Hegel Music Systems V10 Phono Preamplifier Measurements

Link: reviewed by Jason Thorpe on SoundStage! Hi-Fi on January 15, 2021

General information

All measurements taken using an Audio Precision APx555 B Series analyzer.

The V10 was conditioned for 30 minutes at 1Vrms at the output before any measurements were taken.

The V10 offers one pair of unbalanced RCA outputs and one pair of balanced XLR outputs, as well as two pairs of unbalanced RCA inputs, one pair for moving-magnet (MM) and the other for a moving-coil (MC) cartridge. There are a number of DIP switches on the rear panel of the V10, allowing the user to alter MC resistive loading, MM capacitive loading, and gain, as well to turn on or off a subsonic filter. Other than the 6dB difference in gain between the balanced and unbalanced outputs (+6dB for balanced), there were no mentionable differences between both outputs types in terms of THD+N, as long as the gain was kept constant. Settings were left at the manufacturer’s default positions (see specs below). To achieve the reference output voltage of 1Vrms at 1kHz at the balanced output, 10mVrms was required at the MM input and 1mVrms at the MC input.

Published specifications vs. our primary measurements

The tables below summarize our primary measurements performed on the V10. Here we can compare directly against Hegel’s own published specifications for the V10, which are stated as follows:

• Gain (XLR): MM, 40/45/50/52dB; MC, 60/65/70/72dB (default = 40/60dB for MM/MC)
• Gain (RCA): MM, 34/39/44/46dB; MC, 54/59/64/66dB (default = 34/54dB for MM/MC)
• MC load impedance: 100/300/47k ohms (default = 100 ohms)
• MM load capacitance: 100/147/200/220/247/320/420pF at 47k ohms (default = 100pF)
• Subsonic filter: on, -3dB at 20Hz; off, -18dB/octave
• RIAA accuracy: +/-0.1dB 20Hz to 20kHz
• Output noise: -84dB (MM, A-weighted, ref 1Vrms), -81dB (MC, A-weighted, ref 1Vrms)
• Output impedance: XLR and RCA, 200 ohms
• Channel crosstalk: -84dB @ 1kHz (ref 1Vrms)
• Frequency response: 2Hz to 20kHz
• THD: MM, <0.005%; MC, <0.009% at 1kHz ref 1Vrms
• Maximum output voltage: 23Vrms

Our primary measurements revealed the following using the unbalanced MM input (unless specified, assume a 1kHz sinewave, 1Vrms at the balanced output into a 200k ohms load, 10Hz to 90kHz bandwidth):

Our primary measurements revealed the following using the unbalanced MC input (unless specified, assume a 1kHz sinewave, 1Vrms at the balanced output into a 200k ohms load, 10Hz to 90kHz bandwidth):

Gain was measured at 40 and 60dB (Balanced, MM/MC), the same as Hegel’s spec. The MC load input impedance was measured at 124 ohms, closely matching Hegel’s spec and setting of 100 ohms. The input impedance for the MM input was measured at 47 and 46k ohms (L/R), very close to the industry standard 47k ohms.

Output noise (A-weighted) was measured at -85dB (MM) and -79dB (MC), either exceeding or approaching Hegel’s specs of -84/-81dB (MM/MC). Our measured output impedance of 200 ohms confirmed Hegel’s spec of the same value.

Our measured crosstalk values at 10kHz were close to Hegel’s spec of -84dB (at 1kHz), where we measured -83dB for both channels for the MM input and -88/-95dB (left and right channels) for the MC input. For a direct comparison, we also measured crosstalk at 1kHz, and found -98/-100dB (L/R channels, MM input), and -88/-90dB (L/R channels, MC input), bettering the -84dB Hegel spec.

