Doepfer

There is a way to self oscillate a Doepfer ADSR if you have a tirgger modifier 
module as well.  I do it all the time:

Positive out of ADSR into Trigger Mod.

Pulse out of Modifer into Retrigger in of ADSR

Put a cotat high voltage oce ito the gate iput of the ADSR ad remove it before 
the cycle eds.

bingo - you've got an LFO.

As far as a mod to self osc, this would be easy:

Output of the ADSR through a comparitor, going into the - in.  The comp. + 
reference set just a tad above ground (really really close to ground).  Output of 
that through a switch to turn it off and on, output of that to a diode to the gate 
or retrigger input.

This will give you an AR LFO as well.  It's a pain to self cycle an ADSR, 
because it needs sustained gate input to complete the last two phases.

this should do it.





--- In Doepfer_a100@yahoogroups.com, "Tim Stinchcombe <timothy@t...>" <
timothy@t...> wrote:
> Hi all,
> 
> This morning I was having a quick look through the new Analogue 
> Systems group and noticed a comment that Bakis made about not being 
> able to get Doepfer envelope generators to auto-repeat. So, thinking 
> cap on and schematic of A-140 in hand I sat down, and after some 
> while I came up with a simple way to do it. With an extra diode, 
> resistor and op amp I have lashed it up on some breadboard and have 
> been playing with it for the last hour or so, and it seems to do the 
> job. All it does is sense when the envelope has got down to the 
> sustain level, and then generates a pulse that is fed back into the A-
> 140 retrigger input, and hey-presto, auto-repeat!
> 
> A little more thought suggested that the op amp currently used for 
> the inverted envelope output could be used to do this - thus with a 
> few pins, cutting a track or two, add a couple more components, and 
> this could be turned into a nice little mod to the module. The 
> new 'sustain level reached' signal would be output at the old 
> inverted output and fed back to the re-trigger input for auto-repeat -
>  if this was taken through an A-150 switch one could also select its 
> use via voltage control.
> 
> I haven't worked out the full details yet, but I expect it would be 
> about the same complexity as what I suggested to fix the problem with 
> the A-150 (anybody else actually had a go at doing that by the way?). 
> I thought I'd run it by people first to see what the interest is, if 
> any (what might seem simple to some may not be so for others...!). 
> (On the other hand I might just buy another A-140 and do it anyway.)
> 
> As for the A-141, I note that there are currently two unused op amps 
> already on the board, so it's conceivable that the same sort of trick 
> might work with it too - I'll have a ponder on that too.
> 
> Cheers,
> Tim