Film-Tech Forum ARCHIVE: CP45 processor buzzing all of a sudden

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Posted by Bernie Anderson Jr (Member # 410) on 11-29-2008, 10:09 AM:

Can't figure this one out. Hope someone can help.

For 5 years, I've been running the same set up at home: Dolby CP 45 with a Jaxlite (Stereo Cell)on a RCA 9050. The amp I'm using is a regular 6 channel external input Pioneer receiver (home theatre type which I'm just using it to amplify the CP45). I'm running JBL Control 5's on the stage and JBL Control 23's for surrounds. I'm using a relay to switch the projector input, so all the switching is through the processor. My exciter supply is a Kneisley black box, but works just fine. I've always had great sound with this little setup and it has always been quiet until recently. All of a sudden, I'm getting a buzz (not an AC hum); a high pitch buzz in from what I can tell is the center channel. I've tried changing the input to projector 2 and it does the same thing. If I remove the input from the processor, the buzz goes away. If the exciter power supply is off, the buzz is still present. If I unplug the Jax lite preamp and have the exciter power supply off, it still buzzes. The buzz even modulates sometimes with the dialog. I've always had dimmers in the booth (Maestro dimmers by Lutron), until recently I installed a Kelmar 2K dimmer. But even when that is powered off I get a buzz. I also have a 3 way dimmer for hi-hat lights installed, but that has been there since day one. The only time the buzz seems to change is if I play with the 3way dimmer or use the Kelmar or light the ORC 1000 lamphouse. It seems to vary from pretty loud to subtle, but the buzz never does away unless unplugged from the processor. The buzz drops in volume from SR to A to Mono, with it being the quietest on Mono (but still present) I've checked all connections, the cell input is right with no wires touching and the terminals on the jax light are pretty tight. The solar cell wire is in its own conduit going directly to the amp rack. L & R wires are double sheilded and they seem to be in pretty good shape and looks pretty dry, unless oil got down into the watertight conduit and started to eat away the insulation. The shield on the cell wire is grounded to the chasis of the soundhead and on the processor side, it is grounded on the chasis of the CP45. Its been this way for 5 years with no problems! Too me, its some kind of grounding issue all of a sudden (unless its inside the CP45, but why all of a sudden? I practically had everything off in the booth as much as I could while still being able to run and still is present. Even the lamphouse seems to be affecting it now, which it never did. Any thoughts? By the way, the A-chain is perfect, I just did it, but I had the amp off when I did it, so I didn't hear the buzz.

Posted by Mike Babb (Member # 1379) on 11-29-2008, 10:35 AM:

I wonder if this is something Louis clued me in on one day, the main board flexing down and making the tiniest bit of contact with the top of the noise reduction card?

Posted by Bernie Anderson Jr (Member # 410) on 11-29-2008, 10:41 AM:

You're talking about the Cat 511 coming in contact with the SR/A card underneath it, right? I'll check it.

Bernie

Posted by Mike Babb (Member # 1379) on 11-29-2008, 10:53 AM:

I don't have board numbers but that's probably correct, you just flex the board up a little and see if the buzz goes, it did in my situation

Posted by Bernie Anderson Jr (Member # 410) on 11-29-2008, 11:09 AM:

Nope, didn't work. But alittle more info, the buzz gain is affected by turning the volume up and down and is only present on analog projector inputs. Its not on there for external, mic or non sync.

I also noticed that the LED Output indicators light up to indicate the buzz as an actual signal output and the LEDs will decrease as you fade the volume control down.

Posted by Pete Naples (Member # 761) on 11-29-2008, 12:09 PM:

Check your wiring thoroughly, a ground may have come adrift.

Also check earthing in the AC supply to the equipment, perhaps something has come adrift there?

Posted by Tony Bandiera Jr (Member # 2365) on 11-29-2008, 01:43 PM:

I think you have one of three possible problems, in order of likelyhood:

1: Optical preamp board (CAT 514)has a fault;
2: Your SR/A card has a problem;
3: Power supply in CP-45 going bad.

To experiment: in MONO mode pull the SR/A card and see if the buzz goes away, if it does and you can still get sound otherwise then the SR/A card is most likely bad.

IIRC the optical preamp board can be "turned around" so that if one side fails it can still run with the other, but it's been a long time since I dealt with the CP45....

