Calrec Assignable

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Calrec Assignable

Postby DraytonTom » Sat Jun 04, 2011 4:17 am

Hi All

I have been offered several crates of Assignable modules...
Google reveals its probably an MSC3, or at least the photographs I have of the modules in the crates tie up with the modules in the photograph of one I found online.
From rather sketchy research I have made a few deductions/assumptions, and would be grateful if anyone might be able to comment on my reasoning....

My understanding of the Assignable range was that it was digital controlled analogue, so as I cant see any rack mount boxes or cards with Lundahls on them, I am guessing that this is just a rather nice looking control surface...

However, I have seen a number of double length Euro cards that seem to have the potted "blue secret" Side chain modules on them, labelled DF 1724.
Presumably some audio processing took place in the console?

The modules have the Calrec AMS style logo on them, and looks very similarly styled to the M-series. Would it be a fair assumption that the (probably missing) I/O circuits would be a similar topography to that of the M but with digital controlled switching for gain? And possibly an extension of the way the stereo EQ modules worked on the M using a remote CV, only derived digitally?

The console must have been controlled by a "brain" of some sort, would this have been a very early PC running software or a dedicated Z80 or equivalent micro-controller?

The lack of a console frame isn't much of a hindrance, as I the CAD work I did for my M-Series project could be adapted quite easily, and I have already have a reliable fabricator. Same with the Motherboards.

My only real concern is that I will end up with a rather impressive "object d'art" of no practical use at all...

Many Thanks

Tom
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Re: Calrec Assignable

Postby Matt Syson » Thu Sep 01, 2011 12:24 pm

Hi
The assignables were digitally controlled analogue with 'racks' of analogue audio cards and the 'surface' being basically a bunch of pots and switches hooked up to a/d converters.
As a complete desk operated as designed it is a fair proposition but any attempt at further 'customisation will probably lead you into serious software hacking territory. I did not work on the assignables as such although saw several being built and assisted with some activities but not relating to software in any way.
There was some 'audio' in the desk frame but only monitoring functions I think, stuff not 'assigned'.
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Re: Calrec Assignable

Postby DraytonTom » Mon Sep 05, 2011 10:36 am

Hi Matt

Thanks for the response, actually I went ahead and made an offer so now I have a workshop full of lots and lots of Assignable modules, cards, faders, PCB, and without any documentation of any kind
I have been slowly working my way through the cards to try and determine their function which has been fun.
Thankfully, I didnt make the offer based on me buying a console, more on just a kind of experiment/vehicle to relearn some of the stuff I did during my electronics degree.
The nice thing about digital is that as it only expects 1s or 0s its quite a bit easier to reverse engineer.
I have figured out how the data addressing for the long Eurocard Audio cards works, I have also made a few assumptions about the functions of the cards, which I will be testing out during the next few weeks.
Assumptions so far...

PN1746 Mic/Line Input cards with a green and a brown Valley people TA 101 VCA modules and a pair of DBX 2150As in a panning circuit (It occurs to me these VCAs may also control Fader level).

DF 1724 Dynamics card, these have one DBX2150A and the Blue secret sidechain module, I am also hoping that this module uses the one VCA to do both gate and Compression functions.

QN 1749 EQ card, looks like a similar configuration to the stereo EQ channels used on the M-series, with a switched transistor network for the filters. Thankfully, due to the number of pins used for the data addressing this card only has 2 audio inputs and 3 audio outputs. I will probably start my reverse engineering with this card

VN 1603 Aux send and Routing card 8 DBX VCAs which would correspond to the 8 Aux sends, interestingly there are no Op-Amps corresponding to the VCAs, presumably the signal is routed straight to the bus as a current and not a voltage, via the 4053s...

Then I have various types of YN modules all of which feature lots of lots 4053s so I guess they are routing cards.

My suspicion is that to get one audio channel 4 of the above cards are required. I would not be surprised if a type of YN card was also needed, and that the other types might be master section routing cards.

The pallet also came with various other odds and ends including a couple of XN2636 "low noise mixer cards" these appear to be a hybrid design using a pair of transistors and a 5532. At first glance it looks like a balanced bus amp.
I wondered if the assignable might use balanced bussing, especially as all the various types of cards appear to have lived in different rack mount boxes(judging by photographs of a VCS system founf on the net). But I cant find any evidence of the necessary inverting amplifiers to feed the cold side of the bus.
Can anyone confirm that the Assignable used the same BackStop Earth summing method of the M-series? and that this might just be a newer implementation of the summing amp?

Finally, from looking at the control surface, I think that the desk had an architecture as follows:

8 Aux sends (mono/stereo? or configurable?)
8 Groups (stereo?)
4 Main Out Stereo
4 Main Out Mono

Then interestingly there seems to be a routing select panel to route the channel to recording outputs 1-24(Straight forward routing to a balanced output amp?).

Anyway, if anyone can shed any light on any of these musings I would be greatly appreciative.
I have written some simple software that will allow me to write data to the banks of octal latches on each card, and will observe the results and refine the code to try fathom the various functions...
Will keep you posted!

cheers

Tom

P.S. The pallet also contained about 40 odd M-series fader modules and a few other M-series cards that have come in handy for my M-series project!
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Re: Calrec Assignable

Postby Matt Syson » Mon Sep 05, 2011 12:47 pm

Hi Tom
Please email me direct. I haven't read all your piece above but may be able to help with various bits of info.
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Re: Calrec Assignable

Postby DraytonTom » Mon Nov 14, 2011 3:41 pm

Thanks to Matt and various others for help with this project.
I have now pretty much managed to reverse engineer the functionality of the QN 1749 EQ card, using an Ardunio and long hand I can make all the filters switch on sweeep, change Q, and change the signal path routing.
I am currently working on building a program in Processing to allow a graphical Mac based interface to control up to 16 of these cards.

The next reverse engineering project is on the dynamics card DF 1724.
I found a schematic for the dynamics section of the UA8000 console and it seems to bear a great similarity to that of the what I am faced with on these cards, except with Calrecs clever Octal Latch Control Voltage generator circuit in place of all the pots.
The odd bit is the presence of a DBX2150 on the dynamics card, the UA8000 appeared to use one Allison Green 101 VCA to carry out group, mute, and dynamics functions.
The accompanying Input card PN1746 has a green 101, and a brown 101. I assume that the brown module is for input gain, due to its proximity to the edge connector.
It would be logical to think that the Green 101 would carry out the same functions as the on the UA8000, but in that case what is the purpose of the DBX2150? unless it was an addition to the sidechain circuit.
Any ideas?

Cheers
Tom
DF1724.JPG

PN1746.JPG
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Re: Calrec Assignable

Postby adrianeng » Tue Nov 22, 2011 3:04 pm

Hi Tom

Do you have any spare cards you would like to sell?

I'm after:

PN1746, DF1724, QN1749, VN1603.

Thanks

Adrian
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