98% (not quite 100% as it makes static scratching sound at full)
Thanks for all the suggestions. I've got to formalise the wiring as it can't be used until all these boxes and connections are neat and safe.
I have a feeling it might work with just the RCA filter if I could find some shielded RCA cables as the RCA cables themselves seem to be the route of all evil when using only the RCA filter.
Thanks for all the suggestions. I've got to formalise the wiring as it can't be used until all these boxes and connections are neat and safe.
I have a feeling it might work with just the RCA filter if I could find some shielded RCA cables as the RCA cables themselves seem to be the route of all evil when using only the RCA filter.
I bought some thick 'guitar' leads with the 6.35mm jack on both ends. One end goes into the sound card on the PC as that's the interface it has on the card. The other end I cut off and soldered to a ebay high quality phono plug. The leads for left and right are separate all the way along. The filter is quite close to the amp and uses 2 individual ebay high quality RCA leads 20cm in length.