Manley Labs MAHI Mono Power Amplifier Review 
Home Theater Power Amplifiers Mono Amplifiers
Written by Andre Marc   
Wednesday, 18 November 2009

The first time I got to hear a piece of Manley Labs tube gear was when I reviewed their superb Neo Classic 300B Preamplifier a few months ago. To say I was impressed would be an understatement. Albert Schippits, Manley Labs National Sales Manager, was also sure I would also be interested in reviewing their MAHI® mono block tube amplifiers.

Just to recap, Manley Labs, in Chino, CA, has been making pro audio and audiophile gear for several decades, and their leader, EveAnna Manley, has a distinct world view and a lot of common sense, in my opinion. First, she feels that the high end hobby should be fun, and that hifi components should be fun to use and listen to. I could not agree more. Secondly, she believes common sense and minimalism should rule the design. Simple, reliable design, with less circuitry in between your preamplifier, amplifier, and speakers, will allow you to get closer to your tunes.  Solidly built, functional, and superbly crafted products come out of the Manley factory with “Tubes rule!” as their semi official mantra.

The MAHI's are essentially mono block versions of the Stingray integrated amplifier, which has been universally praised by reviewers and consumers alike. The output stage is a push pull design. There are a number of things that make the Mahis unique, most of which I will get to shortly. The most distinct attribute of the MAHI's is that they use the EL84/6BQ5 tubes. These are driven by a 6414 dual triode driver and a 12AT7EH input dual triode. There are not too many EL84 based power amps around as most are only available in DIY kits.

MAHI Tubes Up Close

The EL84 tube has quite an interesting history. It was originally developed by Philips in Europe for audio amplification. It soon found its way around the world, being designated as the 6BQ5 in North America. I won't go into an eye glazing, micro history of the tube, but suffice it to say it has proven quite versatile for more than 50 years. It was also put to use by British Invasion bands during in the mid 60's inside their guitar amps, especially in the prized Vox AC30.

Construction and Features:

Coming back to what I mentioned as unique features to the MAHI's, there are several clever design elements. First, there is a toggle switch on the top right side of each chassis that give the user the option of switching between Ultra Linear mode and Triode mode. According to Manley, Ultra Linear mode offers more power, and a slightly more aggressive sound. Triode mode offers the sweeter, more textured presentation, but is a less efficient way of using a tube; hence less output power.

Next, the user has the option of toggling a three position switch that controls Negative Feedback settings from MIN (3dB's), STD (6dB's), and MAX (10dB's). Feedback is often employed in amplifier designs for greater stability and to lower Total Harmonic Distortion (THD). Basically, a portion of the output signal is fed into the input signal. There have been age old arguments on how much, or if any, to include in the input signal. There is a lot of information about it on the Manley website. I generally preferred Triode Mode with the Feedback setting at MIN, but will describe what I heard with each setting later in the review. The MAHI's are fittied with high quality German made WBT speaker binding posts and Manley's design of gold-plated, teflon insulated RCA jacks. The Manley’s are specified to out put 46 W max in Ultra linear Mode, and 25 W max in Triode mode.

Set Up:

I set up the MAHI's on the floor, supported by two blocks of solid Myrtle wood and connected my preamp / speakers.  I turned the bias pots to set the amps at 250 millivolts as specified in the manual, a simple adjustment to achieve 25mA current draw for the output tubes.  I did experience a ground loop hum when I first powered up the MAHI's. I solved the issue by plugging each mono block into a different side of the room, on separate AC lines. I didn’t encounter any other set up issues during the review period.

Listening:

I’ve recently gone on a bit of an Amazon buying spree, buying a bunch of remastered classic rock recordings and some new releases by variety of artists. First up, I put on some early U2 albums, October, and War.  My jaw absolutely hit the floor.  I did not know if I liked what I heard, or if it was different, but the music exploded out of the speakers.  I love my Harbeth Compact 7’s, but I never thought of them as “rock speakers”; just very versatile speakers that do all types of music quite well.  “I might be wrong”, to quote Radiohead.  The MAHI's grabbed the Harbeths by the throat and declared it was time to party.


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The first word that comes to mind is vivid.  The Edge’s ethereal guitar and keyboard lines rang out for what seemed forever, Bono’s vocals were as center stage as I had ever heard them; surprising after owning these records in every conceivable format. Everything took on another dimension. What shocked me, and I don’t use that word lightly, was the bass. It was punchy, articulate, and just plain life size. I honestly did not know my Harbeth Compact 7’s were cable of this type of performance.  My reference Audio Research VS55 simply cannot compete. Through the ARC, the bass is softer, less defined, and bit warmer.

