iFi Audio iPhono3 Black Label Phono Preamplifier Measurements

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

General information

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

The iPhono3 was conditioned for 30 minutes at 1Vrms at the output before any measurements were taken.

The iPhono3 has one switch and one unbalanced pair of RCA outputs on one end, while the other end has two pairs of unbalanced RCA inputs for connection of a moving-magnet (MM) or moving-coil (MC) cartridge. The switch allows the user to select between RIAA, Columbia, and Decca EQ settings. There are a number of DIP switches underneath, allowing the user to alter MC resistive loading, MM capacitive loading, gain, and variations on EQ (i.e., enhanced RIAA and standard with and without subsonic filter).

For the MM input, capacitive loading was set to 100pF and the gain set to 36dB, which required a 16.2mVrms 1kHz sinewave to achieve the reference output voltage. For the MC input, resistive loading was set to 100 ohms and the gain set to 60dB, which required a 1.18mVrms 1kHz sinewave to achieve the reference output voltage

Published specifications vs. our primary measurements

The table below summarizes the measurements published by iFi Audio for the iPhono3 Black Label compared directly against our own. The published specifications are sourced from iFi Audio’s website, either directly or from the manual available for download, or a combination thereof. With the exception of frequency response, where the Audio Precision bandwidth is set at its maximum (DC to 1MHz), assume, unless otherwise stated, 1Vrms output into 100k ohms and a measurement input bandwidth of 10Hz to 90kHz, and the worst case measured result between the left and right channels.

Our primary measurements revealed the following using the unbalanced MM input (unless specified, assume a 1kHz sinewave, 1Vrms output in 100k ohms, 10Hz to 90kHz bandwidth):

Our primary measurements revealed the following using the unbalanced MC input (unless specified, assume a 1kHz sinewave, 1Vrms output into 100k ohms, 10Hz to 90kHz bandwidth):

Frequency response RIAA - MM input

In our measured frequency-response plot above for the MM input, the iPhono3 is at worst +0.7dB (left channel) or so of flat from 20Hz to 20kHz, not quite meeting iFi’s claim of +/-0.2dB. 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 claim of +/-0.3dB from 10Hz to 100kHz was also not corroborated by our measurements, where at 80kHz, the MM input was at about +2dB. 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 RIAA - MC input

In our measured frequency-response plot above for the MC input, the iPhono3 is at worst +0.7dB (left channel) or so of flat from 20Hz to 20kHz, not quite meeting iFi’s claim of +/-0.2dB. The claim of +/-0.3dB from 10Hz to 100kHz was also not corroborated by our measurements, where at 80kHz, the MC input was at about -2.5dB.

Frequency response for RIAA, Columbia, and Decca settings - MM input (no EQ applied to input sweep)

Above is the raw (no EQ applied in the Audio Precision generator) frequency response of the iPhono3 using the RIAA (blue), Columbia (green) and Decca (burgundy) EQ settings for the MM input with a 0.5mVrms sinewave input swept from 10Hz to 80kHz (the results for the MC input were effectively identical). We find deviations of about 5 dB at 20Hz, and 3dB at 20kHz between all three EQ settings.

Phase response - MM and MC inputs

Above is the phase response of the iPhono3 for both the MM and MC inputs (they measured effectively identically), from 20Hz to 20kHz. 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 6kHz. Because the worst case is -60 degrees, that indicates that the iPhono3 does not invert polarity. 

THD ratio (unweighted) vs. frequency - MM input

Above is the THD ratio as a function of frequency chart for the MM input, where the input sweep is EQ’d with an inverted RIAA curve. The output voltage is maintained at the reference 1Vrms. Since iFi provides specs for 600-ohm loading, here we show data for a typical 100k ohms load (blue/red), and for a 600 ohms load (purple/green). The iPhono3 performed identically with either load. The THD values vary from 0.01% at 20Hz, down to below 0.001% from 100Hz to 200Hz, then back up just above 0.02% from 2kHz to 20kHz.

THD ratio (unweighted) vs. frequency - MC input

Above is the THD ratio as a function of frequency chart for the MC input. The output voltage is maintained at the refrence 1Vrms. Since iFi provides specs for 600 ohm loading, here we show data for a typical 100k ohms load (blue/red), and for a 600 ohms load (purple/green). The THD values vary from 0.1% at 20Hz, down to 0.004% at around 100Hz, then a steady near linear climb to 0.3% at 20kHz.

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

Above is the chart of THD ratio as a function of output voltage for the MM input. We can see very low THD ratio values, ranging from as low as 0.002% at 150mVrms, up to about 0.06% at 4Vrms. Beyond this point there is sharp rise in THD. The 1% THD ratio value is reached at 6Vrms at the output.

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

Above we can see the plot of THD+N ratio as a function of output voltage for the MM input. We can see THD+N ratio values ranging from 0.2% at around 50mVrms, down to about 0.02% at 1Vrms.

THD ratio (unweighted) vs. output voltage at 1kHz (input voltage from 0.1mVrms to 12mVrms) - MC input

Above is the THD ratio as a function of output voltage for the MC input. The MC input behaved almost identically to the MM input, with the lowest THD values recorded also around 150mVrms, at around 0.004%.

THD+N ratio (unweighted) vs. output voltage at 1kHz (input voltage from 0.1mVrms to 12mVrms) - MC input

Above we can see the plot of THD+N ratio as a function of output voltage for the MC input. We can see THD+N ratio values ranging from 1.5% at around 50mVrms, down to about 0.05% between 2 and 3Vrms.

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 that the third signal harmonic at 3kHz is close to -75dB below the reference signal, or at -75dBrA, equivalent to 0.02%. The second harmonic at 2kHz is non-existent. 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 at around -80dBrA, or 0.01%, with the subsequent harmonic (120Hz) at around -90dBrA, or 0.003%. The third (180Hz) and fourth (240Hz) harmonics are just above -100dBrA, or 0.001%.

FFT spectrum, 1kHz - MC input

Shown above is the FFT of a 1kHz input sinewave stimulus for the MC input. Here we see that the second and third signal harmonics (2 and 3kHz) are close to -75dBrA, or 0.02%. The 60Hz peak is at -60dBrA, or 0.1%; the second noise harmonic (120Hz) is close to -70dBrA, or 0.03%; and the third (180Hz) and fourth (240Hz) harmonics are just above -80dBrA, or 0.01%.

FFT spectrum, 50Hz - MM input

Shown above is the FFTs 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 second harmonic of the 50Hz signal (100Hz) is non-existent. What dominate are the power supply noise peaks, which were described in the 1kHz FFT above.

FFT spectrum, 50Hz - MC input

Shown above is the FFTs for a 50Hz input sinewave stimulus for the MC input. The second harmonic of the 50Hz signal (100Hz) is at -90dBrA, or 0.003%. What dominate are the power supply noise peaks, which were described in the 1kHz FFT above.

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

Shown 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) at almost -100dBrA, or 0.001%. We can also see the third-order modulation products (i.e., 17kHz and 20kHz) measure at around -85dBrA, or 0.006%.

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

This chart shows 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) at around -40dBrA, or 1%. We can also see the third-order modulation products (i.e., 17kHz and 20kHz) are also considerably different between the MM and MC inputs, where the MM peaks measure at around -85dBrA, or 0.006%, and the MC peaks are just under -50dBrA, or 0.3%. These differences 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 outperformed the MC input by 36dB.

Diego Estan
Electronics Measurement Specialist