I'm not certain what you mean by truly stable. Yes, it is stable in the usual sense- even if the phase margin drops and there's significant peaking and overshoot in the >1MHz region.
I tested all of the loads 15, 30 and 200-300 ohms with zero and 1000pF, and sometimes in between values as those are the most likely to show the worst phase margin.
I was unable to make the design be unstable (i.e. break into oscillation) either in simulation, using TIs models, or on the bench, but there are combinations of load Rs and Cs that cause the margin to drop.
I have attached simulation results for the 15ohm/1nf and 300 ohm/1nf cases.
If the 10k bypass 1nF is removed then the composite amp IS unstable, both in simulation and on the bench- there is visible oscillation using a 70MHz scope.
I tested all of the loads 15, 30 and 200-300 ohms with zero and 1000pF, and sometimes in between values as those are the most likely to show the worst phase margin.
I was unable to make the design be unstable (i.e. break into oscillation) either in simulation, using TIs models, or on the bench, but there are combinations of load Rs and Cs that cause the margin to drop.
I have attached simulation results for the 15ohm/1nf and 300 ohm/1nf cases.
If the 10k bypass 1nF is removed then the composite amp IS unstable, both in simulation and on the bench- there is visible oscillation using a 70MHz scope.
Attachments
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I have not tried it with Jan's silent switcher. I do have one in my autoranger unit that I use for testing but have not felt the need for it elsewhere.
The PSR of the composite amp is extremely high, especially at 60Hz, and it is very quiet in use, even with a less than pristine +/-15v 0.7A /side SMPS or a pair of 15v 1A wall warts wired in series.
The PSR of the composite amp is extremely high, especially at 60Hz, and it is very quiet in use, even with a less than pristine +/-15v 0.7A /side SMPS or a pair of 15v 1A wall warts wired in series.
Hum is sorted out and I like what I hear through a 18R headphone. Reasons for using the silent switcher were good old "I had it in a drawer" and the idea to build a compact package that I can maybe velcro to my DAC and feed from one of the smps it uses. May instead of velcro I use a Powercon or XLR connector to power the headphone amp and hold it in place.
