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Wednesday, October 8, 2014

Audiophile Review!
Benchmark AHB2 Stereo Amplifier,
Exclusive Benchtest!


Exclusive First Benchtest!
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Brevis...
Price: $2,995
Likes: super smooth and open
Dislikes: not big and heavy
Wow Factor! 130+ dB SNR
More info: Benchmark AHB2


 by John Gatski
  Following my initial first listen to groundbreaking Benchmark’s AHB2 amplifier late last year, I finally got production samples in July and got a chance to do more in-depth listening in stereo — and in a multichannel setup. EAN also performed a series of lab measurements to verify the amazing numbers claimed by the manufacturer — especially signal to noise.
Features
  The $2,995 AHB2 stereo amplifier was designed in conjunction with THX. It features a bipolar-output power section, 180 WPC output RMS, (350W bridged mono), balanced XLR input, three-way input sensitivity switch and dual speaker input options: binding posts and Speakon, a professional termination that uses a twist-on connecter. The AHB2 is housed in a compact enclosure that measures only two times a DAC2 (11" W x 9"D to back of connector x 3 7/8"H). This is not your typical hi-fi sized amplifier.
  The AHB2‘s key highlight is the extremely low noise and distortion. Distortion at .0001% and signal-to-noise/dynamic range measured at more than 130 dB!!!! That is digital-like specs from an analog amplifier, and a source of pride for co-designer and Benchmark VP John Siau.

The AHB2 design
“It was my goal to create a power amplifier that matched the performance of the DAC2 D/A converter,” Siau explained. “After all, the performance of the D/A converter is only useful — if it can be delivered by the downstream power amplifier.”


Note the addition of the input sensitivity switch


  Siau said that the amp has exceeded his expectations — in terms of measured performance. The SNR of the AHB2 was spec'd at 130 dB (A-weighted) and THD is -115 dB, just about as good as the DAC2’s measurements. “The AHB2 power amplifier was designed from the ground up to deliver the full performance of the DAC2 HGC," he emphasized.
  In order to achieve the new amp specs, Siau utilized THX amplifier design concepts, but he also designed his own signal path design in order to get these impressive numbers and audiophile-accurate audio signatures. Siau said the following design highlights enabled Benchmark to create the AHB2’s “fantastic” performance signature: 
 •Low gain (9 dB). This allows +22 dBu input at amplifier clip, which is essential for low noise;
•Patented feed-forward error correction, which virtually eliminates crossover distortion, a problem, Siau says, is still common among typical amplifier designs;
•The feed-forward design also makes bias currents unnecessary, and non-critical. Thus, Class B operation is possible with very low distortion;
•The multiple bipolar output stages are run in parallel to eliminate crossover distortion; one output stage is active, while another is in the crossover region;
•The Class AB output stage uses very low bias current. (Due to low bias currents, idle power consumption is only 20 watts.);

 The Warren Bernhardt recording’s dynamic range is vast, and the AHB2 showcased its dynamics — with a live, accurate, musical portrait of the album, wrapped in a stunning smoothness. The transients were dead-on accurate — without the shrillness I often hear in bipolar amps.

•The feed-forward design even makes the more efficient Class H or G operation possible — with no rise in distortion at class H or G switch point (Class H, or G, rail switching at a 1/3 power threshold);
•A tightly regulated power supply — with high-bandwidth control loop on the switch-mode power supply — responds to amplifier loading over the entire audio band, and at ultrasonic frequencies;
•The amplifier does not rely on capacitive energy storage, and the switch-mode power supply eliminates AC line magnetic interference to levels not possible with a linear power supply;
•The AHB2’s greater than 200 kHz bandwidth allows it to achieve excellent inter-channel phase at 20 kHz and greater-than-0.1 Hz low-frequency cutoff is said to minimize low-frequency phase shift;
•The feed-forward design also improves damping factor for improved bass response, and the PCB uses balanced star-quad signal and power supply distribution to minimize magnetic interference.
•Siau said that certain THX design elements allow him to make the amp as efficient as possible, but the AHB2 design was optimized for low distortion and low noise.
  “It was not optimized for the highest possible efficiency that could be achieved with the new THX topology,” Siau explained. “Nevertheless the AHB2 is much more efficient than a conventional Class AB design. Peak power does not vary with AC line voltage (due to the regulated supply). Likewise, power drawn on one channel does not influence the power available from the other channel.”
  Though the AHB2 utilizes a switching power supply, Siau explained that the overall amp design is not a “switcher.” “The AHB2 is a linear amplifier, it is not a switcher,” he noted. “For this reason, it produces very little out-of-band noise. The A-weighted noise is only 2 dB less than noise measured over an 80 kHz bandwidth. This was an important design goal because ultrasonic noise can be folded into the audio band by the non-linearities in speaker transducers.”


