MEASUREMENTS

Important! The channels on my amp were out of phase. Please check your amp to see if this is the case. I thought the stereo imaging sounded a bit odd. ;-) Most test CD/DVDs have phase test signals. I will post test signals here in future.

Also note that the amp in an inverting amp. Plus in at the input = minus at the speaker terminals.

The switching waveform before filtering looks like the shot on the right. This was measured between ground and the zener diode on the output. The straight line is 0V. No signal at the input. 13VDC battery.

We can see the overshoot and the slight variation in duty cycle. What is most surprising is the 50% duty cycle at idle. The transistors on the other leg switch their duty cycle in opposition. This is how the amp works.

If both sides of the outputs are at 50%, no current flows. If they one or the other changes from 50% there will be an imbalance and current will flow. The switching square wave is filter out and the variation is al that's left. That's what you hear.

This looks like a switching frequency of about 860~900 kHz. On the waveforms page you can see the duty cycle increase with input signal. It's hard to tell if the switching frequency changes.

With my 1st undersized transformer there was obvious clipping at about 2.5-3V at the outputs. That is as measured away from the center line of the scope in AC mode.

The waveform on the right shows severe 1 kHz clipping at a V+ of 13V. It seems that 5V is all you get. In bridged mode that means 10V P-P.

With this heavy clipping the Sonic draws about 1.5 amps.

On "typical" musical content the Sonic draws an average of about 250-300 mA. The more dynamic the music, the less the average draw. Current draw was measured with the musical peaks just clipping. Average power would be around 1 watt/channel.

There is a 50 mV square wave remnant present at the speaker outputs. This seems right, ad the stock low-pass filter calculates to a -3 dB point of 73 kHz. .So if we take 12V as the switching voltage that 50mV square wave is approx. 47 dB down.

Maybe all the ultrasound in the output doesn't hurt anything. Though 55mV equals a tiny 0.0004 watts into 8 ohms, it would still give 51 dB at 1M on my speakers IF it were in the audible range. You can imagine that a stock filter in one of he higher power amps would leave a lot of ultrasound in the system. Don't know if it would hurt anything. Most tweeters have a very high impedance at those frequencies. 700-1000 kHz