The Almarro A50125A Power Amplifier

A similar approach applies to the circuit design; while there’s nothing in the Almarro that we haven’t seen before (bear in mind that the comparative simplicity of valve circuitry and hundred year history sees to that) there are enough unusual features to elevate it from the run-ofthe- mill, and the signature of a designer who has a real understanding of and empathy with valve engineering. Take, for example, the driver valve – with the exception of some more contemporary American products, most designers would have opted to use something along the lines of a ECC82 or ’88, and on paper it would seem to have ample characteristics for the job, certainly for driving a couple of output valves and in theory, multiple pairs. In practice, I have never been convinced. I think that transient demands are not accurately reflected by data sheets and anything over 50 Watts or so requires a different approach. To this end, the Almarro uses an American 5687 valve to do the job, a tube originally developed for use in televisions and rated at three or four times the dissipation of an ECC88 whilst possessing a particularly high peak current capability (pulse current) which marks it down as ideally suitable for a driver stage. Not surprising then that we also find it used in the Kondo Ongaku and Gakuoh and the sadly now departed MFA 120 and 200s.

The output stage is based around a quartet of 6550s a side, running (I’m fairly sure) in straight pentode mode rather than the more conventional ultra linear configuration, while the cathodes of these valves are coupled via the secondary of the output transformer in a fashion favoured by Audio Research until relatively recently. Like most valve amplifiers of this sort of power the Almarro uses fixed bias to set the operating conditions for the output stage; measurement points and adjustment are conveniently located on the top plate avoiding the necessity to delve inside, although the use of a digital voltmeter is required. I would hazard a guess by the amount of heat generated that at the set-point the amplifier is working in class A for the first twenty Watts or so before running toward AB1.

While relatively compact for its power output the Almarro is pretty heavy, and the long thin chassis makes placement a little difficult when it comes to conventional racks and supports. The large enclosure at the rear houses the two output transformers and a smoothing choke. Extending in front of this, between the two rows of output valves, a smaller box hides the slim but substantial C - core mains transformer. Over this sits an arrangement of metal strips that are not close enough together to offer any real protection to the valves (or prying fingers) but do serve to lend an interesting architectural air to the amp’s aesthetics. Connections at the rear are pretty much standard with single-ended RCA inputs and five-way loudspeaker outputs offering matching to 4, 8 and 16 Ohms, while a small switch defeats the internal fan (which is not obtrusively loud) but this should probably be left on where possible. Internally the construction avoids circuit boards in favour of tag strips and hard wiring, and while the amplifier circuit is relatively simple the sheer amount of components reveals the considerable attention that has been paid to the power supply and general housekeeping.

Having created a favourable impression, the Almarro stayed in my system for quite some time, allowing plenty of opportunity to play with partnering equipment. The combination of the Almarro with the SP10 pre-amp was thoroughly engaging and highly musical, but substituting the new LS17 provided both a greater degree of detail and a much cleaner presentation, particularly at high frequencies. As I have already suggested, the bottom end is not the deepest or most taught, but is conveyed in such a positive fashion that it does a good job of laying the foundations for everything else. It has a good sense of rhythm and timing that works well with rock music, while the larger instruments of the orchestra have a reassuring sense of body with a mild hint of ‘fruitiness’ that swamps a little of the texture. The mid is again quite full, and although I would be reticent to label it with the typical ‘valve’ character it is both liquid and informative, with just an occasional tendency to lose its grounding with the bottom end. The top end has a degree of ‘presence’ giving a good sense of detail, albeit with a slightly fuzzy quality that reads on paper far worse than it sounds; and while it doesn’t give the impression of tremendous extension, it’s nicely in proportion to the rest of the spectrum. Worth noting however, is that the Almarro responds well to the addition of some form of mechanical isolation, whether through feet or specialist support. The result is a sound that is altogether cleaner with less grain and smear at the top end. In terms of soundstage, and some further interesting evaluation with the Quad 2805, the Almarro effortlessly projects away from the loudspeakers, and is capable of a solid, palpable image which is certainly three dimensional, but indistinct and lacking focus when it comes to the detail within it. In all other areas, the Quads positively wriggled with delight being driven by the Almarro, the attributes of each unit complementing and balancing each other well, only slightly bettered by the Audio Research Ref 110 at more than three times the price, and even then it might well be a matter of personal taste.