Premium parts, laid out nice and tidy.
Click here  for full benchtest


  The omission of the unbalanced input was intentional, according to Siau. You can use unbalanced sources with the AHB2 (the amp’s 2V and 4V sensitivity settings provide full compatibility with unbalanced sources), but you need adapter cables so that the balanced receiver can connect differentially to the RCA jack at the source device. Pin 2 is wired to the RCA hat, pin 3 is wired to the RCA ground.
  This back-referencing is essential for establishing a low-noise connection over a 2V interface. “The omission of the RCA jack is intentional. It forces the user to use a back-referenced connector cable to establish a balanced connection between the RCA output and the XLR input,” Siau said.
  He noted that the 2V RCA unbalanced output utilized by countless hi-fi equipment impedes high resolution playback performance. Siau claims that most unbalanced 2V outputs struggle to exceed an SNR that is better than 100 dB, and very few unbalanced outputs will come anywhere close to reaching 130 dB SNR, He noted that the Benchmark DAC2 series approaches 130 dB SNR via its unbalanced analog output, due to use of a low-impedance voltage divider (pad).

Like the Benchmark D/As and A/D, the company believes that great measurements correlate to great sound. In the case of the AHB2 I totally agree.

  Though he insists the balanced output/input path is the way to maximize noise performance from a hi-fi component, Siau said that Benchmark has “put considerable effort into overcoming the limitations of 2V unbalanced inputs. The input amplifier on the AHB2 has very low equivalent input noise. We can deliver the full performance of the AHB2 over a 2V unbalanced interface, but only if the source impedance is low. Johnson noise will degrade the performance if the source impedance is too high. The special unbalanced-to-balanced input cable rejects hum that can be introduced by traditional unbalanced connections.”

Production sample review
  For a more thorough sonic and user impression, I spent several weeks with the production version AHB2s. Since my late 2013 audition of the prototype, Siau had tweaked the performance even more before sending me the review samples. He was able to get even better specs in the final version, with S/N exceeding -130 dB. He also assured me that the slightly forward midbass that I heard during the prototype listening sessions is no longer there; the prototype had an out-of-spec part, according to Siau. And that statement indeed is true; the bass on the production versions was tight and clean.

The set up
  For my stereo testing, I auditioned a single AHB2 in a number of audio scenarios, including a two-channel audiophile amplifier, and as a multichannel hi-res audio system at a trade show demo (after receiving two additional amps from Benchmark). I also put the amp into my home recording system, using the AHB2 to power a pair of Bryston Mini-Ts and Legacy Studio speakers.
  In the audiophile system, I mated the AHB2 with several speaker sets including my reference MartinLogan Montis electrostatics, Pass Labs SR-1 three-way tower, the Bryston Mini-Ts, and Legacy Expressions, a two-way tower (review upcoming). Associated equipment included Coda line-stage preamp, Oppo BDP-105 universal player, Benchmark DAC2-D D/A, Mytek Stereo192-DSD D/A, Oppo HA-1 discrete HP amp-D/A. A Dell Venue 8 tablet also was used as a hi-res digital player, via USB Audio Player Pro software — up to 24/384.


