VAC Phi 200 Tube Monoblock Amplifier Review

Four lumps of amplification, please!

There are people who take their coffee black and strong. I take my amplification big and strong. Amplification junkies break down into two types; stereo people and biamp/mono people. I’m the latter. Usually, if you give me a speaker with two sets of binding posts the following thought takes possession of my mind immediately, “Four posts… which cable will I bi-wire with and which pair of amps am I going to use?” I have done so many comparisons of amps running stereo compared to passively bi-amped and bi-wired, or actively bi-amped that I no longer wish to assemble my reference system with just one amp. (So sad. Same here. –Ed.)

From the time that I first heard the King at CES 2008 and learned that Kevin used it in voicing the Phi 200, he suggested that I might use the amp with the speaker. Later, as I had taken ownership of the speaker, the possibility that I not follow up with a review of the Phi 200 was unthinkable! Seeing that only one unit was driving the speakers at the show, I assumed that one would be sufficient for the review. Kevin offered that two would be superior. But of course! Now that’s impressive; a manufacturer who offers a second amp to get the reviewing job done right! I had seldom encountered that level of commitment to me from a manufacturer in setting up a review system. It speaks volumes to me about how Kevin is only happy when the sound is correct. The suggestion revealed to me that Kevin is keen on obtaining the optimal sound, and had confidence that his amps would perform at an extremely high level in mono mode.

At the first California Audio Show, the King was shown with the VAC Phi 200 to much interest and approval. There was a technical issue, as only one Phi 200 drove the pair of speakers but was using the 8-ohm posts versus the anticipated 2-ohm posts. Consequently at higher listening levels the amp was pushed to its limit and did not sound as effortless as it is capable. In my listening at home, I have tested all three settings, 1-2 Ohm, 2-4 Ohm, and 4-8 Ohm, and the King was much more controlled by the Phi 200 with the lower 1-2 Ohm terminals in use. The Phi 200 is the kind of amp that one can play a speaker like the King with confidence in stereo mode and work toward a second unit to operate them in mono mode for ultimate performance.

In extended use, the Phi 200 does not run terribly hot; I was surprised at how little heat they generated. The Cambridge Audio Azur 840W, a solid-state design, throws off more heat. Only if left on half a day in a smallish room would I think that they might test the limits of the listener’s temperature-comfort tolerance.

Unveiling the Phi 200

Perhaps the term unveiling is too strong; I’m here discussing the unpacking, appearance and operation of the amp. “Dis-crating” a high-quality amp can be a bit like the dance of the seven veils, as each layer is carefully stripped away. Surprisingly, no crate was involved; custom foam pieces cradle the amp in a sturdy double box. The casing and transformer covers are nearly of military thickness, fronted by a slab-like faceplate. As a side note, custom formed foam packing pieces are quite expensive. At the time of the delivery of the Legacy Audio Whisper DSW, I was about to toss out an indistinct smaller foam piece perhaps half a meter long which was lying nearby as the transport materials were being collected. Doug Brown of Legacy Audio requested its return, “You wouldn’t believe how expensive these are!” MSRP on the piece of foam – $30. No wonder manufacturers charge hundreds of dollars for a pair of OEM boxes with foam! Take note, owner, as it can save you serious money to save the packaging.

I chortled when I saw daisy chained rubber bands holding a very low tech piece of cloth draped over the thick aluminum face plate. It certainly did the job, as each amp was immaculate. Kevin will not spare a buck to attain ideal sound, but he’s sensible when arranging packaging. He’s not hung up on glam boxes as pretty velour bags inside wooden boxes don’t get the right sound out of a machine. I’ve learned to be less impressed by such things as I work with equipment. Don’t get me wrong, as a thick covering can save a component from shipping damage. I’ve seen more than one speaker’s finish impaired due to flimsy protective transport coverings. Just don’t make the mistake of thinking, “Oooh, high grade bag! This xxxxx has got to sound great!” Some components have great bags and merely acceptable sound. The Phi 200 arrives as a ruby concealed in a paper bag.

