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kmt 16th March 2004 02:48 PM

Noise problems with HP amp
 
2 Attachment(s)
Hello to everyone.

I've got some noise problems with a headphone amp and I'm not shure how to fix. The schematic is attached. The HP amp is driven directly by the output of another NE5532A (not shown in the schematic).

I have noise problems with some digital signals from the rest of the circuit which I can hear through the phones. The strange thing is, that the noise disappears when I touch the input pin by hand.

A 100k resistor or a 100nF-10F capacitor connected from input pin to GNDA doesn't help. The signal GNDA is NOT connected to mains earth/chassis.

Can anyone give me a hint how to suppress that noise?

Thanx in advance!

KMT

Frank Berry 17th March 2004 07:10 AM

Make sure you have bypass capacitors between the +15 rail and ground and between the -15 rail and ground. Try .1uf.
One of the chips may be oscillating.
You may want to insert a low value <100 ohm resistor on the output of the BUF534. Put it in series with the output before the R4 feedback resistor.


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