Note the size compared to a DAC2


  All connecting cables were furnished by Wireworld, and I connected all three-prong power cord components to the AC with Essential Sound Products (ESP) Essence II power cords and their Essence power strip.
  After a few days of break in, I employed the AHB2 into my audiophile system with the PASS SR-1 speakers. The AHB2 is a simple amp to operate. It contains a simple on/off front-panel switch, and rear-panel sensitivity selector switch and bridge mono switch.
  As mentioned, the production version is equipped with the pro-spec Speakon, twist-locking speaker cable connecters, as well as normal binding posts. The Speakon option is due to Benchmark’s new speaker, SMS1, that comes with that connector. According to Benchmark, the Speakon connector option ensures the best connection for a speaker/amp union and is more resistant to terminal oxidation, which degrades amp performance to speakers over time. (Siau said the Speakon also has lower distortion, according to his measurements.
  However, the Benchmark speaker is the only audiophile speaker that I know of with the Speakon connector, thus, this amp’s connecter may not get much use with most other hi-fi speakers. Benchmark sells a Speakon-to-spade cable to at least give half of the Speakon equation. (I did have a chance to use the new Benchmark speaker with the AHB2 for a full Speakon connection, but only for a few days before I posted the amp review to EAN. The speaker will get its own review).

The audition
  The first thing I noticed with the AHB2 is the lack of idle noise. Put your ear to the tweeter, and none of the low-level hiss you hear with conventional, high-gain amps can be heard. With no signal, nary a whisper from the Benchmark — even when adjusting the sensitivity switch to the higher gain positions.
  As with the prototype listening sessions, I first played Warren BernhardtSo Real SACD, an album that has a full dynamic range and spacious soundstage — piano, drums and bass recorded direct-to-stereo. I connected the Oppo BDP-105 XLR balanced output to my Coda preamp then the pre was linked to the AHB2 and the amp to the Pass speakers.
  Versus the prototype, the AHB2 has switchable input-gain settings, which allows the end user to tailor the amp to various preamps. The Coda had no problem driving the Benchmark on any of the settings, but it took a few more twists of the knob to get a loud volume in the low-gain setting. I used the middle gain setting.

 According to Benchmark, the Speakon connector option ensures the best connection for a speaker/amp union and is more resistant to terminal oxidation, which degrades amp performance to speakers over time. 

  The Warren Bernhardt recording’s dynamic range is vast, and the AHB2 showcased its dynamics — with a live, accurate, musical portrait of the album, wrapped in a stunning smoothness. The transients were dead-on accurate — without the shrillness I often hear in bipolar amps. The AHB2’s sonic character is dynamic, open, with quick, taut bass — yet with the silky ease of the best tube amp. But tube amps don’t have the energy and speed in the transients, nor bass, that the Benchmark possesses.
  On the Gene Bertoncini - Body and Soul SACD, the production AHB2 relayed the same character — that warm, percussive guitar tone that I had heard on the prototype. This is one of favorite acoustic DSD recordings — with an expansive stereo image; Mr. Bertoncini’s expert, plucky dynamics were reproduced with precision and the album’s imaging is wide with oodles of depth between the layers.
  No matter what music I played through the Benchmark, the sound was always first rate in the midrange and treble — and with bass authority and smooth delivery at any level. And it did not matter which speakers were connected. Within each speaker’s character, the AHB2’s attributes shone through. Heavy metal. No problem. The fizz and thunderous volume of the Thin LizzyJailbreak CD was a bit easier to listen to with the Benchmark’s smooth (but not soft) delivery. Yet, this amp also handles the delicacy of a wide range of classical instruments, such as Janos Starker - Bach Complete Cello Suites on SACD.
  As a jazz guitar fan, I appreciated the AHB2‘s ability to convey the Kenny Burrell - Midnight Blue SACD, circa 1963, with that warm analog tape sound of Mr. Burrell’s Gibson hollow-body electric guitar. Ditto, for my audiophile LP version of Wes Montgomery - Full House and the Grant Green - Green Streets SACD.

