Plinius M14 phono preamplifier Measurements

Sidebar 2: Measurements

While the Plinius 14 has both low- and high-gain settings, the low-gain setting is really too high for most moving-magnet cartridges, and appears instead designed for medium-gain moving-coils. Unless otherwise noted, the results are for the high-gain setting with unbalanced outputs.

The Plinius 14's output impedance was 170 ohms (right channel; slightly lower, at 163 ohms, in the left). At its balanced outputs, the output impedance measured 354 ohms. Its input impedance measured 47k ohms (L) and 45.6k ohms (R) at the 47k ohm setting of the input impedance control, the other settings also measuring very near the stated values. The DC offset at the Plinius' outputs was 5.5mV (L) and 4mV (R), high-gain, and 6.9mV (L) and 7.7mV (R), low-gain. The preamp is noninverting from its unbalanced outputs; from the balanced outs, pin 2 is positive. At a 47k ohm input impedance setting, the voltage gain measured 54.5dB in the low-gain mode, 60.5dB high-gain. The balanced output increased the gain by 6dB, and reducing the input impedance setting to 100 ohms reduced the gain by 3.5dB (both changes measured at the low-gain setting). S/N was good to excellent, as shown in Table 1.

Table 1 Plinius 14 S/N ratio (ref. 1V)

Low GainHigh GainLow Gain (balanced)

The Plinius 14's RIAA frequency response is shown in fig.1. Note that the response rises a little in the bass. (The curve shown is for the unbalanced low-gain setting; the high-gain and balanced settings are identical except that the HF rolloff does not begin until about 40kHz.) Crosstalk is shown in fig.2 (taken with the Plinius in the low-gain setting). This is a good result, well beyond the needs of any phono cartridge. The THD+noise vs frequency measurement is shown in fig.3. This was taken at a fairly high input level, as is our usual procedure to minimize the effect of noise. The rising THD at high frequencies, largely the result of this high input, is of no real significance in practical use.


Fig.1 Plinius M14, RIAA error into 100k ohms (0.5dB/vertical div., right channel dashed).


Fig.2 Plinius M14, crosstalk (from top to bottom): R–L, L–R (10dB/vertical div.).


Fig.3 Plinius M14, THD+noise (%) vs frequency at 4.75mV (High Gain) and 5.7mV (Low Gain) at 1kHz into 100k ohms (Low Gain bottom below 1kHz) (right channel dashed).

Fig.4 shows the THD+noise vs output in volts (at 1kHz). Note that the high- and low-gain minimums correspond to inputs of 4.75mV and 5.7mV, respectively—the values used to derive the appropriate curves in figs.2 and 3.


Fig.4 Plinius M14, distortion (%) vs output voltage into 100k ohms at 1kHz (Low Gain bottom below 4V output).

One percent THD+noise (with an unequalized source) was reached at an input of 52.5mV at 1kHz, 83mV at 20kHz, and 5.5mV at 20Hz in the low-gain setting; and 27.4mV, 85mV, and 2.72mV at the same respective frequencies in the high-gain setting. These are very good results. The variations with frequency are due to the characteristics of the preamp RIAA phono equalization.

Altogether, these are very fine measured results for a phono preamp.—Thomas J. Norton

Plinius Audio Ltd
Plinius USA
3439 NE Sandy Boulevard #128
Portland, OR 97232
(503) 662-8210

tonykaz's picture

Easy to agree !

A fall in demand for phono will trigger a Glut on/in the market suggesting that many will not be sold. ( according to Cambridge Dictionary )

Well Said, Mr.MF phono marketer.

The 10cent word would be surfeit.

Tony in Venice

Glotz's picture

It's a good one though! MF has displayed continued integrity and transparency.

misterc59's picture

Agreed Mr Glotz!