Two different things, I try to tell you. If it is mains (50Hz) it is radiated and depends on how the wiring is routed, and the transformer orientation. It sounds like a relatively pure tone.
Buzz which is 100Hz + harmonics, sounds a bit like rattle, is from the current in the wiring.
These have quite different solutions. Hum cannot be cured by breaking ground loops (unless you also reroute the wiring).
Buzz cannot be cured by moving wiring around, it needs change of the current routing itself and/or breaking ground loops.
It is important to identify what the real problem is.
So what it the problem you have.
Jan
So by now I tried everything that was mentioned and with no result. I disconnected and turned off preamp and now working only on the power amplifier that still makes buzz noise. I've connected RCA connectors directly to the power amplifiers boards. If I run only one channel then everything is ok, no buzz or hum present at all. But if I connect both channels and their signal grounds are connected I immediately hear buzz from both of the speakers. I've tried adding 10ohm resistors to the signal return path with very strange results.
If I connect resistor into only one channel that channel still has the buzz BUT another channel which is connected directly becomes completely silent.
If I connect 10ohm resistors into each channel's signal return then the same buzz is present in both channels. It seems like it depends more on the balance of resistance than on the resistance itself.
When the signal grounds are connected via resistors how can it happen that the current flows (enough to cause buzz) through this connection? It has way higher resistance then the path via power ground.
At this point I don't understand what's going on at all. I don't understand how any stereo power amp in the world can work at all because any stereo power amp will have to have power supply ground connection between channels and signal ground connection between channels. This creates two different ground paths and there will be current flowing through it which is a definition of ground loop if I understand correctly.
I also tried star grounding where signal ground from RCA goes to PSU ground and from there to boards' signal ground input. Result is the same.
I've also tried connecting chassis to signal ground without any changes.
I think I don't understand something basic behind the ground loop noise because I can't find any explanation to what's going on.
If I connect resistor into only one channel that channel still has the buzz BUT another channel which is connected directly becomes completely silent.
If I connect 10ohm resistors into each channel's signal return then the same buzz is present in both channels. It seems like it depends more on the balance of resistance than on the resistance itself.
When the signal grounds are connected via resistors how can it happen that the current flows (enough to cause buzz) through this connection? It has way higher resistance then the path via power ground.
At this point I don't understand what's going on at all. I don't understand how any stereo power amp in the world can work at all because any stereo power amp will have to have power supply ground connection between channels and signal ground connection between channels. This creates two different ground paths and there will be current flowing through it which is a definition of ground loop if I understand correctly.
I also tried star grounding where signal ground from RCA goes to PSU ground and from there to boards' signal ground input. Result is the same.
I've also tried connecting chassis to signal ground without any changes.
I think I don't understand something basic behind the ground loop noise because I can't find any explanation to what's going on.
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this is the right track to follow... back to basics....first get the power amps running with no inputs connected..... there should be no hum/buzz just a little hiss.
Can I ask, in your photos there is a ground lead that is disconnected from a plug and flopping around like an antenna. Any reason for that and have you tried with both ends disconnected?
I notice from the photos that your grounds seem to be in a daisy chain layout? Have you tried a Star type layout? (All grounds to a single point rather than in a series loop).
Try check for external sources of the noise. I had a wicked hum on an amp I was working on and it turned out to be coming from a craptastic 5V USB mini plug feeding pure junk into the mains. I have also had an overhead fluorescent light cause noise issues as well. Have a look around, perhaps move the amp to another, electrically quiet location and test.
Anyway, hope you find the problem and don't give up!
Sorry, missed that statement. Not sure if the RCA is supposed to go via chassis (psu) ground though..
Have you tried signal grounds to their own star point and PSU to separate chassis connected star ground?
Have you seen this (very thorough) guide on the subject: Audio Component Grounding and Interconnection
I notice from the photos that your grounds seem to be in a daisy chain layout? Have you tried a Star type layout? (All grounds to a single point rather than in a series loop).
Try check for external sources of the noise. I had a wicked hum on an amp I was working on and it turned out to be coming from a craptastic 5V USB mini plug feeding pure junk into the mains. I have also had an overhead fluorescent light cause noise issues as well. Have a look around, perhaps move the amp to another, electrically quiet location and test.
Anyway, hope you find the problem and don't give up!
Sorry, missed that statement. Not sure if the RCA is supposed to go via chassis (psu) ground though..
Have you tried signal grounds to their own star point and PSU to separate chassis connected star ground?
Have you seen this (very thorough) guide on the subject: Audio Component Grounding and Interconnection
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In photos you can see just one of the approaches that I've tried. Basically it was star layout attempt where all grounds were connected to PSU ground output.
Currently I've disconnected power amp input cables from the preamp and connected RCA plug directly to them. Everything hanging out of the amp right now
With this setup I've tried connecting signal ground from RCA to each channel which basically gives variant with signal star ground separate from PSU star ground. Also I've tried single star ground when ground wire from RCA goes to PSU ground and from there ground wires go to each power amp board input. Both variants give the same result, still buzz in the speakers.
The power ground is not daisy chained. Each power amp board is connected to PSU board directly. It's tight there so it may not be seen in photos.
Thank you for the article, will read it now.
Also, most likely unrelated to your problem, check that your IEC socket is wired correctly. It's hard to see from the photos (and probably fine) but you might not have L/N correctly oriented.
Here is an example of how to wire what your socket appears to be:
Wire Up a Fused AC Male Power Socket: 4 Steps (with Pictures)
Also, do you get the buzz when shorting out the input? (Connect input signal - signal GND).
Do you have a multimeter with a Hz function? I have identified gross noise frequency before using a DMM. Not as accurate as oscilloscope but it helped me confirm mains induced hum.
One last thing.. I do a chopstick test when I am hunting for noise. Have the amp running and poke and prod wires with a chopstick to see if the amplitude changes. It can sometimes help pinpoint an area of interest. For the love of god, don't use metal chopsticks if you do this, and be safe around live electronics!!!
Here is an example of how to wire what your socket appears to be:
Wire Up a Fused AC Male Power Socket: 4 Steps (with Pictures)
Also, do you get the buzz when shorting out the input? (Connect input signal - signal GND).
Do you have a multimeter with a Hz function? I have identified gross noise frequency before using a DMM. Not as accurate as oscilloscope but it helped me confirm mains induced hum.
One last thing.. I do a chopstick test when I am hunting for noise. Have the amp running and poke and prod wires with a chopstick to see if the amplitude changes. It can sometimes help pinpoint an area of interest. For the love of god, don't use metal chopsticks if you do this, and be safe around live electronics!!!
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