Aleph 3 oscillations

Koy · 22nd April 2002, 11:10 AM

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 · 22nd April 2002, 11:18 AM

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 · 22nd April 2002, 02:14 PM

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 · 22nd April 2002, 03:04 PM

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 · 22nd April 2002, 04:56 PM

Koy,

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

Jam

22nd April 2002, 11:10 AM	#1
Koy diyAudio Member Join Date: Jan 2001 Location: Zlin	Aleph 3 oscillations 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.

22nd April 2002, 11:18 AM	#2
nar diyAudio Member Join Date: Apr 2002 Location: near the sea	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. __________________ "... Audio needs the thinnest wire ..." Rowan McCombe "Just 'cause they can't hear or sense it themselves doesn't mean you can't !" Allen Wright

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22nd April 2002, 02:14 PM	#3
GRollins diyAudio Member Join Date: Feb 2001 Location: Columbia, SC	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

22nd April 2002, 03:04 PM	#4
Koy diyAudio Member Join Date: Jan 2001 Location: Zlin	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.

22nd April 2002, 04:56 PM	#5
jam diyAudio Member Join Date: May 2001 Location: Charlotte,NC,USA	Koy, Try adding 100uf capacitors between the negative and positive rails and ground, as close to the circuit as possible. Jam

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