Doepfer

Hi list,

I only just discovered all this chat about full-wave rectifying etc., 
and what the A-136 can/can't do, so I'm arriving to the party a 
little late I'm afraid!

Yes, the A-136 can do this, but as Jari pointed out previously, it 
requires some very careful knob twiddling. Here is what I did:

1. Fed a sine wave into the input - the amplitude is deliberately 
kept below about +/-2V, as otherwise the first stage in the A-136 
will clip it.
2. Inserted patch cords into the 'ext level' sockets: the other ends 
are not plugged in anywhere else, and simply act to keep the '+L' 
and '-L' levels from interacting at all.
3. Adjusted all three 'A' controls to get the minimum out - this is 
to get the 'A' gain at the (electrical) centre-spot (care must be 
taken not to touch this again!).
4. Adjusted '+A' and '-A' in opposite directions to get full-wave 
rectification: half-wave is obtained by setting each of these to 
zero, in turn.

If this was going to be a regular occurence, it would probably be a 
simple matter to modify the module with a few switches to 
connect/disconnect stuff, and to put gains at precise settings.

I've posted some scope traces in the 'files' section, folder 'A-136 
rectification'

Tim

Does the A-137 Wave Multiplier also rectify somewhat, via the
"Symmetry" setting, or am I understanding it wrong?

--- In Doepfer_a100@yahoogroups.com, "Tim Stinchcombe" <timothy@...>
wrote:

>
> Hi list,
> 
> I only just discovered all this chat about full-wave rectifying etc., 
> and what the A-136 can/can't do, so I'm arriving to the party a 
> little late I'm afraid!
> 
> Yes, the A-136 can do this, but as Jari pointed out previously, it 
> requires some very careful knob twiddling. Here is what I did:
> 
> 1. Fed a sine wave into the input - the amplitude is deliberately 
> kept below about +/-2V, as otherwise the first stage in the A-136 
> will clip it.
> 2. Inserted patch cords into the 'ext level' sockets: the other ends 
> are not plugged in anywhere else, and simply act to keep the '+L' 
> and '-L' levels from interacting at all.
> 3. Adjusted all three 'A' controls to get the minimum out - this is 
> to get the 'A' gain at the (electrical) centre-spot (care must be 
> taken not to touch this again!).
> 4. Adjusted '+A' and '-A' in opposite directions to get full-wave 
> rectification: half-wave is obtained by setting each of these to 
> zero, in turn.
> 
> If this was going to be a regular occurence, it would probably be a 
> simple matter to modify the module with a few switches to 
> connect/disconnect stuff, and to put gains at precise settings.
> 
> I've posted some scope traces in the 'files' section, folder 'A-136 
> rectification'
> 
> Tim
>

> Does the A-137 Wave Multiplier also rectify somewhat, via the
> "Symmetry" setting, or am I understanding it wrong?

Yes, it does. The waveform is 'folded' about two levels, the sum and 
difference of the 'symmetry' and 'folding' settings, and this folding 
is essentially 'rectification'. This 'rectified' signal is then 
multiplied by a gain determined by the 'harmonics' setting, and mixed 
back into itself: this whole process is then repeated four times, so 
that what comes out at the end looks nothing like rectification at all.

Both the A-136 and A-137 I feel are difficult modules to get grips 
with: even knowing how the circuits work from the schematics, it is 
difficult to abstract to simpler levels and summarize what they do. The 
alternative method is not to worry about this, and just listen to what 
they sound like, and decide what works for you, and what doesn't!

Tim