PrimaLuna DiaLogue Seven Monoblock Amplifiers (TAS 199)

Equipment report
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Tubed power amplifiers
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PrimaLuna DiaLogue Seven
PrimaLuna DiaLogue Seven Monoblock Amplifiers (TAS 199)

Have you ever fallen in love with the sound of a mid-powered amplifier, decided to move up in that manufacturer’s line to a more powerful unit, and found that the sonic magic that originally captivated you had vanished? This has happened to me several times. I’ve learned the hard way that bigger is not always better, and can lead to sonic disappointment and needless expense. Whereas the extra oomph in the bass with higher-output amplifiers can be a real benefit, larger transformers just don’t seem to behave as well, causing the midrange and highs to typically sound more gritty and less sweet when compared with their lower-output brethren. Having truly loved the sound of the PrimaLuna DiaLogue Two, a gem of an integrated amplifier if ever there was one, I approached PrimaLuna’s new DiaLogue Seven monoblock amplifiers with a bit of trepidation, hoping upon hope that these more powerful amps would maintain the glorious sound of the Two, while providing added power and enhanced channel separation.

After using the amplifiers in my second system for background music over the course of several weeks, I was ready to put the Seven monoblocks through their paces. The first serious music I listened to was Albeniz’s Suite Espanola[London/King Super Analogue]. In my opinion, a great amplifier must first be able to reproduce massed strings realistically, with the beautiful lushness, richness, and sense of air and space one hears in live concerts, as well as inner detail and bite without stridency or grain (quite a tough balancing act). If an amplifier fails this test, I don’t really care to listen further, no matter how wonderful its high-end extension, transient quickness, or bass slam and control may be. I was relieved when the DiaLogue Seven passed the massed string test with flying colors, maintaining all the sonic magic of the lesser powered DiaLogue Two (and more). Indeed, with the monoblocks, massed strings were lush and had body, yet they also were dimensional and detailed, and when I switched to triode mode, they were even sweeter and more palpable. In both ultralinear and triode, the soundstage was enormous with excellent width and depth; instruments floated in space with plenty of air as well as body. Castanets and other percussion instruments maintained their transient quickness and thrill without any hint of tube sluggishness.

Admittedly, the ability to reproduce massed strings realistically does not alone make an amplifier great. Several classic tube amplifiers, like my Quicksilver monos (the originals using 8417 output tubes), have that wonderful midrange magic, including lush string tones and an absence of sibilance and stridency in voices. However, the Quickies roll off the highs and lows, lack tight bass control, and don’t have dynamic explosiveness. Many other classic tube units fare far worse, sacrificing transient speed and clarity, homogenizing and darkening the sound, and/or lacking sufficient rhythmic drive to keep those feet tapping. Yes, some flea-powered triode amplifiers, coupled with high-efficiency speakers, can stun you with their midrange lucidity and palpability, but they, regrettably, suffer at the frequency extremes and are not viable options to drive most real-world loudspeakers.

Voice can really ruthlessly expose an amplifier’s ability to reproduce micro- and macro-dynamics, inner detail, the leading edge of transients, and realistic timbre. Whether I was listening to Sarah Vaughan, Mirella Freni, Mary Stallings, Richard Thompson, or Eric Bibb, the DiaLogue Seven tracked voices effortlessly; I never got the feeling that the Seven was straining, nor did voices unintentionally change character on dynamic peaks or across the frequency spectrum. Yet when the performer wanted to change subtle inflection or tone, the Seven was more than up to the task, rendering Sarah Vaughan’s instrument-like use of her voice on Sarah Vaughan[EmArcy Records/Speakers Corner] with all its natural color and fine detail, like the initial transients of consonants and even the spit in her mouth. Freni’s sublime voice, among others, just soared beautifully, with a sonic realism that had me glued to my chair.

Besides massed strings and voice, I marveled at how lifelike other instruments sounded, too, on Malcom Arnold’s English and Scottish Dances, Harry James’Still Harry After All These Years[Sheffield Lab], and Richard Thompson’s The Old Kit Bag[Diverse Records]. Brass instruments not only had that initial ping or blat one hears in a live performance, but they also maintained their harmonic richness as the columns of air continued to move through them. Cymbal crashes not only were explosive but they decayed naturally, and woodwinds had body without bloat. Strummed acoustic guitars sounded lifelike with great transient speed and timbre.

