New Member

[Chris Crosskey]

>At 02:14 PM 2/19/99 -0500, Gene Zumchak wrote:
>
>Welcome to the list Gene! 
>
>>2.  There are some common needs for anyone building their own analog
>>synth.  Has anyone ever investigated putting some of the stuff on a
>>custom chip?  With a group as big as this (almost 600 members), if
>>everyone tossed in $10, there would be $5000 to finance the chip.  It
>>need not be complex, or even include op amps.  Of course, there might be
>>some disagreement about what should be on it.  Specifically, I would
>>like to see the Moog LP ladder with its exponential transistor current
>>source (preferably heated) and a heated section with perhaps three or
>>four free current sources to use for VCO or VCLFO's.  The actual
>
>

This sounds like a fine idea, but might I offer an alternative.....a chip 
with two or three heated expo converters, just as a chip. No need for the 
Moog filter ladder, they can be built just fine out of discretes, and we 
all get to argue the toss for our favourite transistors/capacitoras 
etc.....One thing I think we can all agree on is that good expo converters 
are hard. We seem to be pretty much all using the one that Gene put in the 
ASM-1, but there has to be a better way, the tempco's are a pain, certainly 
if you have to use <Back-to-front> tempcos (the Farnell tempcos are like 
this) the it pulls a lot of current, fine if you've only got one or two of 
them in the synth but a pest if there's half a dozen VCO's in your 
cabinet...A single chip that had a CV input, a CI output, an a couple of 
adjust pins per (make the adjustment very minor, like +/- 5% range/scale
over a whole of a 10K adjuster, use 18 or 22 turn cermet, it'll be stable), 
you could fit three onto a 14-pin package with a couple of power pins, or 
even just make one of them on a 6 or 8 pin package.....Whatever, I'm in for 
this wether it's the one I've just offered or Genes original...

chrisc