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MiniWatt integrated valve amplifier

The world's smallest integrated valve amplifier?

[Miniwatt integrated valve amplifer (blue version)]
[Italian version]

Product: MiniWatt integrated valve amplifier
Manufacturer: MiniWatt - HK
Cost: 229 USD. (Flat-rate shipping fee is 40 USD)

Reviewer: Nick Whetstone - TNT UK
Reviewed: July, 2009

Let's be honest, most of us make initial judgments based on appearance! We will look at something (or somebody) and form an opinion about it/them before we have had the chance for a 'proper' investigation. Perhaps that's why, when our esteemed editor sent us a staff email about a miniature valve amplifier that looked a bit like a toy, there wasn't any response. I was clearing out my inbox a few weeks later and thought that somebody should respond to the manufacturer's offer to supply a review sample, and agreed to take it on. While we have come to appreciate that you can get great sound out of small packages like the Sonic Impact T-Amp and other class-T amplifiers, it's still difficult to believe that squeezing a valve amplifier into such a small package can be anything but a gimmick, something to put on your desk and impress your friends. So having contacted the supplier, and been informed that they would send me a blue version of the MiniWatt, I forgot all about it and got back to reviewing what I considered 'serious' hi-fi.

Only a few days later, the postman turned up with a smallish white box. I hadn't expected the MiniWatt to come all the way from Hong Kong so quickly! It's quite an experience to open a parcel that small, and pull out a working valve amplifier. I should add that the MiniWatt comes very well packed with stout polystyrene inserts. The valves are already installed and a mains lead included. The amplifier is fascinating. Something to handle and observe from different angles, and you can do that while holding it in the palm of one hand! It is quite heavy for an item of its size, and is obviously built to withstand a bit of rough handling, not I hope that anybody would want to be anything but careful with a valve amplifier! Basically, you get what you see in the picture. There is one set of input RCA sockets, two pairs of sockets for the speaker lead plugs (note that these are 4mm sockets and not binding posts). There's a volume control knob on the front and a switched IEC mains socket on the rear, and it sits on four globe-shaped chrome metal feet. The MiniWatt comes with a metallic paint finish (at least the blue version is) and build quality, and finish, is very good. And I nearly forgot to mention that it comes in a choice of six colours.

[Colour choices for the Miniwatt integrated valve amplifer]

The MiniWatt uses a pair of military grade 6J1 valves together with a pair of 6P1's, and these are wired as "as Ultra-Linear Circuitry", something that I take to mean the amplifier operates in class-AB mode. With a power output of only 2.5 watts per channel, and a gain of 18 db, the MiniWatt is never going to go very loud except with the most sensitive of speakers. You can add more gain with an active pre amp, but there is no 'cheating' with that power output although in practice it is not quite as puny as the specification may suggest! The output impedance is specified at 8 ohms so it would appear to be sensible to stick with 8 ohm speakers.

[MiniWatt amplifier shown with CD case for scale]

I've got a valve pre amp that I built with a power supply in a separate box. And that PSU box is something like eight times as large as the MiniWatt. So how do the MiniWatt designers manage to get everything that is needed into such a small package? Well the first step was to ditch a conventional power supply and go for a switched mode type. MiniWatt even developed their own SMPS presumably to get it small enough to fit inside their miniscule case. Anybody who has looked inside a valve amplifier will know that apart from the power supply, there are few other components, so by carefully choosing those other components with regard to their size, as well as their performance, the whole amplifier was able to be built inside a 'box' just 13 cm by 10 cm and 3 cm deep! (That's smaller than three standard sized CD cases!) Of course, the largest components, the output transformers sit outside of that 'box', as do the valves and control knob. Apart from the size advantage of an SMPS, it does not 'sag' under load, so in theory at least, it should improve the bass output from the amplifier.

Well I confess, having seen the MiniWatt, I couldn't wait to hear what it sounded like. So into my second system it went, in a room about three and a half metres square. The system comprised a modified Logitech SB3, Monica3 DAC, the MiniWatt, and a pair of modified Mordaunt Short Pageant II speakers, 8 ohms impedance and around 95 db efficient. With no music playing, the MiniWatt is completely quiet, as is the volume control when adjusted. When the music started playing the first word that came into my mind was 'clarity'. It was almost ruthlessly revealing and transparent! It also went plenty loud enough to listen to in that smaller room, and there was no shortage of bass coming from the Pageants. The top end was also very good, better (clearer) than the Yarland FV-34C that I was reviewing at the same time. In fact, in the 'right' system, the MiniWatt makes it quite clear from the outset that it is no gimmick but a serious piece of hi-fi! The clarity could make it sound a little on the lean side, noticeable more on some recordings than others.

Good as this combination sounded, I thought that I would try giving the MiniWatt a helping hand by adding in the Audiodigit Tube-Pre with a little more gain. Now things were getting really serious. There was a real kick to the bass and it sounded deep too (deeper than the claimed response of 30Hz to 20kHz within 1 db). The sound was ' fuller' and that lean sound on some tracks was gone too. The speed which was already good got even better. It was particularly noticeable on a drum solo where I could literally hear the velocity of the drum sticks hitting the skins and rims. Electrifying was the word that I wrote down on my note pad. And of course speed brings emotion to music, together with excitement, and fun. While the MiniWatt can rival the class-T amps for clarity and transparency, there was much more weight with MiniWatt, and more depth to the tone. Far from sounding puny, those 2.5 watts per channel can make some seriously heavy-weight sounds when connected to the 'right' speakers. The performance is even more surprising than the appearance, and the two together just made me smile as I listened to what was coming out of the speakers.

