Unison Research Unico Primo integrated amplifier Measurements

Sidebar 3: Measurements

I performed a full set of measurements on the Unison Research Unico Primo using my Audio Precision SYS2722 system (see the January 2008 "As We See It"). As always before performing any measurements on an amplifier, I preconditioned it by running it with both channels driven at one-third power into 8 ohms for 60 minutes. Thermally, this is the worst-case situation for an amplifier with a class-B or class-A/B output stage, as one-third power is when the maximum heat dissipation occurs in the output transistors. As the Unico Primo's maximum power is specified in the manual as 80Wpc into 8 ohms, I set it driving 27Wpc into 8 ohms. However, the amplifier turned itself off after just 15 minutes at this power level. The two green LEDs on its front panel were slowly flashing, which, according to the manual, meant that the amplifier's protection circuitry had detected thermal overload. The internal heatsink's temperature was 113.2°F (45.1°C), which didn't seem that hot. But I turned the Primo off and let it cool down for 30 minutes, after which I could turn it on again.

This preconditioning test puts a significant strain on inexpensive amplifiers, which tend to have undersized heatsinks; it appears that the Unico Primo is not the best candidate for use at parties.

I looked first at the phono input, which Ken Micallef had used with the default moving-magnet setting. Measured at the Tape Out jacks, this preserved absolute polarity (ie, was non-inverting) and offered a gain of 40.5dB. The input impedance measured 46k ohms at low and middle frequencies, dropping slightly to 39.6k ohms at the top of the audioband, and both the gain and impedance are appropriate for MM cartridges. Fig.1 shows the RIAA error: The two channels match closely, and while there is a slight rise in the top two octaves and a slight rolloff below 30Hz, both are low in absolute terms. The unweighted, wideband signal/noise ratio, measured with the input shorted to ground and ref. 1kHz at 5mV input voltage, was excellent, at 69dB, increasing when A-weighted to 79.3dB left and 80.5dB right. The phono input's channel separation was also excellent, at >80dB above 2kHz.

Fig.1 Unison Unico Primo, phono input, response with RIAA correction (left channel blue, right red) (1dB/vertical div.).

The MM stage's overload margin was superb, at 26dB at all audio frequencies, this equivalent to an output voltage of 9.5V at the Tape Out jacks. Harmonic distortion was correspondingly low at typical MM signal levels, with the third harmonic of a 1kHz tone the highest in level at a very low –97dB (0.0015%). Intermodulation distortion was similarly low in level (fig.2).

Fig.2 Unison Unico Primo, phono input, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 2V peak into 100k ohms (linear frequency scale).

Turning to the line inputs, the Unico Primo's maximum gain into 8 ohms measured 40dB, which is typical for an integrated amplifier; these inputs also preserved absolute polarity. The input impedance was a usefully high 47k ohms at low and middle frequencies, dropping inconsequentially to 42k ohms at 20kHz. At 0.3 ohm, the Primo's output impedance was on the high side for a solid-state design, presumably due to the low level of loop negative feedback. As a result, the modification of the amplifier's frequency response with our standard simulated loudspeaker reached ±0.25dB (fig.3, gray trace). This graph reveals that the Unison amplifier had a wide small-signal bandwidth even into 2 ohms (green trace), but the 10kHz squarewave (fig.4) shows no overshoot or ringing. Fig.1 was taken with the volume control set to its maximum; turning down this control also reduced the amplifier's bandwidth, but the response was still flat to 20kHz at the lower settings, and the excellent channel balance seen in fig.1 was preserved.

Fig.3 Unison Unico Primo, frequency response at 2.83V into: simulated loudspeaker load (gray), 8 ohms (left channel blue, right red), 4 ohms (left cyan, right magenta), 2 ohms (green) (0.5dB/vertical div.).

Fig.4 Unison Unico Primo, small-signal, 10kHz squarewave into 8 ohms.

Channel separation for a 1kHz line-level signal was a little disappointing, at 65dB R–L and 70dB L–R, and decreased with increasing frequency, reaching a poor 40dB at 20kHz. I also noted significant inter-input crosstalk, at –30dB at 1kHz for adjacent, unloaded inputs. The unweighted, wideband S/N ratio, measured with the line inputs shorted to ground but the volume control set to its maximum, was also disappointing, at 68.4dB ref. 2.83V into 8 ohms, though when A-weighted this did improve to 82.8dB left and 79.3dB right. Fig.5 reveals that the noise floor is dominated by spuriae at the AC mains frequency of 60Hz and its harmonics.

Fig.5 Unison Unico Primo, spectrum of 1kHz sinewave, DC–1kHz, at 1W into 8 ohms (linear frequency scale).

