Dolby Multichannel Amplifier

[Bobby Henderson]

I thought Dolby specifically introduced their multichannel amplifiers with Atmos in mind. A room with Atmos needs a hell of a lot of channels worth of amplification in order to play a movie sound mix that can possibly really sound like Atmos rather regular 5.1/7/1. I say "possibly" since the movie mix itself must have some effort put into it to show off Atmos bells and whistles. Most projection booths have only so much rack space for amplifiers. Separate amps would be better, but if space is an issue these Dolby amps could be a solution. I have no idea how good or bad they are however.

Aren't some cinemas installing amps and other rack equipment in other places around the auditorium besides the traditional projection booth (up in the "attic", behind the screen, etc)? I seem to remember seeing examples of that with QSC's Q-Sys gear. That can solve some of the space issues, provided the hardware is installed in a secure location.

Is Dolby's multichannel amplifier something that can be used in conjunction with other amplifiers? For instance can these multichannel amps be used to drive surround arrays while much more powerful yet separate amps are used to drive the stage channels and sub-bass?

[Steve Guttag]

The DMA was, originally, developed for Atmos to get a high density amplifier. However, it has evolved with the 16 and 24 channel versions having analog inputs to allow processors like the CP750 (analog output only) to use them in a conventional 5.1 and 7.1 setting. The amplifier has the necessary DSP to handle crossovers and can bridge channels to handle subwoofers. The power handling of them has also gone up from the original, partially to ensure that it could handle the needs of stage speakers and subwoofers.

Since the DMA can handle analog (on the two smaller ones), AES67 (after a fashion) and Blu-Link, one can certainly mix and match conventional and DMA within a system. I am definitely looking at it for Atmos surrounds. Q-SYS supports AES67 output but the configuration of the DMA seems like it is just a partial implementation of AES67. I need to verify that it is stable. QSC's 8-channel amplifiers, now, have analog inputs on them, that one is, in one way or another, paying for. I'm designing a system right now where there will be some 50ish unused analog inputs! Yeah, you lose some monitoring, via Q-SYS, on the DMA versus a CX-Q amplifier but it could be a significant cost savings plus less racking needed.

Please note, with Q-SYS, using CX-Q amplifiers, one does get a bit of monitoring (actual audio on the output of the amp, input, diagnostics...etc....all of which can aid in early detection of problems or troubleshooting if there are problems. Having some analog inputs can be quite handy...just not 50.

As others have noted, you do have a maximum power limitation per amplifier. In a surround situation, that is not an issue. A misconception, that I've even heard in an Atmos training is that you need this astronomical amount of electrical capacity for Atmos because if you add up all of the speakers playing at full-tilt at once. The SPL in the room, if that were to ever happen would be dangerous. A movie, be it Atmos or 7.1 is going to have about the same overall level. Moving an object around the room does not use more, OVERALL, power than lighting up the entire side of surround speakers. One just has to ensure that each channel and each speaker can withstand playing that loud by itself as an object passes through.

So, yes, I can see a hybrid approach to Atmos and the DMA making a degree of sense and savings.

[Leo Enticknap]

Aren't some cinemas installing amps and other rack equipment in other places around the auditorium besides the traditional projection booth (up in the "attic", behind the screen, etc)? I seem to remember seeing examples of that with QSC's Q-Sys gear. That can solve some of the space issues, provided the hardware is installed in a secure location.

Not only that, but they can make the signal path cleaner.

By sending the output from the processor digitally (using Q-Sys, Dante, BluLink, etc.) to the power amp and situating the power amp as close as possible to the speaker, you eliminate long cable runs carrying an analog signal, and therefore the risk of picking up a ground hum or other interference; not to mention saving on cabling. I've installed and serviced several houses in which the rack holding the power amps for the stage channels has been situated behind the screen.

[Steve Guttag]

Yup, thus far, all of my Atmos systems have the amplifiers behind the screen (and baffle wall). I use 4-way speakers so the savings on speaker cable, can be significant (not just the cable but actually the time it takes to get them installed. An advantage to having an amplifier with analog inputs behind the screen is if you want to have some form of PA system...the inputs are nice and close by.