Hegel’s claim of better than 0.005% (MM) and 0.009% (MC) THD was also verified. There are many ways to measure THD, and manufacturers are often shy on showing all of the parameters used for the measurement. Here, we assume that Hegel is referring to THD (not THD+N), unweighted, against a 1Vrms 1kHz output signal. The bandwidth for Hegel’s measurement is unknown, but we use 10Hz to 90kHz for our measurements. Under those conditions, we found the V10’s THD to be below 0.0008% (MM) and 0.001% (MC). Even if Hegel’s THD spec is actually THD+N (A-weighted), they still meet spec for the MM input, as we measured 0.005%, and come very close for the MC input at 0.01%.

Hegel’s maximum output voltage (1% THD+N) claim of 23Vrms (balanced) was also confirmed, where we measured 24Vrms.

Frequency response - MM input

The blue (left channel) and red (right channel) traces represent the frequency response without the subsonic filter turned on. In our measured frequency-response plot above for the MM input, the V10 is within +/-0.2dB or so of flat from 20Hz to 20kHz, just about meeting Hegel’s RIAA accuracy claim of +/-0.1dB. An inverse RIAA EQ is applied to the input sweep, so that if a device were to track the RIAA curve perfectly, a flat line would emerge—the V10 has nearly perfect RIAA accuracy from 5Hz to 80kHz. The purple (left channel) and green (right channel) traces represent the frequency response with the subsonic filter engaged, where Hegel’s claim of -3dB at 20Hz is confirmed. In the graph above and some of the graphs below, we see two visible traces; the left channel (blue or purple trace) and the right channel (red or green trace). On other graphs, only one trace may be visible, which is because the left and right channels are tracking extremely closely, so as not to show a difference with the chosen axis scales.

Frequency response - MC input

In our measured frequency-response plot above for the MC input shown with the blue and red traces (left and right channels), the V10 is within +/-0.2dB or so of flat from 20Hz to 20kHz, just about meeting Hegel’s RIAA accuracy claim of +/-0.1dB. The worst-case deviation was seen at around 8Hz, were the V10 over-responded by 0.5dB. The purple and green trace (left and right channels) represent the frequency response with the sub-sonic filter engaged, where Hegel’s claim of -3dB at 20Hz is confirmed.

Phase response - MM and MC inputs

Above is the phase response of the V10 for both the MM and MC inputs (they measured effectively identically), from 20Hz to 20kHz. The V10 does not invert polarity. Since phono preamplifiers must implement the RIAA equalization curve, which ranges from +19.9dB (20Hz) to -32.6dB (90kHz), phase shift at the output is inevitable. Here we find a worst case -60 degrees around 200Hz and -55 degrees at 5kHz.

THD ratio (unweighted) vs. frequency - MM input

The chart above shows THD ratio as a function of frequency for the MM input, where the input sweep is EQ’d with an inverted RIAA curve. The output voltage is maintained at the refrence 1Vrms. The THD values vary from 0.01% at 20Hz, down to below 0.0001% at 10kHz, then back up just above 0.0003% at 20kHz.

THD ratio (unweighted) vs. frequency - MC input

The chart above shows THD ratio as a function of frequency for the MM input, where the input sweep is EQ’d with an inverted RIAA curve. The THD values vary from 0.04% at 20Hz, down to around 0.0004% at 5kHz, then a climb to 0.001% at 20kHz.

THD ratio (unweighted) vs. output voltage at 1kHz (input voltage from 1mVrms to 30mVrms) - MM input

Above we can see a plot of THD ratios as a function of output voltage for the MM input. We can see very low THD ratio values, ranging from as low as 0.0001% at 5Vrms, up to about 0.0006% at the “knee”, just past 20Vrms, and about 0.005% at the lowest output voltage of 100mVrms. Beyond the “knee” there is sharp rise in THD as the V10 reaches its maximum output voltage. It’s important to mention that anything above 1-2Vrms is not typically required for most line-level preamps or integrated amps.

THD+N ratio (unweighted) vs. output voltage at 1kHz (input voltage from 1mVrms to 100mVrms) - MM input

Above we can see a plot of THD+N ratios as a function of output voltage for the MM input. We can see THD+N ratio values, ranging from 0.2% at 100Vrms, down to about 0.0015% between 15 and 20Vrms.

