Film-Tech Forum ARCHIVE: DMA8Plus Sound popping issues

This is topic DMA8Plus Sound popping issues in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=16;t=001616

Posted by Peter Clay (Member # 7844) on 08-30-2013, 06:48 AM:

Hi,

I volunteer as a projectionist for a tiny little one screen cinema in Alderney in the Channel Islands. We have just made the move to Digital and we are having issues with sound dropping out during screenings. I'm pretty sure I know what the problem is it's just trying to get the other volunteers to agree and what the best action to take, so here is all the information of what actually happens.

Whilst the film is playing every now and then we will get sound pops and clicks or even the sound dropping out all together but only for a second or 2 then it comes back on (it did happen the other day for just over 3 secs which was quite worrying). it Also happens when the auditorium lights are switched on or off, and also when the lights are turned on or off in the projection box.

Now the problem here in Alderney is the electricity supply on the island is pretty shoddy and it can range anywhere from 210 volts up to as high as 270 volts and it's not steady. I have noticed when you turn the lights on or off the lights on the DMA8Plus processor go out for a second which is why the sound goes and I believe that when the sound pops during a performance there must be a power surge or something as the lighting circuit is the same circuit as the plug sockets which is what I believe is causing the problem.

I have tried explaining this that we need a separate circuit for the lighting or the plugs but it's difficult here to get someone to sign off on it as it is a volunteer run cinema with trustees and we then need to get the landlords permission to start changing the electrics etc.

what they want to do is get a UPS system which I think would be a good idea anyway to protect the projector from these power surges but nobody can decide on what type to get and that is why I'm posting here to see if anyone here has any ideas on what type of UPS to get, as someone already went and brought a surge protector but all that does is switch the power off completely when it detects a surge which is no good in the middle of a performance as the projector will just switch off.

Thank you for taking the time to read this and I hope it makes sense and isn't to much rambling

Peter Clay

Posted by Carsten Kurz (Member # 5396) on 08-30-2013, 07:21 AM:

What type of projector and server do you have?

Seems a UPS would be a good idea. One would have to think about the proper type/technology and UPS settings to get away with these conditions. I know that the APC SmartUPS have these settings, e.g. configurable thresholds.

You should get a qualified electrician in and let him analyse the situation and wether more/new lines would improve the situation.

- Carsten

Posted by Tony Bandiera Jr (Member # 2365) on 08-30-2013, 12:30 PM:

Carsten is correct but I must "disagree" with him on two key points:

1: Avoid APC UPS!! They have gone WAY down in both quality and reliability since they were bought out by Schneider Electric. I suggest Tripp-Lite or Middle Atlantic instead. Both have proven very reliable over the long term. (And a 1500va or 2200va size is more than adequate to protect the projector's electronics [for those projectors like NEC or Christie that allow a separate UPS connection] and your DMA8plus.) You would select the "240volt" models.

2: A separate or additional circuits installed will NOT do anything to eliminate the problem. If the incoming power is bad, more circuits will NOT "clean it up." That said, it still would be good for an electrician to look at the circuit situation and get the lighting off of the plugs circuit.

Your ONLY real solution is to put the projector electronics, DMA8plus AND cinema sound processor on the UPS.

Do it soon as the power variations you described are very bad for the equipment.

Posted by Peter Clay (Member # 7844) on 08-31-2013, 01:34 AM:

HI guys

Thanks for the advice. I'm showing Monsters U tonight so I will get all the model numbers of the projector and sound processors etc to see what type of UPS rating would be big enough to power them.

I'm trying to convince the others here that we need to get an electrician in as I know a couple over here who do a service where they fit something to the incoming distribution power board that helps to regulate the power, like I said the power on this island is pretty shoddy (very small island, only 3 miles by 1 mile with an oil/diesel powered power station and only about 1500 residents).

again thanks for the advice

Pete

Posted by Marco Giustini (Member # 4544) on 08-31-2013, 05:17 AM:

Maybe you should consider an "online" UPS which will not just filter but recreate a full sinewave out of the mains. If you have frequent spikes and drops sounds like a necessity to me. Digital Cinema parts are expensive, the price of a good UPS will repay itself over time

Posted by Louis Bornwasser (Member # 3063) on 08-31-2013, 06:52 AM:

IREM (the same guys who made the 35mm rectifiers) are also in the business of power regulation. Small and large are available. I saw a regulator for an African hospital at the factory that was a 240v 3 phase model for 1000 amps. Louis

Posted by Peter Clay (Member # 7844) on 08-31-2013, 11:49 AM:

Hi,

OK I'm at the cinema now and here is the equipment we have.

