Dimensions: 1634 in. W x 7'78 in. H x 1634 in. D (42.5 cm x 20 cm x 42.5 cm).

Weight: 51 lbs. (23.1 kg).

Price: $3,995/pair.

Mike Sanders of Quicksilver Audio has outdone himself. With the V4, he has created a mono tube power amplifier that's sonically superior to his state-of the-art M135 yet costs consider ably less. (I reviewed the M135 in the December 1993 issue.) The V4 is very attractive. A black rectangular cover for the transformers and the power supply's four main filter capacitors occupies the rear half of the chrome chassis, while six tubes and a meter take up most of its front half. Rebecca Sanders was largely responsible for this visual design-nice job!

The four largest tubes are KT88s, yielding rated output power of 120 watts into 4- or 8-ohm loads; other output tubes (such as 6L6s, 6550s, or EL34s) can be used instead. Adjusting the output tubes' bias is simplicity itself. To find out a particular tube's plate current, you just push a button next to that tube and its current will appear in the meter. To adjust plate current, you use a screwdriver to turn a pot near the tube in question.

Construction of the V4 is simple, elegant, and traditional. The wiring is point to point (and commendably neat). The chassis serves as the ground bus; many circuit points are tied to it through ground lugs that have serrated contact areas to ensure good connections. And lots of high-quality parts are in evidence. All in all, a very nicely made amp.

I received two Quicksilver V4 mono amps; unless otherwise noted, reported results are for one of them, which I designated as the left channel. I set each output tube's plate current to 40 milliamperes, as Quicksilver recommends.

Figure 2 shows the Quicksilver amp's square-wave responses. There's a slight overshoot in the top trace, which was made with 8-ohm loading on the 8-ohm tap. Overshoot increased when the tap was loaded with 4 ohms and decreased a bit for 4- and 2-ohm loads on the 4-ohm tap. These results correlate with the frequency responses of Fig. 1. The ringing exhibited for a 2-microfarad capacitor paralleled across the 8-ohm load (middle trace) is in the normal range. The 40-Hz square wave (bottom trace), however, has somewhat more tilt than I've seen in other tube power amps. Square-wave rise and fall times at an output level of ±5 volts into an 8-ohm load on the 8-ohm tap were 2.4 microseconds.

Equipment used in the listening tests for this review consisted of

CD Transport: PS Audio Lambda Two Special

CD Electronics: Genesis Technologies Digital Lens anti jitter device, Classe Audio DAC

D/A converter, and DGX Audio DDP-1 preamplifier (see text)

Phono Equipment: Kenwood KD-500 turntable, Infinity Black Widow arm, and AudioTechnica ML150 moving magnet cartridge

Additional Signal Sources: Nakamichi ST-7 FM tuner, Nakamichi DR-3 cassette deck, Denon DMD1300 MiniDisc recorder, and Technics 1500 openreelrecorder

Preamplifiers: Sonic Frontiers Line-3 and Ayre Acoustics K-1

Power Amplifiers: Sonic Frontiers Power-3 and Quicksilver M135 mono tube amplifiers, Ayre Acoustics V-3, and Audio Note Ongaku single-ended tube amp

Loudspeakers: Genesis Technologies Genesis Vs and B&W 801 Matrix Series 3s

Cables: Digital interconnects, Illuminati DX-50 (AES/EBU balanced); analog interconnects, Transparent Cable MusicLink Reference (balanced) and Tara Labs Master and Music and Sound (unbalanced); speaker cables, Transparent Cable MusicWave Reference and Tara Labs RSC Master Generation 2

I have recently changed my listening setup when using B&W 801 Matrix Series 3 speakers, moving them quite a bit farther into the room than before. I connected a DGX Audio DDP-1 preamplifier, which has digital equalization specifically for these speakers, between my CD transport and a Genesis Digital Lens anti-jitter device. The overall sound had been very good with this setup through my reference power amplifiers, and connecting the Quicksilver Audio V4s quickly revealed that these were very good-sounding amps indeed. Space, delicacy, transparency, and overall musical believability were of high order.

With the V4s, bass power, definition, and impact were quite good. At high volume, the sound held together very well. I had recently heard a pair of V4s on my 801s in somebody else's home and was very impressed with the sound quality. The low bass was better, and the region from the upper bass to the lower midrange was smoother than in my room with the 801 s, but overall transparency and space are superior in my own setup.

I then paired Genesis V speakers with the Quicksilver V4 amps. These speakers are quite fussy about the power amps that drive them. It is somewhat of a guessing game as to how a particular amplifier is going to sound with them; an amp that sounds very good on other speakers may sound less than great on the Vs. The problem is not in the bass, since the Genesis V's own servo amplifier handles everything below about 90 Hz, and the speaker's rising impedance from 150 to 90 Hz unloads your system's amp and relieves it of producing power at bass frequencies. With the V4s driving these speakers, the sound was again spacious and detailed but there was noticeable high-frequency edginess on some recordings. I preferred the sound of some of my other amplifiers to the V4s on the Genesis speakers. However, the V4s did sound good when driving the B&W 801 s, which are more representative of the speakers they're likely to be mated with.

TECHNICAL. HIGHLIGHTS

The Quicksilver V4's first and second stages share a 12FQ7 twin-triode tube. The first stage is a common-cathode input amplifier whose plate output is directly coupled to the grid input of a split-load phase-inverter second stage. (A split-load phase inverter has cathode and plate resis­tors of equal values.) The plate current, which carries the signal, is common to the plate and cathode resistors, and the plate and cathode signals are out of phase. Thus, equal but oppositely phased output signals are generated at the plate and cath­ode. The two signals from the phase inverter are capacitor-coupled into the next stage, a push-pull common-cathode driver. It uses a 1213147 twin triode, whose plate outputs are capacitor-coupled to the output stage.

The four KT88 output tubes are pentode-connected, with a nominal 600-volt supply to the center tap of the output transformer and 300 volts on the screen grids. Each output tube has an adjustable negative supply to set its plate current.

There are two feedback loops. Push-pull high-frequency feedback from the output tube plates to the driver cathodes, via low-value capacitors, provides high frequency stability and lowers high-fre­quency drive impedance to the output transformer. The overall feedback loop runs from the output transformer's sec­ondary to the input tubes cathode.

Separate secondaries on the power transformer feed three separate high-volt­age DC supplies, a low-voltage negative DC bias supply for the output tubes, and AC for the tube heaters. For the main high-voltage supply, the main secondary winding feeds a full-wave rectifier bridge and a capacitor-input filter formed by two 1,100-microfarad, 300-volt filter capaci­tors in series, with the winding's center tap connected to the junction of the two ca­pacitors. The output stage's B+ supply is taken across the ends of the filter, and the screen grid supply (about half the B+ voltage) is taken from the junction and one end of the filter. A third transformer winding feeds high voltage to the input through driver circuits via a bridge rectifier, another capacitor-input filter, a series filter choke, and a final filter capacitor. This use of multiple high-voltage supplies is an important part of the V4's design and is partly responsible for this amp's sonic character.                        B.H.K.

The V4s performed flawlessly in the lab and in my listening system. Plate currents

were stable throughout the review period and needed little tweaking to stay at 40 milliamperes.

The V4s are a significant addition to Quicksilver's line of electronics and continue that company's tradition of well-designed, reliable, affordable, and excellent-sounding gear. I enjoyed the V4s and recommend that you go out and listen to a pair.