Unison Research Unico DM V2 and Pre V2: Italian Hybrid Amps That Eliminate Crossover Distortion

Class AB amplification powers nearly everything we sell, from integrated amps under $2,000 to reference separates north of $20,000. There's a reason for that: it sounds great, runs efficiently, and scales well across price points. The topology has been the backbone of high-fidelity audio for decades.

Unison Research knows this as well as anyone. They've been building hybrid amplifiers in Italy since the late 1980s. But their engineering team has also spent 27 years asking a specific question: what if you could keep everything that makes Class AB practical while eliminating its one theoretical weakness? Their answer is called A.S.H.A. (Analog Synchronized Hybrid Amplification), and it debuts in the Unico DM V2 power amplifier and Unico Pre V2 preamplifier.

What's Wrong with Class AB?

If you've read specs on amplifiers, you've seen the alphabet soup: Class A, Class AB, Class D. Each one describes how the amplifier's output transistors handle the audio signal.

Class A is the gold standard for sound quality. Both output transistors stay on all the time, working together to control the signal. No switching, no handoff, no artifacts. The problem is heat: a Class A amplifier wastes enormous amounts of power as thermal energy. It gets hot, it needs massive heatsinks, and it's expensive to build. You also can't get huge wattage numbers out of it without the chassis turning into a space heater.

Class AB is the industry's compromise. For small signals, both transistors conduct (like Class A). For larger signals, the transistors take turns: one handles the positive half of the waveform, the other handles the negative half. This is far more efficient. Less heat, more power, lower cost. Nearly every amplifier on the market uses some version of this topology.

The tradeoff is crossover distortion. When the signal passes through zero and control transfers from one transistor to the other, there's a brief moment where neither device is fully in charge. That handoff introduces a small but measurable distortion into the signal. At low listening volumes, where the signal spends most of its time near that zero crossing, the distortion is proportionally worse. It can smear detail, thin out bass response, and add a subtle hardness that you might not consciously notice but your brain registers as fatigue over long listening sessions.

Good Class AB designs minimize this to the point where most listeners never notice. But Unison Research wanted to go further.

From Dynamic Class A to A.S.H.A.

Unison Research has been working on this problem since 1999, when they introduced a circuit they called Dynamic Class A. The idea was straightforward: instead of letting the output transistors turn off completely during their "off" half-cycle (which is what creates the hard transition in standard Class AB), keep them slightly conducting at all times. This softened the handoff and reduced crossover distortion, though it didn't remove it entirely.

That circuit ran across the Unico line for more than two decades. It was genuinely better than conventional Class AB, and it helped build the Unico line's reputation for musicality at real-world price points.

But the engineering team kept pushing. That's the thread that runs through this company. Unison Research was founded in 1987 by Giovanni Maria Sacchetti, an electronics engineer who spent 25 years teaching and designing amplifiers in parallel. His father was an accomplished pianist, and that musical foundation shaped how Sacchetti approached circuit design: the ear mattered as much as the measurements. The company is now led by the Nasta family, who also oversee sister company Opera Loudspeakers, and everything is still designed, engineered, and assembled in Treviso, Italy.

Agostino Zamai, Unison Research's Project Manager, put it simply: "Amplification. That's the simplest act, but the one that's most important in the listening experience. Because if you don't have a good amplifier, we cannot listen to the music." That's the conviction that drove 27 years of refinement from Dynamic Class A to A.S.H.A. They don't release a new topology every year. They refine one until it's ready.

How A.S.H.A. Eliminates Crossover Distortion

A.S.H.A. stands for Analog Synchronized Hybrid Amplification. Each word carries weight.

Analog because the entire circuit is analog. No digital correction, no DSP tricks, no error-canceling feedback loops. As Agostino put it: "We believe that analog amplification is the best way to amplify music and to reproduce music." The signal path is purely analog from input to output.

Synchronized because the output stage depends on precise coordination between two power MOSFETs. This is the core of the idea.

In a standard Class AB amplifier, the two output transistors trade off: one drives the positive half of the waveform, the other drives the negative half. A.S.H.A. changes the relationship entirely. One transistor, which Agostino Zamai calls the "leader MOSFET," runs in pure Class A and controls the voltage (the shape of the signal) for the entire waveform, positive and negative. The second transistor, the "follower MOSFET," operates in Class AB and handles current delivery during the negative half-cycle.

As Agostino explained: "We have that the leader MOSFET is controlling the signal for all the period of the signal. While the current, the power delivered to the load, is split between the two transistors."

The critical difference: the leader never hands off control. There's no moment where one transistor stops driving and the other takes over. The leader MOSFET shapes the signal continuously, so there's no zero-crossing transition and no crossover distortion. The follower MOSFET only assists with current delivery when needed, and because it's not responsible for signal control, its Class AB switching doesn't introduce artifacts into the output.

