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Topic: DIY PERSPECTA SOUND INTEGRATOR

Mikael Christensen
Film Handler

Posts: 13
From: Vejrup, Bramming, Denmark
Registered: Oct 2015

posted 10-13-2015 02:43 PM

Hi
I hope it is the right place to post this:
I am building a Perspecta Integrator, using the diagrams from Widescreen Museum web page .
My problem is I don't have diagrams for the filters, can anyone please help. [beer]

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Mikael Christensen
Film Handler

Posts: 13
From: Vejrup, Bramming, Denmark
Registered: Oct 2015

posted 10-15-2015 02:29 PM

Yes.............

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David Buckley
Jedi Master Film Handler

Posts: 525
From: Oxford, N. Canterbury, New Zealand
Registered: Aug 2004

posted 10-15-2015 02:34 PM

Is it that you actually want to build one of these things for shits and giggles, or do you actually want to do Perspecta audio and have some media suitably encoded and you'd like to hear it as it is intended to be?

If its the latter, then I'd find a PC, get a multi-output sound card, download Pure Data [link], and build the functions in software. Even learning PD from scratch, it'll still be a lot quicker than assembling a clone of a piece of history.

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Mikael Christensen
Film Handler

Posts: 13
From: Vejrup, Bramming, Denmark
Registered: Oct 2015

posted 10-15-2015 03:17 PM

Yes this is serious business, I don't build anything for shits and giggles [Smile]

.
I have a collection of tube-amps. used in cinemas from 1936 to multi channel racks from 1962, all working and used on weekly basis.
So building one from scratch, is going to be a nice winter project.

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99

posted 10-15-2015 03:50 PM

There exists a Perspecta Sound plug in card that goes in place of the Dolby CAT 150 in any Dolby processor that utilizes that card. It was made in Great Britian but I don't know by whom. It shouldn't be impossible to figure out either way. You just need frequency and level sensitive VCA's and opamps and it should work quite well.

Mark

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Steve Guttag
We forgot the crackers Gromit!!!

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

posted 10-16-2015 06:07 PM

The PAS-1 card. I bought one. Worked well. It is on loan to the AFI/Silver for whenever they happen upon a Perspecta print.

From their sales flyer of years gone by:

quote:
The construction of the PAS -1 is a double-sided PCB with the
same profile as a Dolby Cat150 matrix board, which it replaces
when a Perspecta film is being played. Consequently it will fit
into any Dolby Processor containing a Cat150.
The Perspecta system worked by using
sub audible switching tones buried in
the soundtrack, which when replayed in
the cinema moved the signal to left,
centre, or right stage loud speakers.
The PAS-1 card uses standard
analogue components with mostly TL
074 opamps in the speed filters (30Hz
for left, 35Hz for centre, and 40Hz for
right) and LMI 3700 transconductance
amplifiers in the VCA stages.
Most projectors today run at 24 frames per second and the card
is set for this speed. However the filters can be retuned should
25 f.p.s.or any other speed be required.

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Mikael Christensen
Film Handler

Posts: 13
From: Vejrup, Bramming, Denmark
Registered: Oct 2015

posted 10-18-2015 12:07 PM

Thanks for the suggestions, but I prefer to go tubes all the way.

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David Buckley
Jedi Master Film Handler

Posts: 525
From: Oxford, N. Canterbury, New Zealand
Registered: Aug 2004

posted 10-18-2015 06:10 PM

quote:
Yes this is serious business, I don't build anything for shits and giggles. I have a collection of tube-amps, used in cinemas from 1936 to multi channel racks from 1962, all working and used on weekly basis.

Respect.

I've had a look at the diagrams, and yes, no detail for the filter assemblies, but they clearly use quite large inductors due to the frequencies involved, and they are noticeably big in the photos. One unusual feature is that the first "row" of three are all in series with the plate of V2, so the input of the filter must be an inductor. The input filter of V1 gives an indication of how the filters were constructed, though obviously this is the high pass version rather than the bandpass filters necessary for each channel.

I suspect you'll have to design and build from scratch, Horowitz and Hill being the obvious place to start, and/or try and find an old version of the ARRL handbook, they had information on building audio filters in the valve era.

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99

posted 10-19-2015 04:03 PM

Good luck having those bandpass filters wound and properly tuned. The only tube Perspecta unit I ever heard work correctly was at Dick Prathers house in Portland and it only worked because it was taken to the Tektronix factory where they had proper spectrum analyzers to look at the center frequency and slopes of the existing bandpass filters. They had to melt the wax out of the tops of the coils to access the tuning capacitors and adjust the tuning of each bandpass by selecting new capacitors of the proper values.

Yes, it was impressive! But the Solid State version would likely work even better.

Mark

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Mikael Christensen
Film Handler

Posts: 13
From: Vejrup, Bramming, Denmark
Registered: Oct 2015

posted 10-20-2015 11:47 AM

Yes I know is is going to be a challenge, but that doesn't scare me [Big Grin]

.
I might compromise, and use filters with ICs.

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99

posted 10-20-2015 03:53 PM

That would make it a whole lot easier...

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Robert Furmanek
Expert Film Handler

Posts: 113
From: Clifton, NJ, USA
Registered: Jun 2012

posted 11-23-2015 01:28 PM

I had a 1954 Fairchild integrator that was restored by Bob Eberenz, Robert Fine's right-hand man. It sounded fabulous and the panning/gain control worked beautifully.

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Gordon McLeod
Film God

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

posted 11-23-2015 01:46 PM

Dion Hansen ex Dolby labs made the solid state unit that replaced the cat 150 cartd it is impressive Also Chase Audio in the US made a card as well

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Robert Furmanek
Expert Film Handler

Posts: 113
From: Clifton, NJ, USA
Registered: Jun 2012

posted 11-23-2015 04:29 PM

Wasn't one of the cards lacking the gain control feature on the 3 channels? That's a very important aspect of the system.

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Mikael Christensen
Film Handler

Posts: 13
From: Vejrup, Bramming, Denmark
Registered: Oct 2015

posted 09-25-2016 12:38 PM

Hi again
How time flies :-), due to busy work schedule.
My Perspecta project was not going so fast, but now I am back with full speed.
I have made a test setup with tubes and IC's in the filter section, and it works so so.......
Overall problem is I need to find out what's inside filter boxes !
There has to be somebody out there, who has some info. about this matter ?

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