An amp for the masters
  For recording pros and home audiophiles, who know their way around today’s record/edit systems, the AHB2 amp is definitely an amp to consider for those who like their separate amp and passive speakers. A small foot print, and honest, accurate amplification — without noise in an easy-to-monitor/zero ear fatigue mode. I mated the AHB2 with two Bryston Mini-T passive speakers (review upcoming) and Legacy Studios in my edit suite.
  With either speaker, the playback of hi-res recorded tracks, as high as 24/352.8 and DSD2X, was open, detailed and ultra smooth. The Legacy delivered that exceptional smoothness and the new Bryston speaker beamed copious detail from work station monitoring rig. I spent hours mastering jazz guitar 24/352.8 cuts from recordings of my precious Gibson L5 and Fender Twin Reverb — without one ounce of ear strain from the aHB2 and speakers — especially those Legacy Studios woth ribbon tweeters.
  I also got a chance to utilize three AHB2’s at the 2014 Capital AudioFest in Silver Spring, Md this past July. In a 5.0 system, the Benchmark amps powered two Legacy Expressions and three Legacy Studio’s with various samples from a Windows server, which provided stereo and surround DSD hi-res music files, Blue-ray and DVD Audio surround music, as well as spirited movie soundtracks from an Oppo BDP-95 universal player.

 The AHB2 multi-amp system delivered all the music and film soundtracks, along with plenty of my favorite stereo hi-res, in this medium-sized hotel room; the amp performance was perfection: a wide multichannel spread of instrumental layers, rock-solid center vocals and, best of all, the amps delivered the dBs without strain and exhibited zero harshness.

  The system delivered all the music and film soundtracks, along with plenty of my favorite stereo hi-res, in this medium-sized hotel room; the amp performance was perfection: a wide multichannel spread of instrumental layers, rock-solid center vocals and, best of all, the amps delivered the dBs without strain and exhibited zero harshness.
  In fact, on movie soundtracks, such as Avatar and the first Captain America film, viewed on Blu-ray, I had inadvertently pushed the level to 96 dB, but it did not sound that loud; I, nor my guests, succumbed to any ear fatigue. This is one of the easiest-on-the-ear amps I have ever auditioned.
  BTW, that ease and ability to deliver the finesse and fine detail, does not go away with the bridge mono operation. You just get more oomph (over 300 watts of extra oomph) to fill up the bigger rooms. And the noise still stays low.

The verdict
  In talking to various audio engineers about Benchmark’s amazing signal-to-noise numbers, I heard some skepticism and a array of opinions that an ultra quiet amp does not matter on the real listening world. “Any noise is lost in the music anyway,” one engineer said. But, as I said in my original first look last December, other audio components, such as DACs, players, etc. have shown generational improvements in measured performance, and I believe these improvements have brought audible, if subtle, improvements as well.
  For those who listen with very accurate, discerning speakers, an extra 20 dB of lower noise could be heard — in terms of ultra detail that may be hiding in the noise of an average audiophile amp. The -130 dB noise/dynamic range just gets us that much closer to the live music. After years of amps languishing in the 100 dB SNR threshold, Benchmark has pushed the mark way higher.
  As for specs, I had no doubt that the AHB2 would measure well. In our EAN SpecCheck, Bascom King’s tests (Click here to go to EAN Spec-Check) showed that the amp may be the quietest analog amp ever built. As good as that accolade is, I don’t hear a sterile, thin amp — attributes sometimes equated to amps with stellar measurements. The numbers confirm its impressive audio delivery.
  Like the Benchmark D/As and A/D, the company believes that great measurements correlate to great sound. In the case of the AHB2 I totally agree. I can’t wait to get two more for a full-high-end home cinema amp test in my big A/V room. For now, based on mostly stereo listening, it receives, with certainty, an Everything Audio Network Stellar Sound Award.

John Gatski is publisher/owner of the Everything Audio NetworkArticles on this site are the copyright of the ©Everything Audio NetworkAny unauthorized use, via print or Internet, without written permission is prohibited.

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Benchmark AHB2
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Bench Measurement and Commentary
Benchmark AHB2 Power Amplifier

  The new Benchmark AHB2 is the result of considerable research and patents on its resultant circuitry. The intent was to make it an ultra low distortion design. I would have to say they succeeded as it is the lowest noise and distortion power amp I have measured and I have measured a LOT of power amps in my career.
  Measurements were made at the 2V sensitivity and in stereo mode unless noted. I did spot check amounts of distortion at the lower sensitivities and they were little different than at the 2V sensitivity.


The S/N ratio was about 131.6 dB. Pretty impressive, and this is the lowest output noise level I have seen in any power amplifier I have measured!

