Hum with Brian 3886 kits

[carlosfm]

Re: try this

The solution CarlosFM shows didn't work for me (bad interpretation/implementation - or too efficient spkr (?): residual hum always audible at 20-30 cm 96dB spkr).

Did you put the two channels as close as possible from each other as I recommend, or do you have one at each extreme side of the amp?

4) connect csg to the left pcb AT (NEAR) THE POINT where left speaker (-) is connected

You are injecting the return currents from the speakers on the signal ground.
You are directly joining signal and power ground.

 

[vladimir]

Re: Re: try this

Carlos,

thank you for reply.

Did you put the two channels as close as possible from each other as I recommend, or do you have one at each extreme side of the amp?

two boards were close (closer than your photo shows), ~4 cm, connected with 2.5mm thick Cu wire, separated 4 power ground wires (pg- and pg+ left and right) were connected at the middle of this 4 cm wire. Speaker's (-) and input's (-) were connected directly to the PCBs - as you did. Distance from rectifier (plus big caps for snubberized version) to PCB was ~60cm.
Carlos, do you realy get zero hum with your arrangement (even ear at 5cm from ~100dB speakers, gain=22k/680, left and right inputs connected) ?

You are injecting the return currents from the speakers on the signal ground.
You are directly joining signal and power ground.

Yes, but it works and as I sed, this is the only arrangement (at the moment) when I get absolutely zero hum.
regards, v.

 

[Yoghourt]

common mode rejection, I presume.

 

[chrish]

Thanks for all the suggestions. I have been very busy lately, so have not had time to implement all the suggestions.

In short, I still have the hum. I tried the solution offered by Carlos, I moved the two boards to the same heatsink, and joined the grounds as described. Short (3.5cm) thick wire joining two boards. No change to the hum. I have just tried the same thing with the signal grounds. That is, I joined the two pcb signal grounds with a 3.5 cm copper wire and then brought the two input grounds from the rca connectors to the central point on that wire. The hum is reduced to about 10mv peak to peak (same wave form as posted earlier). While it is a vast improvement, it is still unlistenable. Oh, and now the problem persists if there is one or both inputs connected.

I have a few spare bridge rectifiers lying around, and a few 8200uF caps, so I might try connecting a different power supply to see if that makes any difference.

Once again, thanks for the input, I appreciate the help.

Chris

 

[carlosfm]

Re: Re: Re: try this

... separated 4 power ground wires (pg- and pg+ left and right) were connected at the middle of this 4 cm wire.

This is not what I recommended.

Carlos, do you realy get zero hum with your arrangement (even ear at 5cm from ~100dB speakers, gain=22k/680, left and right inputs connected) ?

Yes, I don't have hum, even with my ear at the speaker.
But I don't have 100db speakers to test.
Who does?
You, and a minority of people, because that's a much above normal sensitivity for a speaker.

Yes, but it works

Great.
It's another solution, then.

 

[nina]

I hope this is clearer now.
Two channels with single PSU.

PS: I don't use the on-board CHG connection to the chassis.

Sorry, may be my english is too poor. //

From my understanding, the mark "PSU Ground" on the wire between the boards is the "0V' wire from the tranny. Then, where the " (FROM the PSU)" from the "Chassis Ground" come from??