Perhaps it is to hot - the amplifier simulates like an amp, not an oscillator, has been built and still persists in acting like an amplifier.
The simulation appears to pit the top half of the output stage vs. the bottom half. It looks like the top half wins, as the overall sense of the feedback is negative.So, efforts to equalize the drive between top and bottom output stages won't be productive. There are two things I have done to improve this design. First thing, I have added a negative supplty to the P-channel fet feeding the bottom output stage. I have also cascoded the 2Sk170 input jfet.
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I have done some extra tinkering in PSpice with the original schematic. One of the things investigated was increasing the source resistor for the IRF540 bottom fet, necessitating changes in the resistors feeding the ZVP3306A that drives the bottom mosfet in order to maintain output centering This results in slightly higher THD, but also lower odd-order harmonic content.
I have found that in practice, a small negative supply is necessary at the drain of the ZVP2206A feeding the bottom IRF540 output (M2 in the original schematic). This fixes a drive problem that shows up in actual square wave excitation of the amplifier in practice that does not show up in simulations, and explains a perplexing issue I encountered. I had one Oppo DVD player that would always cause amps with this configuration of triode emulation to blow a fuse or actually blow up. It looks like the Oppo was outputting some sort of HF parasitic on one of its audio channels that would overdrive the amp and cause cross--conduction in the output fets due to sluggish drive. Adding the negative supply fixes that issue. To generate this, supply, I can either use a small homebrew switcher to generate the negative rail from the +24V, or use a std AC toroid and with an extra winding added to generate the minus output.
I have found that in practice, a small negative supply is necessary at the drain of the ZVP2206A feeding the bottom IRF540 output (M2 in the original schematic). This fixes a drive problem that shows up in actual square wave excitation of the amplifier in practice that does not show up in simulations, and explains a perplexing issue I encountered. I had one Oppo DVD player that would always cause amps with this configuration of triode emulation to blow a fuse or actually blow up. It looks like the Oppo was outputting some sort of HF parasitic on one of its audio channels that would overdrive the amp and cause cross--conduction in the output fets due to sluggish drive. Adding the negative supply fixes that issue. To generate this, supply, I can either use a small homebrew switcher to generate the negative rail from the +24V, or use a std AC toroid and with an extra winding added to generate the minus output.
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