Next up was a slew of Bert Jancsh CD's from his glory period in the mid to late 70’s. Along with being a pivotal member of the Pentangle, an iconic British folk rock band from the 60’s, Jancsh had a prolific solo career. His recordings were generally very well done, with acoustic guitars and vocals at the forefront, with a traditional rock rhythm section thrown in on about half the tracks.  I found myself really getting off on the woody tones of his guitar, any accompanying percussion, and his very distinct, slurred vocal style.

Moving through a variety of discs from the classic rock era I was stunned at the level of detail and immediacy I was experiencing. I believe the operative word for this review is immediacy.  The MAHI's transient speed totally floored me. This is not a “slow” tube amp. It’s as if they want to get the music from the source to your speakers as fast and as dimensionally as possible, so as not to delay your listening pleasure. The highs were liquid, feather light when called for, and extended.  The MAHI's do not offer the clichéd thick congested mids, but rather, the mids are supremely natural and transparent, with a pinch of warmth. I believe that this natural presentation deepens the soundstage, allows instruments and voices to retain their natural timbres, and draws the listener into the musical presentation.

Oddly, I tend to get bored with listening to the same genre of music for extended periods, and enjoy mixing it up. But…the Manley’s made it very difficult for me to break away from rock, soul, and R&B. The music had sense of propulsion and sparkle that I’m not quite used to. As much as I love my ARC gear, I equate the VS55 amp, rated at 50WPC, as a fine red wine. Complex, a bit on the mellow side, and not in a hurry, The MAHI's were more like whiskey; straight down the hatch, no sipping here.  It came through the door ready to kick ass with pure immediacy.  My final session of rocking out was with a few of the new Beatles remasters from the Stereo Box Set. I found it to be astonishing. Sgt Pepper, Magical Mystery Tour, and even A Hard Days Night were incredibly fun to listen to with the MAHI's. This music was alive and as exciting as the day it was recorded.

I tore my self away from the rock section of my cd cabinet and put on loads of John Coltrane, McCoy Tyner, and Bill Evans. The Coltrane tracks, 40 odd year old recordings, were thrilling.  The horns were brassy, dimensional, and inside the room. The legendary Coltrane rhythm section of Elvin Jones and Jimmy Garrison breathed fire on the up tempo pieces, and laid back with velvety ease on the ballads. Bill Evan’s elegant, precise arrangements were once again timeless. The organic interactions of the ensembles were rendered sublimely.

As one could expect from mono blocks, channel separation was superb. I don’t have much recent experience with mono blocks, although I grew up listening to my father’s Quad II’s. Every time I do get a chance to hear them, I wonder why I don’t dive in.  I usually talk my self out of it because the need for extra power cords, more tubes to worry about, and the requirement of expanded shelf or floor space. I tend to exaggerate the inconveniences though. The MAHI's performed flawlessly in my listening room.

Regarding the power ratings, I listen at reasonably high levels; just enough to feel the music and move some air, but not insane rock concert SPL’s. The MAHI's were vastly more than adequate even in Triode mode, which gives you between 18-25 WPC roughly depending on Feedback setting.  I honestly don’t understand when some audiophiles think monster mega watt amps are necessary to provide texture and scale. I have always preferred lower powered amps, as fewer output stages and less circuitry are theoretically simpler devices. I never, not once, hungered for more power, volume, scale, or dynamics in my medium sized listening room.

As mentioned previously, I generally preferred Triode mode with Feedback at the MIN setting. When Feedback was increased to STD and MAX, the music seemed to move back a few feet with each flick of the toggle switch.  Ultra Linear was bit more aggressive, and Triode mode was more seductive and musical. This will vary with your system. Different speakers, cables, preamps, and rooms will find you preferring one setting over the other. If you are a fiddler, you have to option to change the Feedback settings on the fly.  Toggling between Ultra Linear and Triode modes require the amps to be powered down before switching.

John Barker, of Sonic Culture, a local Southern California dealer initially recommended Triode Mode with MIN Feedback, and he was spot on. I’ve recently taken to getting second opinions on everything, and when I asked John to give me his take on the MAHI's, he replied with the following. “The Manley MAHI mono blocks represent an incredible audio performance value with uncommon flexible utility.  Build quality is solid, retro, and tasteful.  Performance rivals much bigger fish in the market for a fraction of the price.  The MAHI monos are fast, dynamic and punchy. The presentation is open, layered and extended with impressive low frequency articulation, control, weight and slam. 