[Marcel Birgelen]

Ever since we moved to Q-Sys in our screening room, we've also moved the power amps for the main speakers behind the screen. Your room design needs to allow for it, as in this case, we've moved everything into a 19" cabinet. Since most power-amps come in 19" form-factor, you need to have the room to put them there. We're lucky we have sufficient room behind the screen to allow for relatively easy access and we have decent ventilation and even the possibility for active cooling there too. I'm only a little bit more concerned about noises originating behind the screen finding their way to the auditorium even with our full-size baffle-wall in place.

But even in this relatively compact setup, you already save considerably on wiring, especially since we've always been running with 5 speakers in the front, excluding subwoofers.

[Marco Giustini]

Please note, with Q-SYS, using CX-Q amplifiers, one does get a bit of monitoring (actual audio on the output of the amp, input, diagnostics...etc....all of which can aid in early detection of problems or troubleshooting if there are problems

Unless they start throwing out false alarms - I indulged myself once in creating a nice UCI with a rich status page of the many amps and speakers installed and that backfired on me when it turned out that those errors can be (will be - at least that was a few versions ago) false alarms.

[Dave Macaulay]

We only used the DMAs once. No major issues with them, but replacing an amp module is quite a job. All power, input, and output connectors (up to 16 - hope you labelled them!) have to be pulled out, the DMA pulled out on and then lifted off its rack slides, the right side slide taken off the chassis, and the right side cover removed - to get at the 8 channel amplifier modules. So an amp channel failure is not a site staff job.
Blulink connection makes installation a lot easier than with analog inputs but for ATMOS using the Dolby 32 channel D-A and compatible amps you can get adapters to provide DB-15 connection rather than cut and strip wires.
The last few we installed have JBL DSi-2.0 four channel amps. More rack space than the DMA plus needing two network switches and more complication to set up AES67 distribution but local staff (with quite a bit of guidance) can program an on site replacement amp and do the swap, or we can program and send a replacement to just swap in. I'm not convinced that the total work to build a rack this way is less than with analog signals, and amp failures are definitely more of a problem.

[Steve Guttag]

Marco, typically, I'll have a main status indicator on my UCIs (if all Q-SYS devices are okay...it says "OK" (status combiner). For a booth monitor, I provide both "processor" and "amplifier" so those amps, behind the screen, have a reasonable monitoring/status of amps one cannot easily see.

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Another thing we're doing in such theatres/screening rooms (not shown above) is breaking up the subwoofer amplifiers and having a "spare" center amplifier. So, Center and one subwoofer will share an amplifier and another amp will have a spare set of channels and driving another subwoofer. Then, all that is needed to back up the center speaker is move the output phoenix connector and, via UCI, tell the system to use the back up center. This is on top of being able to route around ANY screen-speaker/amplifier failure using remaining channels.

For the record, the status screen shown above has never given false issues. In fact, it picked off a couple of dodgy CAT connectors that tested fine but would periodically cause a compromised condition for a split second.

Something that Q-SYS has that most do not is the ability to do Dynamic Pairing so...if people on-site are going to swap the amplifiers (or any Q-SYS component), one can have the system auto-configure the replacement so all the theatre staff have to do is plug it in. This DOES require some planning and creating the dynamic pairing for all of the amps and things and it also has implications for IP addresses since for dynamic pairing to work, a DHCP server has to be available to configure the new unit with the right IPs.

Back to the DMA. Yes, if an amplifier module is what fails...then yes, that is the worst of a field repairs. I would say, from a "manager" standpoint, nothing of the DMA should be considered a field repair as opening the case can exposed the inexperienced to lethal voltages/power. That said, for a theatre technician, it makes the amplifier just about always field repairable rather than having to send the unit back to Dolby. If one has enough DMAs, one could stock DMA parts to be able to fix any/all they may have in the field much the same way we had field kits for Century projectors that had most everything the tech on call could need to get a Century projector up and going.

