Z-Infinity Audio Z120F Tube Monoblock Power Amplifier


Equipment report
Tubed power amplifiers
Z-Infinity Audio Z120F
Z-Infinity Audio Z120F Tube Monoblock Power Amplifier

Customers must specify either 4- or 8-ohm impedance taps. A few tube amplifier manufacturers have opted to optimize the output stage for a single nominal load impedance, sometimes 6 ohms, which splits the difference between 4 and 8 ohms. In reality, speaker impedance often varies by over an order of magnitude between its minimum and maximum values. The applicable international standard for specifying nominal impedance (IEC 268-5) states that the nominal impedance shall not exceed the minimum value by more than 25%. According to this standard, a speaker with a 4-ohm minimum should be rated no higher than a 5-ohm nominal load. There are a ton of 8-ohm-rated speakers out there with an impedance minimum of 4 ohms and lower, meaning that very few manufacturers abide by this standard. From a user perspective, it is always advantageous to have access to multiple impedance taps. That gives the opportunity to experiment with a specific load and a better chance of optimizing the amp/speaker interface.

The Z120 made an excellent impression right out of the box, driving the Basszilla Platinum Edition DIY speakers. Midrange textures were pure and sweet sounding. The overall tonal presentation was suave and refined. It became crystal clear that this Class AB amplifier was being biased heavily into Class A, which was responsible for a benign distortion spectrum—even at moderate volume levels. For the first time in ages I wasn’t tempted to roll-in tube substitutes and was happy to let the stock Russian Tung-Sol reissue preamp tubes simply do their thing. I’ve come to like and respect these tubes for their smooth textures and full-bodied tone. Ditto for the JJ Electronic KT88, which reinforces the virtues of the Tung-Sol preamp tubes. Resolution of complex orchestral passages was nothing short of sensational, and there was plenty of low-level detail. Note that detail flowed naturally from the fabric of the music without giving the impression of being in my face.

There was no tube glare or brightness, which aided the reproduction of hot recordings. In my book, bright-sounding amps are a major annoyance. They may sound exciting in the short term, but a persistent presence region emphasis invariably leads to sensory overload. In fact, the Z120 was found to err in the opposite direction yielding a slightly laid-back presence region. As a consequence, the tonal balance shifted to the core of the midrange, reinforcing the sensation of a smooth and suave midband. Since I happened to have the Bob Carver Cherry 180 amplifier in the house, it gave me the opportunity to let these amps duel it out on three speaker loads; fair competition as both amps are similarly priced. On the Basszilla, the Carver came across as livelier sounding with better boogie factor and depth perspective. But the Z120 was cleaner, evincing a purer musical tapestry from top to bottom. And being a bit mellower, it shifted the listening perspective toward the rear of the hall. The Carver had a slight edge in dynamics from soft to loud, though both amps fell short in terms of microdynamic conviction relative to a good SET amplifier, at least in the context of a high-sensitivity loudspeaker.

The Z120 didn’t much care for the MartinLogan Summit X ESL. This combo sounded far too bright and dynamically compressed. However, the Z120 fared much better partnering the Analysis Audio Omega planar speaker—a true 4-ohm load— and the load I had I mind for the Z120 all along. Here it left no doubt about transient clarity, textural purity, and dynamic prowess. Bass lines were amazingly solid, which implied a high damping factor. Bass drum was reproduced with stupendous punch, and in general, power reserve did not appear to be an issue. Transparency was another highlight. The soundstage was brightly lit making it easy to visualize its inner recesses, and image outlines were palpably localized within a convincing spatial expanse. However, the Carver Cherry 180 provided the more spatially immersive experience, a you-are-there sensation that surpassed that generated by all other amps I’ve auditioned to date with the Omega. Here too I wasn’t entirely satisfied with the Z120’s reproduction of the presence region. It came across as tonally darker than the real thing, reducing the sheen of massed strings, and slightly hardening piano tone. And finally, in head-to-head competition with the far more expensive Lamm Audio M1.2 Reference monoblocks, which feature a solid-state output stage, the Z120 was found to lack the M1.2’s bass precision and punch. But it answered back with tube virtues such as enhanced tonal color saturation, and superior depth perspective and image palpability.

The Z120 is a superb tube amplifier that is sonically competitive with any tube amp I’ve auditioned in the sub-$10k price range. It is eminently listenable and brings plenty of tube charm to bear on conventional speaker loads. I’ve enjoyed my time with it and shall miss it. It is certainly deserving of a serious audition and should work wonders for a brightly voiced box speaker.


Power output: 120W RMS mono
THD: 0.01% at 1KHz, 1W and 0.3% at 60W
Input sensitivity: 0.7V RMS
Frequency response: 3Hz to 50kHz (-1dB)
Output impedance taps: 4 or 8 ohm
Supply voltage: 120V AC
Power consumption: 250VA maximum
Weight: 37 lbs.
Dimensions: 16" x 7" x 10"
Price: $3299 ea.

P.O. Box 2547
Redmond, WA 98073

Associated Equipment
MartinLogan Summit X, Analysis Audio Omega, and BassZilla Platinum Edition mk2 loudspeakers; Pass Labs XP 30 preamplifier, Experience Music Passive Aggressive autoformer volume control ; Sony XA5400 SACD player with ModWright Truth modification: Kuzma Reference turntable; Kuzma Stogi Reference 313 VTA tonearm; Symphonic Line RG -8 Gold MC phono cartridge; SoundTradition Live! MC-10 step-up; FMS Nexus-2, Wire World, and Kimber KCAG interconnects; Kimber KCAG speaker cable; Bybee Speaker Bullets; Sound Application power line conditioners