  Frequency response as a function of loading, not surprisingly, is mostly independent in the audio range with a typical effect of more roll-off with lower loading in the ultrasonic range. Overall HF bandwidth is quite high with a 3 dB down point of 200 kHz or more.  This is shown plotted in Figure 1.

Figure 1 - Frequency Response: Open, 4 and 8 Ohm Loads

  What is a good measure of success in lowered distortion is a plot of THD+N of a 1 kHz and SMPTE IM distortion as a function of power output for 4 & 8 Ohm loading.  This is shown in Figure 2. The THD+N is pretty much noise dominated up to clipping whereas the IM distortion does show above the noise above 10W of output.

Figure 2A - IM Distortion 4/8 ohm Loading


  Clipping with the design is very abrupt and my usual attempts to put extra points in the clipping curve to get the highest power before distortion rises was an exercise in futility. When connected in bridge mode, power was close to 400W into an 8 ohm load.  1 kHz THD+N and SMPTE IM distortion are plotted in Figure 2B.

Figure 2B - 1 kHz  THD+N/SMPTE IM Distortion



  In Figure 3 THD+N is plotted vs. frequency and power.  Here, a 4 ohm load is used and distortion is down in the noise at all power levels up to 2-3 kHz where is start to show as distortion.  The amount of rise with frequency is very low and stays below 0.01% at 20 kHz.  Amazing!

Figure 3 - THD+N Re: Frequency/Power
Red=2W, Magenta=20W, Blue=60W, Cyan=120W, Green=180W


  Damping factor vs. frequency is plotted in Figure 4 and is quite typical of solid stage amplifiers being high at low frequencies and falling above a few hundred Hertz. Damping factor in mono mode, while not measured, would be expected to be about half that each channel in stereo mode as the outputs of the two channels are in series with the load in mono mode. 

Figure 4  - Damping Factor Vs. Frequency


  Another benchmark – pun intended – measurement is a spectrum of 10W 1 kHz THD+N arranged logarithmically along the horizontal axis to show line frequency harmonics as well as the signal harmonics.  I have not seen one of these with such low numbers.  I couldn’t increase the sensitivity any more to show the noise floor.  But look at that third harmonics component at 0.0001%!  That is a low distortion number for sure.  A bit of 5th harmonics also shows with the even harmonics down in the noise.

Figure 5 - THD+N Re:Frequency/Signal Harmonics


  Of interest is how low the noise level is in this amplifier. I measured noise in three bandwidths, wideband (WB), 10Hz – 20 kHz (10-22K), and with A weighting (A wtd) for all three input sensitivities. The inputs were terminated in 300 Ohm per phase.  Results in uV are shown in Figure 6 for both channels. Taking the number of uV of noise and relating them to the reference power output voltage for 100W/8 Ohm, the A wtd. noise for the 2 V sensitivity is a little shy of the claimed 130 dB S/N ratio at 128.1 dB. But at the 4 V sensitivity, the S/N is 130.4 dB and at the 9.8 V sensitivity, the S/N ratio was about 131.6 dB. Pretty impressive and this is the lowest output noise level I have seen in any power amplifier I have measured! (Editor's note: Benchmark measured 3 dB better when input was terminated with 60 Ohm impedance input.)


Figure 6 - A-Weighted Noise (in uV) Re: Wideband, 10 Hz- 22 kHz

 A few final observations: AC line draw at idle was 20W with a power factor of 0.46 and 0.37A. Input impedance was an easy to drive 47K at 1 kHz.


—Bascom H. King


  Bascom King is owner and chief technician for BHK Labs in Santa Barbara, Ca. and a regular contributor to the Everything Audio Network.



Monday, September 29, 2014

Recording Review!
Mojave Audio MA-100 Small Diaphragm
Omni/Cardioid Vacuum Tube Microphone
"A New Look at Royer's First Tube Mic"


