Yamaha CS80

Very good news, Scott!
In the long run, your work will keep many, many of these machines alive.

JH.


----- Original Message ----- 
From: "The Old Crow" <oldcrow@...>
To: <yamahacs80@yahoogroups.com>
Sent: Wednesday, March 18, 2009 6:39 AM
Subject: [yamahacs80] VCO153 project in board test phase


  Hey folks, its been a while, but I have this thing in testing right 
now.  This is an equivalent circuit to the IG00153.  This differs from 
my MOTM-style modular 153 oscillator in that it is strictly the VCO IC 
with a ramp output, linear CV input, current bias input (FT) for octave 
select and exponential modulation (vibrato) input.  It can use the 
original M-board FET and charge pump capacitor, or those can be removed 
and local ones installed.  I made this mainly to see about replacing 
things at the chip level, but not relying on custom devices.  It is 98% 
SMT parts, with only 3 parts left through-hole for the moment (mainly to 
swap things and see how the specs change).  It no longer needs an input 
offset trimmer, or external frequency compensation of the input summing 
amp.  The DIL-16 footprint in the middle of the board is used to install 
it into an actual IG00153 socket. Generally it is low-profile enough to 
fit between M boards (it does in my CS-50).  It has internal temperature 
compensation of the charge switch and comparator, making it much more 
stable than the original device.  The charge pump core circuit runs on 
its own internal 10V reference supply.

  Eventually I want to craft the entire M-board from standard circuits.  
The waveshaper is done (it is the one I made for the 153 module).  The 
EGs are done.  The filters are done.  I know how to build the VCA, thats 
next.  In any case here is an image of the board, a bit larger than 
actual size.  More later...

http://www.cs80.com/VCO153_pic.gif


Crow
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