Trapezoid. Pitch Ribbon, 2mm connectors

[jhaible]

Hi,

I'm not at the office for a few days, so if you want to respond to this,
please send it to my metronet adress as well as to the diy list.
(jhaible at metronet.de)

A few news in short:

(1) TRAPEZOID

Just finished the VCS3 trapezoid envelope generator.
I ran into problems with the diodes that are connected in series to
the on-time and off-time potentiometers. The original shows DK10
germanium diodes. I tried AA119, but they had too much leakage,
and the circuit is *very* sensitive to that. 
Then I tried ordinary silicon 1N4148, and it worked.
Another potential source of problems is the transistor that is used
as a zener diode. The BC550C I used had zener voltages above
8 Volts (I tried several ones, and they were all similar). I replaced
this with an ordinary 7.5V zener diode, and it worked.

The VCA section with the p-channel JFET was ok, too, but I found
it was very sensitive to pick up RF. This was cured by a little capacitor
(390pF) across the input.
OTAH, the mixture of audio signal and a self-oscillating VCA did sound
familiar somehow (from records ?). So I am curious if the original has
these
problems as well.

(2) EMS SCHEMATICS

As I plan to build several VCS3 circuits in the future (just ordered
a few pairs of germanium small power transistors, hint, hint ...),
I thought it was a good idea to contact Graham Hinton to get the
rest of the original schematics published, or at least to get the
permission to do so ourselves. Little chance, so far. He responded
very politely, but he is sceptical to give away all of EMS' intellectual
property. Which is quite understandable - so at least I will not put
additional EMS drawings to a web site.
I will continue to share my experience in cloning, however. And
if someone finds another source of EMS schemos anywhere on the
web (or puts them there), this would be of great help for general
discussion,
of course. I myself cannot - you know, I cannot ask for official permission

and then do it nevertheless.

(3) PITCH RIBBON

I found something that would be the ideal material for a pitch ribbon:
Its a "shorting edge connector" made of conductive plastic and used
for ESD shielding pcb's.
It's 0.5m long, quite flexible, and I measured a resistance of 800 Ohm
across the whole length. 
It costs DM 7,- ( USD 3.50), and it is available from Farnell, order code
is 175-831. (This is from the German Farnell catalogue).

(4) 2mm CONNECTORS

While I always voted for 1/4" headphone jacks on modular systems,
I will probably make an exception now.
The VCS3 with its weighted summing cries for stackable plugs,
if you want to avoid the patch matrix. First I thought of banana plugs,
but they will tower up to considerable height if you stack seval ones
on top of each other. So I looked for something smaller, but still 
sturdy enough, and I ordered a few 2mm plugs, like they are used
in some laboratory equipment. Just soldered one cable with these.
They are not bad. Anyone else tried these ?

JH.