In terms of finish, black and silver are the two standard VAC colors, but beggars can’t be choosers, so while the Signature Preamp Mk 2 that I reviewed in March 2010 is in graphite color face, the Phi 200s features metallic silver gloss front plate. No matter, VAC gear looks rich and refined with nice, complementary hues. As the Einstein “The Light In The Dark” had a low-profile chassis, so also does the narrow chassis of the Phi 200, in a powder coat matte black finish that is uninterrupted, save for the tubes and backing wall of transformers. Sitting just behind these blocks of impedance transforming windings are the main operational switches.

One needs to be careful when handling tube amps as the weight is not necessarily evenly distributed across the chassis’ expanse. Wherever the transformers are, there most of the weight will likely be. In the case of the Phi 200, one must grab the amp nearly at the rear, literally picking it up at ¾ of the way to the back of the unit to prevent it from potentially slipping from one’s grip. It is a good habit to test-lift tube amplifiers to find the balance point. You do not want to be in the middle of transporting one and finding that you chose the wrong place to grab. It’s a scary feeling to have a component turning in your hand because its mass is unevenly distributed. Go about such tasks diligently and save yourself some fear or heartache.

Also on the top of the chassis, just in front of each pair of low-level voltage amplifier/phase splitter 6SN7 tubes, are small toggle switches allowing for selection of balanced (XLR) or single-ended (RCA) inputs. Nearby are corresponding holes for the output tubes in the chassis about the diameter of a pencil. These allow access to the bias adjustment points of the amp. A supplied small biasing tool akin to a tiny screwdriver is employed for adjustment of the bias. Behind each KT88-SC kinkless tetrode output tube is a small amber LED for assessing the biasing. This was a painless process as the controls to perform the operation are within easy reach and sight. You may have heard complaints of biasing tube amps being a PITA, but with the Phi 200 it is almost effortless. Using the tool supplied one turns the adjustment until the point at which the LED lights up. Then it is turned back until the LED just turns off. This requires slight movements; no lummoxes need apply.

When first installed, one has to baby sit the amp for several bias adjustment steps after the unit is first turned on respectively for 60 seconds, 90 seconds, two minutes, five minutes, and finally after 15-30 minutes. Biasing is also required whenever a tube is changed, and approximately once per month of usage. I found the amp to hold its bias extremely well. I would check often and end up not touching the settings as I could not determine that they had changed. The manual states, “Proper setting is indicated by an LED that is dark when no music is playing, but lights ‘with the beat’ as music is played.” The owner is left to determine how “heavy” the beat is to be. I put on some music with stronger bass line to adjust the bias such that the LED is never off completely but winks almost out before being illuminated by the next beat. When listening to Rapcore or Doom Metal music the light never turned off. Just kidding; I don’t listen to these genres of music.

The connections behind the transformers include 15A IEC for power cord, twin sets of binding posts for left and right channels, each having a common/ground post and three posts for 1-2 Ohm, 2-4 Ohm, and 4-8 Ohm to select placement of the positive speaker lead.

Phi foibles

There is an aesthetic consideration in the appearance of the Phi 200 which reveals itself when you hook it up; the inputs are behind the transformers, on the top of the chassis. My first reaction is that of appreciated sensibility; it’s far easier to see what you’re doing when setting up the amp than leaning over its side especially if the amps are in an amp stand! Officially, it was done to keep the front-to-back dimension within the space allowed by some cabinets and racks. However, it’s not so captivating to see the mongo power cord arc in the air because it’s too thick to lay flat emerging from the amp’s top mounted IEC receptacle. However, I will gladly endure this slight visual perturbation to use the Phi 200. I weep for any man who can afford this amp and whose wife kills the purchase because the power cord arises into the air. The amp is good enough that I would suggest offering new furniture as compensation. If you have stiff interconnects, they, too, will stick up in the air. If that is a problem, then consider getting longer interconnects and hiding the amps behind the speakers, a tactic which may get you noticeably improved sound.

The only other operational quirk I found was the fairly close spacing of 0.75-inch of the Cardas rhodium binding posts, the spacing provision of which is controlled allegedly by the insulation parts supplied by Cardas. Cables with oversized spades are placed too close to be casual about hooking them up. Though it didn’t always appear to be, there was enough room for spades of all cable types used. I made sure to use a binding post wrench, available from Audioquest and Cardas, to prevent possible slippage of the spades.