Το Τεσσερα, the difinitive VCA.

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Το Τεσσερα, or Tessera, that means four (4)

The Tessera is a 4 SSM2164 VCAs, with linear response like Mike Irwin, with control over their offset or initial level. One signal IN, one CV IN, one switch per channel that allow to invert the signal before that it enter in the mixer, and the mixer give us, the direct outs of all the channels, 1,2,3 and 4, the sums of 1+2, ALL, 3+4 and 3+4’.

It is a very useful module that it is able to process AC signals and DC signals. It is very clean, start to distort the signals over 20V peak to peak. You can control, manual and with voltage, the amplitude of the signal, sum, split and invert, so also subtract signals.

With fast attack envelope times and processing low frequency signals, appears a noticeable “click”, for mi is OK solving it with more slow attack envelope times. You can also, smooth the click with more big value in the capacitor C3 (and C7, C11, C15). But it compromises the response when AC is introduced in the CV to modulate the main signal.
Also you have the option of configure two capacitors with one switch like did Serenadi. You can read this in this interesting discussion: http://electro-music.com/forum/topic-9134.html

I’m very happy with this project because I did the whole process. This was a very enriching experience: The circuit, the tests in the breadboard, the PCB layout (by hand), the PCB, the front panel layout, the front panel by hand also, all.

I designed it observing mainly the Quad VCA by Marc Bareille, also the 21st century VCA by Thomas Henry and the documentation of Analog Devices, and of course the article of Mike Irwin. I added also the protected power supply IN that are in the Magsmoke PCBs.

http://www.edn.com/article/CA233728.html
http://m.bareille.free.fr/modular1/quadvca.pdf
http://www.magsmoke.com/thomas_henry_books.asp
http://www.analog.com/static/imported-files/data_sheets/SSM2164.pdf

Thanks to Marc Bareille, Tim Servo and also to Thomas Henry, Mike Irwin, to those that answered my questions in this forum and all you.

So here I attach the schematics, the PCB layouts and the pictures, notice that I can only invert two channels, I adapted it for Eurorack without compromising the ergonomics of the front panel. The prototype had 4 switches and it not was very comfortable for me. Although that bypassing the two inverters in the PCB would be enough I did also a PCB layout version with only two inverters. I still not finished the parts placement documentation.

I hope that it will be interesting for all you.

Oscar.

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schematics.pdf
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PCBs LAYOUT:
You need both for one Tessera. Thought for assamble both in sandwich.

UPDATED DOCUMENTATION:
Components Placement, Bill Of Materials, Schematics, Biblography.

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pcb1.pdf
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pcb2.pdf
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documentation_103.pdf
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PICTURE UPDATED.

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ops! devlopers corner. maybe I had to post it in the main DIY forum?

[blue hell]

[fonik]

that's very nice. i still have some ssm ICs in the drawer...
congrats.

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[TekniK]

[Sound]

Ei TeKnik!

I mentioned it because I wondered about when I was breadboarding the circuit, and linked that thread because i thought that was interesting.

All the VCAs, respond with a click when they receive a fast attack. Isnt it?

Regards.

[TekniK]

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[Sound]

[blue hell]

[frijitz]

[blue hell]

[TekniK]

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[frijitz]

[TekniK]

I did more tests, seems it indeed depends what kind of envelope curve u use.

I did first test with my modcan/serge-like adsr wich has a swith to select the responce of the curve.

With the attack set in log. mode there is NO CLICKS whatsever the signal feeded into the vca,its when i changed modes u can barely sometimes hear clicks indeed depending the settings of the stages,also with squarewave as control i indeed have clicks.

But overal the rejection is realy very low,and appears only when u use a short adsr (no decay or release),otherwise i still don't have clicks even with the attack at minimum.

[Sound]

Hello all,

I Added in the second post of this thread the documentation of the Tessera.

Hope you like it,

Regards!

[epk]

thanks, this looks like a great design! I'm adding this to my list of modules to make for sure!

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