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Topic: Exciter voltage DC vs AC ...help?

Paul Vollmers
Expert Film Handler

Posts: 161
From: Sister Lakes, MI, USA
Registered: Jul 2001

posted 05-05-2004 07:43 PM

I'm presantly haveing exciter voltage problems...........if I use AC pwr at 6 volts vs 6 volts DC..........in place of the regular 9 volts DC .....will there be a differance in the sound quality?
This is on an SH1000 stereo cell optical track.
Can differance voltages effect the play back?

Thanks in advance,

Paul

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Sam D. Chavez
Film God

Posts: 2153
From: Martinez, CA USA
Registered: Aug 2003

posted 05-05-2004 08:02 PM

Running on AC will definitely produce a 60 Hz hum in the sound. If your speakers will not reproduce the hum it's not too bad. If you have modern loudspeakers, it will be very noticeable.

AC exciter power supplies are suitable only in emergencies or in Drive-ins where the speakers will not pass anything below 150 Hz.

The reason you can get by with running on AC is because the exciter bulb tends to stay incandescent during the swing from positive to negative so the effect is somewhat minimized.

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Steve Guttag
We forgot the crackers Gromit!!!

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

posted 05-05-2004 09:01 PM

Proper Drive-In exciters are also typically 7.5A rather than the standard 4A versions...again with the larger filliment, there is less hum when running on an AC exciter supply.

Steve

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Paul Vollmers
Expert Film Handler

Posts: 161
From: Sister Lakes, MI, USA
Registered: Jul 2001

posted 05-05-2004 09:27 PM

Thanks for your replies..........however..my question is for low volts say 6 volts inplace of the required 9 volts exciter supply.
Would the lower 6 volts effect the sound pickup, or play back?

Paul

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000

posted 05-05-2004 10:27 PM

Don't forget that all MGM releases will be cyan dye tracks starting at the end of May, and Disney begins conversion this fall and intends to convert 100% by early next year. Now would be the time to consider a red LED reader:

http://www.dyetracks.org

http://www.hollywoodreporter.com/thr/crafts/article_display.jsp?vnu_content_id=1000492312

quote:
MGM and Buena Vista Pictures, the distribution arm of Walt Disney Studios, are opting out of using traditional silver-applicated soundtracks on their film prints in favor of more environmentally friendly pure-dye analog soundtracks.

The moves, announced by MGM on Friday and by Disney today are timed to coincide with the opening of the ShoWest 2004 convention in Las Vegas. The commitment puts the two studios at the forefront of an industrywide effort to eliminate caustic chemicals and conserve some of the water used in the manufacturing and distribution of film prints.

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Lindsay Morris
Expert Film Handler

Posts: 233
From: Darlington, WA, Australia
Registered: Sep 2002

posted 05-05-2004 10:45 PM

Lower voltage will give you lower output from the cell IE less illumination passing thru to the cell.
However running a 9v exciter on 6volts will give you extraordinary long life of the lamp and much less filament sag and thus better overall stereo.
In fact many of the processor makers recommend reducing the exciter volts for those very reasons.
When it comes to running AC exiters the use of the 7.5A lamp is essential in minimizing AC hum as the filament maintains its brilliance thru the AC waveform changes.
A couple of small cinemas where I initially started out had AC exciters and extremely good bass response and you really had to be right up to the bass unit before you could detect any hum from the exciter source using 10v 7.5a exciters.
This is all academic now as with the swing to cyan you will be sunk without switching to the Red light sources be it laser or LED.
Lindsay

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Rick Long
Jedi Master Film Handler

Posts: 759
From: Toronto, Ontario, Canada
Registered: Nov 1999

posted 05-05-2004 11:02 PM

If I understand the question, you are considering using a six-volt supply instead of the usual 9 volts.

Obviously, the exciter will not light up as brightly and, therefore, you will need to increase the gain of the sound system, likely resulting in increased noise.

A second consideration is that the filliament supports act as heat sinks and will draw heat away from the ends of the filliament. This will have the effect of reducing the effictive width of the scanning beam and thus reducing the dynamic range of your reproduced sound.

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Sam D. Chavez
Film God

Posts: 2153
From: Martinez, CA USA
Registered: Aug 2003

posted 05-06-2004 12:52 AM

Well put Rick!

Another way to express it is that you get amplitude compression at the edges of the soundtrack which result in the peaks such as gunshots and other percussive effects sounding mushy. For example a 6dB excursion on the soundtrack results in perhaps a 3 dB excursion from the speaker due to declining light level at the edges.