NEC NC900C-A
DMA8PLUS
CP65 sound processor
QD 4960 Quad Amplifier

the dma8plus cp65 and quad amplifier are in a couple of double plug sockets and the projector is wired direct to its own rocker switch but I couldn't say if that's a different circuit or not.

as I said before when you turn the light switch on in the projection box I notice the (pcm) and (discrete) lights on the dma8plus go out for a second which is when the sound drops, but it also happens sometimes during a performance when nobody has turned any of the lights on or off making me think that must be when we get the power spikes.

thanks for your time

Peter

Posted by Gordon McLeod (Member # 33) on 08-31-2013, 12:19 PM:

Putting a TVSS on the mains would also be a good idea

Posted by Marco Giustini (Member # 4544) on 08-31-2013, 04:11 PM:

Do you have an IMS in the NC900? How's the sound connected to the DMA8plus?

Posted by Peter Clay (Member # 7844) on 09-01-2013, 03:03 AM:

When you say IMS do you mean the actual sever that holds the films etc. if so then yes. From what I can tell the DMA8PLUS is connected by what looks like an Ethernet cable coming from a port on the projector that says AES above it to an adapter like cable which goes into the DMA8PLUS.

Here is a link with the info of the projector with images of the connections

http://www.nec-display-solutions.com/p/uk/en/products/details/gallery/dp/Products/DCP/Current/DCPDLP-NC900C/DCPDLP-NC900C.xhtml?cat=DCP&realm=products%2Fchoice

Thanks
Peter

Posted by Marco Giustini (Member # 4544) on 09-01-2013, 03:53 AM:

I have seen issues with Doremi IMB/IMS (the manufacturer of your Integrated Media Server - IMS) when using ethernet cables for sound. Exactly as you describe. The solution was to use a very short ethernet cable - say 0.5m - and then use an adaptor to a proper AES cable to the DMA8plus.
An UPS is always a good idea, but I would not ignore this point. You can ask your installer to send you a cable and do a quick test just laying the cable on the floor.

Posted by Carsten Kurz (Member # 5396) on 09-01-2013, 06:24 AM:

Well, the NC900 will allow you to operate the whole projection chain through a UPS. Amps would be the only exception. Normally, projectors/lamp houses are not operated through UPS because they need too much power, but the NC900 allows it. You would probably need a UPS in the 2kVA range, which is not too expensive, but will in the long run save your projector.

I am a bit familiar with supply conditions like this in rural areas of Ireland, my brother-in-law works as an electrician there and he repairs and replaces a lot of domestic gear after voltage drops and spikes.

Don't wait too long.

- Carsten

Posted by Peter Clay (Member # 7844) on 09-01-2013, 07:37 AM:

quote: Marco Giustini
I have seen issues with Doremi IMB/IMS (the manufacturer of your Integrated Media Server - IMS) when using ethernet cables for sound. Exactly as you describe. The solution was to use a very short ethernet cable - say 0.5m - and then use an adaptor to a proper AES cable to the DMA8plus.
An UPS is always a good idea, but I would not ignore this point. You can ask your installer to send you a cable and do a quick test just laying the cable on the floor.

Looking at what we have the Ethernet cable is about 2 meters long which then goes into the adapter you describe so should I just get a shorter Ethernet cable and move the DMA8PLUS a bit closer and try that?

quote: Carsten Kurz
Well, the NC900 will allow you to operate the whole projection chain through a UPS. Amps would be the only exception. Normally, projectors/lamp houses are not operated through UPS because they need too much power, but the NC900 allows it. You would probably need a UPS in the 2kVA range, which is not too expensive, but will in the long run save your projector.

I am a bit familiar with supply conditions like this in rural areas of Ireland, my brother-in-law works as an electrician there and he repairs and replaces a lot of domestic gear after voltage drops and spikes.

