[sdiy] VCS3 Like Patch Panels (new)

[JH.]

>Many thanks for the email. Did you use the same Ghielmetti 20x20 patch
>panel on your AKS clone?

No, not at all. Mine is twice as large! I think its from the 621 series;
first digit standing for 6mm spacing. The 321 has only 3mm spacing.
I wouldn't feel comfortable with that.


>Did you make your own resistor pins or did
>Ghielmetti supply them?

First batch I ordered with diodes (there was no resistor option advertised),
removed the diodes and soldered in resistors.
Opening the pins is a pain in the you-know-what, but it's possible.
(With the large ones; don't know about the tiny ones.)

Second batch I ordered with 10k Resistors.
Only to find that the EMS VCS3 value of 2.7k is much better: 11dB less 
crosstalk!

>Is the small size a pain to use, or a problem
>with cross talk?

No idea about the 3mm matrices.

On the 6mm, the main problem is crosstalk from one *column* to the next.
That means, you won't get much crosstalk from a source to a desitination,
because the row and column busbars are only close to one another at one
tiny point.
BUT if you connect a source to, say, a destination in column 12 with a patch 
pin,
this will have a lot more coupling (capacitance) to columns 11 and 13 now.
So the main coupling isn't from source to destination, but from a 
destination
to neighbouring destinations.
This isn't much trouble in practice, as long as you put some thought into 
your
matrix layout. You won't place a main output channel or other sensitive
destination next to a destination that's likely to get modulated with 
steep-sloped
sample asnd hold modulation, or high level noise modulation.

Crosstalk is capacitive - so if you have trouble, then int's in the treble 
range.
As the capacitance of the matrix is fixed, just make the impedance of 
patchpins,
module inputs, and (important!) module output potentiometers as small as
possible.

If you ever wondered why EMS used signals in the 1V range, and impedances in
the 1 ... 2.5 kOhm range, when everyone else did 100k and 5V or 10V, here's
the reason.

JH.