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Reviewer: Srajan Ebaen
Financial Interests: click here
Source: Esoteric UX-1 with APL Hifi NWO 3.0GO modifications
Preamp: ModWright DM 36.5, Esoteric C-03

Amp: Pass Labs INT-150, Yamamoto A-09S, ModWright KWA-150 [on review]
Speakers: ASI Tango R, Zu Essence

Cables: ASI Liveline loom
Powerline conditioning: 2 x Walker Audio Velocitor S
Equipment supports: Ikea Molger with Ikea butcher block slabs
Room size: The sound platform is 3 x 4.5m with a 2-story slanted ceiling above; four steps below continue into an 8m long combined open kitchen, dining room and office, an area which widens to 5.2m with a 2.8m ceiling; the sound platform space is open to a 2nd story landing and, via spiral stair case, to a 3rd-floor studio; concrete floor, concrete and brick walls from a converted barn with no parallel walls nor perfect right angles; short-wall setup with speaker backs facing the 8-meter expanse and 2nd-story landing.
Review Component Retail: $5,995
If it were Musical Fidelity, KWA would signify KiloWatt Amplifier. But for ModWright's new KWA-150 amplifier, it abbreviates something far less excessive. It stands for Kimmel/Wright Amplifier to credit Allen Kimmel, Dan Wright's circuit collaborator already on the LS 36.5 linestage and now chief architect of the amp's input stage. "Alan Kimmel is the genius behind the magic on this one. It is a team effort but the hard-core engineering was done by Alan. There are some cool innovations that I will only be able to refer to obliquely."

Dan Wright's listening room with Greybeard speakers and sound panels disguised as wall art

About obliquatory tech: "It's a single voltage gain stage, zero global feedback design with transformer-coupled true balanced floating inputs and direct-coupling from there into fully differential, pure solid-state circuitry. ModWright Instruments capacitors are used as power supply bypasses in key locations and total power supply capacitance reserves are 216,000uF. Output short circuit protection as well as overload circuit protection operate completely outsid the signal path. Transformer coupling blocks out-of-band noise as well as errant DC from preamp or source. We use the highest-grade Thermal Trak bipolar output devices with auto thermal bias with six pairs per channel, i.e. six transistors per phase. The amp has a hi/lo bias feature for standby or cool operation (low bias); and best sonics and greater heat dissipation (high bias). But even in high bias, it still won't run as hot as pure class A. The amp is bridgeable to mono with a third set of binding posts and a stereo/mono switch. Tests have proven that it delivers 650 watts into a 4-ohm load then. Frequency response is 16Hz to 220kHz, weight is 80 pounds in the box and, including feet, dimensions are 18" x 18" x 8.75" WxDxH. There are three 0.25"x20 threaded receptacles for spikes or other footers and the top cover matches what we pioneered in the 36.5 preamp and external power supply."

At left, Dan Wright, kneeling, with Karl Schuemann of AudioMachina whose Maestro speakers made up part of the CES 2009 ModWright exhibit with two bridged KWA-150s.

Best known for valve circuits, it's refreshing to see Dan Wright embrace an all-transistor circuit to create wide bandwidth and superior load-
invariant drive and power. Expecting reactions to the absence of valves in a ModWright instrument -- we all carry perceptional baggage after all -- I asked Dan to elaborate on this choice:

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I won't speak for Alan entirely but I will share our common thoughts on the subject. They are actually two-fold. 1) Alan has designed and trademarked what he calls the 'Solid State Music Stage'. It is a unique and proprietary design using all transistors, a single gain stage and zero global feedback. It is transformer input-coupled and direct-coupled from there out. Sonically, Alan felt that it incorporated the sonic strengths of tubes with the strengths of solid state, the latter being tighter and more controlled bass, extended highs and an extremely low noise floor. The circuit still retains the holographic imaging and tonal warmth of tubes but without any excessive coloration. Lastly, the circuit requires zero maintenance or tube replacements.

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2) Because this is our first amplifier, we wanted a design that was rock-solid, 100% reliable and 'bomb-proof' in terms of its operation. I did not want to design an all tube amp as I personally don't prefer this sound. I prefer a good tube preamp with a good SS amp. What I don't like are hard, clinical, cold and sterile sounding amps. A neutral and balanced sounding transistor amp with a high-quality tube preamp gives you the best sound in my opinion. I personally feel that tubes excel at amplifying voltage while SS devices excel at amplifying current. Now this would logically lead to our designing a hybrid amp, which we considered.

The reason we decided not to do this, at least for now, is because there is a great potential for problems if the protection circuitry and isolation between high-voltage tube input stage and low-voltage SS output stage are not maintained. It is of course possible to design such reliable isolation and protection but it was yet another level of added complexity and we chose to start with a pure transistor design and see how it sounded. In retrospect, I am very glad we did. I have to say that Alan's 'Solid State Music Stage' is a brilliantly musical circuit. It is also our belief that one of the significant strengths of an amp design lies in the quality of the input stage. The purpose of the output stage is to simply provide an 'ideally' unlimited amount of current on demand and to do so quietly. The amp also has to provide good control of the speaker. This is not as simple as it sounds and also relies on a strong power supply design and overall system synergy within the entire amplifier.

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I understand that it catches people off guard that ModWright has released a product without tubes but we do not believe in limiting ourselves to one medium or design format. We believe in utilizing whatever technology and design will produce the most musical product. I am very pleased with the control, tonal balance, measured performance and, most importantly, musicality of this product. Everyone who has heard it to date has been very impressed. Without any promotion or advertising, we've pre-sold half the first production run already and are busy filling back-orders...

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