Hybrid for two reasons. First, every Unico amplifier pairs a tube input stage with solid-state output devices. Gold Lion tubes handle the voltage gain (they're good at this; tubes are inherently linear), and the MOSFET output stage delivers the current and power. Second, the A.S.H.A. circuit itself is a hybrid of Class A and Class AB operating principles. You get Class A purity of signal with Class AB thermal efficiency.

Amplification because, at the end of the day, that's the job. And A.S.H.A. does it with distortion levels that approach pure Class A while running cool enough to sit on a standard rack without dedicated ventilation.

What Does It Sound Like in a Room?

Bartolomeo Nasta recently demoed the DM V2 in Rome driving a pair of KEF Blade 2 speakers: "I'm not telling you that just because we design product. But it's really true. The feeling that you have is that you never want to stop to turn up the volume because there is no audible distortion in this product."

Then he said something that surprised us: "The quality of the sound is amazing. And we are talking about an amplifier that, of course, is not cheap, but it's not dramatically expensive." Coming from someone whose company also makes reference monoblocks north of $25,000 each, that was telling.

Agostino got more specific about what you hear. On bass: "The bass is full and present even at low volume. This is due to the high current delivery that this technology has." On imaging: "The soundstage is very stable and well focused because the circuit relies on a perfect synchronization between the different parts of the circuitry." And on detail at volume: "We can still hear the detail and the detail stays vivid because there is no crossover distortion that goes to introduce some noise that can hide the details that are still present in the music."

That last point is worth sitting with. In a conventional Class AB amplifier, as the volume goes up, crossover distortion increases and starts to mask fine detail. Your brain registers this as fatigue, a subtle hardness that eventually tells you to turn it down. With A.S.H.A., that masking isn't there. Agostino described the experience in the lab: "We found that we are always going to increase the volume and increase and increase because there is no hearable distortion." The music doesn't change character as it gets louder. It just gets bigger.

The flip side matters just as much. At low volumes, late at night, the signal spends most of its time near the zero crossing where Class AB crossover artifacts are worst. That's where bass thins out and soundstages collapse in lesser amplifiers. With the leader MOSFET maintaining continuous signal control, quiet listening keeps its weight and dimension. For anyone who doesn't always listen at reference levels, that may be the most meaningful difference A.S.H.A. makes.

The Unico DM V2 Power Amplifier

Speaking of protection: the DM V2 uses a microprocessor-monitored system that measures instantaneous power delivery to the speakers. As Agostino explained: "Protections are not going to change the sound, so they are not going to affect the sound quality." When the amplifier approaches high power levels, the front panel LEDs begin to blink. It's not the amp struggling. It's the amp telling you that your speakers might be approaching their limits. "The amplifier is not suffering," Bartolomeo added. "It's just telling you that the current is high. So pay attention to your drivers."

Around back, the DM V2 accepts both RCA and XLR inputs, has speaker binding posts capable of bi-wiring, and includes 12V trigger connections. A rear toggle switches between stereo and mono operation. It weighs 33 kg (about 73 pounds) in a standard 17-inch-wide chassis. Available in Midnight Black ($10,999) or Velvet Gold ($10,999) finishes.

The Unico Pre V2 Preamplifier

The Pre V2 is built to be the center of a system. Phono stage (MM/MC, switchable via DIP switches). Built-in DAC (ESS ES9018K2M with USB, Toslink, and SPDIF). Multiple RCA and XLR inputs. Dual subwoofer outputs. Balanced outputs at up to 16V, enough headroom to drive long cable runs or demanding amplifiers without losing anything.

The philosophy behind including a DAC and phono stage is practical. You can start with the Pre V2 and DM V2, add speakers, and have a complete system on day one. If your source needs outgrow the built-ins, you add a dedicated external DAC or phono preamp later and use the Pre V2 as a pure line stage. The system grows with you instead of asking you to buy everything at once.

Available in Midnight Black ($7,499) or Velvet Gold ($7,499).

Want to Know More?

We've carried Unison Research for years. The build quality has always been there, the tube warmth has always been there, and the value relative to what you'd spend elsewhere has always been there. A.S.H.A. feels like the moment where the engineering catches up to the ambition. Bartolomeo said it simply: "It's so clear the sound that you don't have trouble to pop up the volume, so you want always to turn up."

Both the Unico DM V2 and Unico Pre V2 are available. If you want to talk through system matching, how these compare to the Unico integrateds, or whether the Pre V2 makes sense as a standalone upgrade in your current system, give us a call at 410-239-2020 or reach out through the site.