Michell Apollo Phono Preamplifier and Muse Power Supply Measurements

Link: reviewed by Jonathan Gorse on SoundStage! Ultra on January 1, 2026

General information

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

The Michell Apollo and Muse were conditioned for 30 minutes at 1Vrms at the output before any measurements were taken.

The Apollo offers one pair of unbalanced (RCA) inputs and outputs, which can be configured using DIP switches beneath the unit, for moving magnet (MM) or moving coil (MC) cartridges. The gain settings are: 40, 50, 60, 68, 73dB. The input impedance loading options are: 33, 100, 430, 1k , 47k ohms. Also included is a grounding post. Unless otherwise specified, the MM settings were 40dB of gain and 47k-ohm input impedance, while the MC settings were 68dB of gain and 100-ohm input impedance. 

The Apollo power supply (called Muse) is external. It connects to the main unit using an umbilical terminated with a 4-pin XLR connector. Using the default settings above, to achieve the reference output voltage of 1Vrms at 1 kHz, 7.4mVrms was required with the MM input and 300uVrms with the MC input. An input bandwidth of 10Hz to 22.4kHz was used by default, 10Hz to 90kHz for FFTs and THD vs frequency sweeps, and DC to 1 MHz for frequency response.

Published specifications vs. our primary measurements

The table below summarizes the measurements published by Michell for the Apollo and Muse compared directly against our own. The published specifications are sourced from Michell ’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 was set at its maximum (DC to 1MHz), assume, unless otherwise stated, 1Vrms unbalanced output into 100k ohms and a measurement input bandwidth of 10Hz to 22.4kHz, and the worst-case measured result between the left and right channels. For the gain setting measurements, the input impedance was set to 1k ohm.

Our primary measurements revealed the following using the unbalanced MM input (unless specified, assume a 1kHz sinewave, 1Vrms output into a 100k ohms load, 10Hz to 22.4kHz bandwidth):

Our primary measurements revealed the following using the unbalanced MC input (unless specified, assume a 1kHz sinewave, 1Vrms output into a 100k ohms load, 10Hz to 22.4kHz bandwidth):

Frequency response - MM input

In our measured frequency-response (relative to 1kHz) plots above for the MM configuration, we find a very flat response within the audioband, with essentially no channel-to-channel deviations (relative to 1kHz - there's an absolute difference of 0.4dB between left and right channels, see main Tables above). 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 Apollo is within +/-0.1dB or so of flat from 20Hz to 2kHz, and about +0.4dB up at 20kHz, with a steady rise above the audioband. At 5Hz, the Apollo is only 0.4dB below the RIAA target. These data do not corroborate Michell’s claim of 20Hz to 20kHz +/-0.1dB, but do line-up with the measurements performed by KBO Dynamics International Ltd. published on Michell’s site of “within +/-0.4dB at extreme frequencies only.” In the graph above and some of the graphs below, we see two visible traces: the left channel (blue or purple) and the right channel (red or green). On other graphs, only one trace may be visible, this 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 configuration, the Apollo yields essentially the same results as with the MM configuration above.

Phase response - MM input

Above is the phase response of the Apollo for the MM configuration, from 20Hz to 20kHz. The Apollo 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 -80 degrees at 10-20kHz.

Phase response - MC input

Above is the phase response of the Apollo for the MC configuration, from 20Hz to 20kHz. The Apollo yields essentially the same results as with the MM configuration above.

THD ratio (unweighted) vs. frequency - MM and MC inputs

The chart above shows THD ratios as a function of frequency, where the input sweep is EQ’d with an inverted RIAA curve. The output voltage is maintained at the reference 1Vrms. The red/blue (L/R) traces represent the MM configuration, and purple/green for the MC input. For the MM input, THD values are very low, ranging from 0.002% at 20Hz down to 0.0002% from 2kHz to 10kHz, then up to 0.0006% at 20kHz. The MC input yielded higher THD ratios due to the higher noise floor, ranging from 0.03% at 20Hz, down to around 0.0005% at 8kHz to 20kHz (left channel). The right MM channel deviated from the left from 8kHz to 20kHz, with THD ratios of 0.003% at 20kHz. It’s important to note that in the case of the Apollo, THD ratios are mostly limited by the noise floor (the analyzer cannot assign a THD ratio to a harmonic peak it cannot see over the noise floor). The truest representation of THD ratios can be seen in the FFTs below, as they are averaged over 15 runs, reducing the noise floor to resolve lower-level signal harmonic peaks. For the MM configuration, the true THD at 50Hz is roughly 0.0001%, and 0.00003%, or lower at 1kHz. For the MC configuration, 0.003% at 50Hz, and 0.0006% at 1kHz.

