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Thats a nice looking design, keep forgetting about that site. Bear in mind Piero that a power amplifier of this kind of output is not easy to build and construction of the power supply is potentially hazardous. An oscilloscope is pretty essential I would think too.
If you were to research back through the original McGraw-Hill Electronics professional magazine about the year 1971 or 1972, you'll find a power amp design that I've never seen anywhere else. Rather than a complementary-symmetry output, it used a pair of 2N3055 to yank the speakers around. It developed the driving signal by placing a pair of 10 ohm resistors in series with the power supply leads of a 741 op amp (king of the world op amp in 1972), ground the output through a load resistor and taking the IR signal developed by the supply leads to drive the remaining circuitry. It was a direct-coupled, 100W RMS amp and the danged thing was good from DC to 200KHz, only because there was a snubber in the output line or it would have gone even higher than that.
When I was stationed at the USNSGA at Sabana Seca, Puerto Rico, CTMCS Malcolm Empey built one and we tested it out in the maintenance shop with a function generator, the amp driving a 5W speaker. Watching a speaker cone "breathe" when driven by a 2 Hz signal was amazing back then and when we got done, the speaker's yoke was too hot to touch and the voice coil was wrecked. I need to research that design out. I have the skem, but I'm not sure if there wasn't a mistake in the hand transposition, because my attempt at cloning back in 1974 failed miserably and I've never gone back to the project for some reason. I need to as it would still be quite fun in this day and age of Class D amps.
Hi Dean,
This old project is similar to what you have seen. It uses the supply current of the ICs to drive its ouput transistors, and the ICs don't need to operate at the full supply voltage. https://www.electronics-lab.com/projects/audio/013/index.html
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