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Old 12th November 2004, 08:55 PM   #11
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Quote:
Originally posted by carlosfm


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.
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Old 12th November 2004, 10:07 PM   #12
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SoundNERD,
Sounds pretty much like the core of your transformer is saturated by the static magnetic field from the speaker magnet. That will lead to humming and also lots of harmonics. You can build a magnetic shield around the transformer with mu-metal for example.

/Magnus
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Old 16th November 2004, 05:22 PM   #13
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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?
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Old 21st November 2004, 08:25 PM   #14
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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.
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Old 23rd November 2004, 11:47 AM   #15
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once again: your trafo is too damn small.. wont make anything.. youll not get to know why this is bad until you get to hear this promptly with a larger one(~200VA)
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Old 28th November 2004, 10:26 PM   #16
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Quote:
Originally posted by costiss
once again: your trafo is too damn small.. wont make anything.. youll not get to know why this is bad until you get to hear this promptly with a larger one(~200VA)
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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