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Topic: 35mm Mag

Josh Jones
Redhat

Posts: 1207
From: Plano, TX
Registered: Apr 2000

posted 04-30-2000 02:25 PM

Does anyone out there know the track layout for 35mm mag? the theatre I work at has two RCA 9010 35mm mag heads that have long been replaced. I'm thinking about hooking one of them up for our "lair" screening room.

LittleJosh

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Ari Nordström
Master Film Handler

Posts: 283
From: Göteborg, Sweden
Registered: Jan 2000

posted 04-30-2000 03:12 PM

The mag sound layout is, in order from the right edge of the film (the optical sound strip side) and inwards:

Left ch (1)
Center ch (2)
Surround ch (4)
Right ch (3)

The numbering refers to the numbering scheme in use when mag sound was common, and has nothing to do with the order of appearance...

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 04-30-2000 03:24 PM

tracks 1,2,3,4 are left centre right surround
you need preamps for them and the head impedance can be a bitch to match up on some of the older stuff
Smart still makes a decent 4 channel mag preamp

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99

posted 04-30-2000 04:15 PM

Hey Josh,
If you do hook one up be sure to get a new timming belt for it. It links the two sprockets together and the old one usually takes a bad set from sitting around all these years. You'll have lots of wow in your playback. After use if you don't plan on using it for a while remove the belt and leave it in a visible spot for the next operator to install back in.

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 04-30-2000 04:34 PM

Jeez Gord....SMART still makes "a" pre-amp for 4-track...certainly cost effective (read, cheap) The SMP-435...it no longer has the dual 12KHz filter of the SMP-430.

Dolby's CAT 92C preamp cards also work REALLY well.

Lastly, Panastereo's NEW CSP-4600 accomodates 4-track magnetic 35mm including decoding the 12KHz control signal.

Steve

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"Old projectionists never die, they just changeover!"

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 04-30-2000 05:51 PM

Steve I get the feeling that budget will be the main consideration and there are many of the older 4 track smarts kicking around used with the 12K filter and they did a more than acceptable job on 35mm mag maybe not the best for 70 though
I have often hooked up DBX 3Bx units to the output of the 4 track to quiet them down from the hiss build up

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 04-30-2000 07:23 PM

>>"they did a more than acceptable job on 35mm mag"<<

Provably false.

But I agree with you that in this situation that it is viable solution that should be considered.

Another noise solution is DNR. Teccon incorporated it on their preamps.

Steve

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"Old projectionists never die, they just changeover!"

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Josh Jones
Redhat

Posts: 1207
From: Plano, TX
Registered: Apr 2000

posted 04-30-2000 08:03 PM

The timing belt on the head was holding the shape it was in for the last 20 years. I ran some test film loops to figure out how to thread it. Just like dave(My manager, long time projectionist)told me, the ilers were fluttering like crazy. as for preamps, I thought about building them from scratch.
Impedance matching, I now know, could be a problem.

LittleJosh

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 04-30-2000 08:12 PM

Building the preamps from scratch seems like needless work...unless that sort of thing is your hobby.

Gord is right in that there are preamps out there (SMART or otherwise) that could be had cheap (or even free) that will do the trick well enough.

Depending on your print condition, one of your biggest problems will be print shrinkage...see if the picture will even be watchable...I have seen many a 4-track print (old and shrunk) that wouldn't sit still on the intermittent sprocket or film gate.

Steve

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"Old projectionists never die, they just changeover!"

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99

posted 05-01-2000 06:26 AM

Another route would be to get the small modules from Oampamp Labs in Hollywood. These are high quality small octal plug in modules and are very inexpensive. There are schematics in the Oampamp Labs info for building the preamp. Also Gord/Steve, The Smart mag preamps are the quietest of the lot that you can buy. Disney uses them extensively all over the place, however they are designed and will eq peoperly only with a Teccon Head. Unfortunately these are no longer around. The 92C would be my choice in this case.
Mark

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Sean Weitzel
Jedi Master Film Handler

Posts: 619
From: Vacaville, CA (1790 miles west of Rockwall)
Registered: Dec 1999

posted 05-01-2000 08:13 AM

What about gutting a pair of old cassette decks for preamps? Just run shielded wires from each head to the spots on the deck's boards for each channel. If you could find a cheap or broken 4 track cassette or small 4 track reel to reel deck, then you'd only need one.. and you would have a built in power supply.

-sean

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99

posted 05-01-2000 09:22 AM

The tape preamps would have the wrong time constant for proper eq'ing. Propbably not even close. There are alot of things to take into consideration such as head impedance, gap width,linear speed, etc. The ompamp thing works well though. I know someone that has done it before. Also note that the Dolby CAT92 preamp cards probably won't work well either as they are really meant for low impedance heads. If you crank the gain up too much and apply too much hf eq they can oscillate, possibly leading to disastrous results. The 92C cards work quite well with either high or low impedance though.
Mark
Mark

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Josh Jones
Redhat

Posts: 1207
From: Plano, TX
Registered: Apr 2000

posted 05-01-2000 08:00 PM

Wait just a minute,
In the storage room of the theatre, There was a rack chassis with four little modules each having two tubes and an a shielded transformer. could those be preamps?

Josh

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 05-01-2000 08:42 PM

Mark,

I have tried the SMP-435 with Teccon heads (your's even on your two-strip Centurys) and the EQ was REALLY wanting.

I think we have a couple of either SMP-430s or 435s kicking around somewhere though.

For the best overall, the Cat. 92C is very tough to beat.

Steve

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"Old projectionists never die, they just changeover!"

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John Eickhof
Jedi Master Film Handler

Posts: 588
From: Wendell, ID USA
Registered: Jan 2000

posted 05-01-2000 10:09 PM

Yes, those are the pre-amps...if you email me a model number off each chassis, Ill send you schematics. The only repairs before you hot them up should be replacing all the capacitors with new ones, also, there should be a power supply in that cabinet for these, send me some numbers and I should be able to help! John

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