Solid State poweramp Bias. - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Thread Tools Search this Thread
Old 27th February 2012, 03:41 AM   #1
diyAudio Member
Join Date: Feb 2012
Default Solid State poweramp Bias.

On my GK 800RB bass head, I'm getting a weird hum and slight distortion. I called my tech (who's overseas for two months) and he told me to check the bias (I'm not electronics wiz, but I know my way around a voltmeter).

I checked the service manual and it told me to do the following:

Set bias:
A) Adjust R38 TP to get 5mV across R48, R49, & R50 (the most pos. of the 3), and R54, R55, &R56 (the most
neg. of the 3)

On the PCB, R38 is a pot and R48, R49 and R50, R54, R55 and R56 are large white 5W resistors. How do I check the bias, I'm a little confused how this is worded. Do I want to test each individual resistor?

Here's a copy of the service manual I'm looking at.
  Reply With Quote
Old 27th February 2012, 04:25 AM   #2
davada is offline davada  Canada
diyAudio Member
Join Date: Jul 2004
Location: Fort St John, BC Canada
Set you voltmeter to the mV range. Measure across the 5W resistors and find the resistor with the highest reading. Use this resistor to set the bias for 5mV across the resistor. Proceed with this only if all the resistors read in the mV range. If one or more resistors read extremely high compared to the others, you may need to get the amp services. If this is the case then don't do anything.


Last edited by davada; 27th February 2012 at 04:31 AM.
  Reply With Quote
Old 27th February 2012, 04:41 AM   #3
diyAudio Member
Join Date: May 2010
Location: Chicago IL, Long Beach CA, Vienna VA
Sounds like power supply electrolytics. A 'scope becomes invaluable. How old is the head?
  Reply With Quote
Old 27th February 2012, 04:46 AM   #4
diyAudio Member
Join Date: Feb 2012
Originally Posted by cyclecamper View Post
Sounds like power supply electrolytics. A 'scope becomes invaluable. How old is the head?
It's about 7 years old, but this head is a classic on the talkbass forum, many people have had this head 20+ years without it being in the shop once.

I checked the bias and it was off, about 23mv. I pushed it down to 5ish, but I live in an apartment building so I can't test it this late at night.
  Reply With Quote


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Adjusting Bias on solid state poweramp. whatisacup Solid State 3 27th February 2012 10:38 AM
Solid Solid State Power Amplifier PMA Solid State 265 30th August 2011 08:04 PM
The Solid State Wiki - Your solid state reference guide Jason Solid State 0 25th June 2002 05:26 PM

New To Site? Need Help?

All times are GMT. The time now is 03:02 PM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2