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From: jhess@orion.oac.uci.edu (James Hess)
Newsgroups: rec.audio.high-end
Subject: Re: Dynaco Stereo 70 mods
Message-ID: <10980@uwm.edu>
Date: 12 Apr 91 12:40:06 GMT
Sender: news@uwm.edu
Lines: 22
Approved: tjk@csd4.csd.uwm.edu
Originator: tjk@csd4.csd.uwm.edu

In article <10915@uwm.edu> ts2b+@andrew.cmu.edu (Terence Ronald Spies) writes:
>
>I have completed all the mods in the dynamods file available over anon.
>ftp at csd4.csd.uwm.edu excepting one.  The forward feedback mod worked 
>for a bit and then caused the amp to start howling at various high frequencies.
>
>I realize this is probably due to unwanted coupling in the feedback section,
>but I could not find any problems iwth the wiring.
>
Once as a young technician I was handed a modified Audio Research preamp to 
repair.  It was motorboating and occasionally squealing, as I recall.  I tried
50 things to fix it; no luck.  Finally I sent it off to the manufacturer.  They
returned it in fine working shape, having removed the a capacitor mod which 
altered the transfer function sufficiently to destabilize the circut.  Some of
the tweekers out there are not familiar with the problems of component and 
assembly variability; therefore they do not follow good engineering practice 
and design in a margin of safety.  Another consideration is that changes to 
one part of the system freqquently affect other parts of the system.  If you 
applied a collection of modifications each designed independently, it is 
probable that no one has considered their collective effects.

-Jim Hess-