May 2016

World Premiere!
Tavish Design Minotaur Hybrid Vacuum Tube Amplifier
A marriage made for a discerning music lover.
Review By Ron Nagle

  You might very well consider this story as a follow up to the Tavish Adagio Vacuum tube Phono Amplifier. That appeared in the February 2016 edition of Enjoy The Music.com. That particular Tavish Designed component never left my greedy little hands. My significant other never knew if like Icarus it fell from the sky. Regarding the motivation for this report; Possessed with a huge amount of curiosity and following a logical train of thought, I sought out the Minotaur amplifier. What could be more logical then to combine both of these Tavish designed components into a system?

The Minotaur Myth
In Greek mythology the Minotaur was a fearsome hybrid creature, half Man and half Bull imprisoned within an elaborate maze. Conversely the Minotaur Hybrid amplifier is half transistors and half vacuum tubes, but no Bull. Like the Adagio Phono amplifier the Minotaur Amplifier is a concept that originated in the fertile mind of Scott Reynolds PhD. Mr. Reynolds has incorporated some elaborate ideas into this amplifier that are unique and cannot be found anywhere else.

In This Case
The Minotaur is a Cass A/B Hybrid Stereo line level amplifier contained in a black matte finished steel case. Rated power is 140 watts per channel into 8 Ohms. Suggested retail price as of this writing is $2490 for the standard version. Physical dimensions are, 17.2" wide, 17" deep, and 6" high and it weighs 34 pounds. The linear (non-switching) power supply uses a toroidal transformer and a massive 108,000 micro Farads of energy storage. Inside, the line inputs are handed off to a direct coupled vacuum tube circuit. This in turn drives a direct coupled transistor output stage. The Minotaur is direct coupled from the input stage to the output stage thereby avoiding the use of coupling capacitors.

Most other hybrid amplifiers are really just transistor amplifiers with a couple of tubes added in front as a preamp. The Minotaur is something very different. The Minotaur is one of very few hybrids on the market to directly couple tubes to output transistors. The design uses seven miniature dual triode vacuum tubes at the input. They in turn provide voltage gain to the driver stages of the amplifier. The tube complement consists of one 12BH7, four 12AT7 vacuum tubes, that is a pair of 12AT7 in each channel. And the two 5751 triodes are used one tube each in the left and right channels. The distortion spectrum is dominated by the single-ended 12BH7 vacuum tube and is predominately second harmonic. The unusually complete and detailed owner's manual includes graphs of test data for every Minotaur amplifier after it is burned in at the factory. For this review sample the percent of THD (Total Harmonic Distortion) was measured at 1 kHz, output power was fixed at,112.5 watts into 8 Ohms: Right channel measured 0.042% and 0.048% for the Left channel.

The Class AB output stage in the Minotaur can be switched to operate in two modes, Normal and High Bias. That means it operates in pure Class A Normal bias up to 1 watt. Or switched to operate in Class A up to 5 watts per channel. This selectable bias is unique to the Minotaur amplifier. The amplifier can be placed into High-Bias mode during turn-on. This is how it's done, starting with the amplifier in "sleep" mode (red "sleep" LED on), hold the "5" button while pressing the ON-OFF switch. Release both buttons after the amplifier turns on. An amber LED behind the vacuum tubes indicates that high bias mode is now active. The High-Bias mode is retained for subsequent operation after the amplifier is switched off. To return to normal mode, once again press and hold the "5" button while turning the amplifier on with the ON-OFF switch. By default, the amplifier operates in Normal mode staying in Class A up to about 1 watt per channel into an 8 Ohm speaker. In High-Bias mode, the output stage quiescent current is increased so that it operates in Class A up to about 5 watts per channel into that same 8 Ohm load.

The Minotaur uses the well-regarded MJL3281 and MJL1302 transistor devices at the output in a modified Sziklai configuration for superior linearity. Generically the Sziklai configuration is also known as a "Pseudo-Darlington" circuit and is named for its early popularizer, George C. Sziklai. It is similar to a Darlington pair amplifier design. However it is configured with two dissimilar Bi-polar transistors one NPN and one PNP. In a conventional Darlington pair amplifier circuit both Bi-polar transistors are of the same type, either NPN or PNP. By utilizing two Sziklai pairs at the output there are some real advantages. But I can only list some of them here. Sziklai pairs have the benefit of superior thermal stability under the right conditions. In addition since both pairs use mixed NPN / PNP type transistors, the derived benefit is to lower distortion and improve matching between each channel.

The Interface
The Minotaurs shiny black aluminum front panel is chock full of innovative features and controls, so much so that it is hard to know where to begin. To start with let me mention the tempered glass window on the right side of the face plate. This opening lets you have a view of all seven glowing vacuum tubes while they do their thing.

