Crest CA12 Bias Setting anyone have info? - diyAudio
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Old 13th July 2008, 10:29 PM   #1
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Default Crest CA12 Bias Setting anyone have info?

Anyone have any info on how to set the BIAS for a crest CA12 power amp??? I just repaired one channel and i need to adjust the bias now and while i have most of the schematics for the CA series. nothing has any mention of BIAS adjustments.

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Old 3rd August 2008, 04:15 PM   #2
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Default Crest CA-12 shematics?

Sorry,no bias info but I need a schematic for a CA-12 if you or anyone is willing. Much appreciated.
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Old 4th August 2008, 01:59 PM   #3
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If you can't get the schematic just set bias current to about 20 to 30 mA on one line plus or minus( per each transistor) because there is more paralel output tr. via emitter resistor.
Or easy just adjust bias acording to the measure voltage on one of this emitter resistors.

Ibias=V resistor(V)/ R resistor(ohms).
example: If you like to set bias to 20mA and R resistor is 0.22 ohm, you should measure 4,4mV or 0.0044 Volts.

Vresistor(measured voltage)=R(emitter resistor)*I bias(desired bias current),.

So if you like to set bias to 50 mA and resistor is 0.22 ohms than you should adjust voltage across the resistor to:0.22(ohms)*0.005(A)=0.011Volts or 11 mV.

I hope this will help you until you find original factory settings, but I think that Crest is for professional Audio(high power) not for high end and home listening so better keep bias lower about maximum 50mA on Transistor (each) than higher.
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Old 4th August 2008, 06:22 PM   #4
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Sorry for mistake in current!
So 50mA=0.05A
0.22(ohm)*0.05(A)=0.011V or 11mV
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