If shorting input leads to zero hum, then your amp is ok. Try changing the source like a mobile phone, MP3 player, etc
If running a separate wire from input gnd to PSU star ground helps, then remove diodes, R23 and C13 and just run that input gnd wire to PSU gnd.
also proximity of signal wires to toroid, mains , high current wires, speaker cables, etc also influence hum/noise.
regards
Prasi
If running a separate wire from input gnd to PSU star ground helps, then remove diodes, R23 and C13 and just run that input gnd wire to PSU gnd.
also proximity of signal wires to toroid, mains , high current wires, speaker cables, etc also influence hum/noise.
regards
Prasi
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Thanks.
Tried a tablet feeding it, some strange results. Initially some hum, then I started the music and the hum went. Stopped the music and for about 30 seconds it was totally silent, hum returned. Play music, hum goes, stop, silence for 30 secs then hum.....
Pretty confusing! On the positive side, after stopping music and before hum returns it is totally silent!
Tried a tablet feeding it, some strange results. Initially some hum, then I started the music and the hum went. Stopped the music and for about 30 seconds it was totally silent, hum returned. Play music, hum goes, stop, silence for 30 secs then hum.....
Pretty confusing! On the positive side, after stopping music and before hum returns it is totally silent!
Take care what Prasi say.
Run the wiring diagram exactly as you can see here.
Attachments
Thanks. Yes thats how I had planned to do it if the earth wire is needed to get rid of the hum.
As you can see input wiring is well away from mains, trafo etc. Always use CAT5 twisted pair for input wiring, never been an issue.
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Nice!
Whats your Bias and DC offset final values?
I'm at 25mv bias and have to measure the dc offset again.
My Samsung phone behaved the exact same when I was testing another amp recently. There was a very clear step change between the hum and the silence, just before the music played. I figured it was a 'design feature'..
Glad to hear it isn't just me!
I am leaving the earthing as it till I do some tests with different sources. My feeling is that the hum is more to do with the source given how quiet it was with the tablet as a source, possibly to do with the load on the input.
Hum, what hum!?!
All good now that I am using a passive pre and CD player, in fact it may well be the quietest amp I have ever built!
Before I tried the CD player I did the earthing thing connecting panel input earths to PS star earth. Seemed to improve a little so removed Diodes and R23, couldnt get at C13 without taking boards off the heatsink but I don't think it will have any effect. This didn't change anything. Anyway all to no avail, as I stated above with a CD player all is fine.
Next stage will be to listen through some decent speakers to evaluate SQ.
Ah well, if you don't have any problems with a build how do you learn anything! Thanks all for the help.
All good now that I am using a passive pre and CD player, in fact it may well be the quietest amp I have ever built!
Before I tried the CD player I did the earthing thing connecting panel input earths to PS star earth. Seemed to improve a little so removed Diodes and R23, couldnt get at C13 without taking boards off the heatsink but I don't think it will have any effect. This didn't change anything. Anyway all to no avail, as I stated above with a CD player all is fine.
Next stage will be to listen through some decent speakers to evaluate SQ.
Ah well, if you don't have any problems with a build how do you learn anything! Thanks all for the help.
After running 4 hours in case I checked the temp of the heatsinks, they were considerably lower than before, probably because the fins are now upright and the rest of the case also sinking some heat. So checked voltage across the .33 resistors and found it had dropped 2-3mv. Tweaked it back up to 12mv each. Heatsinks still barely above ambient temp.
No need to as long as the heatsink is not in contact with the board or other components. I didn't use any.