Linear Tube Audio ZOTL Ultralinear Power Amplifier

Twenty Watts Of Joy

Equipment report
Categories:
Solid-state power amplifiers
Linear Tube Audio ZOTL Ultralinear Power Amplifier

It’s important to note that up to this time in the review process I had been using the LTA microZOTL reference preamplifier. While objectively a great-sounding preamp, it lacked the textural richness to fully flesh out the UL amp’s tonal colors. It was a great choice for the ZOTL 40 but in the context of the UL it failed to provide the fat richness of tone, if you will, to satisfy my tube-sound sensibility. You may, of course, feel differently, but it’s something I happen to crave. This is a clean and tonally neutral sounding amp, which is quite revealing of changes in front end components. It therefore made a lot of sense to experiment with matching preamps with the idea of nudging the UL toward textural lushness. 

Enter the PrimaLuna Evo 400. It uses a pair of 5AR4 tube rectifiers, which give it a more classical tube sound. Pairing the UL with a texturally rich and slightly fat preamp turned out to be a transformative experience—a synergy that once heard was impossible to forget. I’m being careful to describe the exact system context in which the UL amp thrived because simply dropping an amp into an existing system is too random a process. Ultimately, it requires some experimentation as well as careful system matching to determine an amplifier’s full sonic potential.

Dialed in just so, I could now have my cake and eat it too: sound with a touch of harmonic lushness but without loss of clarity. The presentation was still a good distance away from being overtly euphonic. And in contrast with vintage tube amps, and I’m thinking here specifically of the Dynaco ST-70, the UL amp did not sound overly liquid or homogenize image outlines. Soundstage transparency was commendable as was layering of the depth perspective. Without even a hint of veiling, it was possible to readily localize individual image outlines within the confines of the soundstage. And despite its lower power output, the UL sounded every bit as dynamic as the ZOTL 40. It had no difficulty shifting through all the gears, revving up from soft to loud without a hint of compression. Female voice was treated with tender loving care, bringing to life plenty of microdynamic nuances. Upper registers were smooth and grain-free, presenting no impediment to long-term listening enjoyment. 

Berning’s ZH270 amplifier was probably his most popular, having stayed in production for 12 years, and according to David it was also his favorite amp, not necessarily because it was the best sounding, but because of its size, reliability, and flexibility. It’s been many many years since I’ve auditioned the ZH270, but if I can still trust my sonic memory banks, I am surprised at how much the UL and ZH270 have in common. Both share transient speed and control beyond the capabilities of ordinary tube amps. Other common denominators are electrostatic-like midrange clarity which allows for resolution of densely layered orchestration and plenty of low-level detail. 

It’s fair to say that the ZOTL Ultralinear amplifier is a smashing sonic success. It isn’t the most powerful, but in sheer sound quality it is in my estimation the best low-power, push-pull ZOTL power amp Berning has designed to date. And as long as you understand the major caveat about matching it to a compatible preamp, it will more than satisfy even the most demanding of audiophiles.

Specs & Pricing

Type: Push-pull Class AB
Tube complement: Two 12AU7, two 12AX7, four 17JN6 power tubes, all NOS (all tubes are auto biased)
Power output: 20Wpc into 8 ohms
Sensitivity: 1.2V RMS
Frequency response: 8Hz to 60kHz , +0, -0.5dB
Output impedance: 1.6 ohms
Input impedance: 50k ohms
Hum and noise: 94dB below full output (measured between 20Hz–20kHz)
Gain: 21dB
Stereo/mono: Switchable 
Dimensions: 17" x 5" x 13.875" 
Weight: 17.5 lbs.
Price: $6800

LINEAR TUBE AUDIO
lineartubeaudio.com
hifi@lineartubeaudio.com

Associated Equipment
Speakers: Basszilla Platinum Edition Mk2 (DIY), QUAD ESL 57
Preamps: Lamm Audio L2.1 Reference, Supratek Chardonnay 2003, PrimaLuna Evo 400
Digital front end: Apple Mac BookPro running Audirvana 3.5 software, Schiit Audio Yggdrasil DAC
Analog front end: Kuzma Reference turntable; Kuzma Stogi Reference 313 VTA tonearm; Koetsu Rosewood Signature phono cartridge; Jeff Rowland Design Group Coherence phono stage
Cable: Acrotec 6N, Kimber KCAG Select interconnects; Acoustic Zen Hologram II & Museatex Crypton speaker cable
Accessories: Sound Application power line conditioners