Sibling rivalry. Sharing the same feature set of capacitive brass buttons, optional phono, standard headfi, Apple remote, microprocessor-controlled precision volume etc., what distinguishes the three LTA integrateds other than power and price? According to the published specs,
• the 10-watt unit has an input impedance of 47kΩ, output impedance of 1.2Ω, sub -94dB hum/noise and runs 4 x EL84 in class AB push/pull triode.
• the 20-watt unit has an input impedance of 47kΩ, output impedance of 1.2Ω, sub -94dB hum/noise and runs 4 x 17JN6 in class AB push/pull ultralinear.
• the 40-watt unit has an input impedance of 47kΩ, output impedance of 1.2Ω, sub -94dB hum/noise and runs 4 x KT77 in class AB push/pull triode.
Price without phono option scales from $4'900 to $7'650. Yes, that's identical coin for the two more powerful ones. Even the remainder of the differences are paper thin. Other than power which works as a log function to deceive, thinking readers must assume that the key differences are sonics baked in by tube choice and hookup mode. Here it's counter-intuitive to read about today's model that "listeners enjoy the less forward distortion-free presentation that's more pleasing to listen to… and "the Zotl Ultralinear was specifically designed with high-efficiency speakers in mind."
That speaker breed starts at ~94dB. Horns easily eclipse 100dB. Here already the Z10 is a nuclear option. With UL being specifically designed for that type speaker clearly wasn't about more power but less noise. Such speakers are ferocious noise sniffers. Like blood-tracking pit bulls, they lock down on power-supply hum which 84-88dB types can't hear. UL would have to be as quiet as a church mouse during silent prayer. That would also benefit higher-efficiency headphones.
Then we remember. Many hi-efficiency speakers run widebanders like the big one at left or the small one above. Most of these, to varying degrees, exhibit a rising response between 2-6kHz which even tamed can lead to some forwardness or a perception of speed over body.
Conventional wisdom—which in this instance must be more common than wise—predicts that pure triodes or triode-strapped tetrodes and pentodes sound mellower than ultralinear tetrodes. It's why SET are so popular in these applications.
The same wisdom would predict that "most detailed" and "more pleasing to listen to" couldn't coexist but will always be at logger heads. Which isn't promising when, clunk, we deal with glass bottles. Cheers. What if this wasn't so for a change?
It'd make the Ultralinear integrated very interesting: the most detailed and simultaneously most refined and pleasing true valve deck for super-lucid fast speakers which dip into the fresh and crystalline side of the gene pool.
Go ahead, apply 20/20. Now you really know why I changed my mind and picked this model. If I had far too ordinary wisdom clog my little grey cells, this would flush it out and give me a more well-rounded view on the subject.
High-efficiency speakers + tetrodes in ultralinear = ?
And just what the hey was a 17JN6, pray tell? Ol' Valve Museum to the rescue. Elsewhere we read that "the General Electric 17JN6 is a duodecar type compactron used as horizontal-deflection amplifier in color and black & white television receivers." Huh?
So what then is a compactron? From Wikipedia, it was a trade name "applied to multi-electrode structure tubes constructed on a 12-pin base. In 1961 General Electric introduced this tube in Owensboro, Kentucky. Television sets were a primary application. The idea of multi-electrode tubes itself was far from new and indeed the Loewe company of Germany was producing multi-electrode tubes as far back as 1926 which even included all of the required passive components. Use was prevalent in televisions because transistors were slow to achieve the high power and frequency capabilities needed particularly in color television sets. The first portable color television, the General Electric Porta-Color, was designed using 13 tubes, 10 of them compactrons. They were also used in a few high-end stereos and by the Ampeg guitar amplifier company in some of their guitar amps. No modern tube-based hifis are known to use this tube type as simpler and more readily available tubes have again filled this niche. The 7868 is used in some hifi systems made today and has the same physical dimensions as the compactron but a 9-pin base. It is currently in production by Electro-Harmonix."
From this we deduce that compactrons like the 17JN6 introduced in 1964 were once very common—consider global TV sales—then lost their place when early televisions embraced transistors. Unlike high-demand boutique triodes, UL output replacements should be very affordable and plentiful. Today they would seem to have no other use than in this one lone amplifier.
With LTA running their tubes at 1/3rd current by superimposing the signal on an HF carrier wave, they make far less heat to promise 10'000 – 20'000 hours of use. With a switching power supply and puny RF transformers, the whole thing weighs just 8.2kg. Its tiny impedance converters afford turns ratios above 300:1. Standard tube output transformers max out at 25:1 "due to saturation and hysteresis". Standard output transformers must deal with a full-bandwidth audio signal. Berning's air-core emulators only work at one fixed frequency of ~460kHz. That avoids common nonlinear and parasitic issues. Berning amps even remain safe to receive signal without an attached load. As LTA put it about the power-amp versions of UL and Zotl 40, "both are fast, fluid and do an excellent job of reproducing the pace and punch of the music. Likewise, both have the black background, high clarity, accuracy, realism and dynamics which fool your brain into thinking the performers are in the room. The Ultralinear is a little more relaxed, refined and a little less forward which is more noticeable with higher-efficiency speakers. Despite 'only' 20wpc, it has very strong bass. The Ultralinear has a little more detail than the 40 and can rival any solid-state amp as far as detail goes."
The spec upshot is 8Hz – 60kHz bandwidth, 1.2Ω output impedance and hum/noise a solid 94dB below full 20Hz-20kHz output. Happy days for a pure 21st-century tube machine that does speakers and headphones.