VCOs as modulation sources

[gstopp at fibermux.com]

     I really don't know why they chose 560K at the time... to be honest I 
     still haven't had the chance to do much linear FM testing. If what you 
     say is true I'm sure I'd be pissed off at the wimpy mod depth.
     
     Also I really can't say if dropping the linear FM input resistors to 
     say 100K or 47K can potentially hurt the expo converter's transistor 
     pair - anybody know the currents involved here? Joachim???
     
     BTW the 3 VCO's in my first modular (which will be set up again soon) 
     are from EN#46, which is a tri-square design using the AD-821 matched 
     PNP pair, a 3080, a FET buffer, and a discrete transistor schmidt 
     trigger comparator, so it's almost identical to the later MAT-03 
     design at least in performance. No linear FM inputs, however, because 
     such things hadn't been published in EN yet. Maybe someday I'll 
     retro-fit it.
     
     - Gene
     gstopp at fibermux.com


______________________________ Reply Separator _________________________________
Subject: Re: VCOs as modulation sources
Author:  Christopher List <Christopher_List at sonymusic.com> at ccrelayout
Date:    7/12/96 2:49 PM


>      in high school in 1976, is the *best* FM thing I've ever played 
>      with!!! The potential modulation depths are about twice as deep on 
>     that machine than on any other commercial system I've got.
     
>     much conversation about it and I think that it's mostly unexplored 
>     territory because mod depths on commercial machines just don't reach 
>     far enough. I'm dying to dive into it again.
     
Funny you should mention this. 
One thing I noticed last night, just looking at the 0-scope, was that when 
modulating the audio with the timbre modulator I got a huge depth of 
modulation, but when I use the FM inputs on the EN tri-square VCO, the maximum 
depth is pretty small. 
     
I wonder why they chose 560K input resistor for the FM (?) to the voltage 
reference op-amp. I mean, it's connected to a depth pot... 
     
I think I will be trying lower resistor values this weekend to see if I get 
stronger FM. 
That won't screw up the MAT-03 pair will it?
     
- Chris