The turn on power sequence begins with the activation of (what else) the power switch. (lower left corner) The red Sleep LED will then illuminate; this is one of three Led indication lamps. Next activate the On-Off button. It initiates a 60 second time delay warm up. During this delay period the center Yellow Warmup LED is on. After 60 seconds the output relay will close and the yellow warmup LED will turn green. At this time the Supply Active LED lights indicating that the amplifier is ready to use. You can then select one of the five line inputs. On the left front panel the line level sources are activated by illuminated (C&K) push button switches.

When selected they activate a low-signal level Omron relay. And the last adjustment would logically be the Alps motorized Blue Velvet volume control. The Minotaur monitors the input signal levels and if it fails to detect a signal at the selected input within a 30 minute time interval the amplifier is programmed to shut itself off. Additionally there is a small remote control that comes with the amplifier. Unfortunately it seems rather slow to react to commands.

System Fault Status
The Minotaur amplifier has a unique built in Micro-controlled "Fault Mode" system monitoring feature. Faults are indicated by the condition of two LED panel lamps. The first is the On-Off button containing a Red LED and the second is the Sleep LED. A very basic functional flow chart description would have you looking to see if both LED's were lighted, or is one of them off, or is the On-Of button LED flashing, and how many times it blinks. A half page long table in the owner's manual tells you how to interpret these amplifier fault indications. The table includes a list of likely causes and ways to correct most of the problems.

Behind The Scene
Around back at the line input side of the amplifier. The review sample represents one of two optional configurations. The Minotaur in a standard version ($2490) has all of the input jacks configured as unbalanced RCA connections. The review sample came with the second version and a, MSRP is $2740. This version has the option of two pairs of balanced XLR input jacks and three pairs of RCA input jacks. Directly in the center of the rear panel is a thermally controlled chassis cooling fan. Just to the right is two pairs of speaker binding posts. Two connections Plus (+) and Minus (-) for the right channel speaker and a duplicate pair for the left speaker. On the right rear is the usual IEC line cord socket which includes a line fuse compartment. And last, just above that is small 2 inch antenna for the remote control receiver.

Virginal Beginning
We have covered most of the nuts and bolts stuff. Now to the business, Most often with a new amplifier the bass sounds a loose mess, no exception here. I have been down this road many times before. Frequently it starts with the lower frequency response sounding like a congested caramel colored blur. For the Minotaur this time burn in was a little different. There was one prominent repetitive bass frequency that dominated all others. It was a repeating monotone overtone that affects the sound of bass guitars, after approximately one half hour it was gone. At that time the bass became more articulate, finally forming a foundation of low frequencies that pulled everything into one coherent composition that made musical sense.

Methodology
I've said this before, I'm not going to run you through the hoops by telling you about the many CD's and vinyl recordings I have and listened to that you do not own. Instead let me tell you about a scant sampling, just to make my case. I can distill the performance down to a few recordings. Additionally the amplifier was left on for a half hour before any serious listening. All evaluations were made with the Minotaur operating in Standard Bias. After one month of critical listening to the Minotaur every conclusion comes down to: One Vinyl recording of the Moody Blues (Polydor 840659-1), two phono amplifiers, the Tavish Adagio and my Wyndsor Phono amplifier both with a Denon 103 MC cartridge. My Digital sources are a Marantz DV8400 universal disc player feeding a Music Hall upsampling DAC 25.3. The speakers are Arum Cantus 2 SE monitors with Mark & Daniels Omni Harmonizer add on tweeters sitting on top. Also two different Polydor CD recordings of TOTO'S performance of the song Africa. The first CD was a Red Book recording and the second version of Africa was from another Polydor DSD (Direct Stream Digital) recording.

The Vinyl Voice
Odd but true, I can only relate but not completely explain my black vinyl results. Both Phono amplifiers were connected to the Minotaur power amplifier operating with Standard Bias settings and with the same RCA cables. Listening to the Moody Blues vinyl recording with the Wyndsor solid state phono amplifier is a very familiar to me clean clear up front performance. However on side 2 listening to the M. B. track, Ride My See Saw I thought the Wyndsor phono amplifier lacked some bass frequency extension. So I reset the Denon cartridges Vertical Tracking Angle. By very slightly lowering the Grado Laboratory Standard tone arm's base. That did the trick, there was a level increase of bass that balanced the mid and treble levels. Next, playing the same recording and same track. But now listening through the Adagio Phono stage the very opposite thing happened. The Moody Blues performance now seemed slightly muted. I had to readjust the Denon cartridge VTA this time moving the Grado arm upward in the opposite direction. The effect was to increase the amount of high frequency detail that highlights the stereo image. Those same treble frequencies impart directional clues that paints the width, height and depth of the performance. It is these same qualities that brings home the wonderful imaging ability of the *Adagio Phono Amplifier. Understand that both Phono amplifiers had cartridge loading values that were identically matched. Also the VTA tone arm adjustments amounted to only a few hundredths of an inch higher and lower. Logically these two Phono amplifiers are inherently different. With Tubes versus Op-amps there can be a myriad of electron circuit massaging differences barring a precise explanation. *Adagio Phono Amplifier review February 2016, Enjoy The Music.com.

