need help setting bias current...

SkinnyBoy · 2nd May 2005, 05:33 PM

apparently...

I have a car amplifier that I recently acquired...

at one stage in its life, the headunit to which it was connected committed a murder suicide, and applied 12volts to the amplifiers RCA input...

this fried the preamps, and input circuits, etc, but the previous owner replaced these...

now, for some reason, the bias current wasn't correct (I'm stupid when it comes to amps) so the guy rigged up a trimpot to each channel to adjust the bias, but the question is HOW do I set it? and, whats it supposed to be??

ANY help would be GREAT!!!

thanx

Frank Berry · 2nd May 2005, 05:44 PM

Why do you need to adjust the bias?
Are you sure that the idling current isn't correct?
You have not provided enough information.

SkinnyBoy · 2nd May 2005, 05:47 PM

thats all I know... thats all I was told when I got the amp...

I'm not sure why the original components wouldn't have yielded the correct bias current...

but like I said, one each channel, one resistor has been replaced with a trimpot and 2 resistors... thats if it was even the bias current.. but I believe it was..

SkinnyBoy · 2nd May 2005, 05:51 PM

http://img87.echo.cx/img87/8601/amplifier6ny.jpg

he said if you set the bias too high, the amp would be running in class B all the time.... is that correct?

SkinnyBoy · 3rd May 2005, 05:36 AM

excuse me while I cry...

no help? I wanted to use this amp to run my frone speakers, till I could afford something better, but I didn't want to use it like this...

rpapps · 3rd May 2005, 05:54 AM

Hi SkinnyBoy

From the picture, it appears that only the centre leg of the trimpot is connected to anything or have I missed something?Cheers
Rob

SkinnyBoy · 3rd May 2005, 05:57 AM

umm... when the turn the trimpot, the resistance across those 2 legs varies...

pinkmouse · 3rd May 2005, 08:09 AM

Before anyone can help, you need to trace out he schematic of the anp, so we know what it is doing. Do you have access to a scope?

SkinnyBoy · 3rd May 2005, 08:11 AM

Quote:

Originally posted by pinkmouse
Before anyone can help, you need to trace out he schematic of the anp, so we know what it is doing. Do you have access to a scope?

my cro stopped crowing...

how much of the circuit do you need?

I guess the whole amp of one side... it doesn't look toooo complicated :P lol

SkinnyBoy · 5th May 2005, 01:31 PM

meh, its a crappy amp anyway... I'll leave it like it is

2nd May 2005, 05:33 PM	#1
SkinnyBoy Banned Join Date: Nov 2002 Location: Adelaide, Australia	need help setting bias current... apparently... I have a car amplifier that I recently acquired... at one stage in its life, the headunit to which it was connected committed a murder suicide, and applied 12volts to the amplifiers RCA input... this fried the preamps, and input circuits, etc, but the previous owner replaced these... now, for some reason, the bias current wasn't correct (I'm stupid when it comes to amps) so the guy rigged up a trimpot to each channel to adjust the bias, but the question is HOW do I set it? and, whats it supposed to be?? ANY help would be GREAT!!! thanx

2nd May 2005, 05:44 PM	#2
Frank Berry diyAudio Member Join Date: Sep 2003 Location: Midland, Michigan	Why do you need to adjust the bias? Are you sure that the idling current isn't correct? You have not provided enough information. __________________ Frank

3rd May 2005, 08:09 AM	#8
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	Before anyone can help, you need to trace out he schematic of the anp, so we know what it is doing. Do you have access to a scope? __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

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2nd May 2005, 05:47 PM	#3
SkinnyBoy Banned Join Date: Nov 2002 Location: Adelaide, Australia	thats all I know... thats all I was told when I got the amp... I'm not sure why the original components wouldn't have yielded the correct bias current... but like I said, one each channel, one resistor has been replaced with a trimpot and 2 resistors... thats if it was even the bias current.. but I believe it was..

2nd May 2005, 05:51 PM	#4
SkinnyBoy Banned Join Date: Nov 2002 Location: Adelaide, Australia	http://img87.echo.cx/img87/8601/amplifier6ny.jpg he said if you set the bias too high, the amp would be running in class B all the time.... is that correct?

3rd May 2005, 05:36 AM	#5
SkinnyBoy Banned Join Date: Nov 2002 Location: Adelaide, Australia	excuse me while I cry... no help? I wanted to use this amp to run my frone speakers, till I could afford something better, but I didn't want to use it like this...

3rd May 2005, 05:54 AM	#6
rpapps diyAudio Member Join Date: Jul 2004 Location: nowhere of interest	Hi SkinnyBoy From the picture, it appears that only the centre leg of the trimpot is connected to anything or have I missed something?Cheers Rob

3rd May 2005, 05:57 AM	#7
SkinnyBoy Banned Join Date: Nov 2002 Location: Adelaide, Australia	umm... when the turn the trimpot, the resistance across those 2 legs varies...

5th May 2005, 01:31 PM	#10
SkinnyBoy Banned Join Date: Nov 2002 Location: Adelaide, Australia	meh, its a crappy amp anyway... I'll leave it like it is

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