The real achievement of the DiaLogue Sevens is that they not only preserve the sonic realism and beauty of the lower-powered DiaLogue Two, they also improve upon its Golden Ear Award-level performance in several areas. What you’ll notice immediately is that these monoblocks have better dynamic range, bass slam, and explosiveness. While testing out Clearaudio’s superb Innovation Wood/Helius Omega/Benz system, I used Telarc’s Omnidisc and put both the turntable system and amplifiers through a torture test on a number of musical selections. This combo yielded excellent performance, without cartridge/arm/’table distortion (except for the highest level of cannon shots), or amplifier clipping. A cut of the Beach Boys’ “Good Vibrations” has dynamics that Telarc suggests “approach those of a live performance.” The Dialogue Seven monos sailed right through it, reproducing huge macrodynamic swings as well as very deep and soul-satisfying synthesizer tones that could almost knock you out of your chair. This is performance one associates with large reference tube amplifiers costing far more than the PrimaLunas.

In ultralinear mode, these monoblocks sounded more powerful than any 100 watt per channel amplifier I’ve had in-house. I kept thinking that they would have been perfect mates for large dipole speakers like the Infinity Betas and (modified) RS-1Bs I owned some years ago. What was “way-cool” was that they also had sufficient output in triode mode so I could listen comfortably to powerful orchestral, big band, and rock music on the 90dB-sensitive Hyperions, as well as on the Quads. While I preferred the added dynamic headroom and rhythmic drive of ultralinear on “Whole Lotta Love” fromLed Zeppelin II [Atlantic/Classic Records], I was surprised at how good the Sevens’ triode performance was, with a striking immediacy and more dimensionality than I’d ever heard on that recording previously.

Indeed, with the ability to switch between triode or ultralinear output, via the supplied remote, owners are likely to feel like they own two exceptional, but sonically related, amplifiers. Deciding between the two modes was more difficult than I had imagined, and I found myself really enjoying whichever output mode I happened to be listening to with full-range, dynamic loudspeakers. However, with the Quads, I preferred to bask in the relaxed beauty, extended soundstage, and delicacy of triode mode. I consider this to be a match made in heaven, but some may consider it too much of a good thing in the midrange and opt for the more balanced ultralinear presentation. In either mode, you’d be surprised how much (mid)bass the Seven monos are able to pull out of the Quads, while still delivering lightning-fast transients and beautiful highs.

It would be easy to generalize that triode mode was better for more intimate and small-scale music and ultralinear for power music, but there were no hard and fast rules. For example, in triode mode on Cannonball Adderley’s Somethin’ Else [Blue Note/Classic Records], the sax was more relaxed and a bit sweeter and more palpable, floating on a larger cushion of air, with soundstage depth that seemed to extend beyond the back wall. Switching to ultralinear, the music became more dynamic and incisive, the string bass was more controlled and seemingly extended, and the sound was somewhat more balanced across the frequency spectrum.

If you’ve been hesitant to try tubes for fear of reliability or maintenance issues, the Seven eliminates those worries, and not only rewards you with trouble-free operation, but also with lots of flexibility. It sports first-rate point-to-point wiring, wide-bandwidth transformers, chassis dampening, and a soft-start feature which helps extend tube life. Its Adaptive AutoBias circuit, said to reduce tube distortion by 50%, lets you choose between KT88, 6550, or KT-90 output tubes, or EL34, 6L6GC, 7581A, and KT66 (which yield slightly less output). Just pop them in the tube sockets and the PrimaLuna does the rest! These features not only combine to produce a highly natural and engaging sound, they also help make the DiaLogue Seven the most hassle-free tube amplifier you’re likely to find. I never had a single issue with it. The only penalty you’re likely to pay from tube ownership is that these amplifiers do put out some heat, but not more than any amplifier with four output tubes per chassis, and certainly a lot less than those with more output tubes. 

As with other amplifiers in the DiaLogue Series, PrimaLuna offers several nice touches that make the ownership experience a bit more special. The excellent user manual, containing a host of information about getting the most out of a tube amplifier, is personally signed by the driving force behind PrimaLuna, Herman van den Dungen, and the serial numbers are written on the front of the manual. A pair of white gloves is included. Packaging is carefully constructed and meant to survive the rigors of UPS shipment.

