[sdiy] VTL vs. H11F (was: Which is better as a VC resistor? FET or BJT?)

[mark verbos]

On Jul 1, 2011, at 8:16 AM, Matthias Herrmann-DEU wrote:

>> -----Original Message-----
>> From: synth-diy-bounces at dropmix.xs4all.nl [mailto:synth-diy-
>> bounces at dropmix.xs4all.nl] On Behalf Of lanterma at ece.gatech.edu
>> Sent: Friday, July 01, 2011 9:55 AM
>> To: synth-diy at dropmix.xs4all.nl
>> Subject: Re: [sdiy] Which is better as a VC resistor? FET or BJT?
>> 
>> On Jun 30, 2011, at 12:23 PM, Scott Gravenhorst wrote:
>> 
>>> H11F series (H11F1, H11F2, H11F3) is a FET optoisolator that might be
>>> useful as a VC resistor.  I cannot speak to linearity, but it's source
>>> need not be connected to ground.
>> 
>> I had a student build a Buchla lowpass gate with these in place of the
>> vactrols. The student needed to change the capacitors, since the resistance
>> range of the FET optoisolators was different than that of the vactrols. It
>> sounded pretty cool, I thought.
> 
> I believe that it sounded pretty cool, however, I wonder if it gave you the typical LPG sound, which I believe is related to the long decay time of the vactrols (VTL5C3 35ms vs. H11F3 25uS). Am I correct?


You could build one with BJTs too. See Korg MS-10/MS-20. 

Mark