Film-Tech Forum ARCHIVE: Ambiental music

This is topic Ambiental music in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

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Posted by Ariel Vocal (Member # 6912) on 07-05-2015, 05:45 PM:

hello
I recently bought a small amplifier of those used for karaoke, I made a wiring from one point to several rooms to distribute music abmbiental through the amplifier, in these rooms have installed both processors 650 and 750 cp.
at first everything it worked ok, but recently, we noticed that the background music is filtered during the show, for some channels a distorted version of the music that is playing while it is projecting the movie, in another room you hear them noise listening to rhythm of the music being played on the amplifier.

A may be due this ?, the signal is coming with very impedance, or is a grounding problem?

Thanks for your help, greetings!

Posted by Justin Hamaker (Member # 2165) on 07-05-2015, 08:47 PM:

This seems like an obvious question, but do you have the music going through the non-sync channel of you processors?

Posted by Ariel Vocal (Member # 6912) on 07-05-2015, 09:54 PM:

Yes Justin, sorry for not saying in the question.

Posted by Carsten Kurz (Member # 5396) on 07-06-2015, 07:13 AM:

Ariel, your system to distribute the music is probably completely screwed up. You can't simply wire an amplifier's output in analog to multiple booths and expect this to run clean. You have to learn something about proper analog audio distribution.

- Carsten

Posted by Harold Hallikainen (Member # 5405) on 07-06-2015, 10:02 AM:

I'm going to guess that the issue is with driving an unbalanced input with audio that MAY be putting voltage on the shield with respect to ground. An audio transformer in front of each processor input might solve the problem.

Harold

Posted by Gordon McLeod (Member # 33) on 07-06-2015, 10:21 AM:

Ultra Stereo makes a nice music distribution amplifier that can provide isolated outputs to each screen. Also there should be many used Smart ones out there
Component Engineering makes one that is daisy chained and I find it not as nice as I would have liked

Posted by Sam D. Chavez (Member # 1841) on 07-06-2015, 11:56 AM:

Aside from all the aforementioned, the level may be so high it develops a slight voltage on the backplane which leaks into everything else. Seen it before.

You may need to use a resistive voltage divider at the processor end such that you have no more than 300 mVolts hitting the non sync input. Just a guess.

Posted by Marcel Birgelen (Member # 6801) on 07-06-2015, 04:10 PM:

Well yeah, if I read "karaoke amplifier" hooked up to the non-sync input of a sound processor, equal alarm bells go off.

What amplifier output exactly did you hook up onto those non-sync inputs? And how did you hook it up? Did you run a dedicated pair of wires per room or did you daisy chain it? And did you did hook it up in parallel I suppose?

quote: Gordon McLeod
Component Engineering makes one that is daisy chained and I find it not as nice as I would have liked

Daisy chaining analog audio just feels wrong. I guess you want a dedicated output per "subscriber" which you can also regulate per output, not just because you can avoid one device screwing it up for all others, but also because every device in the chain will experience a considerable drop in signal strength, because of the increasing distance to the source.

Posted by Sam D. Chavez (Member # 1841) on 07-06-2015, 07:23 PM:

The CE device worked pretty well on account of matching transformers on the receiving end. Kind of like 70 Volt lines where each speaker had a transformer with taps riveted to the speaker frame so it can only take so much of the power.

Old fashioned but it worked without have to use home runs.