The MAHI's are exciting, engaging and vivid amplifiers that bring the listener closer to the music.  Triode and Ultralinear operation and three negative feedback options provide flexibility for component matching or music preference.  Triode with minimum feedback is hard to fault.  Despite the modest output specifications the amplifiers will drive moderate to high sensitivity speakers with authority.   Made in California, with pride, there is little to no competition to match the performance.”

Well, at least I know I’m not the only one that heard what I heard. I could not agree more with this assessment.  When ears you trust come to identical conclusions as you do, after weeks of intense listening, it is a nice validation.  “Exciting, engaging, and vivid” indeed,

Quirks:

About the only issue I had with the MAHI's, outside of an easily solved ground loop hum, was that it has an unusually high input sensitivity.  My Audio Research SP16 preamplifier is a superb sounding unit in its price range, but it has one slightly annoying issue.  It only has 70 volume steps, controllable by a front panel button, or via remote; but no volume knob. Because of this for the first few days I got a bit frustrated by trying to find the volume “sweet spot”. One click up and it was a bit too loud, one click down, and it was a tad bit too soft. Interestingly, Audio Research, in upgrading the SP16 to the SP17, added 32 more volume steps!

Volume settings aside, the SP16 and the MAHI's sounded utterly superb to my ears. I do confess to being curious how the MAHI's would sound with the Manley Jumbo Shrimp preamplifier. As a matter of fact, as a side note, I actually wonder how a high quality passive preamp would work with the MAHI's. I wish I had one on hand, as that would a real purist approach. I’d guess it would be a winning combination.

Mahi Overhead View

Towards the end of the review period, I took delivery of a solid state preamplifier by a top flight manufacturer of solid state gear. The MAHI's performed flawlessly with this unit as well, and the luxury of a volume knob allowed me to find a sweet spot for the volume on each disc I played.  The prospective buyer should thus be aware that your preamplifier selection should one with made with care, whether tube or solid state.

Conclusion:

The Manley MAHI mono blocks are a remarkable achievement. Did I mention the price? $2500 per pair.  I had to double check, and check again. I honestly have not seen a product at this price point with this level of build quality, sound, and made in the USA to boot. These amps are not huge physically, but the sound is BIG.  I can thoroughly recommend the Manley MAHI mono blocks to any audiophile.

 

Specifications

  • Input Tube: 1 x 12AT7EH large plate Eletcro-Harmonix Russian
  • Driver Tube: 1 x 6414 JAN NOS GE or Raytheon branded 
  • Output Tubes: 8 x EL84 Ships with Russian NOS EL84M (aka 6Pi14Pi-EB)   
  • Output Tube Quiescent Standing Current: 25mA 
  • Set Bias for 250mVDC measured across each 10 ohm cathode resistor 
  • Gain: 29dB 
  • Negative Feedback: MIN= 3dB; STD=6dB; MAX=10dB of global NFB 
  • Input Impedance: 110 Kohm 
  • Input Sensitivity for Maximum Output Power: defined as input voltage required in order to produce maximum power output reaching 1.5% THD @ 1KHz
  • Maximum Output Power: defined as power output reaching 1.5% THD @ 1KHz 
  • Triode Mode, 28W
  • Ultra Linear Mode 46W
  • Recommended Speaker Load: Optimized for 5 ohms
  • Dimensions: 11" deep x 10" wide x 5" tall Shipping weight each: 18 pounds 
  • Price: $2500 per pair

Reviewer Setup 1

  • CD Player: Naim CD5x with Flatcap 2X
  • Preamp: Audio Research SP16
  • Amplifier: Audio Research VS55
  • Speaker: Harbeth Compact 7ES3
  • Cables: Kimber/QED/Acoustic Zen (AC)/Transparent (AC)
  • Accessories: Symposium Rollerblocks, Shakti Stone


Reviewer Setup 2

  • CD Player: Marantz 5003
  • Music Server: Squeezebox 3
  • DAC:CIA VDA-2 with XPS
  • Preamp: Belles Soloist 3
  • Amplifier: Revox A722
  • Speaker: Spendor S5e
  • Cables: Kimber/QED/Transparant/Shunyata(AC)/PS Audio(AC)





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