True Sound 7000 - Fully Active Magnepan 3.7i - 8 Channels of Madness

We've been exploring the limits of new audio technology for as many years as we have been in business - If there's a new driver or technology that comes out, you can bet that we've tried integrating and optimizing it into one of our home speaker systems. Amplifier technology is a little more complex - Enter Bruno Putzey, and Hypex Electronics. (Link at end of post to a great interview)

There are very few people that I'd say I trust in the audio world to explicitly state facts - Bruno is one of them. For that matter, even less people seem to understand the concepts and technology they're trying to explain. For this reason, it's very easy to get lost in audiophile terminology and snake oil products that may do "something", but alas, what are we trying to achieve? Bruno has my explicit trust due to his clear understanding of the technology he took back to the drawing board, solving all of the initial drawbacks of Class D amplifier technology from the ground up. Bruno's work, along with his company "Hypex Electronics" has been of interest to me since our engineer mentioned his new Class D amplifier technology about 14 years ago. Steve was in awe at the simplicity of his circuit, and an absolute believer that it should be one of the best sounding, most neutral amplifier designs available.

Around 3 years ago, my focus shifted toward building higher end home stereo systems, and I finally pulled the trigger on a massive 8 channel amplifier with Ncore series modules inside (this is the second generation of hypex amplifiers, lowering distortion over the original designs by an order of magnitude). The amplifier was assembled by Apollon Audio. It features 8 channels of 500 watts, at a practically unheard of %.0017 total harmonic distortion measured. 

Over the last 3 years, my personal goal has been to streamline the optimization of HiFi Home Stereo and Theater systems - that is, to build a system from the ground up that offers the most realistic and detailed listening experience we can achieve. This includes offering advice on room treatment, speaker placement, sub-woofer and speaker selection, custom in home room correction and of course, Amplifier selection. 

Sometimes, speaker selection has already been made, and we need to figure out how to make the best of a mess. In this case, the customer was already set on a pair of Magnepan 3.7i Planar/Ribbon hybrid speakers. First problem? They don't make any bass! Magnepan claims the frequency range covered by these panels extends down to a respectable 35hz. My testing has come short of proving this claim. With careful DSP (utilizing a robust solution from MiniDsp, their DA8), I was able to achieve useful extension down to around 70hz. The subwoofer solution includes a pair of our versatile Zero Phase Subwoofers - A Stereo Dual 12" (that's (4) 12" drivers, in 2 separate enclosures placed near the front stage) subwoofer design that is time aligned and carefully integrated into each space, making note of peaks and dips in room response and adjusting accordingly. At the distortion levels we are trying to achieve, I opted for a 100hz crossover point from the low end panel of the 3.7i. This would normally not be advisable, but it works well in this situation because we have full control over the response of each component, and stereo placement of subwoofers allows the directional nature of higher bass frequencies to blend seamlessly into the Magnepan panels. 

Ok, what now? At the time, we were running the system on 4 separate 1000 Watt monoblock X Series amplifiers from Emotiva. Each of the magnepan panels and subwoofers had it's own channel, and we were running the original crossover equipped in the 3.7i. This crossover design has a practically fatal flaw as far as I'm concerned - 1st order, series design. 6db per octave, combined with MASSIVE distance between the mid panel (planar) and high frequency ribbon - a spacing of more than 3" and a crossover point in the 4khz range. This combination causes severe lobing of output - There is a very small listening window where things sound even close to accurate, and the overlapping frequencies the panels play make it exceedingly difficult to come up with output that sounds natural. So, what can we do about it...

Re-designing a non-series higher order (steeper slope, 4'th order 24db/oct vs factory 6db/oct) crossover is quite prohibitive. It would take a very significant amount of engineering, testing, re-engineering and hair pulling, to work out. The alternative is still quite a lot of work, but exponentially more flexible. We deleted the factory crossover! To do this, you need as many amplifier channels as there are speaker components - in this case there are 3 sections per panel. We needed 6 channels for the Magnepan pair, and 2 additional channels for the subwoofers. Maybe we can increase the power available to the subwoofers while we are at it?