©Everything Audio Network


Brevis...
Price: $795; $1,500 (stereo-pair kit)
Likes: exquisite sound, omni included
Dislikes: why did I not try this mic years ago?
Wow Factor: classic Euro-flavor small mic


by Dr. Frederick J. Bashour

  My previous experience with David Royer’s Mojave Audio microphone line has been with his solid-state models, the MA-301fet and the MA-101fet. — both reviewed on EAN. But before Mojave released those solid-state FET models, the company first produced his vacuum tube originals—the large-diaphragm MA-300 (and MA-200) and the medium-diaphragm MA-100 reviewed in this article. In fact, according to David Royer, the miniature JAN 5840 tube-based MA-100 is his oldest microphone design, dating back to the mid 1980s.
  Since I own so many vintage vacuum tube mics already (and practically no solid state models), I had frankly been more interested in auditioning Royer’s solid state models. Having now heard (and favorably reviewed) those two models previously in EAN, I finally gave in and told my editor, “OK, now you can request a pair of MA-100s, and we’ll see how they compare to the usual Neumann, AKG and Schoeps suspects from my collection of vintage mics from the fifties and sixties.”
  So let’s answer that question first. Just as vintage Neumann KM 53/54s, AKG C60s, and Schoeps M-221Bs sound nothing like each other—to engineers familiar with all of them—the Mojave MA-100 sounds similarly dissimilar to the AKG and Schoeps models. However, I was pleasantly surprised that my pair of MA-100s did sound “in the same family” as my prized pair of (1-micron. Stephen Paul-modified) Neumann KM-54s and original nickel diaphragm KM-253s. I say “surprised” because, first, all the vintage “pencil-type” mics have approximately the same size diaphragms—around ½-inch, while the MA-100s have larger ¾-inch diaphragms.
With the MA-100, Dave Royer designed the quintessential, modern, pencil-type,  vacuum tube microphone for instrument recording. I only regret that I waited so long to try it!

  As I wrote in my earlier article—concerning the Mojave MA-101fets, which share the same capsule with the MA-100s—there are several ¾”-diaphragm mics available today, but “back in the day,” there were only the Sony models (C-37, C-500, etc.), and they were thought of as (or, at least, looked like) the large diaphragm models. Today, such mics are regarded as “in-between” small and large diaphragms—which makes perfect sense—but in the case of the MA-100/101fet’s capsules, they’re set up to act like smaller diaphragm mics, as will soon be explained. 

Features
  Spec-wise the Mojave contains a .8-inch wide, 3-micron thick diaphragm. The mic comes with cardioid or omnidirectional capsules. The frequency response is 20 Hz - 20 kHz, +/-3dB. Sensitivity is listed at -37 dB, re 1V/pa. Maximum SPL is 130 dB. The self noise is 16 dB. Impedance is 450 ohms. As mentioned, the MA100 is a bit longer than typical, small diaphragm “pencil” mics, 5.5-inches long.
  Each MA100 comes in its own carrying case with the power supply, shock mount and the connecting cables. Retail price is $795. You can also buy the mics in a $1,500 “stereo kit” — the MA100SP — with both microphones, a single power supply, the two mounts and a stereo bar, with all the hardware placed in a single case.
  Physically, the size of the parts used in the MA-100 preamp section produced a cylindrical tubular enclosure with the same diameter as the capsule, whereas the large transformer used in the MA-101fet necessitated a larger diameter for the preamp’s enclosure than the capsule’s diameter—almost a seeming contradiction for a solid-state mic.
On a warm-sounding room, the Mojave MA100 omni, again, is one of the very few small mics that can be used to close-mic a classical violinist, without EQ, and it sounds really good, “just like a record.”

  Nonetheless, the vacuum tube MA-100 (containing the same miniature JAN 5840 vacuum tube Royer uses in all his mics) “looks like” a standard small diaphragm mic, only a tiny bit thicker. But appearances can be deceiving, for the MA-100 makes use of an output transformer which might even be larger than the one which forced Mojave to increase the diameter of the MA-101fet’s cylindrical metal enclosure beyond what is usually considered “normal” for a pencil-type microphone. “But where is the MA-100‘s transformer?,” you ask?"
  When I reviewed Mojave’s large diaphragm MA-301fet, I wrote from the point of view that, if I were to build a high-end solid-state microphone (in my head) from scratch, I might end up with one very similar to the MA-301fet. I made that rather strong statement based on my personal experience, over many years, with myriad microphones, and my long relationships with the best of today’s artisan microphone designers, especially the late Stephen Paul.
  Well, I’m about to go out on a similar limb and support a view, in the present article, that Dave Royer — the guiding force behind both Royer Laboratories and Mojave Audio — has combined the best of vintage and modern microphone design philosophies. With the MA-100, Mojave has produced the quintessential modern, pencil-type vacuum tube microphone. I only regret that I waited so long to try it!
  Just as in that previous article, a little bit of history is also in order here. Only this time — thanks to my trusty iPhone — I have a few supplementary photos as illustrations. First, let’s return to the question of that elusive output transformer. From the 1970s onward, engineers who thought “small diaphragm microphone” would suggest the AKG C-451 or the Neumann KM 84. Although they sounded quite different from each other, one thing they had in common was the presence of a little “peanut” output transformer, right behind the XLR connection, opposite the end with the capsule.



