The Manley Mahi (cleverly named since they're monoblocks and when you have two, you have Mahi Mahi) are high-end, mid-powered monoblock hi-fi amplifiers utilizing a quad of EL84s in the power section, a 12AT7 at the input, and a 6414 driver tube. Fans of tube rolling take note: it's best to stick with the EL84M power tubes sourced by Manley themselves for safe, reliable operation--but you can have yourself some fun with the 12AT7s The Mahis come well packed in nice boxes with excellent purpose-made foam packing, and the amps themselves are petit-sized at less than a foot wide or deep and about half a foot tall. They also weigh in at less than 20lbs each, thanks to Manley's own, unique power transformer which pack a lot of punch into a small package. The manual supplied by Manley is also a hoot to read, with a more laid-back, off the cuff prosaic yet highly informative nature that really provides some insight to what a fun and enjoyable yet serious company this is with a character such as EveAnna Manley at the helm. Coupled with the unusual yet lovely charcoal and purple paint scheme of the amp chassis, you get the feeling that Manley enjoy what they do and want the end user to have fun and enjoy their products as well.
The Mahis have a couple interesting tricks up their sleeve compared to similar amps. Using a pair of easily accessible toggles on the top of each you unit, it's possible to switch between Triode and Ultralinear operation, as well as vary the negative feeback in three positions between 3dB, 6dB, and 10dB (labeled as "minimum," "standard," and "maximum" respectively. Output power depends on what settings you're using. Into a typical 8-ohm speaker, in Ultralinear, Manley claims 24 watts-41 watts depending on feedback, while in Triode mode it's 14 watts-25 watts depending on feedback. This makes the amps quite versatile regardless of the speakers you're using, which can happily work with medium- to high-efficiency speakers in a variety of room sizes. Only very power-hungry speakers in large, voluminous rooms will be wanting for more tube power.
The sonic characteristics will, of course, depend on how you're operating the amps. Generally speaking, you can expect a clear, open, and taught sound from EL84 power tubes and this particularly describes the sound in Ultralinear mode. In Triode, you can expect a smoother, more sparkly or sugary coloration. In either mode, you will get the most muscular, up-front sound from minimum feedback, while switching in more feedback will create a greater depth of soundstage at the cost of some bass muscle.
I run these amps with my medium-efficiency Kharma CE-1.0 speakers. The Kharmas are magnificently clean and clear sounding, with a smooth and polished yet precise top end. These 3-way, ceramic-mid driver speakers throw a huge soundstage and the Mahis are quite up to the challenge of matching them with a highly resolving, large, clear sound. The Kharmas have very big and well-damped cabinets and rather large kevlar woofer to control and even in my small listening room, I have preferred the Mahis set to Ultralinear and either minimum or standard feeback settings for the best muscle with rock music in particular, and also softer rock, folk/acoustic or classical recordings mastered at the lower volumes of yore. Of course, given different speakers in different rooms, your amp setting preferences will vary!
The Manley Mahi Mahi monoblocks are a good choice for the person interested in a mid-powered pair of tube monos that have some play in their power and presentation, can throw a big sound that remains clear at frequency extremes, but that nevertheless retains the refined, seductive midrange characteristics that only tubes can provide. Other good points are its low operating costs, since EL84s and 12AT7s in particular are quite ubiquitous and very affordable compared to larger or more esoteric tubes. The efficient power section also drinks less mains power than bigger amps while still giving the amps sufficient bass muscle. Those looking for a more "classic tube sound" with a fatter, more wallowy bottom end and a thicker, more syrupy midrange should look elsewhere--the older EL34-powered Conrad Johnson camps come to mind.
Indeed, the Manleys are amps that can satisfy those craving the broadband clarity of a good solid state design while still offering the big, smooth seductiveness that only tubes can deliver.