Film-Tech Forum ARCHIVE: 70 mm magnetic sound

This is topic 70 mm magnetic sound in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Fredrik A Thulin (Member # 9115) on 06-12-2016, 03:12 PM:

As I have not come across a CP 200 to buy so I have decided to manufacture a unit myself that can handle various 70 mm sound formats. What I need to know is the cut off frequncy for channel 2 and 4 when using baby boom and split surround. I have searched for this info online to no avail. Can anyone please help me out?

Posted by Steve Guttag (Member # 268) on 06-12-2016, 10:00 PM:

You could always look at the CP200 manuals since Dolby published their schematics for it. However, to answer your question. Tracks 2 and 4 were low-passed at 250Hz. Also note, there was a downward expander applied to those channels when used for "baby boom".

You might try to seek out Ray Derrick. He designed/built the Panastereo CSP4600...which was the last processor I know that was built to play the 70mm 6-track formats.

Posted by David J Hilsgen (Member # 2614) on 06-14-2016, 01:29 AM:

I have 3 CP200

Posted by Fredrik A Thulin (Member # 9115) on 06-15-2016, 02:21 PM:

Does this mean that you have one for sale? If so, Please PM me

Posted by David J Hilsgen (Member # 2614) on 06-17-2016, 03:46 AM:

yes i would,last one i got $5900.00 i'm open to offers.

Posted by Martin Brooks (Member # 1269) on 07-10-2016, 09:57 PM:

On the CP200, for split surround, there was a 500Hz low pass filter from channel 6 and a 500Hz high pass filter from channels 2 and 4.

If a subwoofer was used, there was also a 250Hz Low pass filter on that and there was also an anti-resonance filter with a Q cut at <100 Hz.

There were also four options. (Don't know how extensively they were used):
A EQ on channels 2 and 4 for non-Dolby Mag
B Dolby NR on channels 2 and 4 for split surround
C EQ on split surround
D EQ on channel 6 for split surround.

Posted by Steve Guttag (Member # 268) on 07-11-2016, 08:19 AM:

Option "C" included two EQ cards for split surround. It was normally a C/64 to denote CAT64s rather than the cheeseball High/Mid/Low EQ (I forget its CAT number...something like 213).

Posted by Mark Gulbrandsen (Member # 72) on 07-11-2016, 10:13 AM:

Watch EBay for CP-200's. They typically go for 2000 USD and under. There was a complete Dolby MPU on there a couple weeks ago at a starting price of $50.00!
5900 is a little far out unless it has a well equipped accessory rack and every update card available installed in it...

Mark

Posted by Steve Guttag (Member # 268) on 07-11-2016, 10:51 AM:

I decided to look it up. Kit B got you a pair of CAT22 NR cards and the CAT158 Stereo Surround Card. Kit "C" is a pair of EQ cards for the surrounds (C/64 was for CAT64s and C/216 got you the cheeseball EQ). This option was eventually dropped and only the Kit C/64 was available.

A was for EQ on Le/Re
D was EQ for mono surrounds
E was another CAT108 for Projectors 3 and 4.
F was for interchange of L/Le and R/Re (also provided an extra transistor driver to allow for mid p/q VCAs
G was for format 41 so you got two CAT64s and two CAT22s.

As for CP200 prices...they are all over the place and as some have indicated, how well equipped they are should factor in as to what the offering price should be (as well as overall condition).

There are probably several available at any one time too but there was a time when they were in very short supply. They went out of production by 1994 so there was a period where there were people seeking them out when they were not available. Many 70mm rooms don't use them anymore and any that are just DTS have no need for them either so again, they are not as rare as they once were. That is, providing they didn't hit the dumpster as I'm sure many have.

Posted by Sam D. Chavez (Member # 1841) on 07-12-2016, 01:42 PM:

I have a couple of good one no doubt. They do deteriorate over time, esp. the front panel. There are often missing, modified, or incorrect cards and missing cables.

Beware where you by and the recourse if there are problems.