THD ratio (unweighted) vs. output voltage at 1kHz (input voltage from 0.1mVrms to 30mVrms) - MC input

Above we can see a plot of THD ratios as a function of output voltage for the MC input. The MC input behaved similarly to the MM input, with 0.007% THD at 100mVrms, dipping to the lowest THD value of 0.0005% at 2Vrms, then up just past 0.003% at the knee at 20Vrms. The 1% THD ratio value is reached at 24Vrms at the output.

THD+N ratio (unweighted) vs. output voltage at 1kHz (input voltage from 0.1mVrms to 30mVrms) - MC input

Above we can see a plot of THD+N ratios as a function of output voltage for the MC input. We can see THD+N ratio values ranging from around 0.5% at 100Vrms, down to about 0.005% between 15 and 20Vrms.

FFT spectrum, 1kHz - MM input

Shown above is a fast Fourier transform (FFT) of a 1kHz input sinewave stimulus for the MM input, which results in the reference output voltage of 1Vrms. Here we see exceptionally clean results. Signal harmonics are non-existent (i.e., cannot be seen above the -120dB noise floor at 2kHz). The frequency components on the left side of the 1kHz peak are mostly due to power-supply noise, where the typical 60Hz and 120Hz peaks can be seen. The worst noise peak (60Hz) is below -80dBrA, with the subsequent harmonic (120Hz) at around -90dBrA. The third harmonic (180Hz) is just below -90dBrA, and the subsequent harmonics are below -100dBrA.

FFT spectrum, 1kHz - MC input

Shown above is the FFT of a 1kHz input sinewave stimulus for the MC input. Signal harmonics are virtually non-existent, only a hint of a peak can be seen below -110dB at 2kHz. The 60Hz and 120Hz peaks are just below -70dBrA, and the third and fourth noise harmonics are just below -80dBrA.

FFT spectrum, 50Hz - MM input

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output for the MM input. The X axis is zoomed in from 40Hz to 1KHz so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The harmonics from the 50Hz signal (100, 150, 200Hz, etc) are non-existent. The power supply noise peaks can clearly be seen, which were described in the 1kHz FFT chart above.

FFT spectrum, 50Hz - MC input

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output for the MC input. Like the MM FFT, here again, the harmonics from the 50Hz signal (100, 150, 200Hz, etc.) are non-existent. The power-supply noise peaks can clearly be seen, which were described in the 1kHz FFT above.

Intermodulation distortion FFT (18kHz + 19kHz summed stimulus) - MM input

The chart above is an FFT of the IMD products for an 18kHz and 19kHz summed sinewave stimulus tone for the MM input. The input rms values are set so that if summed (for a mean frequency of 18.5kHz), would yield 1Vrms (reference or 0dBRa) at the output. Here we find the second-order modulation product (i.e., the difference signal of 1kHz) just above -100dBrA. We can also see the third-order modulation products (i.e., 17kHz and 20kHz) are extremely low, below -120dBRa.

Intermodulation distortion FFT (18kHz + 19kHz summed stimulus) - MC input

The next chart is an FFT of the IMD products for an 18kHz and 19kHz summed sinewave stimulus tone for the MC input. Here we find the second-order modulation product (i.e., the difference signal of 1kHz) just at -80dBrA, which is very low. We can also see the third-order modulation products (i.e., 17kHz and 20kHz) are extremely low, below -120dBRa. These clean IMD FFTs are reflected in our simplified IMD results (which only account for the sum of the second- and third-order modulation products) in our primary measurement table, where the MM input measured at -92dB for both channels and the MC input at -76/-73dB, for, respectively, the left and right channels. Incidentally, the 3dB difference between left and right channels for the MC input can be seen in the 1kHz peak in the FFT chart above. The fourth-order modulation products are non-existent in this FFT and the one for the MM input.

Diego Estan
Electronics Measurement Specialist