PrimaLuna ProLogue Premium Stereo Tube Preamplifier

Introduction

We have been on a roll with reviewing PrimaLuna and Mysterè products, and they have all sounded terrific. The current review is on the PrimaLuna ProLogue Premium Preamplifier, and would you believe it . . . it sounds terrific too. Compared to the standard version of the preamplifier, the Premium has a new front-end design using all 12AU7’s in a dual-mono configuration, a larger power transformer, home theater pass-through, a remote control while still using the higher end Alps Blue Velvet potentiometer, larger chassis with DiaLogue class cosmetics, tube rectification, and point to point wiring.

The Design

Compared to the PrimaLuna 3 Preamplifier, the Premium has a bit more gain and is about 50% heavier due to the larger power supply transformer. It uses four 12AU7’s instead of two 12AU7’s and two 12AX7’s. Both use two 5AR4 rectifier tubes for full-wave tube rectification. There are two power transformers in this preamp, making it dual-mono.

The preamplifier operates in Class A bias, and does not use global negative feedback.

The connections on the rear panel are all gold-plated brass and very high quality. There are four sets of RCA inputs and two sets of RCA outputs. A tape-out loop completes the configuration. The AC receptacle is grounded.

A very elegant remote control comes with the preamplifier. It is long and slender and has basic functions. It is obviously intended for use with a CD player, and the only functions that apply to the preamp are the volume control and mute button.

There are several protection circuits in this preamplifier. (1) The BTI (Bad Tube Indicator) lamp near each power tube will light up if the tube fails; (2) PTP (Power Tranformer Protection) cuts the power if the amplifier overheats; and (3) OTP (Output Transformer Protection) activates if there is a major amplifier circuit failure.

In Use

I tested the ProLogue Premium with the Mysterè pa21 tube power amplifier that we reviewed a few months ago and I still had on hand. The pa21 outputs 55 watts per channel. The source was an OPPO BDP-83SE/NuForce universal Blu-ray player, and I used the analog outputs from the player to the inputs on the ProLogue. Speakers were Carver Mark IV’s, and cables were Emotiva and Legenburg.

My own reference systems consist of tube preamplifiers and solid state power amplifiers (or hybrid tube/solid state power amplifiers). I like the tube sound, but I want the power that is only available with solid state power amplifiers. For example, my McIntosh MC1201’s output 1,200 watts RMS into 8 ohms. This gives me the dynamic range that I want when listening to classical symphonies at full tilt.

Nevertheless, a full tube setup has its advantages, namely, that all of the sound is tube, which tends to have even order harmonics, which are euphonic. Critics of tubeophiles who say they like the even order harmonic sound state that it is not in the recording, but just something added on top that is artificial. Well, it boils down to this: you don’t have the option of “no distortion”. All amplifiers produce distortion. What you get to choose is which type of distortion. So, I choose the even order type of distortion that tubes produce, for the preamplifier, and I accept the odd order distortion that I get in my power amplifiers because I need that power.

So, 55 watts doesn’t blow out the walls, but in fact, most of the time, we listen at a level of less than 10 watts. It’s the cannon shots in The 1812 Overture that won’t be conveyed in all their glory, but in general, 55 watts is enough for most listening.

The ProLogue was a perfect match with the pa21, producing lush, warm sound that put me into deep relaxation. There is a smoothness to an all-tube hi-fi system that cannot be matched when there is solid state anywhere in the signal path.

This Telarc SACD of some of Debussy’s compositions is quite beautiful, and the music was conveyed with convincing detail and dynamics, nothwithstanding the power limitations. The sound was neutral, but kept its triode foundation. The symphonic poetry as read by the the Cincinnati orchestra definitely increased the flow of serotonin throughout my brain, allowing me to listen, without trying.

Female voices are beautiful enough without seond order harmonics (only a geek would say something like that), but through triodes . . . gorgeous. Sutton’s voice soothed my long day into a restful relaxation in the evening sitting by the window. No overly sibilant words to the music. Just clean, detailed, silk.

In this Telarc recording of the Los Angeles Guitar Quartet, a.k.a., LAGQ, the musicians honor famous guitarists of the past, including Jimi Hendrix and Frank Zappa. Now, if an amplifier had the slightest harshness, the twang of the guitars playing music of those artists from the 1960’s would be like broken glass. But that didn’t happen here. It was like crystal lightly tapped with your finger.

Brass instruments are another area of concern with an amplifier that produces too much odd order harmonics. Since the PrimaLuna ProLogue Premium preamp doesn’t do that, the brass – in this case, French horns – were smooth, yet delivering the slight edge that horns tend to have.

I also played a lot of Vivaldi chamber music, you know, string quartets and such. I don’t remember which track on the third disc where I fell asleep. Ah, tubes deliver such peace.

On the Bench

All distortion measurements were made within an 80 kHz bandwidth, both channels driven, unless otherwise noted.

At 1 kHz and 2 volts output, THD+N was 0.65%. The preamplifier will deliver 5 volts, but 2 volts is plenty for most power amplifiers. Notice that the distortion is primarily second order (you know, that “artificial” stuff that tubeophiles like). The noise floor is way, way down there at – 130 dBv for most of the spectrum, and – 100 dB below 1 kHz. This is one quiet preamplifier!

The ProLogue does not reject that low level 20 kHz electrical noise that I have in my environment, and you can see it at the base of the test signal peaks. Some components reject it, and others don’t. But, in any case, the purpose of this test is to look at the B-A peak at 1 kHz, which for the ProLogue is 40 dB below the fundamentals (19 kHz and 20 kHz sine waves). There are only two visible side peaks around the 19 kHz and 20 kHz peaks, and this represents good performance.

IMD was 0.46% at 2 volts output (6 dBV corresponds to 2 volts RMS). The peak at 14 kHz is the second harmonic of 7 kHz, it is not part of the IMD calculation.

THD+N vs. Frequency remained in the 0.5 to 0.7% range from 10 Hz to 20 kHz. This indicates a neutral sound rather than being bass-shy or overly intense in the midrange. Now there is a term called midrange lushness, and that refers to the addition of those second harmonics to the sound. The reason it is so noticeable in the midrange is that is where the amp is likely to produce low order harmonics that you can hear. At 10 kHz, on the other hand, which is not part of the midrange.

The measured frequency response was 20 Hz – 20 kHz, – 1 dB.

THD+N vs. Output Voltage indicates the sharp knee at 200 mv, and then a gradual increase to clipping (1% THD+N) at 4 volts.

Conclusions

For $2,199, the PrimaLuna ProLogue Premium Preamplifier is an excellent value. It is beautifully constructed and has a warm lush sound that all of us tubeophiles love to listen to. If you have an interest in getting into the world of valve sound, this unit represents a very affordable way to get there.