Review: Promitheus Audio Transformer Volume Control Ref 4 Preamplifier

Category: Preamps

dolal April 15, 2008

It takes guts to move away from the traditional scheme of things and into something relatively unknown. After all, how many of us would think that a $650 volume control would replace a $2800 preamp? And then, how many of us would actually make the leap forward? Yes, you heard right…forward.

In November 2007 I happily purchased a truly balanced Reference 4 Transformer Volume Control (TVC) from Promitheus Audio. Before that time my system consisted of the following:

Meridian 500 Transport and 566.24 DAC
Classe CP-50 preamp
Classe CA400 amp (400 w / channel into 8 ohms)
Revel M20 monitor speakers
Cables are Synergistic Resolution Ref and Acoustic Zen Matrix Ref II IC’s, Transparent Super speaker cables, Synergistic, Cardas and MIT power cords. All connections are balanced.

My soundstage was enormous and it was obvious that all listeners could feel the music (classical and jazz), not just hear the notes. The music had a very hefty weight to it with great dynamics; it sounded live. It sounded as if I had large 3-way speakers instead of 2-way monitors. Bass was big and deep and a little fat (warm Classe sound) and treble a bit bright (Revel M20’s are very accurate and my room is bright). The attack, sustain, decay and release of notes had a natural feel to them. However, my electric power is very dirty with exceptional grunge of high order harmonics. Transparency was lacking. Late night was the only time for a quieter background and enjoyable listening. My thinking was that the preamp was amplifying the grunge. One option was power conditioning, another was a preamp upgrade. More than likely, both would be necessary. My reading (Audiogon, Enjoy the Music, Stereophile, Audio Circle,) brought me to Nicholas at Promitheus Audio.

As with most things in life, the dogma tells us to set up our systems in a certain manner and we generally follow. But there are those that take their hobbies to different levels through experimentation. This is largely made possible through an absolutely divine website: AUDIOGON. If you pick up something that doesn’t integrate well into your system you can flip it. This has a direct effect on my character: I’m much less hesitant to try out different components. BTW, it has its disadvantages too, as I am tired of cable rolling!!!

After a short communication with Nicholas I opted for the truly balanced Reference Version 4 TVC (there are other models). It is a “passive” preamp without electrification (no power supply or power cord connection) and no pots or resistors in the path to dirty the sound. On the rear it has one pair of truly balanced input / output connections (XLR) and 2 pairs of RCA ins and outs. On the face one finds an ebony selector knob in the center and separate ebony stepped attenuation knobs (down to -48 dB) for left and right channels. The sides are made of merbau wood and the top and bottom plates are stainless steel.

It replaced my $2800 Classe preamp and it made a wonderful difference. Break in time was long, about 500 hrs, but well worth the wait. The TVC can only attenuate volume (no gain) and I usually set it between –6 to –10 dB (rarely –4 dB) to yield the same listening volumes as before (quite loud). Surprisingly, even when set at –20 dB (I have not gone lower) one can hear all the nuances in the music, much more so than before. As others have also reported, the most striking characteristic of the TVC is that the background is so dead silent that it is not an issue any longer. IF YOU LOOK UP TERMS LIKE “DEAD SILENT” AND “TRANSPARENT” IN THE DICTIONARY THERE SHOULD BE A PICTURE OF THE PROMITHEUS AUDIO TVC. I can listen to music any time of day now and not worry about the grunge. I cannot detect any coloration in the sound. Now I know what the preamp added! Also, the frequency extremes have been extended for the better. Shockingly, the bass is more obvious and it’s deeper and tighter than before. It makes me worry that my mid-woofers are going to shoot across the room (the Revel’s f3 = 44 Hz and with my big room extension they easily go down to well below 30 Hz). The treble is also extended but not brighter, just extended. Now I know what the preamp stole from my system!

Of course, there are some trade-offs that others have also noted in the literature. The soundstage was reduced but mine was so large to begin with that it is still very acceptable. The music is thinner…it sounds as if my amp or speakers have been reduced in size although they still sounds like 3-way speakers. It seems as if the sustain or decay times have been shortened. There is no remote and one has to count the clicks in the attenuators (1 click = 2 dB). Also, some finer sanding would help its cosmetic appearance.

However, I honestly much prefer the system the way it sounds now with the TVC as compared to before, largely because of the silent background and the frequency extension. In fact, most listeners who did not hear my system before the addition of the TVC will comment on 1) how large my soundstage is, 2) how powerful and musical the system presents itself, 3) how silent the background is and 4) how fine the resolution is. There is plenty of emotion to go around but I would like a bit more body to the music without depleting my funds.

After contacting Nicholas he made a number of suggestions and I will be adding what he terms a Tube Active Preamp. It is usually referred to as a tube active stage or tube buffer stage by other manufacturers. For about another $600 (with my required additions of balanced inputs, etc) for a total of about $1200 together with the TVC, I suspect that I will most likely have the equivalent of a tremendous preamp upgrade. I will add to this review at a later time.

Don’t let the $650 price fool you. The TVC is NOT an entry-level component. It is as high-end as high-end can get. Most reviewers have rated this TVC above others in the market and I thank them for leading me to it. This is truly an outstanding bang for the buck upgrade. Nicholas is also ready to work with the customer to accommodate individual needs. BTW, I received my TVC within a few days after paying for it. Nicholas and the folks at Promitheus Audio have my highest praise for this truly remarkable component and their outstanding customer support.

Associated gear
Meridian 500 Transport and 566.24 DAC
Classe CP-50 preamp
Classe CA400 amp
Revel M20 monitor speakers
Cables are Synergistic Resolution Ref and Acoustic Zen Matrix Ref II IC’s, Transparent Super speaker cables, Synergistic, Cardas and MIT power cords. All connections are balanced.
Dolal; I agre with your evaluation, and I now understand why active preamps have a great influence on the sound of a system.
Thank you for sharing your finding. I too have hear one of this preamp. But personally don't like the idea of a long signal path which is the case when TVC applied... So, active or passive... there is no perfect solution.
Dolal, we'll see if this thread revives....did you ever get the tube buffer? care to voice your .02? I have a Prom TVC ref 4 in the system but could use a bit more gain. Worried that the tube buffer will color the sound vs. the clean and clear tvc alone.