Film-Tech Forum ARCHIVE: Cinemeccanica C 55/PT Amp and Optical Input Help!

This is topic Cinemeccanica C 55/PT Amp and Optical Input Help! in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Jonathan Wood (Member # 4614) on 04-18-2008, 03:37 AM:

Hi everyone,

I am using a Microcine Tau M35 projector with a C/55PT amp. Does anyone have any experience connecting these up? I would like to use the optical input on the amp, my projector has a 5 pin din output marked Pre Amp Out, which I am assuming is just that and designed to feed an aux amp at line level which I dont think will work with the direct optical input. Am I right in believing that the thing to do would be to take a tap directly from the cell leads and connect them to the optical input of the amp? According to the Amp instruction a 2 pole switch inside the amp selects either photo diode or solar cell inputs and this feed s a bias current across the cell? Would I need to make sure that if I did this that the current didin't 'back up' into the projectors pre amp and cause problems? Also I heard somewhere that it is necessary to connect a shunt resistor across the cell to make everything work? Any advice GREATLY appreciated!
Thank you
Jon (UK)

Posted by Phillip Grace (Member # 2262) on 04-18-2008, 04:03 AM:

This probably wont help much at all, but why not use the auxilliary input on the C55PT? The most straight-forward wiring method if you want to use the optical input would be to connect a new lead direct from there to the cell, and disconnect the old pre-amp wiring completely. It is important to know exactly what kind of cell is in the soundhead. I believe the shunt resistor was required with certain older types of solar cell to alter the frequency response characteristics. So now having read this, the best advice I can offer will be to wait until one of the real film-tech technicians responds with the right answer. Cheers! Phil.

Posted by Jonathan Wood (Member # 4614) on 04-18-2008, 04:24 AM:

Hi Phil,
Many thanks for your advice, I had thought of using the aux input but would like to try doing it the 'right way'and bypass the projectors circuitry entirely, but I may well end up doing exactly what you suggest as the projector will have much more modern components being from 1987 than the amp which is probably mid 70's.

Best wishes,
Jon

Posted by Stephen Furley (Member # 1277) on 04-18-2008, 07:50 AM:

Hi Jonathan,

Did you manage to get the projector controls sorted out in the end? What was the problem?

Posted by Gordon McLeod (Member # 33) on 04-18-2008, 09:13 AM:

If you use the c55pt preamp make sure you have the slide switch set for photodiode not cell as your solar cell will notlike the bias voltage that is applied
Also the c55 is not all that great of amp (far better than its predecessor)
The microcine preamp and electronics are relatively decent

Posted by Jonathan Wood (Member # 4614) on 04-18-2008, 01:00 PM:

[Smile]

Hi Stephen, Yes it was all fine in the end, your theory about the feed arm just supplying a bit of gentle reverse torque to prevent the feed from over feeding was spot on. I set it all up and it all worked brilliantly! I tried emailing you several times but for some reason my emails kept getting returned. But thanks again for your kind help and suggestions!! Jon

Posted by Jonathan Wood (Member # 4614) on 04-18-2008, 04:49 PM:

Thanks Geoff,
I checked out the voltage across the optical input with the switch set to cell (C) and there's over 43 v present, which is wierd as I thought diodes needed the bias? My meter read 0v on the D position so would this be OK for my projector? I know what you mean about it not being a great amp. I'm listening to my iPod thru it and it does sound a little harsh. I was actually thinking that I might get better results thru my projectors amp as the projector is from 1987 and the C55 prob mid 70's, stands to reason the projector will do a better job.
Cheers, Jon [Smile]