THD ratio (unweighted) vs. output voltage at 1kHz - MM and MC inputs

The chart above shows THD ratios as a function of output voltage for the balanced output. The red/blue (L/R) traces represent the MM configuration, and purple/green for MC. For the MM configuration, THD values at 100mVrms are at 0.003%, then dip as low as 0.00005% at 5-6Vrms, then up to 0.0001% at the “knee” at just past 10Vrms. For the MC configuration, THD values at 100mVrms are at 0.02%, then steadily decrease down to 0.0003% at 6-10Vrms. The 1% THD values for both inputs are reached at 11.9Vrms at the output. 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 - MM and MC inputs

Above we can see a plot of THD+N ratios as a function of output voltage. The red/blue (L/R) traces represent the MM configuration, and purple/green for MC. For the MM configuration, THD+N values at 100mVrms are at 0.05%, then dip as low as 0.0006% around 8-10Vrms. For the MC configuration, THD+N values at 100mVrms are at 0.6%, then dip as low as 0.007% at the “knee.”

FFT spectrum, 1kHz - MM input

Shown above is a fast Fourier Transform (FFT) of a 1kHz input sinewave stimulus for the MM configuration, which results in the reference voltage of 1Vrms (0dBrA) at the output. Here we see exceptionally clean results. Signal harmonics are non-existent above the -130 to -140dBrA noise floor. This implies that THD ratios are equal to lower than 0.00003%. On the left side of the signal peak, there is a small 60Hz power-supply-fundamental peak at around -100dBrA, or 0.001%, as well as visible peaks at the third (180Hz) and fifth (300Hz) harmonic positions at -110dBrA, or 0.0003%.

FFT spectrum, 1kHz - MC input

Shown above is a fast Fourier Transform (FFT) of a 1kHz input sinewave stimulus for the MC configuration, which results in the reference voltage of 1Vrms (0dBrA) at the output. Predictably the noise floor is elevated compared to the MM FFT by roughly 20dB, due to the extra 28dB of gain. This is also a very clean FFT for a moving-coil phono preamplifier. We can just barely see the second signal harmonic (2kHz) above the -110dBrA noise floor at roughly -105dBrA, or 0.0006%. The 60Hz power-supply noise peak is more pronounced due to the higher gain, at -65dBrA, or 0.06%. The third (180Hz) and fifth (300Hz) power-supply noise harmonics can also be seen at -85dBrA, or 0.006%.

FFT spectrum, 50Hz - MM input

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the line-level output for the MM configuration. 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 (100Hz) from the 50Hz signal can just barely be seen above the noise floor at -115dBrA, or 0.0002%. The 60Hz power supply fundamental peak can be seen at around -100dBrA, or 0.001%, as well as visible peaks at the third (180Hz) and fifth (300Hz) harmonic positions at -110dBrA, or 0.0003%.

FFT spectrum, 50Hz - MC input

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the balanced output for the MC configuration. 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. Only the signal’s second harmonic (100Hz) can be seen above the noise floor at -90dBrA, or 0.003%. The 60Hz power-supply noise peak can be seen at -65dBrA, or 0.06%. The third (180Hz) and fifth (300Hz) power-supply noise harmonics can also be seen at -85dBrA, or 0.006%.

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

Above is an FFT of the IMD products for an 18kHz and 19kHz summed sinewave stimulus tone for the MM configuration. The input rms values are set so that if summed (for a mean frequency of 18.5kHz), they 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 a very low -105dBrA, or 0.0006%. We can also see the third-order modulation products (i.e., 17kHz and 20kHz) sitting at a vanishingly low -120dBrA, or 0.0001%. This is an exceptional IMD result for a phono preamplifier.

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

The last graph is an FFT of the IMD products for an 18kHz and 19kHz summed sinewave stimulus tone for the MC configuration. Here we find that the second order modulation product (i.e., the difference signal of 1kHz) cannot be seen above the -110dBrA noise floor.  We can also find no evidence of the third-order modulation products (i.e. 17kHz and 20kHz) above the -135dBrA noise floor. Another exceptional IMD result.

Diego Estan
Electronics Measurement Specialist