Harman Kardon Citation 12 distort sound

vacs2000 · 13th November 2009, 06:29 PM

Hello
I am not at all good on debugging transistor amplifier so help is needed.
I have this HarmanKArdon 12 amplifier that distortes horribly. I exchange ALL electrolytics caps small/big AND the voltages on the transistors as well the Bias are on specs. I cleaned Deoxit etc. Can it be that some transistors are bad ?
The distortion is on both channels..Pretty weird for me sinc eI have experience only on Tube amps..

thank you
George

atcgreg · 1st February 2011, 12:59 PM

[QUOTE=vacs2000;1979722]Hello

I have this HarmanKArdon 12 amplifier that distortes horribly. I exchange ALL electrolytics caps small/big AND the voltages on the transistors as well the Bias

HI I think it is still a wrong setting of the BIAS it should be between 80mA to 150mA when measered at the PLUS rail of the power supply. I had that when I had the "old " caps 80ma was enough but when changed to new ones I had to adjust it to 100mA. Best way is to run 1kHz tone sinewave and look at the picture on the osciloscope and adjust the bias until the sinewave is pure.

13th November 2009, 06:29 PM	#1
vacs2000 diyAudio Member Join Date: Feb 2008	Harman Kardon Citation 12 distort sound Hello I am not at all good on debugging transistor amplifier so help is needed. I have this HarmanKArdon 12 amplifier that distortes horribly. I exchange ALL electrolytics caps small/big AND the voltages on the transistors as well the Bias are on specs. I cleaned Deoxit etc. Can it be that some transistors are bad ? The distortion is on both channels..Pretty weird for me sinc eI have experience only on Tube amps.. thank you George

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1st February 2011, 12:59 PM	#2
atcgreg diyAudio Member Join Date: Jan 2008	[QUOTE=vacs2000;1979722]Hello I have this HarmanKArdon 12 amplifier that distortes horribly. I exchange ALL electrolytics caps small/big AND the voltages on the transistors as well the Bias HI I think it is still a wrong setting of the BIAS it should be between 80mA to 150mA when measered at the PLUS rail of the power supply. I had that when I had the "old " caps 80ma was enough but when changed to new ones I had to adjust it to 100mA. Best way is to run 1kHz tone sinewave and look at the picture on the osciloscope and adjust the bias until the sinewave is pure.

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