Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!snorkelwacker!ai-lab!mikec
From: mikec@wheaties.ai.mit.edu (Mike E. Ciholas)
Newsgroups: comp.sys.mac.hardware
Subject: Re: SID Board: UPDATE!!!
Message-ID: <8254@rice-chex.ai.mit.edu>
Date: 3 May 90 21:15:37 GMT
References: <8223@rice-chex.ai.mit.edu> <55692@coherent.coherent.com>
Reply-To: mikec@rice-chex.ai.mit.edu (Mike E. Ciholas)
Organization: MIT Artificial Intelligence Laboratory
Lines: 27

In article <55692@coherent.coherent.com> dplatt@coherent.com (Dave Platt) writes:
>In article <8223@rice-chex.ai.mit.edu> mikec@rice-chex.ai.mit.edu (Mike E. Ciholas) writes:
>> Due to the very limited availability of 1.558Mhz resonators, I have been
>> searching exhaustively for a replacement circuit.  Criteria are: cheap, 
>> avaiable parts, and close frequency.  But how close is close enough?
>How about the 1.558 MHz quartz-crystal substitution that the SID Trio
>suggested in their followup note?  Drop out the resonator, drop in the
>crystal, and change the value of the two resonator capacitors.  They
>even provided a source or two for the crystal.
>
>The parts cost was at the high end of the range you specify, when the
>crystals are bought in 1-sies... the price might come down significantly
>if you bought a few dozen at once.  The biggest advantage, I think, is
>that it doesn't require any changes to the circuit topology.

Well, that is an option.  I can get 1.557818 MHz crystals made for
$7 in 100 unit quantities (large case style).  When you need that much
quartz, it costs money.  A faster crystal costs only about $2 to be made.

I dunno, $7 seems like such a high percentage of the cost for just a timer.
I am still hoping that people find the 800Khz resonator solution acceptable.
One fellow said he is using 3Mhz and dividing it down by 2.  This is off
by about 4% so the 800Khz being off by 0.145% doesn;t sound so bad.

Mike Ciholas

mikec@ai.mit.edu