This turned out to be a twofer review—two for the price of one—shortly after I accepted the Ultravalve assignment and considered compatible loudspeakers. Speakers are a critical decision that can make or break an amplifier review. It seems to me that many reviewers simply drop an amp into their existing system and allow it to sink or swim. That’s equivalent to playing Russian roulette with the outcome. A more elegant approach is to investigate load compatibility by using several loudspeakers, giving the amp under test several chances to shine. In fact, the DALI Helicon 400 Mk2 ($7000/pr.) and the JAS Audio Oscar ($3450/pr.) turned out to be perfectly happy with the Ultravalve. However, a secondary criterion for speaker selection in this case was cost. It would only make sense to evaluate a budget amp with speakers that were not too far apart cost-wise, as that would represent the most likely real-world scenario. The ideal solution, it appeared, was to duplicate the coupling that our esteemed Editor-in-Chief, Robert Harley, was mightily impressed with during the 2009 Rocky Mountain Audio Fest. And that’s how Salk’s SongTower entered the picture. I’m glad it did, as this turned out to be a hugely synergistic coupling, a marriage made in audio heaven.
According to Frank Van Alstine, the Ultravalve’s lineage is traceable to the Dynaco Stereo 70, which he denotes as its “great grandmother.” The ST-70 has got to be the most successful basic power amplifier of all time with estimated sales in excess of 300,000 units. This is the amp that in the 70s steered me clear of solid-state designs and cemented my lifelong love affair with tube amplification. In fact, I still own a beautiful Will Vincent ST-70 rebuild. Frank started taking a close engineering look at the ST-70 in the late 70s, the result being an upgrade kit that achieved reduced distortion and improved stability. Power-supply design improvements followed later, including a separate high-voltage regulated power supply for each plate of each small-signal tube, and these were incorporated into a new board design. The end result was the Ultimate 70 amp-rebuild kit, which is said to be the “mother” of the Ultravalve amplifier.
In essence, the Ultravalve represents the distillation of over 30 years of design experience. It is intended as a thoroughly modern and rationally priced vacuum tube amplifier. A new polished-steel chassis is sourced from Dynakitparts, while the double-anodized, bead-blast-finished gold faceplate is sourced from a local vendor. The basic Dyna internal layout has been maintained, as it was felt that it works very well. However, all active electronics are located internally. Coupling and feedback circuitry use a new double-sided ground plane PC board. The power bandwidth is said to have been widened to -3dB at 50kHz and 5Hz while still maintaining the goal of no feedback-related overload under any condition of use. The basic signal path and tube choices remain unchanged from the original. A single 6GH8A pentode-triode tube is used per channel. It is similar in performance (but not as far as pinout) to the 7199 used by Dynaco prior to the ST-70 Series II. The switch was necessitated when the supply of 7199s dried up. The pentode section provides plenty of voltage gain while the triode is deployed as a cathodyne phase-inverter. The power supply is tube-rectified via a single 5AR4. The push-pull output stage uses a pair of 6CA7/EL34s in ultralinear connection. My sample was outfitted with Electro Harmonix 6CA7EH beam power tetrodes. Of course, EL34 power pentodes may be used as well. The whole thing, says Frank, except for some active and passive electronic parts, is made in the U.S.A.
Individual bias pots are provided for each channel to set the bias. You’ll need an inexpensive digital multimeter in order to measure and tweak the voltage to the specified 1.6VDC, which corresponds to a combined 100mA quiescent current flow for each pair of tubes. The amp is plug ’n’ play right out of the box; tubes are already installed and the bias is preset at the factory. The bias was right on after a few minutes of warmup. However, the bias does drift a bit after about 20 hours of break-in and should be rechecked at that time.
The SongTower is advertised as a mass-loaded quarter-wave transmission line. I will concede that the internal cabinet volume is stretched to form a tall column, but its length is not nearly sufficient to approach that required by a classic transmission line, possessing a lowest quarter-wave pipe-resonance of only 80Hz. Its bass performance appears to be equivalent to that of a conventional bass-reflex design with a nominal box-tuning frequency of about 37Hz. Current production uses a pair of SEAS ER-15RLY five-inch cone mid/woofers featuring edge-coated-reed/paper-pulp cones, a large magnet system, and a long copper-clad aluminum voice coil. These woofers recently replaced the CA-15RLY and are a bit more expensive, but are said to measure a tad better. The tweeter is the Danish Hiquphon OWII ¾" soft dome, which features multiple coatings, excellent frequency linearity, and exponential horn loading to improve phase response. By the way, the O and W in the tweeter model name are the initials of Hiquphon’s owner: Oskar Wroending who is personally responsible for all research and development.
The drivers are arranged in a D’Appolitto MTM configuration to improve vertical dispersion. Jim Salk points out that the woofer was specifically chosen for its extended response, which permits the implementation of fourth-order acoustic slopes at a crossover frequency of about 2.4kHz with a minimum of passive parts. The point being that the combination of steep acoustic slopes and a relatively low crossover frequency are desirable attributes in an MTM vertical array since they minimize off-axis interference effects between the woofers. The OWII tweeter is perfectly happy being crossed over at this frequency due to its well-damped low-frequency resonance. Plinths, spiked feet, and grilles are all included. However, it is highly recommended that the grilles be removed for critical listening.
