Primaluna
Prologue Premium
Power Amplifier

Overview

PrimaLuna amplifiers have long been known for their Adaptive AutoBias circuitry, a PrimaLuna trademark that makes traditional tube biasing a thing of the past.  This design allows a wide range of tubes to be used in the output sockets:  KT88 or EL34 tubes work equally well—every ProLogue Premium Series amplifier comes with either set of tubes installed.  (The KT88s produce 36 watts per channel; the EL34s produce 35 watts per channel.)  The new premium version of the amp adds a switch on the side of the chassis, allowing you to optimize the amplifier to your choice of tubes, in order to achieve the lowest possible levels of noise and distortion.

PrimaLuna has updated the front-end circuitry for this amp, which now uses 12AU7 tubes instead of the 12AX7s in the company’s earlier amplifiers.  The inveterate tweak-geek in me could not resist fooling with those 12AU7s, even though the amp sounds great with stock tubes.  New old stock GE tubes render a smoother top-end response, but offer a different listening perspective, as if I had moved back about five rows in the orchestra.  Next, a set of RCA clear tops (with side getters, for the tubeophiles in the audience) provides a big jump in frequency extension, as well as more transparency and a more palpable midrange.  Best of all, Kevin Deal, the owner of Upscale Audio (and the PrimaLuna importer) has a massive cache of these tubes in stock, so you can experiment at will; the 12AU7s aren’t nearly the cost of the 12AX7s.

Features 

• Innovative, new Adaptive AutoBias circuitry. By simply flipping a switch, users can re-calibrate the amp for optimum operation of EL34s or KT88s. Every ProLogue Premium Series amplifier can be ordered with either set of power tubes installed. And remember, this circuit continuously monitors and adjusts each tube to run in its sweet spot. No biasing—ever!
• New output and power transformers. Modeled after those in the DiaLogue Series, these heavy-duty, high-efficiency transformers offer better control over challenging speaker loads, as well as increased detail and musicality.
• New front-end circuitry. Optimized to use two 12AU7 tubes per channel. With the improved transformers, produces lower distortion.
• Zero negative feedback – as with the ProLogue Series power amplifiers, the ProLogue Premium Power Amplifier uses a zero negative feedback topology for greater tonality and better overall musicality.

Next, the ProLogue Premium Series introduces four innovative circuits that protect the amp at every level:

• BTI-circuit. BTI stands for “Bad Tube Indicator.” On the chassis’ deck in front of each power tube, is a small LED that lights up if the tube goes bad. This circuit works hand-in-hand with the new Adaptive Auto-Bias circuit.
• PTP-circuit. If the power transformer should overheat, this “Power Transformer Protection” circuit cuts primary power, allows the amp to cool down, then resets itself.
• OTP-circuit. The “Output Transformer Protection” circuit protects the output transformers in the event of a massive tube failure or user error.
• +B relay. Replaces the plate fuse and works in conjunction with the OTP-circuit to protect the amp against tube failure. This method is less intrusive sonically and the relay resets itself once the faulty tube is replaced.