I have build a simple linear power supply, as per the circuit diagram with a +/-25v, 25VA transformer, and 15,000uf capacitors.
This power supply will power my gainclone amplifier. I realise it is underpowered, but my gainclone never draws more than 200ma from the supply, and over 150ma of that is for the cooling fans, so I feel it will be adequate.
The DC is fine, ~+/-35v output, but there is also ~0.5v AC on each output. So my amplifier now has a nice 60Hz tone along with the music. How can I get rid of this voltage?
Sorry about the messy diagram. Everything is connected correctly, even if I have drawn it incorrectly. Both 0v outputs are connected together, to the mains earth, and to the case.
This power supply will power my gainclone amplifier. I realise it is underpowered, but my gainclone never draws more than 200ma from the supply, and over 150ma of that is for the cooling fans, so I feel it will be adequate.
The DC is fine, ~+/-35v output, but there is also ~0.5v AC on each output. So my amplifier now has a nice 60Hz tone along with the music. How can I get rid of this voltage?
Sorry about the messy diagram. Everything is connected correctly, even if I have drawn it incorrectly. Both 0v outputs are connected together, to the mains earth, and to the case.
Attachments
Aside from the diodes drawn backwards..... you can save a FWB by connecting the windings in series. Which reminds me, what is it with these SS guys and their whacked up rectifiers anyway? 
Not to mention the capacitance, a 25VA transformer is what, 1A, maybe 0.5A DC? At 15mF that's more like 300mA...or less! Certainly no more than 200mA with +/-35V output.
And 200mA for a what, 20W amp? Sounds to me like your chip is toast...(have you tested it at full power?) It should have hum immunity built in anyway.
Tim
Not to mention the capacitance, a 25VA transformer is what, 1A, maybe 0.5A DC? At 15mF that's more like 300mA...or less! Certainly no more than 200mA with +/-35V output.And 200mA for a what, 20W amp? Sounds to me like your chip is toast...(have you tested it at full power?) It should have hum immunity built in anyway.
Tim
Sch3mat1c said:Aside from the diodes drawn backwards..... you can save a FWB by connecting the windings in series. Which reminds me, what is it with these SS guys and their whacked up rectifiers anyway?
And 200mA for a what, 20W amp? Sounds to me like your chip is toast...(have you tested it at full power?) It should have hum immunity built in anyway.
Tim
Im not bothered, the current power suppy is a bench supply rated at 1A max and it has never drawn more than 200mA.
I dont know the output of my amp. My sub reached xmax before full power so I havent tested the amp exept into a dummy load. It still hums.
carlosfm said:Matttcattt, you will blow the trafo if you really think in using it with a GC.
How?
Matttcattt said:
How?
As soon as you feel like listening at a little louder volume the primaries will go pffffffffffzzzzzzzzzzzzzzt.
Even at idle that trafo will run very hot.
If you want to use a small trafo at least use a low voltage, like a 2x12V trafo at 2~3A.
With a low PSU voltage the chip will demand much less current.
I have a small amp with a PSU like this and no problem, works very well.
You will have 10~15W RMS.
Feeding the chips at +/- 35V with such a weak trafo won't do.
Sorry.
Use that trafo for something else, like a preamp, not a power amp.
carlosfm said:Matttcattt, you will blow the trafo if you really think in using it with a GC.
I dobut it.
I'm probably the only one cheap (and dumb) enough to think of using 2 16V 10VA doorbell transformers I got for about a dollar apice at a garage sale.
And guess what I powered with it??
2 x LM3886 driving small speakers, and 2 x OPA549 bridged driving an 8ohm sub.
And it worked fine. Although the transformers got quite warm (could feel it was very warm even through the 1/2" MDF case.)
Now I have upgraded to 2A transformers I got for cheap at science and surplus, and it sounds much better, though I get a low frequency humm from the sub. Thats because the transformers humm
Are you sure the humm you are hearing isnt transformer humm?
carlosfm said:
Are you sure it's humm, or the small trafo vibrating like a mad cow because it's working on it's limits?
Yep, i meant vibrating transformers. Which is odd since the transformer is a 2A, while the 10VA ones I had didn't vibrate at all.
And, the vibration is caused by the magnet on the speaker, I think because if I take the speaker out of the case, the humm disappears.
No, the transformer does not hum. At least not audiably unless my ear is less than a few centimeters from it.
I have re-aranged the wiring so it is less of a mess and now there is ~0.05v AC on each output. The amplifier now hisses.
It never did this with a regualted power supply.
Im tempted to just buy some ~25v voltage regulators. 
Any help with the hissing?
I have re-aranged the wiring so it is less of a mess and now there is ~0.05v AC on each output. The amplifier now hisses.
It never did this with a regualted power supply.
Im tempted to just buy some ~25v voltage regulators. Any help with the hissing?
Ok, solved the problem.
The PSU was fine, one of the opamps in my array of filters had blown. I've replaced the blown chip, and it all works fine now.
The transformer does get warm (only very slightly) at maximum volume, but this is unbearable to listen to, so there is no problem with heat.
There is now not turn-off thump, as after I turn the PSU off, the amplifier still runs for several seconds off the capacitors before fading to no output.
The PSU was fine, one of the opamps in my array of filters had blown. I've replaced the blown chip, and it all works fine now.
The transformer does get warm (only very slightly) at maximum volume, but this is unbearable to listen to, so there is no problem with heat.
There is now not turn-off thump, as after I turn the PSU off, the amplifier still runs for several seconds off the capacitors before fading to no output.
costiss said:
I really should state that I am not an audiophile at the start of each thread.
I have listened to the several different gainclone amps I have constructed, with serval different power supplies. I have never heard any difference between them. Apart from various hums and hisses that is.
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