AKG C 60, Neumann KM 53 and 54, MA-100
An inside peek: C 60,  KM 53 and MA-100


  However, to the previous generation of engineers, working in the late Fifties and throughout the Sixties (before the days of the 451) AKG sold a markedly smaller small-diaphragm microphone, the C 60 — and that mic even had a vacuum tube in it! In fact, I own six of them; there are several angles of one of mine visible in the pictures below. If you examine my photo carefully, you’ll notice the tiny AC701k vacuum tube, a few passive parts, but not much else. No transformer! Now, please examine the Mojave MA-100. Its innards are even more spartan than my C 60’s; all one can see is the 5840 tube—no resistors, nada, that’s it; just the miniature tube!
  I did not photograph one of my C 60 power supplies, but please take a look at the Mojave power supply, with its cover conveniently removed. The two large cylindrical Jensen JT-MB-C mic output transformers sort of jump out at you, don’t they? Besides the multi-voltage AC transformer, they are the largest parts in the box!
  Thus, the answer to the question is: just as AKG did with its C 60 mic (from the 1960s), Mojave also “separated” the connection between the output from the vacuum tube and the mic’s output transformer by the microphone cable! Yes, there are vacuum tube circuits that can easily drive a 10-meter microphone cable without noticeable degradation, and the various flavors of the cathode-follower circuit are some of them.
You can also buy the mics in a $1,500 “stereo kit” — the MA100SP — with both microphones, a single power supply, the two mounts and a stereo bar, with all the hardware placed in a single case.

  One also shouldn’t forget that Mojave supplies two capsules per mic—cardioid and omnidirectional. And, yes, one can swap capsules between the MA-100 and MA-101fet! The colors don’t match on a normal MA-100, but it’s a cool look, reminiscent of a vintage AKG C 60, with its shiny capsule and matte body! (See photo.) Swapping the MA-100’s capsules with the MA-101’s gives you a completely black mic, if you ever need that on stage. I noticed no obvious difference (besides the color) between the MA-100’s silvery capsules, and the black ones that came with my MA-101fets.

The audition
  So now, let’s talk about the sound of the Mojave MA-100, and the reason why it didn’t stay long in the closet with my vintage mics; these modern small condensers spent most of their time on a pair of mic stands, out in the large room at Studio Dufay — ready for numerous recording projects that might come along.
  One “advantage” of modern digital recording practice is that—with today’s interfaces and DAWs—it’s really easy to add extra recording channels/tracks. Accordingly, many classical music engineers, yours truly included, often record extra mics (or mic pairs), “just in case — tracks which usually don’t end up in the final mix or, if they do, are sometimes mixed so far down that they just add a little “atmosphere” to the mix.
  And if that engineer happens to be auditioning new microphones, such a scenario is perfectly conducive to extended listening — simply put up the new mics, bus to a pair of extra tracks, and record the session normally. Later on, when everyone has left, the engineer now has an entire session’s worth of “examples” of how the new mics sound, recorded in sync with all the “normal” mics. Even better in my own case — recording classical music for CD release — all the tracks stay together during the editing process (using the Pyramix DAW), right up to the absolute final mixdown. So, at any time, it would be possible to put together a “finished edit” using only the mics I just happened to be auditioning while I was originally recording the session(s).



