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Topic: Audio Crackling DSS220 CAT745

Carsten Kurz
Film God

Posts: 4340
From: Cologne, NRW, Germany
Registered: Aug 2009

posted 07-04-2014 05:44 AM

With these videos, I would approach Dolby for a swap of the CP750, it should be under warranty?

- Carsten

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Peter Maddock
Film Handler

Posts: 19
From: Benalla, Victoria, Australia
Registered: May 2013

posted 02-09-2015 07:36 AM

Yesterday we had consistent crackling fro the system. We did get some high resistances between the projector, audio rack and CP750; 20 + ohm. We have run some extra earth cables particularly between projector and audio rack.
Ae appeared to

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Derek Martin
Film Handler

Posts: 12
From: Charlottetown, P.E.I., Canada
Registered: May 2013

posted 02-09-2015 08:41 AM

We fixed a similar sound problem by replacing cat-6 cables and odyssey adapters with aes cable. Our problem started after a neighboring building was renovated and a transformer box installed for it in our parking lot, though that could be a coincidence.

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Dave Macaulay
Film God

Posts: 2321
From: Toronto, Canada
Registered: Apr 2001

posted 02-09-2015 04:59 PM

We had a bizarre site with nasty noise bursts in the server audio - on a schedule! Every evening at 7:40, and a few other times during the day, you heard awful noise for a minute or two if the system was set to play the digital server audio. The noise is on standard time though... it happened an hour earlier after we went off summer time.
No nearby interference source was found: no medical offices or tv or radio stations nearby, no taxi stands, no ham antennae visible...
After relocating the d-a nearer the remote sound rack, installing shielded cat6 cabling for the AES lines, replacing the D-A, even replacing the projector and server... we brought an AM radio into the booth. Tuned to a dead frequency, it squawked up a storm at the same time the film audio went crazy.
A spectrum analyzer showed that a nasty periodic HF burst on the AC line was the cause. No explanation as to why it happens on schedule. The power utility is still investigating: the site has a second (apparently clean) power feed and the digital projection system is now running on temporary cable from a panel on that feed - with no noise problem.

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Peter Maddock
Film Handler

Posts: 19
From: Benalla, Victoria, Australia
Registered: May 2013

posted 02-09-2015 05:36 PM

Thanks Dave. For me a lot of ths seems bizarre having got involved with 35mm and now digital projection at a late stage of life and not much experience with audio.
We seemd to have solved the problem after a number of CP750s were supplied to us originally because of a faulty display screen. It appears we may have had a faulty DB25 input socket on a replacement CP750 which was a reworked unit.
We now have a new CP750, albeit one which was reworked because of a quality issue during manufacture. We have not had any more crackling since this CP750 was installed.

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