Film-Tech Forum ARCHIVE: Setting Dolby Tone with Dodgy CAT 109

This is topic Setting Dolby Tone with Dodgy CAT 109 in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Matthew Taylor (Member # 2310) on 09-05-2005, 05:12 PM:

I have recently bought a CP-50 but it got damaged during transit from the US. Both meters on the CAT 109 got smashed. The seller is sorting out a replacement card but in the mean time, is there a way of roughly setting up the preamps by perhaps using a multimeter or something like that just until the card arrives?

Posted by Steve Guttag (Member # 268) on 09-05-2005, 05:41 PM:

Snappy answer: Yes

More complete answer:

Connect your meter (preferably an accurate one that reads true RMS) to the test points on the optical preamp (Cat. 108). Red is Left and Green is right...the ground terminal is still on the Cat. 109 though I think they added on for the Cat 108C...can't remember.

Anyway, thread up and run some Cat 69T (Dolby tone) and meaure the tone at the test points, set both to exactly 300mV.

Posted by Matthew Taylor (Member # 2310) on 09-06-2005, 12:10 PM:

Thanks Steve.

Posted by Matthew Taylor (Member # 2310) on 09-07-2005, 10:50 AM:

I did what you said but the minimum voltage I get with the meter set on AC is 1.6v - several times too much I think. To be fair, I couldn't find a grounding point on the cat109 so I grounded the other lead on first the case and then the metalwork of the cat64's. There are 2 meter points on the cat109 - a black and white - should I be using the black?

My 6v cinemacannica exciter lamp is running at 6v. Should I turn this down?

Posted by Sam D. Chavez (Member # 1841) on 09-07-2005, 10:54 AM:

I would bet you still have voltage wthout the projector running as in no ground when you are trying to measure Dolby level.

The black wire test point is the ground. I hope you are not paying too much for a replacement Cat. 109.

Posted by Marin Zorica (Member # 1716) on 12-18-2005, 01:33 PM:

Hmmm one time i got same problem.

With what kind of meter you set 300mV??

Did you use regular multimeter, digital or analog?

Posted by Mark Gulbrandsen (Member # 72) on 12-18-2005, 08:14 PM:

Hi Marin,

Use a true RMS meter for doing this and any other meter read settings. There are many available but they do cost a bit more.

Mark

Posted by Marin Zorica (Member # 1716) on 12-19-2005, 02:40 AM:

How i can know is it thrue RMS?

If i do this with osciloscope what level that would be?

Or can we measure with normal multimeter?

Posted by Gordon McLeod (Member # 33) on 12-19-2005, 11:45 AM:

With a scope (assuming the signal is a sine wave) then measure the peak voltage and the rms is the sine of 45 degrees of it