Linear Tube Audio ZOTL40 Reference+ Power Amplifier Review

I have had the pleasure of reviewing every amp that Linear Tube Audio (LTA) has produced except for the ZOTL40, the ZOTL40 Reference+ Power Amplifier, and the Z40+ Integrated. When I talked to Nicholas at LTA about replacing my Butler Audio MONAD 100-watt monoblocks in my retirement system, he suggested that I give the 40+ power amps a listen. 

The 40+ power amps are switchable for mono or stereo, so my initial thought was that I would use them as monoblocks with my DeVore gibbon Super Nines (reviewed here). LTA had such a demand for these amps, however, that they could only send me one to try out. I told Nicholas that this was fine with me and would give me a chance to be sure if these would be the right amps for my system.

As it turned out, one stereo 40+ power amp was more than enough for my Super Nine Speakers. So, I purchased the 40+ power amplifier. Now, I want to share with you my thoughts on the sound of this amplifier.

Description

The LTA Z40+, like all of the LTA amps, is designed by David Berning and incorporates his patented ZOTL amplification.  You can read all about ZOTL technology here on the LTA website, including the original patent from 1997. The amp produces 50 Watts of transformer-less of output power despite being named the 40+. The power is generated by four NOS EL34 tubes that peek out from the unit’s top plate. The Z40+ has a full tube complement that consists of a pair of matched 12AX7s, a pair of matched 12AU7s, and a matched quad of NOS EL34s.

Here’s what you will find on the LTA website describing the improvements in the 40+ compared to the previous model: 

The 40+ is the next generation, and first-ever upgrade, of the Ultralinear flagship amp. After trying over two dozen component combinations, and countless hours of listening tests and comparisons, the new ZOTL Ultralinear+ power amp improves the tone and texture across all frequencies, and there is more detail and clarity around the performers. 

These sonic upgrades are achieved through adding a massive 100,000µF of additional capacitor storage and changing the resistors in the audio path to non-magnetic Audio Note Tantalum and Holco Metal Film resistors, each type and value specifically chosen for each location.

lineartubeaudio.com

Review System

I used this amp with two speakers. I started with the DeVore Fidelity O/Baby speakers that had in for a review that will come out soon. I also used my DeVore Gibbon Super Nines 9 (reviewed here). The rest of my system consisted of the Innuos Statement Music Server (reviewed here), the PS Audio DirectStream DAC (reviewed here), and LTA Reference Preamp Level 2 (reviewed here). All of the cables were Audience FrontRow (reviewed here), and I plugged everything into my HB Cables Marble Power Slave.

Listening With the O/Baby Speakers

Wow, what a fantastically fun combination! If you value pace, rhythm, and timing, it will be well worth your time to hear the O/Baby speakers with the 40+ amp. I have always highly valued PRAT in any system I owned, and I never expected to hear the Teresonic Ingenium/WAVAC EC300B bettered, but the little O/Baby speakers and the 40+ amp are even better. The combination has such dynamics that you can’t imagine how much fun they are to listen to.

The midrange was very transparent, and the top end was beautifully extended. The bass was dynamic and full of rich tonal colors without being overly warm, and the soundstage was huge. In a word, the Z40+ and O/Baby speakers made music sound very alive and just plain fun!

Listening with the DeVore Super Nine Speakers

With the Super Nines and the LTA 40+ in the system, I could hear how refined the amp was capable of sounding. The 40+ was capable of allowing me to hear many layers of the music, which drew me emotionally into the music.

The Super Nines go deeper than the O/Baby speakers. The 40+ played very deep and provided very satisfying deep bass. The timbre of the drums and the tones of the bass and cellos were beautifully rendered by the 40+ with the Super Nines. The dynamics of the deep bass all the way through the lower midrange were quick and controlled, but they were also well fleshed out.

I positioned the Super Nines nearly 18 inches further out into the room than the O/Baby speakers. This enabled me to hear the incredibly huge and coherent soundstage the 40+ is capable of producing. The soundstage was very wide and deep with good vertical height. It was also beautifully layered, and I could hear the individual vocals and instruments within the context of the whole stage.

Conclusion

The Z40+ is capable of revealing detail, delicacy, and nuance. Few amps can combine this with a rich and full sound. I hope I have been able to convey what an exceptional amplifier this is. You should take note that I had been listening to a $20,000 pair of monoblocks driving the Super Nines.

To drive the point home, you should know that I have chosen a single LTA 40+ to drive the Super Nines and the LTA 40+ in my retirement system. The idea of a retirement system versus a reference system will be covered in a “Boppin’ With the Beatnik” column before the end of the year.

Price – $6,800 USD
www.lineartubeaudio.com

ZOTL40 Reference+ Power Amplifier Specifications:

• Sensitivity: 1.2V provides full output
• Output impedance: 1.6 ohms
• Input impedance: 50k
• 100V / 120V / 240V operation: Auto-switching
• Hum and noise: 94dB below full output (measured between 8Hz-60kHz +0/-0.5dB)
• Gain: 23db
• Power output with 4-ohm load: up to 51W, 0.5% THD
• Power output with 8-ohm load: up to 46W, 0.5% THD
• Frequency response (8-ohm load): 8Hz to 50kHz, +0, -.5dB
• Amplifier class: Push-pull Class AB
• Net weight: 17 lbs
• Dimensions: 17 inches (43 cm) wide, 5 inches (12.7 cm) tall, 13.875 inches (35.2 cm) deep
• Finish: Aluminum case
• Tube complement: two 12AX7s, two 12AU7s, & four NOS EL-34s – No adjustments – tubes are auto-biased