I should also point out that I found the performance of the MiniWatt much improved having planted it on a VertexAQ tripod system that coupled it to the granite platform. I also coupled some mass to each of the four valves. With so little mass, the MiniWatt will benefit a lot from this type of measure, and it did. If I had one criticism of this miniature marvel, it would be those four metal feet that won't do much for coupling it properly to the mass that will be required to wick away the vibrations that it produces. With the MiniWatt thus supported it ticks all the right boxes! Wonderfully musical and communicative. Transparent, detailed, tight bass and clear top end. Great timing, large sound stage, great imaging.

I had commenced this review with the idea that the MiniWatt would only be suitable to try in my second system, in the smaller listening room, but the MiniWatt is a very persuasive piece of gear and I just had to find out how it performed in my main system. That comprised a modified SB3, Havana DAC and Hawthorne Duet open-baffle speakers. The MiniWatt would power the coaxial drivers in the Duets that have an efficiency of around 95 db, while a solid-state amp would power the woofers (up to around 60 hz). The room is actually two rooms joined by a 1.2 metre opening, the total floor area being around 25 square metres.

It may seem obvious but in the main system, the MiniWatt sounded different. The sound was more relaxed, not un-exciting, just a little more laid-back. The sound-stage was wide and noticeably very deep. I didn't think that it sounded quite as 'fast' as with the MS Pageants (was this the speakers or the room, or both?) but the timing was spot on. The tone was rich and made all instruments sound beautiful, and vocals were accurate, and on some recordings, quite intimate. That clarity was still prominent, with all the little details coming out of the 'better' recordings. Suffice to say that it had me riveted to my chair for a long session, thoroughly enjoying what I was listening too. All in all it was another very good performance although there was a limit to how loud it would go in that much larger room. It was 'loud enough', but certainly nowhere near 'partying level'!

So the next option was to add in the Audiodigit Tube-pre buffer between the Havana DAC and MiniWatt. This increased the overall gain of the system and added some weight to the presentation. I would say if using the MiniWatt in a larger room, some extra gain from a pre amp or buffer would be almost obligatory for optimum sound quality at higher levels. Again a lot depends on the actual speakers and the room (furnishings as well as size)! There is a slight trade-off inserting another stage but I would say that it is worth a very slight loss of transparency for the extra 'weight' and scale that is gained.

To sum up the sound quality, it would be very good coming from any sized valve amplifier. Could it be even better without the obvious constraints of building it into such a small package? Who knows? And why such a small package apart from the obvious reason that you may need a valve amplifier that will fit into a small space? Perhaps achieving the performance level of the MiniWatt in such a small package was a design challenge that was taken up simply because it was there - rather like climbing Mount Everest. Then we arrive at the third shock that the MiniWatt has for us, the price. At 229 US dollars, it's an absolute bargain given the sound that it can produce. Yes, you will need speakers to do it justice but efficient speakers are not necessarily expensive speakers. Yes, I would say to get the very best out of the MiniWatt you should add in a pre amp with a bit of gain, and then of course you are loosing some of the advantage of the small size. It depends how serious you are about the music but the MiniWatt is deserving of a serious system, rather than being seen as a low-budget amplifier. If you have not heard valves and always wondered what the fuss is about, treat yourself to a MiniWatt and find out!

Negatives? There aren't any really when something sounds this good but the MiniWatt does run quite warm. In fact, after a while, those large valves get too hot to touch. The case also gets a bit warm and as a DIYer, I could worry a little about the longevity of components inside. But I spoke to MiniWatt about this issue and they assure me that the case is designed to get warm and wick away the heat (ie it is acting as a heatsink). All components are operating well under their maximum temperature rating, and in prolonged heavy testing under load, no problems have been experienced.

It was tempting at the start of this review to say that the MiniWatt is to valves, what the Sonic Impact T-Amp was to solid state. But that would be to understate the sound quality of the MiniWatt by quite a margin! There is of course a huge price differential and I doubt that we will see the same sort of stampede to buy a MiniWatt as there was with the T-Amp. However, I suspect that once a few more people have tried them, and spread the word, they could just become another one of those components that will go down as something of a cult item in hi-fi history. If you are interested in one, believe me, this is no toy to leave on your desk! If you are prepared to find the right speakers, the 2.5 watts per channel isn't the obstacle that it may appear. It would be good to see a commercial speaker developed to match the MiniWatt, otherwise finding something on a similar budget to the MiniWatt is probably going to involve a bit of research into the second-hand market. Given the performance with the MS Pageant II's, it shouldn't be too hard to find something that will pair with the MiniWatt and offer very good sound for the money. The alternative is probably a single-driver design of which there are many around. If you can't DIY one yourself, it shouldn't be too hard to find somebody (ie local carpenter) to build one for you. On the other hand, if you prefer to spend out on an expensive set of speakers to go with the MiniWatt, I won't be accusing you of system mis-matching!

The moral of this story? Check your inbox from time to time, and don't rely on appearances!

© Copyright 2009 Nick Whetstone - www.tnt-audio.com

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