Path: utzoo!mnetor!uunet!cbmvax!grr
From: grr@cbmvax.UUCP (George Robbins)
Newsgroups: comp.sys.amiga
Subject: Re: Filter.
Message-ID: <3020@cbmvax.UUCP>
Date: 27 Dec 87 22:13:42 GMT
References: <1301@sugar.UUCP> <1509@loral.UUCP>
Reply-To: grr@cbmvax.UUCP (George Robbins)
Distribution: na
Organization: Commodore Technology, West Chester, PA
Lines: 36
Keywords: Amiga audio out

In article <1509@loral.UUCP> dml@loral.UUCP (Dave Lewis) writes:
> In article <1301@sugar.UUCP> peter@sugar.UUCP (Peter da Silva) writes:
> 
> >I've just turned off the 5khZ audio filter in my buddy's 2000. Incredible. So,
> >can anyone post the docs on cutting the filter out in the 1000?

Basically jumper between pins 14 and 3 of U5G and pins 8 and 5.  This is a
TL084/LF347 or equivalent located just in front of the power connector and
under the rear edge of the RAM/ROM tower.  For dynamic control, you can
adapt the circuitry used in the A500/A2000, but you will probably need to
disconnect the LED driving circuitry to get and adequate negative swing for
the control signal from the 1488.

>   That's not all -- the output level from a 1000 is pitifully low. I have to
> turn my stereo WAY up to get decent sound from the Amiga's audio outputs. I'm
> thinking about installing an LM1303 stereo preamp in there somewhere. A little
> equalization, a level control, switchable noise filter.....

I't not so sure about this.  Remember that the A1000 has provides software
controllable "volume" settings and that not all software is going to set these
to full volume.   In any case the actual output level is set by the ratios
of R1/(R1+R2) and  R3/(R3+R4).  If you want lots of output for some special
application,  simply apply the old wire clippers to R1 and R3...


Remember than anytime you disable the anti-aliasing filter, it is your
responsibility to provide some kind of filtering appropriate to the
sampling rate and characteristics of the output amplifier.  Don't blame
us if you blow your tweeters or turn your Amiga into a giant ultra-sonic
dog whistle...  Just because you can't hear the high frequency components
of the signal doesn't mean they aren't there.

-- 
George Robbins - now working for,	uucp: {uunet|ihnp4|rutgers}!cbmvax!grr
but no way officially representing	arpa: cbmvax!grr@uunet.uu.net
Commodore, Engineering Department	fone: 215-431-9255 (only by moonlite)