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Manley Labs MAHI Mono Power Amplifier Review  Print E-mail
Home Theater Power Amplifiers Mono Amplifiers
Written by Andre Marc   
Wednesday, 18 November 2009
Article Index
Manley Labs MAHI Mono Power Amplifier Review 
Listening Session cont.
Quirks and Conclusion

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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