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Measurements of SMSL AO200 EQ Settings

jasonRF

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Joined
May 21, 2021
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Location
New England
I picked up one of these units a few weeks ago and have been pretty happy with it. While I just use the treble and bass tone controls, I was curiuos to see how the other EQ settings work. In particular, I wanted to know if the SDB setting was 'dynamic' - which to me would mean that the response changes with the volume control setting (along the lines of the Yamaha variable tone control). I know that SMSL has a plot of some of the EQ settings on their web site but I cannot make heads or tails of it. So I went ahead and made some measurements, all using the unbalanced input and with a 4.1 Ohm resistive load. At the end I will give a littler more detail about the measurement process.

First, here is a plot of the direct response with the volume set to 30. The little wiggles on the gain could be due to my measurement setup. The phase isn't particularly interesting, and for the rest of the plots I will only show gain. If someone really wants to see the phase plots I can put them in another post.

direct_v30.png



Here is a plot of both the direct and the SDB responses for three different volume settings:

SDB_response.png


It doesn't look like the volume control has any bearing on the response. When I plot them all relative to the direct responses, the curves all fall on top of each other

SDB_relative_response.png

so there isn't anything 'dynamic' about this setting. I do think it sounds good, but is a little heavy-handed for my setup.

Here are the rest of the EQ settings and tone controls, all with the volume control set to 30

EQ_responses_v30.png


BassToneControl_v30.png


TrebleToneControl_v30.png



For those that are interested, the test equipment I used was a Picoscope 5244B USB oscilloscope with built-in signal generator, driven by the free FRA4Picoscope software. I adjusted the signal generator amplitude for the different runs to keep the power under about 1 Watt since I didn't want to have hot resistors laying on my desk. The measurements were complicated a little since the unit is a filter-less class-D amp with differential outputs (the raw signals are UGLY). So I breadboarded a simple circuit that includes a differential amplifier and some lowpass filtering. This gives a reasonably clean signal that is suitable for a single-ended scope probe. I measured the response of this circuit and adjusted all of the frequency response measurements accordingly. Here is a schematic

testJig.PNG



jason
 
Last edited:
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jasonRF

Member
Joined
May 21, 2021
Messages
6
Likes
21
Location
New England
Looking at the tone control curves and the built-in EQ curves, I had a hunch that EQ settings are simply selections of the bass and treble tone controls. So I did a few more measurements to confirm - the plots are attached. I guess it shouldn't be surprising since this would be an easy way to implement everything, especially since the njw1194 volume control chip has the tone controls built in.

jason

sdb_tone_compare.png



superbass_tone_compare.png



bass_tone_compare.png



rock_tone_compare.png



soft_tone_compare.png



clear_tone_compare.png
 
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