How to adjust biasing on amp?


2005-08-24 3:49 am
Hi! I am a DIY newbie, but there's something I'd like to try and hope you guys might guide me.

I have an ADS P850 8 chanel amp and my configuration is

Chanel 1 & 2 bridge for left tweeter
Chanel 5 & 6 brdge for right tweeter
Chanel 3 & 4 bridge for left mid
Chanel 7 & 8 bridge for right mid

Question is, I read somewhere that you can actually tweak the A/B bias to some extent. I like the class A sound a lot, and was wondering that since chanel 1 & 2 together with 5 & 6 would be used to power tweeters, can I increase the class A bias on the said chanel and leave the others used to power the mids alone safely as in not frying the amp?

If yes, how to go about it?

Thanks for looking.


2005-08-24 3:49 am
I did not get to open the amp out yet. But was kinda hoping some one had done it before and perhaps share the experience.


I am not sure if there are pots, if there are pots, it would be easy?

As for brideging the amp for tweeters, just using up the spare chanels. Probably don't need to though.
If you increase the bias of a A/B descrete amp, you have to be careful that Vbe multiplier keeps the thermal runnaway under control or the outputs will fry. :hot: In A/B the outputs bias with each other and not with a controled current source. Sure you could turn the bias up a little, and mesure the voltage across the emitter resistors to measure the bias current(V/R=I). If you are not that experienced, then I wouldn't recommend doing it. It can be easy to let the smoke get out...unfortunatly you can't put it back in. Also I wouln't risk bridging while you mess with this. :smash: