[modwright]

The Evolution of MWI Tube Design

In July of 2015, Dan Wright visited Jack Elliano of Electraprint Audio, Master transformer winder.  The intent of the visit was to learn to wind our own chokes for R&D and custom work.  In the process, Dan also learned many of the secrets involved in winding audio output transformers, which are the key to the magic of any tube amp’s sound!

While visiting Jack, Dan heard a 10W, Single Ended (SE) EL34 based prototype that Jack had been working on.  The technology, dubbed Isolinear by Elliano, focused on the reduction of IMD (Intermodulation Distortion) as well as THD (Total Harmonic Distortion). Jack found a way to design a circuit, in single ended mode, with the EL34 (only), operating as a Pure Pentode with a specific transformer design.

Dan was struck by how natural, dynamic and ‘live’ the sound was, from the 10W amp. Working alongside Jack, Dan wound a pair of these special design transformers so that he could build a 10W EL34 amp for himself.  The results were stunning here, as they were at Jack’s, and from this, the ‘Ambrose’ line of tube amps from MWI was born.

The Original Ambrose
(Debuted at Capital Audiofest in DC with rave reviews, in late August 2015)
Retail Price: $10,000

Power: 10W Pure Class A.

Tubes: (1) EL34 per channel and (1)12AT7 per stereo amp.

Inputs: (1) Pair RCA.

Outputs: (1) Pair 5-way binding posts.

Transformers: Power and Audi Output Transformers: Custom Electraprint transformers, wound for 6 ohm load.

Finish and Build: Mirror polished Stainless Steel top plate.

Precision machined and engraved, 1” thick solid AL billet top and bottom plates and edge trim. Highly figured Flamed Maple enclosure with dovetail joinery construction and hand-rubbed oil finish. All point-point internal construction with custom MWI capacitors and the best possible components.

The desire for more power prompted the next concept build. The 845 SET (Single Ended Triode) is capable of putting out as much as 32W in Class A1.  32W is enough power to drive a much broader range of speakers.  While the 10W Ambrose sounded beautiful, it required speakers of a higher efficiency.

An inquiry to Jack Elliano again returned a transformer and circuit design with custom reactors and output transformers, capable of achieving this result, with the same Isolinear technology.  It was decided that this would be a CNO (Cost No Object) Statement design!

NOS (New Old Stock) Westinghouse ceramic 845 tube sockets, Tektronix ceramic wire mounts with silver contacts, PSSS (Partial Silver Stranded Secondary) audio output transformers, MWI caps, and Skogrand Beethoven Ultra-Reference internal wiring were chosen for the internal build.

The enclosure was designed similarly to the original Ambrose, but with highly figured Instrument Grade Walnut enclosure, mirror polished stainless steel top plate and 1” thick AL billet top and bottom plates.

Due to the size of the transformers and tubes, these were designed as mono-blocks.  Each enclosure was 16”W x 24”D x 6”H, not counting tubes or transformers. Where the original Ambrose featured exposed transformers, the 845 DS included AL transformer covers (two per mono block), finished in ‘Oxblood Hue’ prismatic powder coat, for a deep and rich burgundy wine color.

The sound of the 845 DS is spacious and deep, with an ‘unworldly’ soundstage. We have never heard such a boundless soundstage and open presentation in our reference system. Operating at 1200V plate voltage, the 845 SET, driven by 6HV5 Compactron Beam Triode allowed for enormous voltage swing and unparalleled headroom. The 845 DS offers the sweet midrange of a good SET amp with the power and dynamics of a high power amp.


Ambrose 845 DS Mono Blocks
(Debuted at Rocky Mountain Audio Fest in Denver with ecstatic reception in early Oct, 2015)
Retail Price: $49,995/pr.

Power: 32W Pure Class A.

Tubes: (1) 845 Direct Heated Triode and (1) 6HV5 Compactron Beam Triode per mono amp.

Inputs: (1) Pair RCA.

Outputs: (1) Pair 5-way binding posts.

Transformers:  Power, Audio Output Transformers, Chokes and Reactors. Custom Electraprint design, wound for 6 ohm load.

Finish and Build: Mirror polished Stainless Steel top plate.

Precision machined and engraved, 1” thick solid AL billet top and bottom plates and edge trim. Highly figured Flamed Maple enclosure with dovetail joinery construction and hand-rubbed oil finish. All point-point internal construction with custom MWI capacitors and the best possible components. Oxblood Hue prismatic powder coat finished transformer covers.

Photo courtesy of Part-Time Audiophile.

The evolution of these concept designs culminated in the Ambrose A30 mono block amplifiers, as production models. We determined that 30W was needed to drive a greater variety of loudspeakers, and the EL34 tube provided the right combination of excellent sonics, tube availability and reasonable build cost.

We knew that a single EL34 tube could produce a clean and low distortion (IMD and THD) 10W of VERY musical power.  Further research with Jack Elliano proved that the same could be done with two EL34’s in parallel for 20W, but at the time, three tubes was problematic, leading to oscillation and instability.  This initial research was done with Dan and Jack Elliano in July of 2015.