The PrimaLuna Seven monoblocks are so good that it’s really picking nits to find fault with them. No tube amplifier I’ve auditioned comes close to their performance for anywhere near their modest price, and they hold their own against many reference amplifiers, particularly in terms of soundstaging and truth of timbre. While I love these amplifiers, they may have a touch too much warmth for some, but, boy, do they sound like music! Others may opt for the crystalline clarity, ultra-detail, and/or vice-grip bass control that some reference solid-state amplifiers offer, but not I. Some of the reference tube monoblocks that I covet (but cannot afford) may offer slightly better overall performance, but the DiaLogue Seven monoblocks come so surprisingly close that I could live happily with them.

The PrimaLuna DiaLogue Seven monoblocks are so musically captivating that you’re likely to fall in love with your system all over again. They eliminate the sonic and maintenance drawbacks of classic tube amplifiers while letting audiophiles and music lovers without fat wallets get surprisingly close to the sound one hears in a live performance. Moreover, the remote lets you easily switch between the more dynamically explosive, incisive, and tonally balanced ultralinear sound, or the even more beautiful and palpable triode mode. It’s a tough choice. Let me conclude by saying that I’ve been searching for affordable, reliable, and flexible tube monoblocks with near-reference-quality performance for decades and have finally found them.

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Sidebar: Preserving the Sonics with High-Powered Amplifiers

The design team at PrimaLuna faced a formidable challenge; namely, how to match (or exceed) the sonic signature of its DiaLogue Two in a set of monoblock amplifiers with twice the power. This was no small feat because the DiaLogue Two possessed a natural and highly engaging midrange, outstanding soundstaging, extended and articulate bass and highs, and a musicality reminiscent of a live performance. As many designers can attest, it’s quite easy to take a step backwards rather than forwards when creating a more powerful amplifier. 

PrimaLuna’s Chief Engineer, Marcel Croese, was no stranger to design challenges. As Goldmund’s principal engineer for several years, he was credited with many innovative designs, including the Mimesis 29 and 28 power amplifiers, and the MM29.4 and MM28.4 monos, among others. He also developed PrimaLuna’s innovative, and highly effective, Adaptive AutoBias circuit.

While many may have used larger transformers to double the output power, Marcel ruled that approach out because big output transformers don’t behave as well or sound as good as their smaller brethren. He opted to use the same outstanding wide-bandwidth output transformers in the DiaLogue Two (described in Issue 175), employed two discrete audio channels on one chassis, and paralleled them at the loudspeaker terminals so that the outputs would be summed, resulting in double the output power. He also added a 16-ohm tap to each transformer, which when paralleled resulted in an 8-ohm output.

However, the summing approach created other challenges, since a percentage of power from one free-running transformer was pushed into the other, due to output voltage differences caused by circuit tolerances and tube aging. To deal with this problem, Marcel developed a specific cross-coupled positive/negative feedback scheme to balance out both channels perfectly. It also enabled Marcel to offer a 2-ohm tap to drive very low sensitivity/low impedance loudspeakers.

Since less total gain was needed than in the integrated amplifier, Marcel was able change the pre-stages in a way that improved the drive capacity to the power tubes, resulting in even lower distortion, without the need for extra negative feedback. The circuit was inherently more stable and virtually immune to drive imbalance and its accompanying distortions with tube aging.

This innovative twin-channel-summing approach with cross-coupled positive/negative feedback not only resulted in surprisingly low harmonic distortion, but also matched (and improved upon) the sonic signature of the smaller DiaLogue Two.

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SPECS & PRICING

PrimaLuna DiaLogue Seven Monoblock Amplifiers

Power output: 70Wpc, ultra-linear; 40Wpc, triode
Frequency response: 10Hz to 100kHz +/- 3dB
Inputs: One RCA
Outputs: 2-, 4-, and 8-ohm speaker taps
Tube complement: Two 12AX7s; two 12AU7s; four KT88
Input impedance: 100k Ohm
Dimensions: 15.9" x 15.2" x 8.3"
Weight: 63.8 lbs.
Price: $5495 per pair

Upscale Audio
2504 Spring Terrace
Upland, CA 91784
(909) 931-9686
www.upscaleaudio.com

Associated Equipment

Clearaudio Innovation Wood turntable with Helius Omega Silver Ruby tonearm and Benz Ebony H cartridge; VPI Aries turntable (TNT V platter & bearing), Graham 1.5 arm (w/2.2 bearing), and Koetsu Black cartridge; Electrocompaniet EC 4.8 and MFA Venusian (Frankland modified) preamps; Electrocompanient AW250-R and Quicksilver 8417 amplifiers; Hyperion HPS-968, Quad ESL-57 (PK modified) loudspeakers; Virtual Dynamics and Goertz cables; etc. 

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