Don't wait too long.

- Carsten

The guy who installed the projector has sent us a link for some UPS that should be upto the job they're about 2200VA but he said we would only put the projector on it as the DMA8PLUS and amps etc would be to much for it and we would get a seperate surge protector for them, does that sound about right? We've got an electrician coming next week so hopefully we will get everything sorted soon.

Thanks for all your help.

Peter

Posted by Carsten Kurz (Member # 5396) on 09-01-2013, 09:24 AM:

DMA8 does not consume much. CP65 the same. These should be powered from the UPS as well as the NEC.Not the amps, though.

The NEC is rated around 1kVA, DMA8 + CP65 may add another 10%, so 2000kVA is completely sufficient. You shouldn't buy the first UPS you come across, though, there are differences and some models may cope better with your conditions than others. It should at least be line-interactive, not a simple switching UPS.

I would think that other businesses in your area will have UPS like this in operation as they are potentially suffering from the same line conditions - maybe you can ask around for experiences with specific models and sources?

- Carsten

Posted by Marco Giustini (Member # 4544) on 09-01-2013, 11:28 AM:

Well, 2 metres is not a massive lenght. What I know is that when using 5-10m long ethernet cables as AES cables, the Doremi give trouble. Cannot say for sure whether 2m is enough to give you trouble or not.

If you go for a UPS, listen to Carsten, do not buy the first UPS on the shelf, at least line interactive, but if your budget allows it, I'd go for an online model.

Posted by Pete Naples (Member # 761) on 09-01-2013, 03:36 PM:

is this Ethernet cable shielded? (metal connector shells)

Posted by Carsten Kurz (Member # 5396) on 09-01-2013, 04:40 PM:

I don't think any AES cable/shield issues would cause this:

quote: Peter Clay
I have noticed when you turn the lights on or off the lights on the DMA8Plus processor go out for a second

No matter what quality the cable is, the signal is still symmetrical/balanced.

- Carsten

Posted by Ian Freer (Member # 1940) on 09-03-2013, 05:58 AM:

I have recently noticed similar issues in a couple of new installations.
Servers in both cases are GDC SX-2000AR.
Both have Dolby DMA8+ adaptors.
One projector is NEC NC-2000, the other is NEC NC-3240

I thought it may just be a weird incompatibility between the GDC's and the Dolbys, but if the original poster here has the Doremi/NEC IMS unit then that rules out the GDC...

Unfortunately, plugging the DMA8+ into a UPS does not resolve the issue (for me at least). I have a current support query open with Dolby, but have not had a chance to get to site recently to check on things.

In both cases I am using the 10m Shielded Cat6 supplied by GDC.
It is probably unrelated, but both cases are film festival venues where we have kept reel-to-reel 35mm installed for archival requirements. One site is a CP65/DA20, the other a CP650.

Dolby have suggested trying a shorter Ethernet cable and also checking for high impedance of the earthing between the audio rack, server and projector.

In one venue the projectionist noticed what was happening and worked out if they leave the lights etc in the booth alone, it is fine.
In the other venue, it seemed to be also be caused by actions outside of the projection room, so it was essentially un-controllable as it is a large theatre with many staff, so we've pulled the DMA8+ for now until we get to the cause of the issue.

Once I have had a chance to get back to one of the sites to check the earth impedance, and maybe make myself a long audio cable so I can try a shorter ETH cable, I'll report back, but that will be a week or two away yet.

Cheers,
Ian

Posted by Steve Guttag (Member # 268) on 09-03-2013, 06:49 AM:

For yucks...I'd try a real AES cable in one site to prove/disprove the cable theory. CAT cable is "compatible" with AES though the impedance is in the lower part of the approved range. Proper 110-Ohm cable will rule that out.

Posted by Pete Naples (Member # 761) on 09-05-2013, 11:17 AM:

That's exactly what I was getting at.

I've had a similar problem, site was getting drop outs every time a light switch was thrown, film tower switched etc. The cable in use was the very common green stuff from Canford, which whilst being 100ohm twisted pair, has an overall screen.

I switched to a 'proper' AES cable, 110ohm twisted pairs individually screened. End of problem.

