Sidebar 3: Measurements
I measured a different sample of the PREi from that auditioned by Jason Victor Serinus; mine had the serial number PRO37. I used my Audio Precision SYS2722 system to perform a complete set of tests using both the PREi's balanced and unbalanced inputs and outputs.
The PREi preserved absolute polarity (ie, was noninverting) with all the inputs and outputs. (The preamplifier's balanced XLR jacks are wired with pin 2 hot, the AES convention.) The volume control operated in accurate 0.5dB steps, and with this control set to the maximum of "+6dB," the gain was 5.9dB for the balanced inputs at the balanced outputs and the unbalanced inputs at the unbalanced outputs. The gain with the balanced inputs feeding the single-ended outputs was –0.1dB; it was 11.9dB with the unbalanced inputs feeding the balanced outputs.
The PREi's balanced input impedance was close to the specified 40k ohms, at 39.4k ohms, which was consistent from 20Hz to 20kHz. The specified single-ended input impedance is 20k ohms; my estimate was half that value, at 10k ohms across the audioband. The output impedances were 149 ohms, balanced, and 75 ohms, unbalanced, agreeing with the specified values.
Fig.1 EMM Labs PREi, balanced frequency response with volume control set to "+6dB" at 2V into: 100k ohms (left channel blue, right red), 600 ohms (left green, right gray) (1dB/vertical div.).
The preamplifier's balanced frequency response was flat from 10Hz to 200kHz into both 100k ohms (fig.1, blue and red traces) and 600 ohms (green and gray traces). Fig.1 was taken with the PREi's volume control set to its maximum. Both the frequency response and the superb channel matching were preserved at lower settings of the control and with the unbalanced inputs and outputs. The EMM Labs preamp's channel separation was superbly high, at >120dB in both directions below 1kHz, and decreased only slightly at the top of the audioband.
Fig.2 EMM Labs PREi, balanced spectrum of 1kHz sinewave, DC–1kHz, at 2V into 100k ohms with volume control set to "+6dB" (left channel blue, right red) and to "–6dB" (left green, right gray) (linear frequency scale; 20dB/vertical div.).
From balanced inputs to balanced outputs, the PREi offered extremely low levels of random noise (fig.2). The blue and red traces in this graph were taken with the volume control set to the maximum of "+6dB." The levels of the noise components dropped by approximately 6dB when I repeated the spectral analysis with the control set to "–6dB" and the level of the input signal increased by 12dB so that the output level remained the same (gray, green traces). The wideband, unweighted signal/noise ratio, measured at the balanced outputs with the single-ended input shorted to ground but the volume control set to its maximum, was a very high 84.4dB ref. 2V in both channels. Restricting the measurement bandwidth to the audioband increased the S/N ratio to a superb 97.3dB, while switching an A-weighting filter into circuit further improved this ratio, to 102dB.
Fig.3 EMM Labs PREi, balanced distortion (%) vs 1kHz output voltage into 100k ohms.
Fig.4 EMM Labs PREi, unbalanced distortion (%) vs 1kHz output voltage into 100k ohms.
Fig.5 EMM Labs PREi, unbalanced distortion (%) vs 1kHz output voltage into 100k ohms.
EMM Labs doesn't specify the PREi's maximum output levels. Fig.3 plots the percentage of THD+noise in the balanced output against the output voltage into 100k ohms. With the clipping voltage defined as being when the THD+N reaches 1%, the balanced output clipped at a very high 20V into 100k ohms. The balanced clipping voltage into 600 ohms was 16V (fig.4), and the unbalanced outputs clipped at 10.5V into 100k ohms (fig.5).
Fig.6 EMM Labs PREi, balanced distortion (%) vs frequency at 4V into 100k ohms (left channel blue, right red) and 600 ohms (left green, right gray).
The downward slope of the trace below 4V in fig.3 indicates that the actual distortion lies below the (low) noisefloor. To be sure the reading was not dominated by noise, therefore, I measured how the distortion in the PREi's balanced outputs changed with frequency at 4V into 100k ohms (fig.6, blue, red traces). Commendably, there was no increase in the THD+N in the top audio octaves, which implies that the circuit has a wide open-loop bandwidth. Unusually, distortion was even lower at the same voltage into 600 ohms (green, gray traces). When I repeated this test with the single-ended outputs, the THD+N was slightly higher than from the balanced outputs but was still very low at all audio frequencies.
Fig.7 EMM Labs PREi, balanced spectrum of 50Hz sinewave, DC–1kHz, at 4V into 100k ohms (left channel blue, right red; linear frequency scale; 20dB/vertical div.).
Fig.8 EMM Labs PREi, unbalanced spectrum of 1kHz sinewave, DC–1kHz, at 4V into 100k ohms (left channel blue, right red; linear frequency scale; 20dB/vertical div.).
Fig.9 EMM Labs PREi, balanced HF intermodulation spectrum, DC–30kHz, 19+20kHz at 4V into 600 ohms (left channel blue, right red; linear frequency scale; 20dB/vertical div.).
The second harmonic was dominant in both the balanced (fig.7) and unbalanced outputs (fig.8) at the same voltage, but was negligible at –110dB (0.0003%), balanced, and –100dB (0.001%), unbalanced. Tested for intermodulation distortion with an equal mix of 19kHz and 20kHz tones at a peak balanced voltage of 4V, the second-order difference product at 1kHz lay at an extremely low –114dB (0.0002%) even into 600 ohms (fig.9). The higher-order products all lay close to –130dB!
Overall, the EMM Labs PREi offered superb measured performance, in the same class as the PS Audio PMG Signature that RvB reviewed in the May 2026 issue.—John Atkinson