Fig.6 reveals that the Unico Primo exceeded its specified maximum output power of 80Wpc into 8 ohms (19dBW), clipping (defined as 1% THD+noise) at 105Wpc (20.2dBW). However, into 4 ohms (fig.7), the output voltage dropped, the amplifier clipping at 135Wpc (18.3dBW), which suggests that its power transformer is undersized. While performing this test, I noted that at levels above 20W or so the transformer audibly buzzed, which suggests the same thing. These two graphs indicate that the THD+N level remains relatively constant over a wide range of powers, from 100mW to 10W, but that the amplifier becomes more linear as the output current increases.

Fig.6 Unison Unico Primo, THD+N (%) vs 1kHz continuous output power into 8 ohms.

Fig.7 Unison Unico Primo, THD+N (%) vs 1kHz continuous output power into 4 ohms.

I plotted how the THD+N percentage changed with frequency at a level, 8.95V (equivalent to 10W into 8 ohms, 20W into 4 ohms, and 40W into 2 ohms), where I could be sure that I was examining actual distortion rather than noise. The results are plotted in fig.8: The rise in THD in the top two octaves is lower than usual, suggesting that the circuit has a wide open-loop bandwidth. The distortion also remains relatively constant over the range of impedances.

Fig.8 Unison Unico Primo, THD+N (%) vs frequency at 8.95V into: 8 ohms (left channel blue, right red), 4 ohms (left cyan, right magenta), 2 ohms (left gray).

The distortion signature at 1kHz and low powers appears primarily to be third-harmonic in nature (fig.9), but at higher powers, the second harmonic and higher-order odd harmonics make appearances (fig.10). The graph of intermodulation distortion (fig.11) looks a little alarming, but other than the products at 18 and 21kHz, the spuriae are all at or below 70dB (0.03%).

Fig.9 Unison Unico Primo, 1kHz waveform at 1W into 8 ohms, 0.1% THD+N (blue); distortion and noise waveform with fundamental notched out (red, not to scale).

Fig.10 Unison Unico Primo, spectrum of 50Hz sinewave, DC–1kHz, at 20W into 8 ohms (linear frequency scale).

Fig.11 Unison Unico Primo, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 40W peak into 4 ohms (linear frequency scale).

Some of its measured behavior suggests that some corners have been cut to keep the Unison Research Unico Primo's price relatively affordable. But despite its disappointing levels of noise and distortion, the Unico Primo appears to maintain a relatively constant level of performance over a wide range of frequencies and power levels, which is always found subjectively to be a good thing.—John Atkinson

Unison Research
US distributor: Colleen Cardas Imports
PO Box 912
Brewerton, NY 13029
(970) 275-9086

fetuso's picture

That was fun reading. Being a first generation Italian-American myself (Sicilian actually) I enjoy reading about Italian designed audio gear. Puzzling that they would take such little care in the packaging. I can't wait for your review of the Music Hall mmf7.3. It's on my upgrade list. I currently use a mmf2.2 that has served me well, especially considering it only cost $300 after the price dropped.

ken mac's picture

Thanks for your nice comments. The UR is a great sounding piece, even if the packaging is negligible.

scott.w's picture

Doesn't matter how nice the sound if it arrives broken.

audiodoctornj's picture

Dear Ken,

I read the review with gusto, you hit this review out of the park, except for a couple of caveats, one the fact that the way less expensive Primo has a bigger sound stage was a great point, and underlays how good the Primo is, and the fact that you were comparing a very affordable integrated to much more expensive Shindo gear, demonstrates how special this gear is, okay so you were having a little less extreme deep bass then you would like. I would say to that, it is still a relatively inexpensive amplifier, I wouldn't expect to be be better in all ways to much more expensive equipment.

We have found the Primo is very sensitive to good cables, especially power cords. We have gotten spectacular results with the Wire World cabling, and good component isolation, which helps bring out the deep bass as well as improving all aspects of the Primo's performance.

In our shop we have compared the Primo to almost all of the major competitors, and quite frankly the Primo smokes them all.

The Primo is a hybrid so you get the best of tubes with the best of solid state, the Primo offers a true glimpse into the magic of really expensive gear.

If you want to hear everything in an integrated amplifier, the more expensive Unico 50 which is now the Unico 90 model, gives you the warmth and huge sound stage of the Primo, with even better bass, and far greater resolution.

We used to sell a very expensive line of Japanese components and ones from Denmark, and when ever you compared the Unison product the customers almost invariably picked the Unison.

Under $10k you would be hard pressed to find a better integrated amplifier, which has this number of magical properties as the upper end Unico line from Unison, the stuff is absolutely killer, and Collen and Marc are the best importers with fantastic customer service.