Aleph 3 oscillations

[Koy]

I have finished the A3, but I experienced oscillations in one channel (freq. up to 500kHz). Unfortunatelly I have no professional scope , so I checked it with small radioreciever. It can be heared only when one channel and with the load. I have no notion what to do. Thanks.

 

[nar]

A3 ooooooops

Theoricaly shoudn' happen.
Check if the 221 R gale resistors are close possible to the Fets.
You know that theorical roll-off is -3 dB at 100 kHz.Then is the 500 kHz test valid.

Also check for ground loops,especially if happens on only one channel.Check connections I/O and PSU for that.

 

[GRollins]

Try redressing the power leads and such. My Aleph 2s here were prone to oscillation depending on the orientation of the negative power lead.
I'd recommend finding an oscilloscope. If you don't get this under control, it could roast your tweeters.

Grey

 

[Koy]

Redress the power lead? To say true I cannt see it at all. What should I do?
I tried some measurement with scope from PC sound card. Such awfull distorsion I have not seen so far. At about20W on output I has nothing to do with sinus wave. The bias current is OK. The puzzle.

 

[jam]

Koy,

Try adding 100uf capacitors between the negative and positive rails and ground, as close to the circuit as possible.

Jam