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Topic: Buzzing

Kevin Wheat
Film Handler

Posts: 5
From: College Station, TX 77840
Registered: Jul 99

posted 03-23-2000 10:24 AM

Several of our auditoriums have developed a buzzing that I can't seem to locate. It is not in the amps. We recently made the conversion to Jax lights,which were wire wrong originally, but they were to have been fixed by our tech. The buzzing is constant through the movie and nonsync. Any suggestions would help.

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000

posted 03-23-2000 10:44 AM

Start with the speakers that have the buzzing and work your way back:

Are all channels affected?
Is the buzz 60hz?
Does it vary in loudness as you change the fader?
Is is a smooth hum (sine wave) or raspy (clipped or distorted)?
When exactly did the buzzing start? (e.g., immediately after the Jaxlight wiring problem?) Any chance the Jaxlight power supplies were damaged during installation, putting some AC ripple on the line?

My guess is that you have a ground loop somewhere, perhaps when someone changed the wiring during the Jaxlight installation. Since the buzz is also in nonsync, it's probably somewhere in the processor, or between the processor and the power amps.

------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Professional Motion Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 03-23-2000 11:16 AM

The big question list
What type of processors, amps, monitors do you have

When trouble shooting it is a good idea to break the problem in the middle so listen to the monitor and
a determin which channel (s) the buzz is in and also switch between amp and processor out and look for a difference
If it is only on amp out look at the amp connections
Most likely it is on both since my gut reaction is it is the shield on the cell cable
The Jax lite has a little preamp that mounts in the soundhead and that is where the fun starts
1q try unhooking the cell input from the processor and see if it goes away
yes it is in the jax hookup if no try the nonsync input

If in the jax check that the shielded cable is not terminated at both ends. It should only be terminated at the processor!
Also try reversing the input power connection to the little preamp and also isolate it from the soundhead casting
If you have a Mod2/3/4/5 processor from Smart UltraStereo has a post on there web site as does smart regarding special hookup instructions
goodluck

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Joe Redifer
You need a beating today

Posts: 12859
From: Denver, Colorado
Registered: May 99

posted 03-23-2000 03:27 PM

Just an odd question: How can a Jaxlite be wired wrong? From the ads I gathered that you just plop 'em in like an exciter bulb and do an A-chain.

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Richard Hamilton
Phenomenal Film Handler

Posts: 1341
From: Evansville, Indiana
Registered: Jan 2000

posted 03-23-2000 10:16 PM

I found one problem with the Jaxlight is the fact that the polarity is not marked on the input from the existing exciter supply to the preamp power supply. I have always wondered why the power input on the Jaxlight preamp doesnt matter what the polarity is. The first one that I installed, I had a terrible buzzing noise and the only fix was to switch the exciter power supply from DC to AC.

Rick

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David Johnson
Film Handler

Posts: 54
From: Melbourne Vict Australia
Registered: Oct 1999

posted 03-24-2000 02:48 AM

With an open sound head such as a Kinoton, AC light from the room or light reflected from the porthole can give rise to quite a loud hum. The problem is even worse if a "Jax lite" is fitted as the light output from the LED is much lower than the old exciter lamp hence the need for the small preamp. This system will increase the signal to noise ratio.
David

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000

posted 03-24-2000 05:32 AM

David ---

The possibility of picking up room light (especially flourescents or lights on an SCR dimmer) by the solar cell is worth checking. I forgot the need for additional amplification with the JaxLight, which would make it more sensitive to stray light. The quick check to see if this is the part of the problem would be to turn off the room lights. But it doesn't explain why the buzz also occurs in nonsync too. I still suspect a ground loop caused when the wiring was changed to install the JaxLight.

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 03-24-2000 10:39 AM

The preamp that comes with the jax lite has its own bridge rectifier in it so that it will work on ac or dc supplies
The usual culprit is iether the shild terminated at both ends or the ground of the excitor lamp powersupply versus the input dc to the preamp as that can also create a loop

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Jesse Skeen
Phenomenal Film Handler

Posts: 1517
From: Sacramento, CA
Registered: Aug 2000

posted 09-14-2000 02:39 AM

The hearing-impaired systems can cause noise in the sound system too; this was a common problem at the theater I used to work at. If your theater has these, try re-aiming the antenna or turning the system off and see if the noise goes away. I found a buzzing problem at the theater I just started working at; turning off the hearing-impaired transmitter helped but the noise did not go away completely, I'll have to play with it some more next time I'm there.

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Greg Pauley
Expert Film Handler

Posts: 173
From: Huntington, WV, USA
Registered: Jun 2000

posted 09-14-2000 10:09 AM

9 times out of 10 this is a ground loop problem. Check your grounds first.

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Scott Norwood
Film God

Posts: 8146
From: Boston, MA. USA (1774.21 miles northeast of Dallas)
Registered: Jun 99

posted 09-14-2000 10:20 AM

I don't know about Jax lights, but with regular exciter lamps it's worth checking to make sure that someone didn't accidentally flip the exciter supply switch to "AC/Emergency"; this would cause a 60Hz hum...not sure if this is a problem with Jax lights.

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Pat Moore
Master Film Handler

Posts: 363

Registered: Mar 2000

posted 09-14-2000 10:22 AM

Assuming this is not a new problem that suddenly started last week, this kind of troubleshooting is a pain and can be tedious. All the above are good suggestions. Some others:

Since the buzzing is present at all times (both film and non-sync), it's probably not anything in the projector A-Chain. Something is getting into the preamp or power amp input. Check other sound formats -- is it the same "buzz" in analog and digital? Any more prevalent in stage channels than surrounds? This will give you some paths to follow. Problems in one or two channels might indicate a wiring and/or ground and/or component problem. If it's "everywhere" there's an external noise source that needs to be isolated.

With everything powered up, start turning things off to isolate the source. Dimmers are a real obvious source -- be sure to de-power them, not just dim them down -- same for aisle lights and such if their transformers are in the booth. Are there neon signs? Is air conditioning running full time? Booth monitors occasionally cause some problems, as well as non-sync sources, etc.

You need to be a bit of a detective and have a little patience. I know of one instance where noise was finally traced back to speed controls for overhead fans -- NOT an AMC Theatre, by the way. Good luck.

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John Walsh
Film God

Posts: 2490
From: Connecticut, USA, Earth, Milky Way
Registered: Oct 1999

posted 09-14-2000 11:11 AM

This is probably not it, but we had a big problem with the filaments buzzing in the light fixtures. Also, at another place, no one noticed the electrictian ran the theater lights and speaker wires in the same conduit.

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000

posted 09-14-2000 12:37 PM

SCR dimmers are notorious for generating "hash", as they essentially work by "chopping" the sinusoidal AC power to the lights being controlled. The harmonics can extend into the RF spectrum (e.g., the buzz picked up by an AM radio in a location with SCR dimmers). Extraneous light shining on the solar cell pick-up, or just the "hash" picked up by low level audio cabling and being amplified, can result in hum or buzz in the sound.

------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com

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Aaron Sisemore
Flaming Ribs beat Reeses Peanut Butter Cups any day!

Posts: 3061
From: Rockwall TX USA
Registered: Sep 1999

posted 09-14-2000 03:12 PM

Slide projectors are another culprit for nasty untraceable hummmmmmms... Hell, I can hear the slide projectors in the TELEPHONES at one of our theaters

Aaron

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