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From: booth!roger@spool.mu.edu (Roger Abrahams)
Newsgroups: rec.audio.high-end
Subject: Re: Mods for Hafler 100 Power Amp
Message-ID: <7886@uwm.edu>
Date: 26 Nov 90 19:52:38 GMT
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Approved: tjk@csd4.csd.uwm.edu
Originator: tjk@csd4.csd.uwm.edu

In article <7696@uwm.edu> you write:
>
>About 8 years ago I built a Hafler DH100 power amp from the kit.  Throughout
>the years, it has suited my needs admirably.  'til now.  I am getting
>increasing hum and hiss in both channels, and I assume it's due to aging
>of important components and/or solder joints.  I would ideally like to
>replace the Hafler with a better unit, but at this point my budget
>(and wife ;-) won't allow it.
>
>I've heard of good modification kits for the DH100, and would like to hear
>from those who have experience, good or bad, with any of them.  Your help
>is greatly appreciated.

Unfortunately, Hafler used some pretty inexpensive transistors in the 
front end of these, and it was well before the point where they tried
to keep electrolytics out of the signal path.

It is important to note if the increasing noise is equally apparent 
in BOTH channels.  If it is, it most likely is a problem with increasing 
series resistance in the power supply capacitors, if the problem lies 
with the amp at all.  It also could be caused by aging corrosion of the 
interconnects, etc.  A good high-quality cleaning and general "tune-up" 
might just be indicated.

						- Roger