Doepfer

Hi All,

I own an A136 and have been using it more lately and it occured to me
that the most radical timbre changes are caued by turning the center
"A" knob.  Does anybody know why this feature is not voltage
controllable? Also, is there a simple mod to add a "CV in" to the A136
"A" knob?

Thanks,

Ethan

Hi Ethan,

> I own an A136 and have been using it more lately and it occured to 
me
> that the most radical timbre changes are caued by turning the center
> "A" knob.  Does anybody know why this feature is not voltage
> controllable? Also, is there a simple mod to add a "CV in" to the 
A136
> "A" knob?

As you turn the 'A' knob, not only do you alter the gain, but at it's 
centre point, the gain actually changes sign. Whilst this is 
relatively easy to do with the pot and op amp configuration used in 
the module, doing it with voltage control (especially the changing 
sign bit) is probably a considerably more complicated proposition 
altogether. Thus from what I know of the module, and with my 
understanding, I think a 'simple' mod is probably not possible.

Tim

(... and hopefully this time I won't change my mind 2 seconds after 
hitting the send button...)

If the positive/negative gain isn't an issue, couldn't you just route 
the audio thru an A132 VCA and get voltage control of the gain that 
way?

--- In Doepfer_a100@yahoogroups.com, "Tim Stinchcombe" <timothy@t...> 
wrote:
> Hi Ethan,
> 
> > I own an A136 and have been using it more lately and it occured to 
> me
> > that the most radical timbre changes are caued by turning the 
center
> > "A" knob.  Does anybody know why this feature is not voltage
> > controllable? Also, is there a simple mod to add a "CV in" to the 
> A136
> > "A" knob?
> 
> As you turn the 'A' knob, not only do you alter the gain, but at 
it's 

> centre point, the gain actually changes sign. Whilst this is 
> relatively easy to do with the pot and op amp configuration used in 
> the module, doing it with voltage control (especially the changing 
> sign bit) is probably a considerably more complicated proposition 
> altogether. Thus from what I know of the module, and with my 
> understanding, I think a 'simple' mod is probably not possible.
> 
> Tim
> 
> (... and hopefully this time I won't change my mind 2 seconds after 
> hitting the send button...)

Hi Joe,

> If the positive/negative gain isn't an issue, couldn't you just 
route 
> the audio thru an A132 VCA and get voltage control of the gain that 
> way?

Internally in the A-136 the signal is split into three paths, and 
the 'A' gain knob affects just one of these, and it's the interaction 
of this path with the other two that produces all the interesting 
waveshaping effects. I suspect that doing what you suggest just 
probably wouldn't be so interesting.

Tim

Timothy, the A136 User's manual says that the signal is split into 
three parts, but no signal flow diagram is provided. (This is only 
the least of the problems with the A136 documentation). The 
signal diagram on the module front panel suggests that the "A" gain 
is applied BEFORE the signal is fed to the positive and negative 
clipping circuits. That's why I made the suggestion that I did.

I suppose I could spend some time experimenting to determine the 
actual signal path, but it's a tedious business without a scope. I 
wish bakis would nudge Dieter to describe the A136 signal path, and 
correct all the errors in the User's Guide while he's at it.

Joe

--- In Doepfer_a100@yahoogroups.com, "Tim Stinchcombe" <timothy@t...> 
wrote:
> Hi Joe,
> 
> > If the positive/negative gain isn't an issue, couldn't you just 
> route 
> > the audio thru an A132 VCA and get voltage control of the gain 
that 
> > way?
> 
> Internally in the A-136 the signal is split into three paths, and 
> the 'A' gain knob affects just one of these, and it's the 
interaction 

> of this path with the other two that produces all the interesting 
> waveshaping effects. I suspect that doing what you suggest just 
> probably wouldn't be so interesting.
> 
> Tim

Timothy, you're not the only one who needs to correct himself five 
minutes after posting :-)

That's how long it took me, adjusting the voltage from an A176 CV 
Source, and watching the LEDs on an A170, to convince myself that the 
A136 does indeed process the A, +A, and -A paths independently, and 
then sums the result. My A132 suggestion was all wet.

If nothing else, I've learned a little bit more about the A136 today.

Joe

--- In Doepfer_a100@yahoogroups.com, "Joe Buechler" <buechlerjoe@t...> 
wrote:
> Timothy, the A136 User's manual says that the signal is split into 
> three parts, but no signal flow diagram is provided. (This is only 
> the least of the problems with the A136 documentation). The 
> signal diagram on the module front panel suggests that the "A" gain 
> is applied BEFORE the signal is fed to the positive and negative 
> clipping circuits. That's why I made the suggestion that I did.
> 
> I suppose I could spend some time experimenting to determine the 
> actual signal path, but it's a tedious business without a scope. I 
> wish bakis would nudge Dieter to describe the A136 signal path, and 
> correct all the errors in the User's Guide while he's at it.
> 
> Joe
> 
> --- In Doepfer_a100@yahoogroups.com, "Tim Stinchcombe" 
<timothy@t...> 

> wrote:
> > Hi Joe,
> > 
> > > If the positive/negative gain isn't an issue, couldn't you just 
> > route 
> > > the audio thru an A132 VCA and get voltage control of the gain 
> that 
> > > way?
> > 
> > Internally in the A-136 the signal is split into three paths, and 
> > the 'A' gain knob affects just one of these, and it's the 
> interaction 
> > of this path with the other two that produces all the interesting 
> > waveshaping effects. I suspect that doing what you suggest just 
> > probably wouldn't be so interesting.
> > 
> > Tim