We have 15 cinemas, and that means running 15 CD players for between-show background music. CD players can be difficult to keep maintained, and the music from one disc can get a bit stale if you stick around enough.

Question: If one had to loop all 15 cinemas to a multi-disc changer, or to a satellite music source, where can I find a simple decent amplification circuit that would allow me to split low-level audio signals 16 ways or more? I'm doing a test now looping 5 cinemas, but I notice that, the further from the source, the lower the signal level gets. I'd like a decent boost to send the signal via a star configuration to all 15 cinemas plus the lobby and bar areas.

What you want is called a DISTRIBUTION AMP.

They are made by cinema audio maufacturers such as:

SMART (probably the least expensive and most popular though silly construction).

USL (nearly identical to the SMART but a more sensible card cage)

Both Component Engineering and Odyssey Products have a daisy chain method of distribution. The big advantage to these systems is that you don't have run separate lines from a central DA to each sound system. You start at one and go to the next and go to the next......etc until all cinemas are connected.

Lastly, there are Pro audio manufactuers that also make Distribution Amps too. Examples include RANE, BGW and Radio Design Labs plus many many others.

So, in short, there are many maufacturers out there for you to choose from to do exactly what you are trying to do.

Steve

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"Old projectionists never die, they just changeover!"

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Ground loop hums are caused by just that...ground loops. Distribution Amps do take care of the grounding issues since the good ones are indeed transformer out (like the SMART).

Steve

You should see the mess I have to contend with at the radio station....Plug it in one receptical, the audio hums like a hummingbird. Plug it into another receptical that is on the same phase, and it is quiet as a mouse. It drives us nuts! Many times I had to use a distribution amplifier or an isolation transformer to eliminate the ground loops. Our electrical power in that building is so rottin' that we can't fix it without a complete re-wiring of the building.

But yes, a distribution amp is the way to go.

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I was advised to replace the wiring with Belden Special Purpose Audio cable.

If I understand correctly, this new wire will be two pairs of shielded twisted-pairs (4 conductor) and possibly also a "drain" wire. Does this sound right? I haven't actually received my new wire, so I haven't had a chance to examine it yet.

I'm also advised to run the wire through a metal conduit; not running freely through the ceiling and also not PVC.

This cinema complex has been experiencing SEVERE hum in the non-sync ever since the time of installation. They are using an older version of the Smart DA-226. I am using two of the newer ones and they have been trouble-free. If I'm still hearing the hum when I'm done with the rewiring then I'll start to suspect the distribution amp.

I'd appreciate any suggestions you might have. These people should have music. I know they'll be a lot happier with some tunes.

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~Manny.

"The brown acid that is circulating around is not specifically too good."

-- An announcement in the film, "Woodstock: 3 Days of Peace & Music."

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Thanks for the Belden number. I went to their website and I see that they also make a 9451D (Dual) so you won't have to run two of the 9451.

What's your opinion about the computer multiconductor wire being the cause of the hum? These wires are tiny, tiny, tiny!

~Manny.

"They are using an older version of the Smart DA-226. I am using two of the newer ones and they have been trouble-free. If I'm still hearing the hum when I'm done with the rewiring then I'll start to suspect the distribution amp."

Manny, for the older version to which you are referring, are you sure it is a DA-226? We made a model DA-8 which used resistively isolated outputs which is OK but nowhere nearly as good as the isolation provided by the DA-226 transformer isolated outputs.

Steve, the construction may be silly, but it is a fairly inexpensive method which has served us well over the years. The only real problem we had was with the card edge contact fingers not always lining up properly with the motherboard edge connectors. We solved this by routing locating notches in the plug-in cards which positively locate the fingers in the edge connectors.

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Oscar Neundorfer
Chief Engineer
SMART Devices, Inc.

oscar@smartdev.com

Steve

I asked the manager to double-check the model number and it is indeed a DA-8.

Is the hum a "known issue" in this model? In other words, will I be wasting time/money by rewiring?

Also...Where can I get more of the Phoenix connectors for the Smart DA's? Are they generic?

The DA-8 was not particularly noisey in terms of hum, although it could have something wrong with it. Since it used resistive isolation, it was not as good at reducing hum due to ground loops as the DA-226 is with the transformer isolation. Is the hum present in ALL screens connected to the DA-8? If so, the DA-8 could have a problem. A test would be to remove all outputs from the DA-8 except for one and then check that one cinema to see if the hum is still present. If it is still there, then the DA-8 probably has a problem. If not, then there might still be ground loops causing the hum.

The early DA-226 units used a connector made by Entrelec. It is gray in color. The later units used the green Phoenix connectors. We can supply either one you need. BTW, as long as you have the proper mating connector, cards with each type of connector can be used in the same DA-226. If you ever need to order a replacement card for a DA-226 it is a good idea to let us know which type of connector you have. That way we can send you the card that matches your mating connector already attached to your wiring.

If you need actual Phoenix or Entrelec part numbers, let me know. I am home at the moment, so I don't have the numbers here with me, but when I get to work a little later, I can get them for you.

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Oscar Neundorfer
Chief Engineer
SMART Devices, Inc.