October 2014


PrimaLuna Dialogue Premium Preamplifier
One of the best things PrimaLuna has ever done.
Review By Dick Olsher

  The high-end scene is littered with a plethora of line-level preamplifiers. So what makes the PrimaLuna Dialogue Premium (PDP) standout in such a crowded field? According to Kevin Deal, PrimaLuna's man on the ground in the USA, "we have really tried to do some things in quality of build never done before." Kevin invites a comparison with the Audio Research LS-17SE which is priced at $5500 and weighs 30.4 lbs. The math works out to $181 a pound for the LS-17SE. On the other hand, the PrimaLuna at $3199 weighs 52.9 pounds and thus is merely $60 per pound. I agree with Kevin that it's a bit silly to think of it that way, but it definitely bears looking into.

Let's Get Going
Let us start with the weight aspect as it gets to the heart of the matter. The main reason for the PDP's heavy weight stature is that it is built like an amplifier. When I extracted it from its shipping container, it was a case of déjà vu all over again. Cosmetically it looked much like the PrimaLuna Premium Integrated amplifier I had previously reviewed. There's more iron in here than meets the eye. The circuit layout is dual mono – even when it comes to the power supply. No kidding, there are two toroidal power transformers as well as two 5AR4 tube rectifiers, one per channel. Heck, there are plenty of stereo tube amplifiers in the 10 to 20 watt range that are only outfitted with a single 5AR4 rectifier. But it's gotten hard to find a commercial tube preamp these days that is tube rectified. To my mind, a tube rectifier is an essential ingredient of a great sounding preamp. The Conrad-Johnson Premier Two, one of the great preamps of all time, was introduced in late 1981 and featured a 12AX4 rectifier. But even C-J moved quickly toward solid-state rectification. Nowadays PrimaLuna and Lamm Audio seem to be the only true believers. Yes, it is a more expensive solution but my ears tell me that it's a worthwhile investment.

The toroidal transformers are dead quiet thanks in part to an AC Offset Killer circuit installed right after the power switch. PrimaLuna's parent company, Durob Audio B.V., sells this device as a stand-alone item under the Ah! brand name. Its job is to keep the main AC power transformer as quiet as possible. Each filter network includes a 30H choke and a 330uF Nichcon capacitor; the latter are mounted on the top deck adjacent to the rectifier tubes. Wiring is point-to-point with workmanship that is said to equal or better the competition at any price. In addition, the wiring within the signal path is Swiss-made continuous crystal oxygen free copper with a Teflon dielectric. A soft start circuit is provided, though I'm not convinced that one is absolutely required for an indirectly-heated tube rectifier power supply.

The audio gain stages are all 12AU7 based. Selection of triode type is a major design decision. One of the main reasons PrimaLuna opted for an all 12AU7 circuit is that there are more NOS 12AU7's available on the market than any other tube. The plentiful supply translates into more fine choices and lower prices for the consumer, especially relative to the 12AX7. One of the secrets of this design is that all of the 12AU7 triode sections are connected in parallel, so that in effect there are only three triodes in use per channel. Important benefits accrue by connecting a twin triode in parallel, and it's fair to say that the end result is really a "super" tube. For starters, the transconductance doubles in value as does the plate dissipation. Anode resistance is cut by a factor of two which reduces noise. And of course, lower plate resistance results in reduced output impedance. As an added bonus, there's less sensitivity to imperfectly matched triode sections. It makes you wonder why other manufacturers don't follow suit. Another design secret is aiming at a fairly low overall gain of only 10dB (about a factor of four) rather than the 20dB or greater of many competing preamps. Most digital sources output a hefty line-level of 2V and don't really require any additional gain. Keeping the gain low also helps improve the signal to noise ratio and explains what is, for any line stage and in particular a no global-feedback tube preamp, a spectacular S/N ratio of 93dB. Care will be required when selecting a matching phono front end to ensure that its gain is at least 60dB in order to accommodate a MC cartridge.

There are two gain stages and a cathode follower output stage per channel. Looking at the 12AU7 tube array on the top deck, the two inner tubes comprise the first gain stage for each channel, the next two 12AU7's over are the second gain stage, and the outer tubes are the cathode followers. Use of a cathode follower results in an exceptionally low output impedance of 256 Ohm, meaning that the PDP should be able to drive long cable runs with no problems whatsoever. SCR (France) tinfoil capacitors and Takman (Japan) audiophile-grade resistors are used in critical circuit locations.

The two main functions of a line preamp are volume control and input selection. Input switching is totally relay-based. Only the source you're listening to is actively engaged. One of five line inputs may be selected, either from the front panel selector or from the remote control. Volume control is via a pair of Alps Blue Velvet 100K motorized conductive plastic potentiometers. I've voiced my take on these pots previously. Since both channels are adjusted in tandem, there is no provision for channel balance control. In addition, it is difficult to reproduce a given volume level with a motorized pot. Aside from these functional limitations, I can tell you that sonically the Blue velvet is a fine volume control.

