Fast analog sw. plus various

[gstopp at fibermux.com]

     Hi DIY,
     
     <various subjects included>
     
     No quantizer post here yet, Chris! However this could be due to our 
     company discovering (the hard way!) that the computer room UPS is 
     malfunctioning, for most of the day yesterday (wind storms took out 
     the power grid). Dead gateways tell no tales.
     
     Re: ASM VCO FETs (whoa acronym crazy) - I've heard the MPF-102 dies, 
     which I've never tried, how about the 2N4391? Those work for me, as 
     does the NTE466, but to be honest I've never let an ASM-1 run for an 
     extended length of time (one of these days I'll build a synthesizer 
     with one, I swear!). I suspect that the thing that blows FET's in this 
     application is repeated cap discharge current being beyond the FET's 
     rating. The original Electronotes circuit specified the 2N4859 which 
     is a fairly high-current chopper.
     
     Re: Chris - heard you're building a frequency shifter from EN. Hey I 
     did one of those, cool box man. Anyway here's some testing tips (if I 
     may). With a circuit of that complexity I am of course in a hurry to 
     get it running, but that feeling is tempered by the fact that if I 
     just throw it all together and try it I'd be setting myself up for a 
     fall when it doesn't work right off the bat. So I try to test each 
     part before integrating the whole mess, in some haphazard way. Well 
     the real stinker in this case was the 90 degree Phase-Difference 
     Network (which creates a sin and cosin output for any input frequency) 
     due to all those carefully tuned filters. So the trick I used was to 
     form a lissojous figure on the O-scope (X-Y input mode) with the two 
     outputs, and stick a microphone on the input (pre-amped of course) and 
     yell into the thing. All inputs (grunts, whistles, etc.) should 
     produce a rough circle on the scope. This is a quick way to see if 
     you're gonna get some well-defined 90 degree shifted signals for the 
     ring modulators to mess with. I predict that you will pee your pants 
     when you get this thing working. Be afraid. Be very afraid. :)
     
     Re: Jurgen's SSM2040 clone: Good Job! Anxiously awaiting the schematic 
     at synth-fool. Any PCB plans? The 2040 VCLFP is truly a great sound. 
     BTW there is a phase shifter in my first modular (circa 1976) that 
     uses two 2040's for an eight-pole phaser. It's a very good sound as 
     well, no radio stations.:)
     
     Re: VC'ing Envelope Generator times - a nice floating "resistor" (for 
     cap charge/discharge anyway) can be made from an opto-isolator like 
     the 4N37. The main problem with this idea is that the exponential ADSR 
     slopes will become linear due to the fact that the opto is not a 
     resistor but instead a constant current device. The time constant 
     range becomes real large (from zero to minutes) but you need to be 
     able to tolerate the linear operation. But you can't beat the parts 
     count! Sorry no three-terminal pots however.
     
     Can't think of any other new developments... most bench time now being 
     spent re-building a Hammond B-3 in the garage.... oh yeah also I need 
     to mess around with the Vortex my wife gave me for Christmas (god I 
     love that woman!).
     
     - Gene
     gstopp at fibermux.com


______________________________ Reply Separator _________________________________
Subject: Re: Fast analog sw. as VC resistor
Author:  Christopher_List at Sonymusic.Com at ccrelayout
Date:    1/7/97 8:42 AM
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ps.
Someone mentioned a replacement FET for the ASM-1 with a different pin-out 
could you repost it? - Those NTE466's are $2.50 a piece!
     
Did anyone get my post about the quantizer? It seems to have been lost on 
the way to the list....