This applies to people using the Chipamp.com Dual Mono PCB boards and possibly others using a similar arrangement.
I have been pulling my hair out trying to solve the hum problem from my amp, using large csa copper wires to connect the chassis ground points and trying input capacitors... not to mention watching every thread on this website hoping an answer would become clear. I had my amp set up as shown below.
I have been pulling my hair out trying to solve the hum problem from my amp, using large csa copper wires to connect the chassis ground points and trying input capacitors... not to mention watching every thread on this website hoping an answer would become clear. I had my amp set up as shown below.
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Listening to the hum the amp produced is seemed all too similar to that of the transformer which got me thinking. I had all the same issues that other people had, connect one channel to the pre-amp and all was fine, connect the second and it all got noisy. This indicated that there was some interaction between the channels and the only two points of connection are the chassis ground wires, which when disconnected from each other worsen the hum and the connection through the power supply.
So with the amp unplugged I disconnected the chassis grounds and measured the resistance between the two RCAs to find that there was approximately 5M Ohms between them, confirming my suspision that the transformer noise was what I was hearing.
To validate this theory I connected both amps to a single rectfier board and voila, hum gone!
So there are two solutions to this problem, one is to use a single rectifier board and the other is to use the amps in true dual mono and use two transformers, one for each channel!
So with the amp unplugged I disconnected the chassis grounds and measured the resistance between the two RCAs to find that there was approximately 5M Ohms between them, confirming my suspision that the transformer noise was what I was hearing.
To validate this theory I connected both amps to a single rectfier board and voila, hum gone!
So there are two solutions to this problem, one is to use a single rectifier board and the other is to use the amps in true dual mono and use two transformers, one for each channel!
If you have one of these kits or you are running two rectifier boards from a single transformer one of these approaches should solve your hum problem.
Vikash, if you could get hold of some nice potted 160VA transformers the would sell like hotcakes with the dual mono chipamp boards you sell (I'll be buying another 300VA one from you in the very near future.... nothing like overkill!
)
I hope this helps a few of you that have been stuggling with this problem for a while.
I also look forward to hearing other people's experience of trying this solution and others.
Vikash, if you could get hold of some nice potted 160VA transformers the would sell like hotcakes with the dual mono chipamp boards you sell (I'll be buying another 300VA one from you in the very near future.... nothing like overkill!
)I hope this helps a few of you that have been stuggling with this problem for a while.
I also look forward to hearing other people's experience of trying this solution and others.
The problem exists whether the chassis grounds are connected to earth or not.
There is some noise when the preamp is completely disconnected, although this goes if the rca is shorted.
The RCAs are indeed isolated from the chassis. Though they are effectively connected when the chassis grounds are connected to earth, as indicated in the diagram.
There is some noise when the preamp is completely disconnected, although this goes if the rca is shorted.
The RCAs are indeed isolated from the chassis. Though they are effectively connected when the chassis grounds are connected to earth, as indicated in the diagram.
Just to clarify I am posting a solution, I have spent a lot of time reading through threads on this site which have suggested some extreme measures to eliminate the hum problem, including suggesting that the boards are badly designed and that you need to cut some of the traces. Now I am not being funny, but if you had just shelled out a load of cash on some PCBs it would be nice to have a solution that didn't involve hacking them to death in a potentially vain search for a solution that is relatively easy.
I think what is perhaps missing from the chipamp.com installation manual for these kits is to point out a suggested implementation to ensure interaction free operation, i.e. just use one rectifier for a pair of amp boards or use a transformer for each rectifier board, i.e. one per channel.
I think what is perhaps missing from the chipamp.com installation manual for these kits is to point out a suggested implementation to ensure interaction free operation, i.e. just use one rectifier for a pair of amp boards or use a transformer for each rectifier board, i.e. one per channel.
Ian,
I bought the stereo boards from Chipamp (single rectifier board) and paid no special attention to earthing, and have no noise problems at all.
In fact, contrary to most advice on here, my chassis grounds are joined together and earthed to the main chassis case, about 15cm from the mains (safety) earth. The chassis is a simple sheet aluminium affair I knocked up in a couple of hours. Nothing else is earthed to the chassis except the body of the pot, via its attachment nut.
In fact, there IS noise if I leave the chassis grounds joined, but remove them from the connector on the chassis.
My implementation is most basic, with simply a pot on the inputs. If I turn the pot up full, there is the faintest hiss.
FYI, anyway...
Stuey
I bought the stereo boards from Chipamp (single rectifier board) and paid no special attention to earthing, and have no noise problems at all.
In fact, contrary to most advice on here, my chassis grounds are joined together and earthed to the main chassis case, about 15cm from the mains (safety) earth. The chassis is a simple sheet aluminium affair I knocked up in a couple of hours. Nothing else is earthed to the chassis except the body of the pot, via its attachment nut.
In fact, there IS noise if I leave the chassis grounds joined, but remove them from the connector on the chassis.
My implementation is most basic, with simply a pot on the inputs. If I turn the pot up full, there is the faintest hiss.
FYI, anyway...
Stuey
this thread is timely for me as i am in the process of rebuilding my first chip amp and was considering using a second rectifier board.
i am motivated to try a second rectifier as i have read at least a few times on this forum that it can improve channel separation. Limited channel separation is definitely an issue with a single board (at least compared to my monoblocks).
prior to the rebuild the amp has been dead quiet with absolutely no attention paid to wire routing or grounding.
i will try using two rectifier boards and will post my results.
i am motivated to try a second rectifier as i have read at least a few times on this forum that it can improve channel separation. Limited channel separation is definitely an issue with a single board (at least compared to my monoblocks).
prior to the rebuild the amp has been dead quiet with absolutely no attention paid to wire routing or grounding.
i will try using two rectifier boards and will post my results.
I hope you don't mind me drawing over your diagram 
After a few experiments, this is the grounding scheme I use for my 4ch GC - it runs off a single 500VA and uses 4 rectifier boards. Only 2 chanels shown but you get the idea.
No hum, no hiss, no turn on/off thump either
After a few experiments, this is the grounding scheme I use for my 4ch GC - it runs off a single 500VA and uses 4 rectifier boards. Only 2 chanels shown but you get the idea.
No hum, no hiss, no turn on/off thump either
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Hi AndrewT,
Yup, that's what has worked. I've used the same scheme on both my amps (I took the top off one to double check before posting the diagram)
It's the only scheme I tried that gave zero hum. I disconnected one 0V or ground at a time - wired them to the chassis ground, tested for hum and so on until I ended up with everything connected to the main chassis ground and no hum.
The circuit is roughly as shown on the attachment - I've used the optional cap Ci on both amps.
Yup, that's what has worked. I've used the same scheme on both my amps (I took the top off one to double check before posting the diagram)
It's the only scheme I tried that gave zero hum. I disconnected one 0V or ground at a time - wired them to the chassis ground, tested for hum and so on until I ended up with everything connected to the main chassis ground and no hum.
The circuit is roughly as shown on the attachment - I've used the optional cap Ci on both amps.
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