Comparison of AIYIMA A07 with DIY class AB amplifier into complex speaker dummy load (and more amps added soon)
This is a measurement comparison of AIYIMA A07 amplifier (powered by SMPS Mean Well RS-100-24 27V)
https://www.audiosciencereview.com/...-100-24-smps-power-supply-measurements.19507/
with my new 250W/4ohm class AB amplifier
https://www.audiosciencereview.com/...on-blameless-topology-and-measurements.21542/
with respect to operation into complex dummy load that simulates a 2-way real speaker.
I have built a dummy load to simulate speaker impedance years ago. It simulates a simple 2-way box and uses highly nonlinear ferrite 18mH coil to simulate woofer impedance nonlinearity.
The load looks like this
This is the circuit schematics of my dummy load
and this is a measurement of the dummy load impedance
The plots were shown in the DIY amp thread but I re-post them for easier orientation.
First, let's see frequency response of both amplifiers into the dummy load. We can see quite considerable modulation of the AIYIMA frequency response due to its output LC filter interaction with the complex load impedance.
Frequency response of two amps into dummy load
The complex load includes highly nonlinear ferrite core coil of 18mH, which simulates quite well the nonlinearity of the real woofer near resonance. So let's measure THD vs. output voltage at 70Hz first. At 70Hz, we have 8ohm magnitude and -45° phase.
We can see quite similar distortion of both amps at this frequency, with AIYIMA having slightly lower distortion between 2V and 8V and of course a big difference in output power. Please note the fast rise of ferrite coil nonlinearity effect above 10Vrms.
Now let's make measurements at 70, 130, 400 and 1300 Hz. Why these frequencies? Because there is a non-comfort combination of impedance magnitude and phase. 70 Hz was already mentioned, 130 Hz has 6 ohm minimum of magnitude with 0° phase, 400 Hz has 12 ohm magnitude with +45° phase and 1300 Hz has 15 ohm impedance with -40° phase.
Class AB distortion vs. amplitude into dummy load at 70, 130, 400 and 1300 Hz
AIYIMA distortion vs. amplitude into dummy load at 70, 130, 400 and 1300 Hz
Distortion at 70Hz is similar, at 130Hz and 400Hz AIYIMA has lower distortion but at 1300Hz AIYIMA has considerably higher distortion.
Now let's compare distortion vs. frequency, it was measured at 9Vrms which is still comfortable and almost optimum for AIYIMA.
One can see fast rise of distortion below 80Hz, which reflects high nonlinearity of the ferrite core 18mH coil, this is reflected in nonlinear load current and this again in voltage distortion at amp terminals due to its finite output impedance.
AIYIMA has a bit lower distortion near woofer resonance (due to lower output impedance at lowest frequencies), slightly lower distortion between 80Hz and 1kHz, however much higher distortion above 1kHz.
Conclusion
So it goes, there are hints that the level matched AB listening test will bring differences. Mostly because of the differences in frequency response, but even the distortion differences might be interesting.
This is a measurement comparison of AIYIMA A07 amplifier (powered by SMPS Mean Well RS-100-24 27V)
https://www.audiosciencereview.com/...-100-24-smps-power-supply-measurements.19507/
with my new 250W/4ohm class AB amplifier
https://www.audiosciencereview.com/...on-blameless-topology-and-measurements.21542/
with respect to operation into complex dummy load that simulates a 2-way real speaker.
I have built a dummy load to simulate speaker impedance years ago. It simulates a simple 2-way box and uses highly nonlinear ferrite 18mH coil to simulate woofer impedance nonlinearity.
The load looks like this
This is the circuit schematics of my dummy load
and this is a measurement of the dummy load impedance
The plots were shown in the DIY amp thread but I re-post them for easier orientation.
First, let's see frequency response of both amplifiers into the dummy load. We can see quite considerable modulation of the AIYIMA frequency response due to its output LC filter interaction with the complex load impedance.
Frequency response of two amps into dummy load
The complex load includes highly nonlinear ferrite core coil of 18mH, which simulates quite well the nonlinearity of the real woofer near resonance. So let's measure THD vs. output voltage at 70Hz first. At 70Hz, we have 8ohm magnitude and -45° phase.
We can see quite similar distortion of both amps at this frequency, with AIYIMA having slightly lower distortion between 2V and 8V and of course a big difference in output power. Please note the fast rise of ferrite coil nonlinearity effect above 10Vrms.
Now let's make measurements at 70, 130, 400 and 1300 Hz. Why these frequencies? Because there is a non-comfort combination of impedance magnitude and phase. 70 Hz was already mentioned, 130 Hz has 6 ohm minimum of magnitude with 0° phase, 400 Hz has 12 ohm magnitude with +45° phase and 1300 Hz has 15 ohm impedance with -40° phase.
Class AB distortion vs. amplitude into dummy load at 70, 130, 400 and 1300 Hz
AIYIMA distortion vs. amplitude into dummy load at 70, 130, 400 and 1300 Hz
Distortion at 70Hz is similar, at 130Hz and 400Hz AIYIMA has lower distortion but at 1300Hz AIYIMA has considerably higher distortion.
Now let's compare distortion vs. frequency, it was measured at 9Vrms which is still comfortable and almost optimum for AIYIMA.
One can see fast rise of distortion below 80Hz, which reflects high nonlinearity of the ferrite core 18mH coil, this is reflected in nonlinear load current and this again in voltage distortion at amp terminals due to its finite output impedance.
AIYIMA has a bit lower distortion near woofer resonance (due to lower output impedance at lowest frequencies), slightly lower distortion between 80Hz and 1kHz, however much higher distortion above 1kHz.
Conclusion
So it goes, there are hints that the level matched AB listening test will bring differences. Mostly because of the differences in frequency response, but even the distortion differences might be interesting.
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