Doepfer

Dirk,

it took a while but now we found the reason and a solution ...

We had problems to understand why the combination of A-110 (rectangle)/A-113
is working perfect but not A-111(rectangle)/A-113 at low frequencies.
Strangely enough the combination A-111(sawtooth)/A-113 causes no problems.

The reason is the negative slope of the A-111 rectangle ! Our oscilloscope
showed in high res mode (1us/div) that the negative slope is not a single
slope but has some ups and downs (a bit like a down-going triangle).
Obviously the waveform converter inside the CEM3340 has this behaviour as
the rectangle output of the A-111 is nothing but the rectangle output of the
CEM3340 (only via 1k protection resistor and AC coupling capacitor). In
normal applications this causes no problems and cannot be heard (each VCA or
VCF or mixer behind the A-111 smoothes this multiple slopes which are in the
microsecond range). But the A-113 is very fast and detects these multiple
slopes at low frequencies. This causes the problems of the A-111/A-113
combination you described.

There are several solutions for this problem:

1. Do not use the rectangle but e.g. the sawtooth output of the A-111 to
trigger the A-113 (the sawtooth has no multiple slopes)
2. Process the rectangle output by any other module (VCA, VCF, mixer) before
it is used to trigger the A-113.
3. Add a capacitor to the A-113 (in parallel to diode D3). We tried 2n2 and
then the A-113 tracks perfect from about 10Hz. If you contact me directly
(hardware@doepfer.de) I can send you a picture that shows the position of D3
on the A-113 board. In this case even the rectangle output of the A-111 can
be used to trigger the A-113.

Best wishes
Dieter Doepfer

> -----Ursprüngliche Nachricht-----
> Von: Doepfer_a100@yahoogroups.com
> [mailto:Doepfer_a100@yahoogroups.com]Im Auftrag von vliesgaard
> Gesendet: Donnerstag, 27. April 2006 12:35
> An: Doepfer_a100@yahoogroups.com
> Betreff: [Doepfer_a100] Re: A-113 input sencetivity/tracking problems
>
>
> --- In Doepfer_a100@yahoogroups.com, "Dieter Doepfer" <hardware@...>
> wrote:
> >
> > OK, I'll check this with an A-111 and A-113. But it may take a few days
as
> > we are very busy with testing and modifying the BBD modules as the
customers
> > are waiting anxiously for their modules.
> >
> > Best wishes
> > Dieter Doepfer
> >
>
> Don't worry, you get the full 100 points for customer service. If only
> other company's were that good.
>
>
> One use the A-113 is creating interesting rhythms.
> E.g. if you divide the 16th notes of the sequenser, with the A-113, by
> 2 3 5 and 7 you get a very complex rhythm patern.
> Thats why it should track low frequenty's.
>
> Greetings Dirk