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With its single gain stage post op, the UA-S1 would of course invert polarity had the modification not wired the speaker outputs reversed to restore polarity automatically. So red is red and black black as usual. Because the ECC99s are longer than the 12AX7 stockers and just a tad too tall to clear the top plate, two small holes now let their nipples protrude just barely. My amp at first wouldn't play because it came with the wrong mains fuses installed. Since Alex Peychev beefs up storage capacitance from 60,000uF to 90,000uF, there are large in-rush currents on turn-on, requiring 6.3A/250V slo-blows on 240V lines. Apparently mine were premature fast blowers. Once I'd swapped out the relevant two fuses on the power supply board flanking the rectifier, I was in business.

The first thing I noted then was the lowered gain. On my 101dB Zus, I sat at an unexpected 1:30 on the dial with the first disc which has lower-powered amps sit at 10:00. High-sensitivity speakers always battle redundant gain, attenuators that come on too fast and noise. This amp is quiet when the music stops, even with an ear on the drivers. The long gradual taper one must traverse before room-filling SPLs accrue could simply surprise those who anticipate more crank sooner based on the amp's original power specs. "The amp has a gain of around 15dB now. It achieves 150wpc into 4 ohms with 1.75V at the input. Into 16 ohms, it will be around 37wpc with 1.75V input, 56wpc with a standard 2V CD output. The volume pot is logarithmic so there's a lot happening at the end of it." In other words, there's no lack of power, just a delayed volume reaction which makes for far more usable range.

The second thing I noted were ultra-refined gentle sonics with excellent depth and highlighted lead vocals similar to how power triodes extricate them from their surroundings. Low bass was weaker than Red Wine Audio's Signature 30.2 I'd listened to previously. With the active bass systems on the Zu Presence, a quick twist on their input attenuators rectified the desired low-frequency weight out of the gate while proper break-in of the amplifier might mitigate the perceived need for this initial adjustment over time. Initial impressions were of a very refined and relaxed presentation. If I had any criticisms, they'd have been about a perceived lack of drive and low-end impact. Not enough Wagner heroics if you will.

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This gentle amplifier never transformed fully to develop the crunchy transient blister and impact Renaud Garcia Fons' percussive self accompaniment on Légendes [Enja] merits. This solo album is a brilliant showcase for arguably the most virtuoso double bassist alive who here overdubs himself for mindboggling visions on the many sounds a true freak can coax from a 5-string upright, with pitch-perfect intonation from the highest flageolet through the
fastest runs and over octave-doubled slides. Vigorous sawing, virile spiccato where the bow taps and rebounds off the strings and assorted drum effects on the bass body all were rendered with less than ultimate crack, pop and snap. In short, the UA-S1 isn't as incisive or edge specific as some others. Hence the impression of gentleness and softness from which one easily makes the transition to sophistication as suggested by the utter lack of graininess and resultant liquidity.

Would this character migrate to my 98dB Rethm Saadhanas? Though non-representative of common loads, their active bass system makes them ideal for the low-power triode amps I fancy. More to the point and regardless of religion, the heavily modified Lowther DX55 in this speaker makes it the most resolved, microdynamically astute transducer in my stable. It's become de rigeur around here to wheel in the Indian challengers and with them hold up my best microscope to whatever is on assignment. With the optional stand, 'wheeling' is literal. It leaves the docked twin modules permanently attached so no take-down is necessary, a huge boon for the constant flux that is any reviewer's rig.

The inherently leaner, more lit up ultra reflexes of the Saadhanas were an excellent match for the UA-S1 which also proved deathly silent on these magnifying glasses. However, I had the same urge to drive up the bass attenuators by a few clicks as I had on the Presence. The Red Wine Audio Signature 30.2 had been responsible for the last settings as it had been on the Zus. While expectations would scoff at the notion that a half-priced 30wpc amp would have overtly stronger bass than a triple-power contender, the sealed lead acid batteries in the 30.2 have proven their worth in the current/drive department in earlier reviews. While there will be speakers beyond the Red Wine Audio's reach, those within it produce some of the best bass you'll have ever heard 'em make.

