• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

help checking/setting bias and dc offset

izeek11

izeek11

drumz pulleeez
Subscriber
i am attempting to work on this adcom gfa 5500 i have.
cracked it open. a little dusty but looks good.
no bad looking caps. no heat marks. resistors look good. nothing looks modded.
these are the instructions for setting bias and dc offset.

BIAS ALIGNMENT
Prior to performing BIAS ALIGNMENT turn unit on and allow to idle for approximately 5 MINUTES before
attempting adjustments.
1. Connect millivoltmeter across emitter resistor R52 for left channel (R51 for right channel)
2. Adjust bias pot P2 until meter reads 50mV +/- 5mV
DC OFFSET ADJUSTMENT
1. Connect millivoltmeter across speaker output
2. Adjust DC offset pot P1 until meter reads 0mV +/- 10mV

fotor-1645791273296.jpg

do i simply attach my mm to each side?
do i connect to it before turning amp on?

and for dc offset, i go across this post?
0225220718.jpg

do i turn amp off then back on and wait for it to settle for each measurement?
been a looong time.
thanks for your help.
 
Register to hide this ad
Yes on all of your questions. You don’t have to attach your multimeter with the amp turned off unless you want to. I like to use clip on mini grabber meter probes to free up my hands to make the adjustments. I think the 5 minutes is for everything to reach normal operating temp and if you shut it down for a moment, it shouldn’t require 5 minutes to stabilize. Be careful that you don’t slip and short the speaker terminals.
 
El Rubio said:
Yes on all of your questions. You don’t have to attach your multimeter with the amp turned off unless you want to. I like to use clip on mini grabber meter probes to free up my hands to make the adjustments. I think the 5 minutes is for everything to reach normal operating temp and if you shut it down for a moment, it shouldn’t require 5 minutes to stabilize. Be careful that you don’t slip and short the speaker terminals.
Click to expand...
thank you so very much for answering so clearly. :beerchug:
 
Shouldn't the amp be able to handle a no-signal short? It's supposed to be protected even with an output present - no?
 
You must log in or register to reply here.
Back
Top Bottom