I recently had the opportunity of comparing this Alps volume control with the Texas Instruments (Burr-Brown Division) PGA2320 IC, a digitally controlled analog volume control designed specifically for professional and high-end consumer audio applications. Internal operational amplifier stages are used to generate an attenuation/gain range of -95.5dB to 31.5dB. As implemented in the Ayon Stealth DAC Preamp, this control is strictly used for analog signal attenuation. There is also a built-in balance function that allows left-right channel attenuation in 1dB steps up to a total of 6dB. I've run the Stealth directly into a power amp and have found its volume control to exhibit low coloration levels. I love its functionality, nevertheless, the question of how the PGA2320 compares to a conventional resistive potentiometer deserved an answer. It turns out that the Stealth's volume control can be bypassed by switching over to Fixed Volume mode on its remote control, in which case the audio signal goes directly to the analog output stage. With the Stealth connected to the PDP I switched between Fixed and Variable volume modes on the Stealth, and at equal volume levels, I listened for any sonic difference with the PGA2320 in and out of the signal path. Although not necessarily a definitive test, I did prefer listening with the Stealth in Fixed volume mode. There were improvements in spatial presentation as far as depth perspective and image outline separation. Additionally, the treble range was a bit purer sounding. These results suggest that the Alps pot is sonically more benign.

The Gear
I was fortunate to have the Enigmacoustics Mythology M1 loudspeaker on hand for the duration of this review. The M-1 is a compact two-way stand-mounted speaker that is specifically designed to partner the Sopranino super tweeter in the extreme treble, which in this application, sits on top of the M1. If you don't know what the Sopranino is all about, let me simply state that it represents a new breed of self-biased electret tweeters. To a great extent, the M1 reflects the sonic character of the front end and matching amplification. It is extremely revealing of the rest of the chain and only performs its best with top notch gear. Matched with Lamm Audio's M1.2 Reference monoblocks, the M1 wields considerable emotional power and is capable of generating an almost magical sense of transparency. The PDP was very comfortable in this elite company. Any sonic misstep would have been clearly audible. Yet, distortion products were vanishingly low. There was no gratuitous brightness or treble brashness to interfere with the reproduction of violin overtones or the upper registers of soprano voice. Transients were negotiated with excellent speed and control. The treble range was simply sweet and detailed. Pardon my Italian, but I can't resist characterizing the PrimaLuna's treble as "il dolce suono."Struck cymbals shimmered with plenty of air and massed string sound was supremely realistic. Textural purity was another sonic hallmark. In particular, the midrange flowed smoothly with just the right dose of harmonic liquidity. There was nothing to complain about at the other frequency extreme. The bass range was reproduced with excellent pitch definition and sense of timing. Of course, ultimate bass extension would be totally dependent on the associated loudspeaker and matching power amplifier. But know that the PDP can dig as deeply as your system will allow.

In the context of the M1 loudspeaker, the PDP facilitated pinpoint imaging that could only be described as spectacular. Image outlines were tightly focused within the confines of a soundstage of remarkable depth and breadth which was totally untethered from the speakers. Midrange clarity was such that it allowed each recording's ambient information to be readily discernible. Given an excellent front end, the PDP proved itself time and again NOT to be the weak link when it comes to low-level detail or spatial resolution. Neither did it impede the program material's dynamic prowess. Its feel for microdynamic nuances and ability to scale the macrodynamic range from soft to loud captured much of the music's dramatic content. And there's no need to worry about solid-state sterility - the PDP stayed true to its tube heritage and negotiated complex musical passages with dynamic flair.

The Sound
Out of the box, the PDP did not editorialize, being tonally neutral and faithful to the recording. The stock Chinese 12AU7 tube complement is quite good and I did not feel compelled to roll in vintage types. More out of curiosity, and in order to obtain a complete sonic picture, I first substituted for the first voltage stage and later also for the second voltage stage. I started off with a Mullard long plate ECC82 for the first gain stage, and later experimented with CBS 5814A for the first two voltage gain stages. It became clear that the stock tubes are all business. By contrast, the Mullard delivered a bit more sex appeal:  a richer midrange and greater textural finesse. The CBS 5814A went further down the road toward a lush tonality, being even more velvety and dynamic. And to be honest, that's a sound that's easy to fall in love with. Let me emphasize that the stock tube complement is plenty good. But if you're interested in improving the sound further, especially in the areas of tonal color saturation and microdynamics, then by all means explore vintage 12AU7 options such as the CBS 5814A and Mullard ECC82 long plate. And there are probably many other interesting options – that's the fun of tube rolling.

The Dialogue Premium line preamp strikes me as one of the best things PrimaLuna has ever done. In particular, purity of expression and tonal realism are two of its strongest sonic assets. The incremental improvements to the Dialogue Three have borne fruit. The Premium version is now able to swim with and compete effectively against high-end's cost-no-object heavyweights. And that, my fellow audiophiles, is a rarity. If you're looking for a basic line preamp that is sanely priced and offers genuine tube magic, this is it! An enthusiastic two thumbs up recommendation!

Specifications
Type: Analog Vacuum Tube Stereo Preamplifier
Frequency Response: 9 Hz to 95 kHz (+/- 1dB)
Tube Complement: Two 5AR4 rectifiers and six 12AU7
Gain: 9.7 dB (4x)
THD +N: <0,5% at 2V output level
S/N Ratio: 93dB
Input Impedance: 220 kOhm
Output Impedance: 256 Ohm
Inputs: Five pair stereo RCA, one pair Home Theater Input
Outputs: Two pair stereo RCA (main); one pair RCA (tape)
Weight: 52.9 lbs.
Dimensions: 15.9" x 15.2" x 8.3" (LxWxH)
Price: $3199

Company Information
Durob Audio BV
P.O. Box 109
5250 AC Vlijmen

Website: www.Durob.nl

United States Distributor 
Upscale Audio
2504 Spring Terrace
Upland, CA. 91784

Website: www.UpscaleAudio.com