Like many audiophiles, I wish that my flea-powered amplifier wasn’t quite so … anemic … when it came to modern loudspeakers. I mean, if it wasn’t for all the crazy-low impedance swings or sub-90dB sensitivity ratings, SET amps might still be relevant. Sadly, most loudspeaker designers could give two farts about all that — and I suppose that an argument can be made that blah blah blah sound quality blah blah blah. Whatever. The upshot is that most SET amps are pretty much useless, unless you opt for some wildly compromised or terrifically marginalized product to pair them with. Yes, yes — there are some manufacturers that “do that” sort of thing (Zu Audio and Rethm spring to mind), but the sad fact is that the average Dynaudio, Wilson, or B&W will never sparkle with 8 watts — it’s long past time to get over it and move on, right?
R-i-i-i-i-i-g-h-t.
Well, not so fast. Maybe not.
Enter the Unison Research Unico UPower amplifier, shown here in a rather unassuming black box and positioned directly below the very comely $2,495 Simply Italy integrated amplifier in a cleverly elegant stackable Splintr Designs Trellis rack ($2,000, as configured). An El34-based SET amp, the Simply Italy is “good for” 12wpc, which is plenty with just about any loudspeaker — assuming that it has a sensitivity of 95dB or higher. The very shapely (if you’re getting a vibe about the look and feel for the gear in this room, that’s not an accident) Opera Grand Mezza loudspeakers ($2,795/pair) are only 89dB. Common wisdom would tell you that this is not a match. Tone should be “just fine”, especially through the mid-band, but turn it up and you should expect the bass to flabbify, the treble to turn glassy or hard, the imaging to collapse, and cats and dogs to suddenly opt for cohabitation (or something equally horrible, YMMV).
Now, with the UPower, that changes a bit. Wire the amp into the “booster” and the booster into the loudspeakers and that 12 watts becomes 48. Ta-da! And yes, Virginia, 48 wpc should be more than enough to rock your world — with an 89dB loudspeaker.
Sounds great, no? Sure! It also sounds familiar. But wait:
There are already some “booster” amplifiers on the market, but they use the amplifier with a dummy load (typically a fixed amount of resistance) to produce only an amplified voltage output. These “booster” amps are characterized by a suitable voltage gain. In this way, however, the character of [the] sound due the [original] amplifier … is completely lost.
The Upower does not use a dummy load. The amplifier is always loaded by the actual impedance of the speaker; the voltage and the current that the amplifier provides are both simultaneously amplified by the Upower. This [is] a true “amplifier of power,” having both voltage gain and current gain well defined. The sensitivity of the amplifier to the impedance of the speaker remains unchanged as the speakers “appear” as directly connected to the amplifier output terminals, an operative condition that, as already stated above, [maintains] the character [of] the sound.
Okay. I’m curious. Where’s mine? Price is $2,695 in silver, $2895 in black. A Unison Research Unico CDE player ($4,120 with dual mono DAC upgrade) provided the tunes. All speaker cable, ICs and power cords came from the Cardas Audio Clear Light line.
The Burson PP160 (recently discontinued) has a “tube booster” feature.
From 6 moons review:
“The differential class A/B dual-mono stereo amplifier is unusual by providing high-level inputs. These auxiliary speaker terminals tap into the current power buffer and bypass the class A FET input. Thus connected, the PP 160 becomes a booster amplifier for low-power tube amps. Burson asserts such transparency for their output stage that the harmonic fingerprint of the preceding amplifier—most likely a SET but up to 25 watts of input power are permissible—will be passed unaltered yet ‘turbo-charged’ to 95/180wpc into 8/4 ohms. The Nelson Pass FirstWatt F4 amplifier with current but no voltage gain proposed a similar application. The F4 could necessitate that a SET’s output be stabilized with a small load resistor. The PP160 implementation does not.
Simply connect the speaker outputs of your low-power tube amp to the speaker inputs of the Burson amp, select the latter with the rear-mounted toggle switch, then connect your speakers to the regular output terminals. As proud owner of Shigeki Yamamoto’s stupendous—and for many applications under-powered—A-09S direct-heated 300B SET, I was all set to boost its 8-watt output and put Burson’s confident claim to the test.”
I have used the booster feature on my PP160 just to see if it worked and indeed it does not seem to alter the SET sound signature in any appreciable way. That said I have not used it extensively so results may differ with different SETs.
Didn’t Musical Fidelity do something similar a few years ago with the Supercharger. It didn’t catch on….
The MF unit tended to change the sonic characteristics of the original amplifier to the point where you asked yourself, “Why don’t I just get a more powerful amp?” The Upower excels at preserving the sound of the original amp since it only provides a boost when needed. And I’ll tell you that a 48 wpc Simply Italy for about $5K is a beautiful thing. I’m using the Upower right now with the 27wpc Unison Research Sinfonia, giving me 108wpc of 6550-based tube sound that is much more dynamic and controlled than any 6550/KT88 amp I’ve heard.
So, how did it sound?
IIRC, the room was a bit noisy, so, hard to say anything other than: “very nice”.