MA-100 power supply


  As I mentioned, I’ve concluded that the Mojave MA-100s sound “in the same family” as my vintage Neumann KM 54s. By that, I mean, first, that they sound much closer to my KM 54s than they do to any of my comparable Schoeps, or to any of my comparable AKG pencil mics.
  Second, compared to other members of the Neumann KM 53/54 family (I own multiple examples of each) here at the studio, it sounds close enough to them (capsule for capsule, etc.) to actually be considered sounding more like one of those actual vintage German mics, than any other model of mic I’ve heard.
  I’m not theorizing about how Dave Royer accomplished this sound quality with a ¾-inch capsule design; I’m just guessing that it’s a whole combination of factors; the sum total has contributed to this happy serendipity. Or maybe, we should just call it good engineering! Certainly, remoting a high-quality, large mic output transformer to the power supply was a smart move.
  The capsule, itself, sounds wonderful to my ears, with good off-axis sound pickup — maybe 80% as smooth as that of a true ½-inch diaphragm. And by choosing to use 3-micron Mylar film, as in the MA-101fet and MA-301fet models I previously reviewed, Dave Royer has, again, made a sensible compromise between “peakiness/smoothness” and diaphragm stability and longevity.



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  My own 1-micron pair of KM 54s, which I’ve owned for about twenty years, are still OK, but I treat them with kid gloves. However, their upper midrange peak is a bit lower in amplitude, and farther up the frequency spectrum, with the end result that they have a bit less of the typical Neumann “brash” sound quality than do the Mojaves. But we’re talking very subtle here — the difference in sound between 3-micron and 1-micron diaphragms!
  When I compared the Mojave MA-100 with its omnidirectional capsules to a matched pair of my Neumann KM 53s, the difference went in the opposite direction. That is to say that, since my vintage Neumanns still have the original nickel diaphragms, they sounded a little more aggressive, a little more “Neumann-like,” than did the 3-micron Mylar diaphragms of the Mojaves. And this is a good thing, for I feel that the omni diaphragms are the unsung heroes of this mic. In a good room, used close-up, or even medium-distance from just about any acoustic source, it doesn’t get any better, any more faithful to the original sound, than a small diaphragm omni.
In a good room, used close-up, or even medium-distance from just about any acoustic source, it doesn’t get any better, any more faithful to the original sound, than a small diaphragm omni.

  And with the Mojave MA-100’s extremely wide frequency response — coupled to the outside world by that awesome large Jensen transformer and elegantly simple cathode-follower circuit featuring the tiny 5840 tube, a few premium passive parts, and not much else — it can reproduce any source’s low end with just the right weight and authority.
  Just try a pair of the omnis: about three directly over a 9-foot grand piano, lid removed — one centered over the treble strings, one over the lower strings — and be amazed! On the other end of the spectrum, in a warm-sounding room, the Mojave omni, again, is one of the very few small mics that can be used to close-mic a classical violinist, without EQ, and it sounds really good, “just like a record.”
  And either of the cardioids or the omnidirectional capsules work beautifully, in pairs, on acoustic guitar. I know that sometimes I’ll use two large diaphragm mics on acoustic, but for those situations where that approach simply produces too “large” a sound, switching down to omni MA-100s first, and then down to the cardioids, if necessary, will reduce the “size” of the sound without ever making any of the “sizes” sound thin or gutless.

The verdict
  I wish I could illustrate this article with some of those tracks I’ve recorded over the past year or so with the MA-100, but copyright restrictions (both in the pop and the classical repertoire it was used on) preclude my doing so. All I know is that, having this pair of Mojave MA-100 mics at Studio Dufay for the past year has brought smiles to the faces of just about everyone I’ve tracked and, as a new addition to the “small diaphragm tube Neumann” category in my mic locker, it has made my life a whole lot easier.
  Thank you, Dave Royer. You’ve done it again! Now how about a small-diaphragm stereo mic—on the line of the Neumann SM 2 or 23, but like the MA-100, with the transformers down in the power supply? You’ve got all the ingredients, and I’ve already built it, in my head, for you...

  Dr. Fred Bashour has been a classical recording engineer for the past 45 years, with recordings released on over twenty labels, including Musical Heritage Society, Naxos and Dorian. His studio, Dufay Digital Music, is located in Western Massachusetts. He holds a Yale Ph.D. in Music Theory and is also an gigging keyboardist. He can be reached via the Everything Audio Network, everything.audio@verizon.net


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