AW: VC envelopes

[List, Christopher]

Hey Tim, good suggestion, these look cool!

Gene, are these the opto device you've been using? Or would these give
an RC envelope shape? (Obviously, I'm no FET expert)

Check out the info here;
http://www.qtopto.com/oi/o0801.htm

The H11F3 actually looks like it'd work fine. I mean, it just means
you'd use a smaller cap and wouldn't be able to get as long of a rise /
fall at the slow end of the ADSR. But even with a resisance range of
500ohms to 300M, you've still got a range of 1:600,000, and that means
you could got from a 1ms envelope to a 10minute envelope! The only
possible problem is that the F3 has a 15v breakdown voltage for the fet,
but you'd probably be running your input bewteen 0 and +14v anyway... 

The data sheet has a current controlled VCA (using single opto + opamp)
and has the description; "This basic circuit can be used to provide
programable fade and attack for electronic music" :)

Prices;
Source	H11F1	H11F2	H11F3
Digikey $3.11	$2.75	$1.75
Mouser	$2.94	$2.59	$1.65

I'm definitely gonna get a couple to play with in a VC-envelope setup.

- CList
	

> -----Original Message-----
> From:	Tim Cockram [SMTP:tim at redragon.demon.co.uk]
> Sent:	Thursday, June 04, 1998 9:14 AM
> To:	Haible Juergen; synth-diy at mailhost.bpa.nl
> Subject:	Re: AW: VC envelopes
> 
> Hi,
> 
> How about using the H11F1 opto fet (available from RS etc)?  A 0-16mA
> current varies the ISOLATED fet's resistance between 300M and 200
> Ohms.
> 
> They are 2-3 ea in one off quantities.  The H11F3 is about half the
> price but the minimum fet resistance is circa 470 Ohms.
> 
> These devices have been around for a while now.  I must Thank Fred
> Mundell (who used them in synth designs in the early eighties) for
> introducing me to thes devices.  Unfortunately Fred's designs never
> made
> it to the stores.
> 
> Where are you Fred?
> 
> Regards
> 
> Tim
>  
> 
> From memory the Korg PS envelopes were linear (I think) but with a bit
> of feedback Viola.
> -- 
> Tim Cockram