Film-Tech Forum ARCHIVE: Sound head light pipe

This is topic Sound head light pipe in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Matthew Taylor (Member # 2310) on 05-15-2004, 04:30 PM:

My projector (Philips FP3) uses a lightpipe to transmit the slit lens light to the cell. Would a light pipe maintain the light separation of stereo tracks so a stereo cell could be mounted on the top of the pipe?

Posted by Mark Gulbrandsen (Member # 72) on 05-15-2004, 07:14 PM:

Is the FP-3 sound head reverse scan? If it uses the light pipe then I am assuming that it is in which case a direct fit stereo cell already exists for this. No need to glue it to the end of the pipe and so on. If its more like the FP-20 repeoducer then a cell may also be available.... A photo would be appreciated if possible!!

Mark

Posted by Sam D. Chavez (Member # 1841) on 05-15-2004, 07:29 PM:

The FP 20 series used a plastic light bar to transmit the light to the mono solar cell (originally a PEC cell). It was front scan but the light was on the base side of the film and the light bar and solar cell were on the emulsion side.

I replaced many of these with stereo cells directly behind the film. I once did a before and after test and found the light bar was attenuating the light by 14 dB.

Now of course, there is a reverse scan kit available for this projector (BACP of course). There is a picture of it on my site, bacpinc.com.

Posted by Matthew Taylor (Member # 2310) on 05-16-2004, 03:35 AM:

It is not a reverse scan. Would the light pipe maintain optical separation?

I am trying to do a home modification on this and use the easiest way possible. It is too difficult to try and mount a cell behind the film.

Posted by Christos Mitsakis (Member # 143) on 05-16-2004, 05:10 AM:

Matthew,
To maintain stereo separation you need two light pipes and two mono cells for the L and R channels, a configuration that (If I am not wrong)Bauer used in the early stereo reverse scan soundhead readers of the B12 projector. With a sigle light pipe, even with a stereo cell you can not achieve stereo reproduction.

Regards,
Christos

Posted by Mark Gulbrandsen (Member # 72) on 05-16-2004, 07:57 AM:

I would first look into Sam's reverse scan kit and see if it'll work out. Send Sam some pictures of it and he should be able to tell you. If it won't fit then a Dolby Cell mounted in there would be the next best way to go. SOmetimes you have no choice but to go to a shop and haev a custom bracket made up. I've done this many times.

Mark

Posted by Matthew Taylor (Member # 2310) on 05-16-2004, 10:26 AM:

Here's a pic of the head with the sound pickup. I doubt whether there is a reverse scan kit available for this old portable!

Posted by Sam D. Chavez (Member # 1841) on 05-16-2004, 11:28 AM:

There are similarities to the FP 20 soundhead, but it is not the same. The best approach is to mount a stereo cell directly behind the film.

I will look and see if I have a cell and bracket around. You need to get rid of the light pipe as it is very inefficient even for mono. I will also ask Larry Shaw of Kinoton about this.

What is the diameter of the sound drum?

Posted by Matthew Taylor (Member # 2310) on 05-16-2004, 11:38 AM:

Hi Sam,

The diameter of the sound drum is 30mm.

Posted by Mark Gulbrandsen (Member # 72) on 05-16-2004, 11:38 AM:

Looks the same as the little small boxy FP-4 t me...... I wonder what the differences between them are....

Mark

Posted by Matthew Taylor (Member # 2310) on 05-16-2004, 11:47 AM:

Mark, is this an FP4? -

Here's a couple of other pics of my FP3