This is how we arrived at the need for the - True Sound 7000 -

 This amplifier utilized Hypex Ncore and UCD technologies to pack a total of 7200 watts inside one massive chassis. 

Here's the breakdown -

100x2 for the tweeter Ribbons

500x2 for the midrange Planars

500x2 for the low end Planars

2500x2 for the Zero Phase Subwoofers

To achieve actual RMS power output, standard 120v mains wouldn't do - each 15A circuit is only capable of supplying around 1800 watts of power. Class D amplifiers are highly sensitive to voltage drop, and can only output as much power as they can pull from the wall, (at a factor of about 90-92% efficiency in this case). We opted to have new circuits run in the library (listening room), and the amplifier receives power at 2 240v receptacles on the back, originating from their own 20A, 240v Circuits all the way back at the breaker box. 

Ok, power is sorted. Now to design and build the amplifier. We worked with a company called diyaudiostore through their website to purchase a custom chassis with massive heat-sinks and incredibly solid build. Shane and I spent a full week back and forth on design of the engraving/print work. I obsessed over ensuring every detail worked out for my rather unorthodox balanced RCA connections that I custom built for the equipment. This required 12 wires per each of the stereo channels to get clean audio signal to the amplifier modules - for this I used a 12 pin connector from Deutsch DT Series. Every bit of custom machine and art work drawing checked and re-checked before final approval to have this beautiful art piece made, and shipped in from Italy. Shane and I remained quite skeptical that it would match our vision, but to our delight, every single piece came out FLAWLESS! We delicately unpacked our masterpiece with wide eyes.

From here, all that was left was... well, honestly a huge undertaking. I was able to secure dealer status with Hypex roughly 9 months before this point, and had assembled a couple of small modules into enclosures (I may post about this once I actually finalize the design), and had a running prototype of this same configuration already in place at the customers home. This was a whole different beast. The machine work, the wiring, integrating power/signal/heat dissipation/mounting/more wiring. It took around 2 weeks to complete all the internal amplifier work. There are a couple more features I'm still working on - the main one being an auto-on/off circuit that senses signal and makes sure the amp is only active when necessary without having to worry about physically turning it off. She's close. 

Time to swap out the True Sound 7000 with the prototype, and swap over to the newly installed 240v circuits. From here, I already had a base configuration I'd been working on and optimizing for months with the test amplifier. I scrapped it. Starting over from scratch with my 2 laptop mobile measurement rigs, I was finally able to integrate the system like never before. See, Magnepans are not only a Line source (meaning they're a tall panel which interacts differently than a point source tweeter/mid with the room as well as with your ear), but they are also a Di-Pole - There is no box behind them, so they output the same thing on the rear as they do the front. This causes a wide range of issues in integrating components, but at this point I finally had enough experience fighting with them to figure out how to quickly dial them back in. Here's the current basic configuration

System range 15hz-24khz 

Zero Phase Subs 15-100hz (LR24)

Low Panel 100-400hz  (BW12)/(LR24)

Mid Panel 400hz-2khz (LR24)

Ribbon Panel 2khz-24khz (LR24)

There is still work to be done on the system - primarily we're planning to build a custom stand solution which showcases the amplifier and DSP as a centerpiece, which will also integrate additional cooling for the amplifier to keep temps low and overall longevity high. The customer response after the most recent integration of his custom amplifier?

"You have a problem here, It's too good"

-True

More pictures, including the installation coming soon!

[Left - True Sound 7000    /   Far Right - Apollon NCMP8350 - My introduction to Hypex, currently on demo in our showroom]

If you're interested in exploring some of the genius behind the technology we are using here, this is a really good interview with him by Sound and Vision a few years ago. I aspire to understand even half of the things he's written on the subject of amplifiers and audio in general. 

https://www.soundandvision.com/content/bruno-putzeys-head-class-d