Barista Posted May 13, 2002 Share Posted May 13, 2002 Equipment: Sony 5 Disc Changer Sony Vintage ('77) PS-T3 Turntable with Shure V15VxMR Cartridge Sony 333ES (as Preamp and for Solid State Comparisons) Sound Valves VTA-70i Tube Amplifier Klipsch RF-5 Mains VTA-70i Specifications: Price: $899 Kit 35W RMS Class AB 15W RMS Class A Frequency Response: 10-50,000Hz THD: <.25% @ 1000Hz, <.7% 20-20,000Hz Hum & Noise: Inaudible, less than -85db below rated power unweighted. Sensitivity: 1.3V RMS for maximum output power Power Consumption: 190 watts, 120 Volts, 50/60Hz (Capable of 220V) Tubes: (2) 6GH8A Gain Stage, (4) EL34 Electro-Harmonix Output (All Tubes Matched and Included in Kit) Size: 13W x 10.5D x 7H Weight: 32Lbs About the VTA-70i: After much debate I picked up a Sound Valves VTA-70i tube amplifier. The VTA-70i is essentially the modernized version of the old Dynaco ST-70 that was so popular and respected in the 60s and even today. Its a push-pull design embracing the same low open-loop gain philosophy from the original famous for its exceptionally low Transient Intermodulation Distortion. The VTA-70i is very similar to its original predecessor, though much of the original troublesome point-to-point wiring, and rectifier circuit has been modernized or all but eliminated by a double sided Epoxy fiberglass PCB board. Assembly: Great instructions, with a nice bit of background on tube amps, the original Dynaco ST-70 design philosophy, as well as what has been changed, and why. Sound Valves states a 5 hour construction time, though I was able to do so under 2.5 hours (Taking time to verify all actions thoroughly after assembly). The kit consists of 26 basic steps including mechanical and soldering, along with a nice checklist to cover before initial fire up. The amp is also capable of being wired for 220V, if you choose, and a 15Amp minimum circuit is required for 120V operation. The actual assembly did miss the first step of wiring up the hot lead from the power cord, but the first diagram made it obvious (as does basic understanding of Ok, this wont work without a hot lead!). Once completed, the tubes were installed and the kit was turned on and the low bias LED came to life. After about 2 minutes the Hi bias LED slowly faded into existence. Tube biasing is done though a little pot in between two blue LEDs with the supplied diddle stick. Two LEDs per channel (Low & Hi) on the amp face help determine proper biasing. To bias, simply wait for the tubes to warm (15 Minutes or so) and turn the pot so that each LED is lit equally. Easy? You bet! Aesthetics: The VTA-70i remains loyal to the original layout of the ST-70, though the chromed chassis has been replaced with a flat black finish, matching more so with modern components. The front is a ¼ thick piece of black anodized aluminum, with 4 blue LEDS for Hi and Low biasing of each channel, as well as the general silk screen labeling. Tube biasing is a synch, and can easily be checked at a distance by simply matching LED intensity for each channel. A neat little side note, when the amp is playing the LEDS will flicker as the draw of current intensifies on the tubes. It adds a nice touch, and a little eye candy to the already nice red/orange glow of the six tubes. All components are of respectable quality and finish staying loyal to the 1% tolerances we all are familiar with. However, one of the output transformers was dented, I assume through shipping. After removing the transformer plate and hammering out the dent it is hardly noticeable by anyone other than myself. The VTA-70i has a very modern yet retro look, maintaining a no frills, all business demeanor. It matches well with current equipment, and gives the whole system a very seriously technical look. Sound: Though the tubes should still need time to burn in, the initial sound is still worthy of evaluation. First off, the amp is absolutely silent. There is no perceivable hum or noise, just dead silence. This pleasantly surprised me, as I expected more noise and analog hisss from a tube amp. I did some basic A/B compassions using various source materials I am familiar with. Each passage would be played taking effort to maintain an adequate 90db SPL between the Sony SS and VTA-70i so that each comparison would not be biased by the volume. After playing a few passages once on the tube, and next on the SS my initial impression was how much fuller the tubes sounded. There seemed to be more depth in the sound field where instruments tended to pop out more at you. There were more mid-bass frequencies, which could explain the presence of fullness. Even though the SPL remained essentially the same, the tubes seemed to generate more umph as I could feel more of the sound in my legs, chest, and though vibrating objects around me. Bass response is more than adequate, and very punchy. Bass drums had a clean pop to them, and snares were equally as snappy. The amp still retained very high-frequency response, and didnt roll off high transients as much as I thought it would. In fact, I had to bump the treble back -1 db from the SS comparisons. Everything was there, and in adequate quantities. Which is good, as its better to have too much, than not enough. Going back to the Sony SS left one feeling a bit empty. The music seemed to take a step back, and produced a dry, limp sound. Though the resolution and clarity did remain, the overall sound seemed more produced, and less live, especially with some Creedence Vinyl, or other vintage recordings. Vinyl Sources, such as CCR, Jimi, Ella, seemed to really shine. The guitar and bass had the same kind of presence I experience with seeing live performances where tube amplification had been employed. Bass was very reminiscent of the old Ampeg tube bass cabinet I used to play personally, and had a real personality to it. Very sweet sound that was easy on the ears, even at high levels. Even with high transient peaks around 100db, I was unable to detect any clipping, each performance was reproduced with the accuracy and clarity I would expect from a amp of this level. Volume was no problem, as I was able to attain more than adequate high SPL levels with ease, so the power is there, and in abundance. Final thoughts: Very pleasing in about all respects, I am highly satisfied. I highly recommend this amp to anyone seeking a minimalist, tube amplifier with adequate power. Throw in a pre-amp of your liking and you have a system capable of blowing your hair back with ease, and sending you into a tube audio nirvana. Personally, I need to find something other than the Sony ES Pre, but its all I have right now. Even though, the quality is very impressive, and surpassed the quality of internal amplifier of the Solid State Sony ES. Care should be taken though, as the intensity was vas very subtle, and left my ears ringing before I had realized things were getting a little loud. Even at high levels, there was little fatigue that is sometimes associated with horns. All things considered its an excellent tube amp following the well established philosophies of its predecessor. The Dynaco ST-70 was a quality kit respected even to this day, and the VTA-70i is the modern day equivalent taking no loss from the original conception. ------------------ Barista T. Bill This message has been edited by Barista on 05-13-2002 at 02:15 PM Quote Link to comment Share on other sites More sharing options...
Mallette Posted May 13, 2002 Share Posted May 13, 2002 Excellent review. I've a Dyna ST-70 paired with Khorns. More power than I could ever use. I suggest you consider the Supre PAS 4i or other Dyna-based preamp from Frank Van Alstine. I've the 4i and am totally happy with it. Price is a bit over 800.00 wired, and about 650.00 for the kit. See http://www.avahifi.com/price.htm if you are interested. Best regards, Dave ------------------ David A. Mallett Average system component age: 30 years. Performance: 21rst Century Quote Link to comment Share on other sites More sharing options...
Colin Posted May 13, 2002 Share Posted May 13, 2002 good job, thanks for posting, lets us know what you do for the pre-amp, have you looked at Bottlehead's Foreplay? ------------------ Colin's Music System Cornwall 1s & Klipsch subs; lights out & tubes glowing! Quote Link to comment Share on other sites More sharing options...
Barista Posted May 13, 2002 Author Share Posted May 13, 2002 Colin, I didn't even think about the forplay, though I've read many good things about it. That is definitely an optin worthy of consideration. The price is definataly right. ------------------ Barista T. Bill Quote Link to comment Share on other sites More sharing options...
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