[Mark Hathaway]

I’ve installed 12 DMA’s, 24 and 32ch.

zero issues but that’s a meaningless sample size. QSC DCA install footprint is somewhere over 3500 pieces.

while out drinking with Dolby staff one night back in late 2019, after way too many single malts and much banter about reliability, a sales force report was run. Less then 10 RMA’s granted world wide for all variants of DMA’s. Module failures sure, don’t recall numbers but it wasn’t anything alarming.

the paranoia around failures to me is unjustified.

The DARDT workbook, whatever the latest version is, probably version 7530 this week, is overly optimistic with total system capability and isn’t totally psu draw and factoring in mains current limit it would seem. Run your typical big studio action movie trailer at a fader of 7 and watch the lovely VU go crazy with a visual representation of Hal saying “I’m sorry Dave I can’t do that” despite every channel being 3-6db off clipping It’s a very gentleman like limiting though, can’t hear it at all. I’d also add, the sound quality improvement going to Aes67 and placing high quality DAC’s inside the amp is a welcome improvement. I’ve not had one apart (again that’s a good thing), but I’m guessing the CAT1421 is decoding the Aes67 stream and passing i2s to each 1422/1433 board.

I’m implicitly interested, I’m developing a hifi amp for the consumer market with Dante and 8 channels.

[Darin Steffl]

I wanted to followup here that we purchased and installed the DMA16302 a month ago with no issues. It arrived with the latest firmware, which is fairly old from 2019.

The install was easy by following the online manual. The sound is great compared to our old QSC amps that were 20+ years old. The hum that existed on our old setup when idle and buzzing at the beginning and end of shows is gone as well. I can tell there is an improvement in sound quality. The amount of wiring it reduced in our rack was staggering since we use a CP950 so all the input wiring was reduced to two ethernet cables.

Overall, I'm a happy camper with this new amp and hope it lasts as long as our old amps

[Martin Brooks]

While I'm sure that this Dolby product is good, I'm sorry, I just don't like all-in-one devices.

As others say, it's a single point of failure. That's not good.

Back in the 90s, I used to work at a store selling TVs, stereos and home electronics. Back in those days, all-in-one TV/VCR combos were popular. I used to tell every customer that, as nice as they seem, if one part of the unit goes down, the whole TV has to be repaired or scrapped and replaced. Still, people bought them.

Probably about a third of those combo-TVs would come back for warranty service within the 90/365 warranty period. (90 days parts+labor. 1 yr. parts only.)
A significant fraction of the sales receipts (required for warranty service) on those items had my name on them. I know that I told those people about the consequences of failure because, whenever I sold one of those, I'd underline the warranty statement at the bottom of the receipt when I warned the customer.
(This scenario repeated so frequently that I developed a code so that I would remember if I told them.)

Almost every customer who brought one of those back for repair would complain that they didn't have a TV just because the VCR was broken.
The store policy was to replace only for DOAs or soon after. After that, it was repair first then replace only if the repair shop said it was a goner.

After having to stand there, broken hearted, to see a customer unhappy with their TV, even after I know that I warned them, I just resolved to never buy any kind of all-in-one system unless the benefits were so good that they outweigh the consequences of failure or unless the device is being used for a non-critical purpose where it doesn't matter.

In a movie theater where amplifiers are mission-critical, I would never recommend an all-in-one.

I think it's invalid to compare a consumer level all-in-one device, which were designed to be low-end even in terms of consumer devices, with a professional amplifier. Up until recently, at home I was using a Crown power amp that I had in use since 1977. It still works perfectly fine, but I replaced it with something better. Since the digital projector is also a single point of failure, as is the all-important center channel speaker, I don't see it as any more risk. Frankly, I'd be more concerned with whether it sounds good. At one multiplex I go to, I find that some of the 5.1/7.1 auditoriums generally have better overall fidelity than the Dolby screen, in spite of the extra "channels" in the latter. Now I don't actually know what amps are in those booths, but I think it's a safe assumption that there's probably a Dolby amp in the Dolby auditorium and something else in the other auditoriums.