Path: utzoo!mnetor!uunet!cbmvax!daveh
From: daveh@cbmvax.UUCP (Dave Haynie)
Newsgroups: comp.sys.amiga
Subject: Re: A2000 Audio filter problems
Message-ID: <3327@cbmvax.UUCP>
Date: 16 Feb 88 20:47:16 GMT
References: <1090@percival.UUCP>
Organization: Commodore Technology, West Chester, PA
Lines: 29

> Keywords: Attn CATS

> 	I seem to have discovered that my lowpass filter in the A2000 has
> channels wired in reverse of each other (if that's even possible). When I 
> run Mark Riley's LED program to disable the filter, the left channel clearly
> loses its high frequency response and the right channel acquires additional
> highs (as expected).

This sounds very weird, if not impossible.  First thing I'd check is the
audio system you're attached to.  Try reversing the left and right channel
cables.

> 	Man, this thing is wierd. The left channel apparently behaves just
> the opposite of expected while the right channel appears to be on target. 
> However, I dread having to explain this to one of our local repair outfits,
> much less trying to prove to them that it is actually happening. ARrgggghhhh..

So you tried that, and it's still looking weird.  Maybe something is messed
up.  What you (or your repair guy) want to look at is Q200 and Q201, which
are both MPF102 JFETs used to jump around the filter section of the audio
amp.  Q200 controls the left side, Q201 controls the right.  R204 is a 470K
current limit resistor into Q200, and R205 for Q201.

> 		Thanks,
> 		Bob L.
-- 
Dave Haynie  "The B2000 Guy"     Commodore-Amiga  "The Crew That Never Rests"
   {ihnp4|uunet|rutgers}!cbmvax!daveh      PLINK: D-DAVE H     BIX: hazy
		"I can't relax, 'cause I'm a Boinger!"