Integrated Amp Reviews

To more systematically examine the sound of the DiaLogue Premium HP, I compared it and the ProLogue at matched levels: <0.1dB difference, measured with a voltmeter at the output terminals, using the 1kHz tone of Stereophile's first Test CD (Stereophile STPH002-2). Both amps had EL34 tubes installed, and the DiaLogue Premium HP was set to ultralinear, to match the ProLogue Premium.

Some audiophiles hold that at higher power you may gain maximum volume but lose some finesse, and that as long as the amplifier is not driven into clipping, the fewer the tubes, the better the sound. Whatever the merits of this view, it was not confirmed by this comparison. It would be overstating things to say that the DiaLogue Premium HP "blew away" the ProLogue Premium, but it was the clear winner. The most obvious superiority was in the bass. I hadn't thought of the ProLogue Premium as being deficient in this department, but bass in my usual test tracks, such as "Temple Caves," from Mickey Hart's Planet Drum (CD, Rykodisc RCD 10206), extended deeper and was more solid with the DiaLogue Premium HP. And while the ProLogue Premium didn't seem deficient in allowing the speakers to project a soundstage, with the DiaLogue Premium HP the soundstage was more clearly defined, and the music generally seemed to "breathe" with greater dynamic freedom.

The tonal balance throughout the midrange and highs was very similar through the two amps, the DiaLogue Premium HP perhaps sounding a bit more extended at the top. The ProLogue Premium's 35Wpc was enough to drive the Focals to levels high enough for me, but my 16' by 14' by 7.5' listening room doesn't greatly challenge a speaker's room-filling ability, and while I sometimes listen at what I like to call "realistic" levels, I'm by no means a headbanger. The DiaLogue Premium HP is rated to produce 70Wpc in ultralinear mode with EL34s, and up to 85Wpc with KT120s, thus justifying the "HP" in its name, which PrimaLuna says "stands for High Power . . . and HeadPhones!" If you need more power than the ProLogue Premium, the DiaLogue Premium HP is ready to provide it.

But what about the triode/ultralinear comparison? The ProLogue Premium runs only in ultralinear, so for that amp the question doesn't apply. For the DiaLogue Premium HP, PrimaLuna's having put the triode/ultralinear selector button on the remote makes it easy to make this comparison. I'm not a fan of comparisons made on the fly, or switching in the middle of a piece of music; I prefer to listen to a track all the way through (or to the same point in the music), then start it again with the switch in the other position, so that I'm comparing exactly the same selection of music.

Staying with EL34s, ultralinear mode resulted in a sound that was a little more forward, a bit more dynamic than triode mode, and with some recordings seemed to communicate a greater sense of excitement. Triode mode sounded more laid-back, more relaxed. With my usual test piece of Ana Caram's performance of "Viola Fora de Moda," from the Chesky Records Jazz Sampler & Audiophile Test Compact Disc, Vol.1 (CD, Chesky JD37), ultralinear mode allowed the various percussion instruments to ring out with greater clarity. Clark Terry's entrance in "Pennies from Heaven," from the same disc, was more dramatic: again a bit more forward, triode mode placing his trumpet a bit deeper in the soundstage.

Which was more "natural," and which a more accurate representation of the music as heard in the recording venue? Search me . . . I was content to listen in either mode, most of the differences being apparent only in direct comparisons. Forced to choose between triode and ultralinear, I'd choose triode—while a little less dynamic and extended at the extremes, it had a smooth musicality and an easy-on-the-ears quality that I found quite beguiling. Of course, with the DiaLogue Premium HP, triode or ultralinear is easily selected using the remote—you can use the mode that sounds better with a given recording, or that better suits your mood. My advice to those not keen on tweaking: Use triode mode as the default, and switch to ultralinear only when you want a bit more oomph.

Tube Rolling
Having satisfied myself that I had a handle on the sound of the EL34-equipped Premium HP in triode and ultralinear modes, it was time to switch tubes. The KT120 is a more macho tube, bigger than the EL34; it requires higher bias, a difference that's handled by the DiaLogue's autobias circuitry and the switch that helps optimize the bias for tubes in the KT88/KT120 category.

Compared to the EL34s in triode, the KT120s in triode and at the same level sounded more dramatic, more immediately impressive, with voices more forward—not unlike the EL34s in ultralinear. With recordings such as Ariel Ramirez's Misa Criolla, conducted by José Luis Ocejo (CD, Philips 420 955-2), KT120s/triode had more slam, with greater dynamic drive. I could hear why this tube has been winning adherents. However, on prolonged listening, switching back and forth with the EL34s at matched levels, my ultimate preference was for the EL34. There was just something right about the sound of this tube in the DiaLogue Premium HP. This preference remained unchanged—in fact, grew stronger—when I switched the Premium HP to KT120/ultralinear. In the Gloria of Misa Criolla, things were fine with José Carreras's singing, but the choral voices sounded more homogenized, more artificial than in triode. In this selection, the best sound was produced with the EL34s in triode mode.

Finishing Up
The final comparison involved my own reference combination of Convergent Audio Technology SL-1 Renaissance preamplifier ($10,000 with phono stage, $8000 without) and McIntosh Labs MC275LE power amp ($6500, now available in a Mk.VI version for $5500). Each is rated Class A in Stereophile's "Recommended Components," and is widely recognized as a classic.

The CAT SL-1 has a switched-resistor volume control with fairly large steps; I first set this at a suitable level, then matched the DiaLogue Premium HP to the CAT. Levels thus matched, and with the DiaLogue Premium HP in my preferred EL34/triode mode, the similarities were more evident than the differences. Both evinced the smoothness and musicality that tube aficionados appreciate, but without the excessive warmth and rolled-off treble that characterize some tubed gear. Background noise was conspicuous by its absence, and both amps' power transformers were quiet.

I heard even more transparency and detail from the CAT-Mac combo, but the difference was surprisingly small—and smaller than the difference in price might suggest. Dynamics were comparable, with perhaps just a slight nod to the CAT-Mac.

Conclusion
Built to a high standard, with some very useful features—including Adaptive AutoBias, Bad Tube indicator, on-the-fly switching between triode and ultralinear modes from the remote control, and headphone output—PrimaLuna's DiaLogue Premium HP is an integrated amplifier whose sound quality closely approaches that of pairings of reference Class A preamps and power amps. The ability to use a variety of output tubes gives the user great flexibility in tailoring the sound to his or her preference. In today's audio marketplace, $4199 for an integrated amp of the DiaLogue Premium HP's level of performance represents excellent value. PrimaLuna has another winner.