The fit and finish are quite remarkable at this price point. I should add that the SongTower is not stocked; each order is finished to meet the customer’s preferences. Just as remarkable is the inclusion of frequency-response plots for both channels. Now, these speakers measure very well, and the factory plots closely matched my own in-room measurements, so there’s no reason to hide them. But how many speaker manufacturers take the time and energy to do this? This is your assurance that the speaker meets basic specifications when it goes in the box and will, in fact, sing as intended right out of the box.
On balance, I found the SongTower to be an inspired design in driver selection and integration. So many multiway designs appear to sound like an ill-fitting sonic jigsaw puzzle. By contrast, the SongTower sings with one voice, both on and off axis—almost as cohesively as a full-range driver. As a consequence, this speaker is capable of performing a convincing disappearing act. The resultant soundstage is exceptionally wide and stable when the speakers are toed-in so as to intersect the tweeter axes just in front of the listening seat. Bass response in my listening room was extended to below 40Hz, but don’t expect the punch of a 12-inch woofer from a pair of 5-inch woofers. The midbass was well delineated and adequately damped by the Ultravalve amplifier. I could have used a bit more upper bass, but otherwise tonal character was pretty neutral. Midrange textures were quite revealing of the associated power’s amp’s quality. I’m typically allergic to dome tweeters, but the upper mids and treble range were well behaved, which speaks highly of the OWII tweeter’s natural voicing. Consequently, fidelity of instrumental timbres was excellent, and in particular, female voice was fleshed out with believable harmonic colors.
The question I’m sure everyone is dying to ask about now is: Just how does the Ultravalve perform compared to the original ST-70? Well, for those of you clinging to your vintage gear, I have to say that it’s not even close. The Ultravalve’s perspective is not as romantic, but it is far better focused, clearly more dynamic, and in general higher resolution. The metaphor that comes to mind is a confrontation between Fuzzy Wuzzy Bear and a big bad tiger. Really, no contest.
With the stock output tube complement, midrange textures were not as smooth as those of the Audio Space 3.1 Reference (300B). But then it’s hard to match the civilized suave sound of a good 300B-based amp with either beam tetrode or pentode power tubes. However, I did try a set of Mullard reissue EL34s, purchased from the Tube Store, and manufactured at New Sensor’s Russian tube factory in Saratov. These good-looking tubes imbued the midrange with quite a bit more warmth, smoother textures, and further enhanced delineation of image outlines to the point that they appeared etched in space. On the flip side, there was a slight loss of immediacy. So it’s not entirely a clear call. In addition, the Electro Harmonix 6CA7 sounds more bluesy, and may be preferred for this reason as well.
The Ultravalve consistently sounded more powerful than its nominal 35Wpc. It handled bass lines with superb control and good impact. This was quite a surprise as I was fully prepared to have to render the obligatory faint praise of “pretty good for a tube amp.” Well, no wonder Frank named this guy Ultravalve—it is ultra-special in the bass. But be sure to respect its need for a speaker with a sensitivity of at least 88dB, and please don’t venture below a 4-ohm impedance. Within these constraints, which are of course met by the SongTower, I can safely state that the Ultravalve is capable of dishing out plenty of boogie factor. Its ability to retrieve microdynamic nuances allowed the full scope of the music’s dynamic intensity and of the interaction between musicians to shine through. And it didn’t shy away from driving the music from soft to loud with conviction, being far more assured macrodynamically than the vintage ST-70 ever was.
Music lovers rejoice! In my estimation, the Salk Sound SongTower and Ultravalve combo represent the most musical audio dollars you’re ever likely to spend during a lifetime of consumption. Pricewise, at under $2k each, this coupling represents but a fraction of some of the amps and speakers that pass through my listening room. Yet, it proved to be one of the most enjoyable in some 30 years of audio reviewing, and enjoying the music is what this passion of ours should be all about. A four-star recommendation!
SPECS & PRICING
Power output: 35Wpc into 8 ohm at less than 1% THD, 20Hz–20kHz
Input impedance: 470k Ohm
Dimensions: 13.125" x 5.75" x 10.75"
Weight: 26 lbs.
Price: $1699 (plus $40 shipping in US)
Salk Sound SongTower QWT Loudspeaker
Frequency response: 42Hz–20kHz (+/- 3dB)
Sensitivity: 88dB (2.83 V/1 meter)
Nominal Impedance: 4 ohm
Recommended Amplification: 30–150Wpc, tube; 80–250Wpc, solid-state
Weight: 49 lbs. each (not including plinths and spikes)
Dimensions: 8" x 44.5" x 12" (not including plinths and spikes)
Price: $1795/pr. in black satin finish; $1895/pr. in standard veneer finish
AUDIO BY VAN ALSTINE, INC.
2665 Brittany Lane
Woodbury, MN 55125
2700 Long Winter Lane
Oakland, MI 48363
Kuzma Reference turntable; Kuzma Stogi Reference 313 VTA tonearm; Symphonic Line RG-8 Gold MC phono cartridge; Air Tight ATE-2 phonostage; Weiss Engineering Jason transport and Medea DAC, Sony XA5400 SACD player; Concert Fidelity DAC-040 DAC, PrimaLuna ProLogue Eight CD player; Concert Fidelity CF-080 and Mystère CA21 line preamps; Bybee Speaker Bullets; FMS, Acrotec 6N and 8N copper, Kimber Select KS-1030, Kimber KCAG interconnects; FMS Nexus-2, Acrotec 6N and 8N copper, Kimber Select KS-1030, Kimber KCAG interconnects; FMS Nexus speaker cable