A Tale Of Two CDs
This time two digital sources painted a very different picture. The difference was between a Red Book CD 16-bit/44.1 kHz and the same musical selection from a DSD recording with a native sampling rate of 2.8224 MHz. That is 64 times the sampling rate of 44.1 kHz, but only sampling one bit at a time. The DSD encoding of TOTO's performance of Africa made a huge difference. By direct comparison the Red Book CD seemed bland, it did not have the dynamism I knew was present on the original Vinyl recording. The DSD version was an ear opening experience. There was a huge dynamic transformation that swung open a door like a husband checking on his wife. The music had power, pace and drive that surprised me I had really underestimated the Minotaur's ability to portray dynamic contrasts.

Lesson Learned
Before we move on, at an Audio Society meeting we used a Minotaur amplifier to drive a set of Pipe Dream's speakers. They are impossibly difficult to drive seven foot tall multi-driver speakers. All who attended experienced a remarkable and unexpected high level of performance, no problems. Not a typical hollow state tube amplifier and not your typical solid state sounding amplifier either. You have the option to operate the Minotaur in Class- A normal bias up to one Watt or change the amplifier bias point to operate (still in Class A) up to five watts per channel. This unusual option allows the user to tailor the sound to compliment their favorite music genre. At the five watts bias setting the sound is noticeably warmer with a wide and deep sound stage. Those who share my love of air and space will agree the Hi Bias Minotaur amplifier speaks more to the Audiophile who listens to classical music and acoustic ensembles. Additionally you will find the Adagio Phono stage and the Minotaur line amplifier are cut from the same fabric and compliment each other. The expansive performance panorama and all the subtle harmonic tonal structures contained in music are made even more evident by this combination. During the audition period the amplifier was invariably in the normal bias setting matching the kind of music I listen to. At this setting the performance has better transient attack, but there is a trade off. Some of the warmth and subtle wood overtones inherent in the sound of say, a string quartet would be less evident. But no matter how you set the bias the second harmonic sound of tubes is always there. At one Class A watt I believe it combines the best qualities of both tubes and solid state.

Bottom Line
Dear audiopals we are gathered here today to join man and Minotaur in an aural bond. Remember for better or worse the Minotaur is a highly detailed and discriminating device. All made obvious to me in a direct source comparison. Can you promises to provide a proper acoustic environment and employ only quality music? Feed it with a substandard signal and you relationship will surely suffer, I found out that a random pick of some of my music selections sounded just mediocre. Needing to reset the phono cartridge/tonearm alignment provided positive proof the Minotaur was telling the truth and nothing but the truth. Ask yourself how compatible are you? That will depend on a little soul searching and self-assessment. Are you an extrovert, a party person or are you more into some creature comforts. Although capable of lease breaking dynamic balls you would most certainly be missing the point. It's not really about raw power. You can find that amplifier in the back of somebody's SUV. A lasting relationship can only endure with an abiding love of subtle minutiae. I would much rather settle down with a good book and a little libation to smooth off some rough edges. By virtue of its power to resolve instrumental timbers with pace, pitch definition and an immersible three dimensional space (and gravitational waves). It can carry you back in time to the place where it was recorded. And this is where I choose to stop my search, and to listen. Highly recommended, this would be a marriage made for a discerning music lover. If this describes you, then by the power of the Large Hadron Collider I pronounce you man and Minotaur.

Remember to Enjoy The Music. And from me, Semper Hi-Fi.

Specifications
Type: Integrated stereo amplifier
Frequency response: 3 Hz to 150 kHz
Rated Power Output: 140 W per channel @ 8 Ohms, 220 W per channel @ 4 Ohms
Tube Complement: Two 5751 (or 12AX7), four 12AT7 and one 12BH7
Output Transistors: Four MJL3281A and four MJL1302A
Output Noise: < 110 uV RMS (C-weighted 30Hz - 8kHz)
Input Sensitivity And Gain: +0 dBu (0.78 V RMS) for full output, 32 dB gain
Total Harmonic Distortion: Typically <0.08% 
Input Impedance: ~50 kOhms
Output Impedance: 40 MOhms @ 1 kHz 
Dimensions: 17.2" x 17" x 6" (WxDxH)
Weight: 34 lbs.
Price: $2490

Company Information
Tavish Design, LLC
P.O. Box 129
Amawalk, NY 10501

Voice: 914-262-6988
E-mail: info@tavishdesign.com 
Website: www.TavishDesign.com