'Rallyfinnen capacitor', I'm flatteredHowever, my real name is actually Sam, not Andreas
BTW, maybe it would be good to update the original document with the stability and bias upgrades, easier for new builders to get the whole picture without reading through this tread?
Ah, Sam! I’ll update it. The build document will be updated!
For dual mono, there should only be one connection between the channels and that is right at the input connectors. In this way you ensure no internal ground loops and no cross channel ground loops.
I have never built a dual mono, but in theory it should be as quiet as a standard design. I would recommend you use the ground lifter - again this will ensure no connection to the
chassis below c. +-1.2V.
Best thing is to start from the beginning and wire everything up step by step. Building a quiet amp is a challenge and it does take practice (I am still learning
Please see below.
Thank you for drawing ,I try.
I have done it like that with dual mono and it works for me.
Another way would be to try with ground lifters on each channel (rectifier, resistor and small cap in parallel if I'm not mistaken), but then you create a possible loop via double ground paths (common ground at source and common ground at amp via ground lifters).
You can try that option too, and compare the hum. Remember to try switching the polarity on the transformer primary on one channel, if you get hum with two channels connected.
You can try with ground lifters and bypassed R9 too.
Using ground lifters will improve electrical safety, but personally I'm happy as long as the metal case is connected to safety ground.
I think the reason for the hum is leakage via your main transformer(s). What I would call a common mode current (not sure if it is the correct term though) created by leakage in the transformer. I guess it's mainly capacitive coupling between primary and secondary.
I'm sure others can tell you more and give you better advice. You can also try to read the papers linked to before and get an understanding of what happens.
Another way would be to try with ground lifters on each channel (rectifier, resistor and small cap in parallel if I'm not mistaken), but then you create a possible loop via double ground paths (common ground at source and common ground at amp via ground lifters).
You can try that option too, and compare the hum. Remember to try switching the polarity on the transformer primary on one channel, if you get hum with two channels connected.
You can try with ground lifters and bypassed R9 too.
Using ground lifters will improve electrical safety, but personally I'm happy as long as the metal case is connected to safety ground.
I think the reason for the hum is leakage via your main transformer(s). What I would call a common mode current (not sure if it is the correct term though) created by leakage in the transformer. I guess it's mainly capacitive coupling between primary and secondary.
I'm sure others can tell you more and give you better advice. You can also try to read the papers linked to before and get an understanding of what happens.
On a dual mono, provided you join the two channels at only the input sockets, you should not need the HBR with the ground lifter. Since the 0V on the amplifier modules are off separate power supplies, there is no cross channel ground loop.
Also, check that the HBR is not blown open circuit.
(Radoslav, I seriously recommend that that you put the input sockets next to each other. Also, on your amp I am a bit worried that the rectifiers might overheat. How hot are they getting in class A mode? They should be mounted on the solid part of the chassis - not over the slots where the heat cannot be easily conducted away by the aluminium.)
Also, check that the HBR is not blown open circuit.
(Radoslav, I seriously recommend that that you put the input sockets next to each other. Also, on your amp I am a bit worried that the rectifiers might overheat. How hot are they getting in class A mode? They should be mounted on the solid part of the chassis - not over the slots where the heat cannot be easily conducted away by the aluminium.)
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I think for dual mono there is no need to join them at the input of the amp, it's enough to only join the two channels at the source. By doing that you also eliminate the loop between the two ground leads in the interconnecting cable. It is very small if the cables run parallel, but if for example the inputs are spaced apart on the amp, the loop area could grow to be significant?
You can still get a cross channel ground loop outside the amp, but not inside if you use the ground lifter. I would still bond the inputs together at the input! It’s good practice as well.
Interconnect cables are always bonded together and input connectors on (good) commercial and professional equipment are next to each other in order to keep the loop areas between equipment as small as possible.
Interconnect cables are always bonded together and input connectors on (good) commercial and professional equipment are next to each other in order to keep the loop areas between equipment as small as possible.
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