Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!husc6!sri-unix!teknowledge-vaxc!dplatt
From: dplatt@teknowledge-vaxc.ARPA (Dave Platt)
Newsgroups: comp.sys.mac
Subject: Re: Mac II Fan Noise
Message-ID: <17798@teknowledge-vaxc.ARPA>
Date: Fri, 9-Oct-87 16:48:39 EDT
Article-I.D.: teknowle.17798
Posted: Fri Oct  9 16:48:39 1987
Date-Received: Sun, 11-Oct-87 17:20:31 EDT
References: <240@ssds.UUCP> <925@uhccux.UUCP> <2082@Shasta.STANFORD.EDU>
Organization: Teknowledge, Inc., Palo Alto CA
Lines: 19
Summary: Shouldn't be too hard to hack
In-reply-to: mrh@Shasta.STANFORD.EDU's message of 9 Oct 87 00:50:27 GMT


Agreed, it's pretty noisy.

My venerable Dynaco ST-416 audio amplifier has a nice hack installed
in it for fan control.  In series with the fan's power leads is a
little frammis consisting of a thermostat in parallel with a rectifier
diode.  At low amp-power, the thermostat (mounted on the heat sink)
remains open;  this forces the fan to draw power through the
rectifier, thus receiving only half-cycle current and running at half
speed (or even less).  If the heat sink warms up beyond the
thermostat's set point, the 'stat closes, effectively shorting out the
rectifier and delivering full-cycle current to the fan, which happily
speeds up and cools the heat sink down more.  Under intermediate load
conditions, the fan will cycle between low and high speeds every
minute or so (the massive heatsinks provide a relatively long time
constant).

I'd imagine that a little hack like this could be applied to the Mac
II fan, assuming that it uses 120VAC and is of the usual mini-plug-in
variety.  I may just look around for the parts...