The Sig 30.2's one minor shadow of blue -- blemish would be far too strong a word -- is a small reticence in the upper-most harmonics where other amps may shed more light. Here the UA-S1 seems more developed by the appropriately small amount. Despite this perceptional shift -- less bass weight, more treble energy -- the Lowthers didn't turn remotely spiked as might be inferred if percentages were blown out of proportion. What both Zus and Rethms suggested was a very fine, minorly slim and somewhat polite amp with beautiful subtle textures and a concomitant reluctance to get fully grimy and gritty when the material demanded it. The propulsive elements of drive seemed scaled back in favor of suavé factor.

To my ears, the UA-S1's main attraction are the -- probably ECC99 induced -- textures. I'm familiar with the 6H30s from my Ancient Audio and ModWright machines where they seem very stout and endowed with excellent drive. I can drive the hi-gain Polish CDP amp-direct through its analog volume control and don't experience the bleaching effect that foregoing an active preamp usually entails. Alex fits the JJs also to the outputs of his NWO Esoteric players for amp-direct drive so I must assume the noval Slovakians are similarly suited. Looking at the pre/post op guts of the Bada, its stock iron and
output transistors are retained. It'd be pure speculation to point at specific parts to explain why the machine seems a bit soft on raw grunt and bass amplitude. But that's how it compares to the more pedestrian-looking, half-sized battery-powered T-amp. With speakers like my Rethms or Zus, that aspect can be compensated. Exactly how would fully passive but full-range speakers like Xavian's N360s react to the UA-S1's lack of badass machismo? How about real watt suckers like my compact but ultra potent Mark & Daniel Maximus Monitors I keep on a hungry leash for just such occasions?

The UA-S1, on all speakers I tried, was overtly lightweight in the bass, producing noticeably less amplitude than the far lower-powered Red Wine Audio Signature 30.2 or AudioSector Patek SE. Considering the expensive mod concept, I'd have to call this a substantial weakness.
That said, the upper midrange/treble performance is truly fantastic - extended like superior semiconductors; elastic, airy and grain free like tubes. Because the gain comes on slow and self-noise is utterly non-existent, the UA-S1 is perfectly positioned for speakers such as the Rethms and Zus whose active bass systems can easily compensate for the lack of LF oomph. With the above Xavian XN360's fully passive array of top-line ScanSpeak Revelators however, there were no such means and the Bada unit simply didn't get it up on the woofers. The same held true for my Mark & Daniels which thrive on being dominated by an amplifier to then be hellaciously dynamic and jumpy little buggers. The APL amp didn't unleash their bad selves and remained in a lower, more genteel gear.

For the asking price, the ambitious subtext of ultimate amp in the UA-S1's name promises more than it delivers, i.e. an amp for all seasons. Instead, its showing in Cyprus suggests more of a special purpose machine whose exceptional refinement lacks raw grit, low-end moxy and large-scale dynamic commitment. Its reduced gain and tremendous S/N ratio do however make it quite perfect for highly efficient loudspeakers, particularly those with self-amplified bass systems.

The polite yet sophisticated nature of this amp can be
shifted by preceding it with a suitable preamp that swings a lot of voltage. While that preamp won't need to contribute SPLs -- the modified Bada goes far enough -- it does inject what one customarily associates with a robust higher-current signal: drive and low-end fortitude. However, the addition of a preamp defeats the integrated amp concept. Mr. Peychev seems to prefer amp-direct connections with his NWO players (precisely why he outfits them with variable outputs - the picture above shows his new WiFi-enabled NWO driving an UA-S1). I'm thus assuming that his own custom-built loudspeakers are perfectly voiced to complement the Bada's particular set of strengths. If you fancy a limpid, liquid sound that rates beauty over tension and poetry over drama, the APL Hifi UA-S1 delivers a very non-transistory sound with certain single-ended triode virtues - but without relying on actual power tubes.

Quality of packing: Original Bada issue - perfectly adequate.
Reusability of packing: Yes.
Ease of unpacking/repacking: Unproblematic.
Condition of component received: Perfect.

Completeness of delivery: Contains fitted tubes, remote and power cord.
Website comments: APL's sorely lacks in details and images and doesn't yet list this model.
Warranty: 1 year.
Global distribution: Direct.
Human interactions: Prompt.
Other: Remote control over volume and input switching.
Pricing: Considering the very affordable Chinese platform, the modification surcharge seems steep.
Application conditions: Not a muscle amp and a bit weak in the bass.
APL Hifi's website