This is where the reverse scan reader does its best work.

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William Hooper
Phenomenal Film Handler

Posts: 1879
From: Mobile, AL USA
Registered: Jun 99

posted 05-06-2004 02:58 AM

quote:
Don't forget that all MGM releases will be cyan dye tracks starting at the end of May, and Disney begins conversion this fall and intends to convert 100% by early next year. Now would be the time to consider a red LED reader:

Unless you will be running prints with silver tracks, not cyan.

The fidelity of reproduction of silver tracks on red readers was found to be poor enough that the high magenta track had to be developed to support the red readers.

Now that cyan tracks are being issued to support the red readers, the playback of silver tracks on red readers is being touted as "acceptable", which is quite discontinuous with the reasoning needed for creation of high magenta tracks.

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Edward Jurich
Master Film Handler

Posts: 305
From: Las Vegas USA
Registered: Jul 2003

posted 05-07-2004 11:01 PM

Having just put in 2 red readers using current non-cyan tracks, I found the fidelity to be outstanding. You do need the pink-noise loop to set phase and focus, otherwise you'll never get the reader set right.

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000

posted 05-08-2004 09:24 AM

quote: William Hooper
The fidelity of reproduction of silver tracks on red readers was found to be poor enough that the high magenta track had to be developed to support the red readers.

The "high magenta" (magenta+silver) tracks have a cross-mod (XM)optimization density that is nearly the same for both tungsten light and red LED readers, so the tracks are more compatible with the MIX of readers out there now. The old (cyan+magenta+silver) tracks had to be XM optimized for one or the other, so the one they were not optimized for would have more cross-mod distortion.

If you optimize an old (cyan+magenta+silver) track for red LED readers, the tungsten readers will have less "fidelity" (more sibilant distortion). If you optimize the cross-mod of a B&W print silver track for a red LED reader, the old tungsten readers will have less "fidelity".

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Josh Jones
Redhat

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

posted 05-08-2004 04:38 PM

quote: John Pytlak
If you optimize an old (cyan+magenta+silver) track for red LED readers, the tungsten readers will have less "fidelity" (more sibilant distortion). If you optimize the cross-mod of a B&W print silver track for a red LED reader, the old tungsten readers will have less "fidelity".

So what exactly are you getting at? both ends of the scale have less 'fidelity' with one extreme resulting in sibilance distortion, what is left at the other end? A HF rolloff?

Don't worry, I'm just confused...

Josh

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Bruce Hansen
Jedi Master Film Handler

Posts: 847
From: Stone Mountain, GA, USA
Registered: Dec 1999

posted 05-08-2004 05:35 PM

Paul,

If you need a cheep excitor supply try All Electronics ( www.allelectronics.com 1-800-826-5432). They have a couple of switching type supplies that will give you nice clean DC.
Stock # PS-655, 6.5 VDC 5 AMP $11.75 (needs an IEC power cord)
Stock # PS-865, 8 VDC 6.5 AMP $9.50
These are "fixed" (not adjustable). Do not exceed current rating. An IEC power cord is a computer type 3 pin power cord. Shipping not included.

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000

posted 05-08-2004 07:03 PM

quote: Josh Jones
So what exactly are you getting at? both ends of the scale have less 'fidelity' with one extreme resulting in sibilance distortion, what is left at the other end? A HF rolloff?

With an old (cyan+magenta+silver) track, you have to optimize the printing for one or the other to minimize cross modulation (sibilant) distortion. So an old track optimized for tungsten light would play best on a tungsten light reader and have some distortion on a red reader, and one optimized for a red LED reader would play best on a red reader and have distortion on a tungsten reader. With the mix of readers in use today, one or the other would have some sibilant distortion.

"High Magenta" (magenta+silver) tracks optimize at about the same density for both types of reader, and are recommended for the mix of readers in use today.

Distributors like MGM and Disney have already decided that there are enough red LED readers in use to allow complete conversion to prints with cyan dye analog soundtracks, to take advantage of the environmental benefits, and eliminate quality defects from sound redeveloper application and washoff problems.

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Rick Long
Jedi Master Film Handler

Posts: 759
From: Toronto, Ontario, Canada
Registered: Nov 1999

posted 05-08-2004 11:36 PM

Sam D. Chavez said "Well put Rick!"

It should be, Sam, it was only one of the many things you taught us during your brilliant seminars here in Toronto. [Smile]

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