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
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.
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 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!
United States Distributor