Posted by Steve Guttag (Member # 268) on 09-05-2013, 11:35 AM:

Odds are, this is indicative of another issue (grounding) and the proper AES cable covered it up. With proper AES cable, one has screens over each pair and an overall...plus the impedance is going to be spot on for maximum signal transfer.

Posted by Harold Hallikainen (Member # 5405) on 09-05-2013, 12:12 PM:

I am surprised people have as much trouble as appears to be the case with cables. I believe the characteristic impedance of the cable has to match the terminating impedance, 110 ohms for AES/EBU and Ethernet, to prevent reflections, which distort the signal waveform. Shields prevent electrostatic coupling of signals into the cable (capacitive coupling) but do not prevent I ductive coupling due to magnetic fields. In either case, the coupled signal is coupled equally into the two conductors of the twisted pair. The transformers at each end of the cable SHOULD reject this common mode signal.

Shields can introduce ground loop problems. I like using cat5 cable for AES/EBU, but you need to do what you need to do!

Harold

Posted by Pete Naples (Member # 761) on 09-05-2013, 02:23 PM:

In all of the hundreds of screens I've installed, that was the only time I've ever had such an issue.

The place was really rather badly wired, so it wasn't really a great surprise. Steve I'm sure you're right about the grounding, but I wasn't about to waste time finding wiring issues for the owners to simply refuse to do anything about it. I'm merely making the point that in the OP's venue, it's worth trying.

Posted by Steve Guttag (Member # 268) on 09-06-2013, 01:12 AM:

CAT 5 (or 6) is not 110-Ohm cable...it is in the 100 and under range. We have taken another approach too...when we use CAT cable, we often use skew free. The type we use also has an impedance in the right AES range, all cables are the same length so there shouldn't be any timing issues between the channel pairs...and the cable color (Maroon), is unique enough that it is quickly spotted compared to any other CAT cables in the system. Thus far, NONE have given any issue. That said, I'll still use proper AES cable for more critical installations or where the CAT cable could be nestled in with noise. Proper AES cable has NEVER failed me either.

Posted by Peter Clay (Member # 7844) on 09-07-2013, 09:16 AM:

Hi thanks for all the info. The guy that installed it is going to send us over another cable to try out so hopefully we should start to get things sorted.

Luckilly we normally only do two showings of each film a week during the summer months and now we are moving into winter so we only do the two showings every two or three weeks.

For instance we showed "Song for Marion" on Thursday and again this Monday, then the next film we will have is "The Wolverine" on Thurs 26th Sep and Mon 30th Sep. So at least the projector isn't getting hammered all the time.

Pete

Posted by Carsten Kurz (Member # 5396) on 09-07-2013, 10:29 AM:

Can you tell us which indicator lights on the DMA8+ go off when switching booth lights?

- Carsten

Posted by Peter Clay (Member # 7844) on 09-07-2013, 12:02 PM:

Hi Carsten,

The lights that go out are the "PCM" and the "Discrete" lights. All the other lights seem to stay on it's just those two.

Pete

Posted by Carsten Kurz (Member # 5396) on 09-07-2013, 12:28 PM:

I won't step away from the UPS suggestion for your location, but in that case the popping might indeed be solved by improved AES cabling and/or cable routing.

Try to get ethernet cable with individual shielded pairs and proper braided common shield. These are not expensive, you could buy two and cut one to see what's actually in there. S/FTP or SF/FTP. CAT6 or CAT7 patch cables should have these shielding features. As suggested, leaving the ethernet cables cables as early as possible in favor of proper AES cables would be an option. Although in your location a proper DB25 4*AES cable is probably not easy to source.

The CAT5->AES converter itself is unshielded/plastic to my knowledge, that could be improved as well I guess. Using a shorter cable and placing the DMA8+ closer to the IMB could be a temporary test to see wether it improves the situation. Seems the problem with the booth light switching can easily be reproduced for testing.

Or, get a replacement cable for one of the existing CAT cable, cut the previous in two halves, unwrap the screen and check if there is any shielding at all.

- Carsten

Posted by Marco Giustini (Member # 4544) on 09-07-2013, 01:54 PM:

I'm with Carsten.

Replace the cable is a cheap and quick operation you can try before buying an UPS - which is always recommended anyway.