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Old 5th April 2010, 10:51 AM   #1
diyAudio Member
Join Date: Aug 2007
Default bias current on rockford punch 200.4


i repair a punch amp 200.4 (4x25wrms)

the guy who have this amp before burn the mosfet in the supply and he modify the bias current

i find information to set the correct bias current here

Rockford Corporation Technical Library CD

but I do not know which way to turn the potentiometer to set it to the minimum before turn on the amp and procede to the bias set

is it in clockwise or counterclockwise ?

and what are the resistors to set the bias because i must put my multimeter on it to mesure 4 or 5 millivolt on each (rockford say that in the service manual)
I surrounded the resistors if you can confirm me if it is good please ?

Click the image to open in full size.

I think the amp was build in 2000

Thanks for your help
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Old 5th April 2010, 01:38 PM   #2
diyAudio Member
Join Date: Sep 2009
Location: Wisconsin
Turn them counter clockwise. I watch the idle current of the amp using a .005 ohm resistor in series with the amp B+ terminal. If you turn the pot slowly the idle current will increase quickly, then I back it off. You can find the knee at which the current takes off. I usually set it there and let it warm up and verify current doesn't increase.
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Old 5th April 2010, 05:06 PM   #3
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Join Date: Aug 2007


Yes the current increase quickly i move a little and the current increase...

i use a 12 volts supply with 5 Amp to set up the bias current i set up to 4.5mv on the 0.1ohms resistor and now the amp works fine and without heat

I mesure before adjust the bias and i have for channel front Left 17.5mv and 2mv for channel front right

for the rear channel i have 3mv and 18 mv

the guy who have this amp before me make nonsense

Now i run the amp in my car and works better

The bias was verry difficult to set 30 minutes to do because I am a perfectionist
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