My research into Atmos and other immersive audio continues. In fact it consumes most of my time every day. All the variables in immersive audio make two channel seem like child's play. Fortunately, one area that's pretty straight forward is amplification. In this update I'll cover some of my amplification considerations and reveal the amp choice for my Atmos / immersive audio system.
Dolby is pretty loose with its consumer requirements for playing Atmos content. Configurations from headphones, to a single sound bar to 11.1.8 systems and everything in between are OK. Take a look at this speaker setup guide from Dolby (link) to see many of the options. I bring this up only because one can't get too deep into amplifier selection without knowing how many channels need amplification.
When I first decided I needed to go down the path of an Atmos system, I reached out to friends and people in both the consumer and professional industries. I wanted to know which of the seemingly endless configurations is recommended. What I heard from most people was that I needed at least a 7.1.4 system to do it right. I was also directed to the Dolby Atmos Music delivery specification for professionals (link). This specifications says, among other things, "All deliverables must: have been approved for home listening and monitored in a room with at least a 7.1.4-ch speaker layout." My roads were all leading to a 7.1.4 system.
Note: This specification also states, "All deliverables must: use 24-bit PCM resolution at a sampling rate of 48 kHz."
A 7.1.4 system requires 12 channels of amplification. Given that my two channel system is the foundation of the Atmos system, I'll continue to use my Constellation Audio Inspiration mono amps for the front left and right channels. This is where Constellation amps come in extremely useful, in addition to sounding fantastic. Constellation amps have three inputs, 1 RCA, 1 Balanced XLR, and 1 Direct XLR. I never use the RCA inputs and don't plan to do so in the Atmos system. The balanced XLR input is a traditional balanced input using an XLR connection. The Direct input also uses an XLR connection, but is designed to receive its signal from a Constellation preamp. I connect this Direct input to my Constellation Inspiration Preamp's output. A benefit of this Direct input is that it bypasses one gain stage in the amplifier and produces even better sonics.
In the image below, one can see the little switch for Direct, BAL, and RCA. When listening to two channel audio, I will leave this switch set to Direct. When I want to listen to Atmos / immersive audio, I'll flip the switch to BAL. The BAL input will receive audio directly from a DAC or processor. In a perfect work this switch would be remote controllable or auto-sensing, but I'm not complaining.
Two of the 12 channels are covered by the Constellation amps. The .1 (point one) channel is already covered because I will use a powered subwoofer. This leaves me with 9 channels in need of amplification. It's a difficult number because high end audio companies don't design 9 channel amplifiers. There's zero chance I'm going to use a jumbo AV receiver with "a million" channels of amplification, so it's time to get creative.
In addition to the number of channels, I also need to consider the type of amplification I'll use. Class A is out because the heat would make my listening room unbearable. Class A A/B is a possibility as is Class D. I though about a Krell Theater 7 XD Multi-Channel Amplifier with an iBias Class A topology, but I'd have to use two of them to cover 9 channels. Sure, I could use the 7 Krell channels and use a 2 channel amp for the remaining two, but I moved on. After talking to friends, I decided to look more seriously at using Class D amplification.
The NAD M28 7 channel amp uses new Purify amp technology and should be outstanding. I still run into the issue that it's "only" a 7 channel amp and I need 9. I decided to go down a different route. Use Class D stereo amplifiers that I know perform very well. This also gives me great flexibility with respect to placement of the amplifiers. If I want to place two on the left side of the room and two on the right, I can easily do that. The more I thought about this approach the more I liked it.
Note: I considered amps from a few other manufacturers, even some that build them based on the number of channels needed, but I was unsure of the reputation of these manufacturers. I had no experience with them and neither did anyone I know.
After endless research, I decide to go with 5 Mytek Brooklyn+ amplifiers. Four of the stereo amps will power the surround and height channels. I'll use a single Mytek Brooklyn+ in bridge mode to power the center channel. I love this configuration because the amps are very small and efficient, I have great placement flexibility, and I know how well the Brooklyn+ amps perform. I haven't decided on the final placement of the amps though. A couple on each side of the room, with XLR cables under the floor is a possibility. I've also considered placing the bridged Brooklyn+ behind the center channel, but I think this is a bit difficult to do because running a power cable to the amp in the middle of the floor will be more difficult than a speaker cable. At least that's what I'm thinking for now. I could change it up and test each setup as I get to installing equipment.
One other amp I considered for the Atmos / immersive system was the Schiit Vidar. I love the Vidar! Two things give me hesitation when I think about using Vidars in this system. First, in order to use them with balanced XLR connections, each amp has to be use as a monoblock. This means 9 Vidar amps would be needed. Second, the Vidar puts off quite a bit of heat. Nine Vidars in my room could turn it into a sauna.
Readers may be thinking to themselves, how can one select amplification without knowing which loudspeakers the amps will drive? Oh don't worry, speakers have been selected. Be patient, that will be included in a later Immersive Audiophile update :~)