Film-Tech Forum ARCHIVE: Smart Mod VI Humming When Projector Run

This is topic Smart Mod VI Humming When Projector Run in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Demetris Thoupis (Member # 833) on 01-26-2003, 04:22 AM:

One issue for you masterguys.
One of the theaters here in my country has a smart MOD VI processor and it is connected to a stereo solar cell on a Cinemeccanica Victoria 4E projector. When light is being send on the solar cell without film on the projector, even at the lowest level there is humming on the speakers of the cinema. When the projector runs, with no film on, the humming is still the same. No change. It is very disturbing when watching a film because when there is only vocals and no music the humming sometimes overkills the vocals. Any ideas what causes this?
Demetris Thoupis

P.S: I cannot see the new empire theater picture additions even though how long I wait. Is it just me?

Posted by Daryl C. W. O'Shea (Member # 1303) on 01-26-2003, 07:36 AM:

I tested you account. It works fine. Make sure you are using the correct link (January 17th's link).

Posted by Jon Bartow (Member # 241) on 01-26-2003, 07:53 AM:

Demetris,
Sounds like you have a grounding issue to me. Make sure that both the projector and the sound rack are properly grounded.

Posted by Steve Kraus (Member # 476) on 01-26-2003, 10:27 AM:

Are you saying the hum is only there when the exciter lamp is on? With no film in the projector does it go away when you block the light beam?

Posted by Gordon McLeod (Member # 33) on 01-26-2003, 11:08 AM:

Check and make sure you have a well filtered DC excitor supply. If it is AC or poorly filtered you will here the AC current modulating the cell output

Posted by Demetris Thoupis (Member # 833) on 01-26-2003, 02:21 PM:

Yes Steven.
Even if no film is on the projector but the exciter lamp light hits on the solar cell, the humming still exists. I too believe it is a grounding problem but I have not managed to find it. The sound rack should be properly grounded since no humming is heard if the lamp is off or if it plays non-sync. I tried to connect the ground of the projector directly on the rack but still the humming exists. I even attached a wire from the ground (solar cell input) from the processor to the rack itself but still the humming is there. How can I check if the grounding on the projector is ok?

Posted by Oscar Neundorfer (Member # 458) on 01-26-2003, 07:33 PM:

Demetris,

This sounds very much like the exciter supply is AC voltage instead of DC. If there is no hum with the exciter lamp off, then I cannot think of another reason.

Make sure you have a well filtered DC supply for your exciter lamp. In some exciter supplies, the main voltage is DC, but the backup is sometimes AC. If you have an exciter supply like this, check to make sure the supply is not in backup mode which would place AC voltage on the lamp. This will definitely cause hum.

Since the hum is NOT present in non-sync or in film mode with the lamp off, I think this is your problem and not a grounding problem.

Posted by Gordon McLeod (Member # 33) on 01-26-2003, 10:46 PM:

I just did some checking and the standard Vic4 excitor supply is AC only so you need to replace it with a good regulated DC one

Posted by Demetris Thoupis (Member # 833) on 01-27-2003, 07:27 AM:

Where can I get one Gordon?
Does it have to be specifically for projector or can I find one at my local hardware store?

Posted by John Pytlak (Member # 331) on 01-27-2003, 11:28 AM:

One quick way to determine if the hum is coming from an AC-powered or poorly filtered DC exciter lamp supply is to block the light from the cell with a piece of cardboard -- if the hum disappears, the exciter lamp power supply is the source.

Another thing to check is whether stray room light is falling on the analog photocell. Fluorescent lights or incandescent lights (especially on SCR dimmers) will cause hum if they shine on the cell.

Posted by Gordon McLeod (Member # 33) on 01-27-2003, 11:30 AM:

Cinemecanica makes one Smart also has a good regulated one as well

Posted by Mark Maxwell (Member # 1355) on 01-28-2003, 02:12 AM:

What kind of amps do you have. I once worked with a unit that had a Smart modVI processor with Haffler amps. When I comlained about the problem same problem,I was told that the ModVI didn't work well with Hafflers and to go to mono. When that didn't work I was told to fold down the top of the ModVI. Push against the top and then bring it down very carefully. There will be a red switch. Flip it to the other side and run down to see if the buzzing is still there. If not, run with it. It's better to loose the suround verses a loud buzzing sound coming out of the speakers. Do this only if you have time before a public viewing, and if you have Haffler amps. Other amps might do the same, but I haven't dealt with them and don't want to give you the wrong advise. Also, with that ModVI, if you start a movie and it goes back to movie tunes and only plays the movie soundtrack when certain stereo buttons are held down, disconect the wire in the back of the proccesor that is labelled music. You won't have any music between movies, but it's better than having a doorman sit in a chair for 2 hours at a time with his index finger pushing the button labeled "Stereo A".

Posted by Oscar Neundorfer (Member # 458) on 01-28-2003, 06:28 AM:

Mark,

To my knowledge, there is no reason a MOD VI should not work with a Hafler amplifier. If anyone else knows differently, please tell me. As usual, attention has to be paid to proper wiring and grounding practices to kepp hum and other noises out of any given system. So, unless the Hafler has _exceptionally_ high gain (which can mess up the proper system gain structure), there should be no more hum problems with that brand than any other.

As to the problem with the MOD VI going back to MUSIC format unless you disconnect the wire to the MUSIC terminal, you have an automation problem of some sort, NOT a MOD VI problem. The automation terminals to select formats on the MOD VI work just like other processors on the market: a pulse to ground from any format terminal will select that format. It sounds like your automation is holding the music format terminal low, or is randomly pulsing the music format terminal.

NEVER should you have to have someone sit there and hold a button to keep a format selected. If that happens, and you disconnect ALL the format selection wires and unplug any digital player you might have from the MOD VI, and it STILL happens, then there is something wrong with the MOD VI. Please call us at that point, and we will arrange to have the problem fixed.

The only other times a normally working MOD VI will go to MUSIC format on its own is if the AC power has a sudden large increase (spike) or a sudden low line voltage followed by a quick increase back to normal. (This could be a momentary outage or a sudden heavy load such as a HVAC system starting.) The MOD VI logic circuitry interprets this as a power up condition and switches to MUSIC format, which is its normal wakeup format.

Posted by Gordon McLeod (Member # 33) on 01-28-2003, 09:19 AM:

Never had a problem with a Mod6 and any brand of amplifier. That just sounds like an excuse for a shoddy installation
As to format switching as Oscar says any interuption of the power will cause it just like any processor to revert to the wakeup state and that the fact it goes away with the automation unplugged sur says the fault lies outside of the processor
But based on everything said the problem is the excitor supply since it only hums with the excitor on

Posted by Darryl Spicer (Member # 711) on 01-28-2003, 09:29 AM:

This does sound like an A.C. modulation in the sound from the solar cell. However in your original post you state that the projector is running without any film in it. Have you tried to check it without the motor running on the machine.

Posted by Demetris Thoupis (Member # 833) on 01-29-2003, 06:33 AM:

Yes I did try it
And yes the humming (buzzing) is still there. Thanks Gordon for your help. Do you know the price for this thing?

Posted by Gordon McLeod (Member # 33) on 01-29-2003, 09:46 AM:

If the problem is the excitor supply issue call you equipment dealer and they can quote you one