Posted by Demetris Thoupis (Member # 833) on 11-29-2008, 02:19 PM:

Is it a buzz or is it a high frequency hiss that you are hearing. If you are hearing a high frequency hiss then maybe you are passing your readers' wire along the speaker lines or other line level wires in your rack (tied together) cables with poor insulation do have this effect in high volumes in the CP as far as I know. Try to separate the cables or even replace them with a good quality twin balanced cable. That is if you are having a hiss. Also of course the usual reseat the cards e.t.c
Demetris

Posted by Monte L Fullmer (Member # 2797) on 11-29-2008, 02:58 PM:

Would that "Jaxlight" thingey be doing a weak, to open contact in this buzz situation?

Since using Jaxlights, the preamp has to be cranked up more than if used the old exciter lamp setup and with preamps being cranked up, more noise can come into the circuitry.

Did someone crank up the preamp circuit if doing Dolby Tone level settings?

Posted by Bernie Anderson Jr (Member # 410) on 11-29-2008, 04:54 PM:

So far to date:

I wired in a new cell input figuring that maybe oil was eating away the rubber insulation (it wasn't), From the new stereo cell to a new preamp, to a new cable with isolated 2 pair conductors to the second projector input. Its all new. Still getting the buzz. Yes, it is a buzz. I know what you're saying by a high freqency hiss, this is different and present even at low volume. This is similar to a sound that a dimmer makes while its dimming. I had the new cell wired outside of the projector as a test before I installed it, and it had no buzz at that point. The minute I put it in the projector, I get the buzz back. In the meantime, I took out each board and they all looked good. I reseated them and tested with a reel. It was decoding just fine, but with the buzz and it only seems to be coming from the center channel, at least the stage speakers. Surrounds are just fine minus a slight amplification hiss.

So to sum up what I did, I reseated the boards, buzz still present, I wired in an entirely new cell with new jax light preamp, buzz still present. Each step along the way of wiring the new cell, I stopped and checked for buzz. There was no buzz until the new cell was in the projector and everything was on. I didn't change the original jaxlight. Prior to the cell being in the projector (Just hanging outside the projector), the pickup was working with no buzz. Grounding issue?

I tried grounding the CP45 from the grounding spade on the back panel to the AC box, I would get a major hum and buzz. If it is a ground loop, where do I start?

"Did someone crank up the preamp circuit if doing Dolby Tone level settings? ". I'm not sure of the question. I did touch up the A-Chain using a scope and a RTA. The Dolby Tone on the scope was dead on and azimuth was right on. I was achieving a flat response all the way to 12.5k on both channels. I ran dobly tone and set levels. Now I had to turn both input pots about 2 full turns to achieve proper level.

The other thing I noticed in the wiring diagrams was that pins 1,2 and 4,5 are used for wiring L & R + & - . On the CP 500 I know we use pins 6 & 9 for shield. On the CP45 diagram it says shield soldiered to body of connector. Well 1) can you use 6 & 9 in the case of a CP45 and 2) when I attach the sheild to the body of the connector, I get major noise, hum, etc.

Posted by Monte L Fullmer (Member # 2797) on 11-29-2008, 08:07 PM:

quote: Bernie Anderson Jr
Now I had to turn both input pots about 2 full turns to achieve proper level.

..did you have buzz before you turned these pots up on the preamp card?

Also, I had a similar situation where I had a 5 Star with only a 4 conductor going from the reader to processor (CP55). This wiring had both minuses were tied together. I figured that with both minuses tied together, my output from the reader was cut in half.

Thus, I completely removed that 4 couductor and installed 6 conductor with shield to where I isolated the minuses. Then I ran my CAT69 Dolby Tone loop and my gain was tons higher due to separating those minuses where I had to really crank down the pots on the preamp card to Dolby Level and got rid of my buzz in the same time.

How old is that Jaxlight unit? LED could be getting weak why you have to crank up the preamp..

Posted by Louis Bornwasser (Member # 3063) on 11-29-2008, 08:54 PM:

Besides the Jax lite, which should be replaced, the only thing I am questioning is the grounding of the soundhead to the cell shield. Typically this causes much hum/buzz. Louis

Posted by Demetris Thoupis (Member # 833) on 11-30-2008, 01:02 AM:

Did you try switching the jaxlight on without the projector running and any film on the projector? Try it and raise the CP volume up to see if you still have the buzz or if it is happening only when power is applied on the projector. On the other hand, try and connect the centre channel pre out to the left channel of your pioneer amp to see if the problem moves to a different channel or if it stays in the centre channel again. If that happens then perhaps your amplifier unit has gone bye bye. Are you powering up the Jaxlight with a DC transformer? If so it might be wise to wire the 0V cable also to the chassis ground of the projector. If you think that the problem is only in the centre channel it would seem logical that there is an issue after or inside the CP but try those things out and get back to us.
Demetris

Posted by Gordon McLeod (Member # 33) on 11-30-2008, 08:00 AM:

Look at the output of the Jaxlight preamp and see if the noise is there with a scope
If so I would suspect that the powersupply for the Jaxlight isn't filtering properly

Posted by Bernie Anderson Jr (Member # 410) on 11-30-2008, 11:07 PM:

I've taken everyone's comments into consideration. It seems to be some kind of ground issue. I thought first that maybe because of a fading LED, the inputs were too hot and they were just giving me alot of noise by being almost maxed out. I put a new LED in with a new preamp, I did get the signal to go into the processor at a less considerable rate. I figured that would do it. NOPE! So I played around with the wiring on the cell, when I thought I had the cell running pretty quiet, I'd come back about 40 mins later to run another reel and the buzz would be back again. I discovered by accident that possibly a AC switch was the culprit. I ran a ground from this switch to all the grounds in the trough. It helped. But what I'm getting now is an intermittent buzz that seems to be affected by anything electrical. I can get it to be quiet during a reel and when the projector is off, but if I light the lamp, close the masking, close the curtain, turn a switch on or off, I get buzzing, popping, etc. Any kind of electrical contact closure will set it off. Its really becoming annoying. Its intermittent and everytime I think I got it, something seems to set it off again. This is a buzz, not a hum, but I'm sure it has something to do with grounding. Any thoughts? What should the proper wiring be for something like this? Do you have these problems with Reverse Scans?

Posted by Monte L Fullmer (Member # 2797) on 11-30-2008, 11:45 PM:

quote: Bernie Anderson Jr
Do you have these problems with Reverse Scans?

I have both the BACP RSTR-20 and the CE-40 units and no problems with these two units at all. I did have one Kelmar unit fail, but that was in the power supply unit, not the reader itself along with some of the LED arrays starting to fail.

As I mentioned above in an earlier post where my problem was attached to a BACP reader, which was the wiring connections, the readers themselves are absolutely bulletproof when they come to having problems.

I'd fully recommend replacment to reverse scan readers if budget conditions allow.

-Monte

Posted by Eric Robinson (Member # 2966) on 12-01-2008, 09:04 AM:

quote: Bernie Anderson Jr
I had the new cell wired outside of the projector as a test before I installed it, and it had no buzz at that point. The minute I put it in the projector, I get the buzz back.

THIS....is a very important piece of evidence.

This would tell me that the projector sound head is introducing the buzz.

Additionally...you said that the projector sound head had a ground connection from the CP45 to the head. Perhaps you could try using a 14g or heavier wire to connect the sound head frame to the rear spade ground terminal of the CP45 (just a temporary loose wire). In combination with that, you could try lifting the ground on the audio wire on the processor side first, then reattach. Then try lifting the audio wire ground on the sound head side.

Posted by Demetris Thoupis (Member # 833) on 12-02-2008, 02:15 PM:

I too believe that you should change to a BACP one. It rocks!

Posted by Bernie Anderson Jr (Member # 410) on 12-03-2008, 04:52 PM:

I think I got it figured out. I talked to a friend about it. The first thing he asked was if the solar cell wire is in its own conduit. It is. He asked if the water tight tube that goes from the wall to the projector was metal lined. It wasn't, the original one was just rubber. He suggest that I replace it with a metal lined tube and ground the conduit to earth ground, this way the whole separate conduit would act as an extra shield for the solar cell. The way he explained it is, the jaxlite and wire were acting as a big antenna and picking up everything and amplifying it. I changed out the tubing, the buzz was gone, quiet, but I was still getting pops whenever a switch was thrown or the masking moved. I now grounded the Processor to an earth ground (in the past, that would make it worse), I made sure that the shield connections to the projector and the processor were tight. That seems to have done it. I don't hear any buzzes or pops anymore. I'll run something else tomorrow to see if its still good. But what I can't understand is, why would it change so drastically after all these years?

Posted by John Hawkinson (Member # 1135) on 12-03-2008, 05:10 PM:

Well, a ground reference changed.

Maybe someone else in your building installed a new piece of equipment. Maybe your neighbors drove a new ground rod. Maybe somebody nearby started drawing a lot more current through the ground. Maybe it rained and the soil resistivity changed. Maybe the power company changed out an upstream transformer.

Or maybe someone fired up a new radio station (or swapped out an antenna with a different pattern), or a TV station added a new DTV transmitter in anticipation of Feb, 2009.

--jhawk

Posted by Eric Robinson (Member # 2966) on 12-04-2008, 12:53 PM:

Good job figuring it out Bernie. It looks like my advice was a little astray.

The solution has also provided valuable information for those who may have a similar problem in the future.