Both the DiaLogue Premium preamp and the HP power amps use a heavy-gauge slotted bottom panel to allow ready airflow into the fully ventilated, panel-mounted tube sockets. The choice of tube sockets and panel mounts as well as the point-to-point solder work are very good, quite reminiscent of that found in costlier designs. Circuits are populated with French-made audiophile-grade DuRoche and SCR tin-foil capacitors, and Japanese TAKMAN resistors. Swiss-made, silver-plated, continuous-crystal, oxygen-free copper wire, with Teflon dielectric, is used in all critical signal paths. The power and output transformers are massive custom toroidals, rated for 200% of their duty cycle, and are potted to protect the windings from moisture and deterioration.
The front of the Premium HP power amplifiers shares the livery of the preamp, and sports only the power/standby lamp dead center, flanked by two additional indicator lamps, red to the right to indicate ultralinear mode, green to the left for triode mode. While the amps also have their power switches at the front of the left side panel, they also include a tube-type selection switch (down for EL34s, up for KT varieties) at the front of the right side panel. The back panel includes, left to right, single-ended inputs (again, no XLR connections), a stereo/mono toggle switch, followed by the right (also used for mono) then left speaker outputs, with 16-ohm, 8-ohm, 4-ohm, and ground binding posts, then the IEC socket. Each amp comes with its own narrow (7⅞" long, 1¼" wide, 13/16" high), rounded side, single button remote, also equipped with twin rubber O-rings, allowing for mode switching.
The Premium HP amplifiers use a set of eight EL34s, arranged in two rows of four, directly in front of the transformer compartment. Two sets of four red LEDs, part of the BTI system (read on), are oriented in a square in the space created at the center of the four EL34s on the right, the other set for the quad to the left. These LEDs are numbered to match the tubes, and indicate when a tube is failing, or has failed. The system will mute itself until you replace the bad tube, then restart. In front of the EL34 complement is a row of 12AU7s, also in a slightly curved alignment as with the Premium preamp. Honestly, to my tastes, these are some extremely good-looking designs.
The EL34 is a classic pentode with five elements (cathode, anode, and three grids). First introduced in 1953, it is generally lauded for its midrange tonal properties. Its use in such classic amplifiers as Saul Marantz’s Models 5 and 9 monos and Sid Smith’s Marantz 8B stereo, and David Hafler’s Dynaco ST-70. The Conrad-Johnson MV55 and MV60 are most likely what inspired its use here. One of the first things you notice, even before powering on, is that all the tubes are PrimaLuna-branded. In conversation with Kevin I learned that these tubes are sourced from Shuguang, giving PrimaLuna the option of careful selection, and allowing them yet another layer of quality control.
As to features, the PrimaLuna Premium HP amps in particular are second to none in my experience at, or anywhere near, their price points. As already stated, their output circuits can be switched on-the-fly between 40 watts (triode) or 70 watts (ultralinear) in stereo mode, or between 85 watts (triode) or 148 watts (ultralinear) in mono configuration, as reviewed here. Ultralinear output is about 3dB louder than triode mode—something that should be kept in mind when doing live mode-switching.
Maybe most interesting of all is that, though the HP power amp, as equipped from the factory, runs EL34s, in that same switch position you can run 6CA7s, EL34s or EL34LSs. And, if you are all right with a slight drop in output, you can even run 6L6GCs, 7581As, or KT66s. With the switch in the KT position, you may use 6550s, KT88s, KT90s, KT120s, or KT150s, should you care to! Though I had no store of other power tubes on hand to explore those options, the HP amplifiers are obviously a tube-rollers delight.
A big part of the PrimaLuna amplifier technology (and sales pitch) is something they call Adaptive AutoBias. Essentially, PrimaLuna claims it is an entirely passive process allowing tubes to run less stressfully, with greatly reduced distortion, yielding longer life and affording some large degree of safety and convenience. This circuit constantly monitors tube operation to sense when a tube is failing or has failed, at which point, it both mutes the circuit, protecting the amplifier from damage, and lights an LED indicator, notifying you of just which tube is affected. This eliminates the guesswork of swapping tubes one at a time to locate the culprit.
Though the Premium HP amplifier manual claims the Adaptive AutoBias circuit is, “an exclusive PrimaLuna feature you won’t find anywhere at any price,” PrimaLuna’s sister company Mystere, (also run by Herman) uses the same circuit. Further, Kevin Hayes’ Valve Amplification Company’s (VAC) employs his unique patented iQ Continuous Automatic Bias System throughout his entire amplifier line.
PrimaLuna employs a number of other technologies, including Soft-Start, used in conjunction with the Adaptive AutoBias circuit to slowly bring the amplifier up to full power. Another, called AC Offset Killer, utilized in both the preamp and amplifiers, is said to remove problems that may occur in your AC mains before power gets into the circuits and to keep the main AC power transformer as quiet as possible. There is also the aforementioned BTI (Bad Tube Indicator), which lights a red LED on the chassis to indicate which tube is experiencing any degree of failure. Finally, there are PTP (Power Transformer Protection) and OTP (Output Transformer Protection). In the event that the power transformer’s internal temperature becomes too high, PTP uses a thermal switch to cut off the main AC input. With OTP, the transformers are protected from improper loads during hook-up or under play, or while changing speakers with the power turned on.
I must mention that packaging is every bit as exquisite as the components’ fit and finish. Triple-boxed, in custom-formed foam, with individual sleeves covering the power tubes and a set of white cotton gloves included for handling, these things couldn’t be packaged any better or more safely.
As one of my strongest axioms is “change only one item (component, cable, isolation device, etc.) at a time,” when my review samples arrived, I installed the amps in place of my Pass Labs XA160.8 monos, switched them into mono mode, and connected them to my VSA VR-55 Aktives, with the rest of my reference system intact. However, so as not to squander break-in time, I also installed the Premium preamp into my theater system and ran it consistently there.
Immediately apparent on insertion of the HP amplifiers, using the 8-ohm taps, was the signature EL34 midrange performance. Bass was a bit cold and constricted, both in extension and impact, and treble was a bit soft and muted, not at all atypical for brand-new amplifiers, but it was pretty clear that this ride was going to be fun. Just to be sure I wasn’t missing some unexpected magic, I tried brief connections to both the 4-ohm and 16-ohm taps after run-in. But the slight midrange emphasis with the 4-ohm tap further exacerbated the slight bass leanness. As I really heard no advantage or detriment with the 16-ohm tap, I settled on the 8-ohm tap for the bulk of the review. (Note that when operating as a monoblock, the taps are marked as 2, 4, and 8 ohms.)