Early in 2016, Jack called Dan to tell him that he found a way to stabilize the Trio of EL34 parallel pentodes for a 30W Ambrose amplifier. Dan travelled to Vegas again to work with Jack and listen to the prototype.  It was GOOD and Dan felt that a sweet spot had been found. It was a clean 30W of power that did not require HUGE power transformers operating at 1200V and expensive 845 tubes.

Dan requested a special pair of output transformers designed for a 30W EL34 Ambrose mono block pair, capable of EXCELLENT low AND high frequency response.  This was a special design because transformer designs often require a compromise of bandwidth due to the physics involved in Single Ended output transformers.  More core mass was added and the design was revised by Jack Elliano to deliver what we needed.

The Ambrose A30 Mono Blocks were born. The A30’s possessed the sparkle, dynamics and lively sound of the 10W Ambrose AND enough power to drive a much greater variety of speakers.  It was also much less costly to build than the Reference 845 DS mono blocks, making it more attainable for a greater customer base.


Ambrose A30 Mono Blocks
(Debuted at T.H.E. Show, Newport, CA, in early June 2016. We knew we had hit the mark!)
Retail: $15,000/pr.

Power: 30W Pure Class A.

Tubes: (3) EL34 and (1)12AT7 per mono amp.

Inputs: (1) Pair RCA.

Outputs: (1) Pair 5-way binding posts.

All point-point internal construction with custom MWI capacitors and the best possible components.

Transformers:  Power and Audio Output Transformers. Custom Electraprint, wound for 6 ohm load.

Finish and Build: 3/8” precision machined and engraved AL billet top and bottom plates.

Highly figured Flamed Maple enclosure with dovetail joinery construction and hand-rubbed oil finish. Oxblood Hue prismatic finish transformer covers.

Photo courtesy of Positive Feedback Online.

MWI’s Tube Amp Journey

ModWright has always designed tube source products and preamps, from digital to analog, but our amps have always been solid state.  The reason for this is that Dan has never been satisfied with the sound of tube amps that he has heard.

Having owned OTL, Push-Pull and SET (Single Ended Triode) amplifiers, Dan has always been familiar with the strengths of each and also their weaknesses. Dan has always felt that tube amps, while beautiful sounding in many respects, tend to fall short in terms of speed, dynamics, resolution and frequency response. This is where SS amps have the edge.

The best SS amps can achieve the shortcomings of tube amps and still offer remarkable sonics without edge, glare or grain.  It is for this reason, that MWI has always designed tube preamps for their beautiful sound and SS amps, for their control and power.

This process of design, education and enlightenment has taught Dan that Tube Amps CAN be remarkable and achieve a level of sonic realism and beauty that SS amps cannot. While the laws of physics and magnetics will always set SS and tube designs apart, in what they are ultimately capable of, we feel that the Ambrose line of amplifiers has reached a level of performance and power that we feel merits the MWI name.

The Ambrose A30 mono blocks, with Daedalus speakers at T.H.E. Show, Newport CA, 2015, showed the world a level of sonic beautify and live sound that we have never achieved at a show before. Musicians, audio engineers and audiophiles alike who heard the system, all remarked that there was a magic in the system that was special and new.

The Journey is never over, but we at MWI are enjoying the ride.  This chronicles the evolution of the Ambrose A30 mono block tube amplifiers.

[zybar]

Cool journey Dan!   

I loved what you did with tubes back in the day when you were modifying CD players and the Transporter.

Would love to hear one of your tube amps.

George

[modwright]

Thanks George, we still modify players with tubes: Oppo BDP-95, 105, 105D, Sony XA-5400ES and Sony HAP-Z1ES.

We also have our own full line of products including tube DAC, phono, preamps, and more.

I appreciate your support!

Dan

[Phil A]

Dan - keep up the great work.  I got a XA-777ES (Absolute Truth) modded probably more than 15 years back.

[dodgealum]

Dan thanks for sharing this information as it provides wonderful context for your current product offerings and some technical background on your current tube amplifier designs. I am seriously lusting after your new Ambrose A30 monos to drive my Daedalus DA-1.1's. Question: Are you winding the transformers for 6ohm loads to better match with Lou's designs or are there other reasons? And do the amps offer a single set of binding posts rather than multiple sets for different loads as seen on many tube amps?

[modwright]

Hi, to answer your question, the 6 ohm winding is to be able to handle all loads well with a single tap.  When multiple taps/windings are added, you increase inter-winding capacitance and decrease bandwidth and fidelity.  I found that a 6 ohm winding meets all loads best.  For a load > 6 ohms, it is absolutely no problem.  For a 4 ohm load, it is still compatible.  It is just a coincidence that Lou's speakers are 6 ohm.

I will say however, that they are especially magical with Lou's speakers!

Thanks,

Dan

[dodgealum]

Thanks, Dan. Have you had a chance to do some of your photo wizardry on the A30s yet? Would love to get a better look at these from different perspectives.

[Phil A]

Thanks, Dan. Have you had a chance to do some of your photo wizardry on the A30s yet? Would love to get a better look at these from different perspectives.

There's a few more shots here - https://parttimeaudiophile.com/2016/07/13/newport-2016-modwright-daedalus/

[Phil A]

If you click on the pics of the amps you can see them up close better and also see what they were shot with - https://parttimeaudiophile.com/2016/07/13/newport-2016-modwright-daedalus/#jp-carousel-36828

[modwright]

Thanks, yes, they did a great job!