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