Doepfer

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

Hi Tim,
Good idea, if you do try it let us know what happens. If it works 
please post a pic of the mod so I can try it.

JOhn.


--- 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

me three.
-psm

> Hi Tim,
> Good idea, if you do try it let us know what happens. If it works 
> please post a pic of the mod so I can try it.
> 
> JOhn.
> 
> 
 <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

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

Hi Peter,

> 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.

I don't have an A-165, but I assume that when you do this the re-
trigger level is at the mercy of whatever is inside the 165 which 
decides when it has seen a 'trigger'?

> 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.

Mmm, I can see a philosophical debate coming on about what a cycling 
ADSR really _is_. The 'mod' I've been playing with (I'm still 
pondering over it, because I keep having trouble deciding what is 
sensible and what is not, and this kind of comment reinforces this 
fact...) is almost exactly what you describe _except_ that the 
reference level will be the sustain level. Thus whereas with your way 
the ADSR swings through its full output range, my way it will only 
swing between the max output level and the sustain level, which 
perhaps is more flexible (?), i.e. it will be as your way when the 
sustain level is set very low. I've certainly had some great 'echo' 
like effects with it.

> 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.

Not quite sure what you mean here - what I'm thinking of will only 
cycle _as long as_ the gate remains there. Since it re-cycles each 
time the sustain level is hit, there is no sustain phase per se, and 
when the gate closes, you get the release phase as normal.

My idea is actually working out a deal more simple than I thought, 
and in its simplest form will only require cutting 1 track, adding 1 
strap, and snipping through 1 resistor. I'm trying to organise a 
friend who has a digital camera so that when I do it I can post some 
pikkies. (There are also several pairs of diodes in the circuit whose 
purpose I haven't fully grasped yet, and I don't want to rush into it 
and overlook something....)

You've also made me want to check what happens if I switch it in and 
out via an A-150 _whilst the gate stays open_ to see if it restarts 
cycling when I switch it back in.

Tim