The “CYA Version,” below. The “KISS version” (for direct coupled BJT amps) is forthcoming, but I want to lock in the bootstrap network first.
220n is the largest value for those positions that allows either 25V PPS (ECHU-X) or 25V C0G (GRM), affordably.
Note the shortlist of duals it should work with, covering a range of price points, eins, and 1/fs. Feedback attenuator values take advantage of the 1656’s noise characteristics if chosen. 17.7mA seems like easy driving for all, into 600 ohms. Again, no DC protection drawn at the output.
1. Thor, did I get your amp architecture description right?
2. (a) Any potential issues with using such a high value - 6M8 - for gate bias, and (b) I had previously put in X7R for the sense caps at the output because we’re not listening to the result, but is it smart to use C0G there just because we want the values to remain accurate under full rail bias?
3. (a) Does the LPF created by the 1K/10p at the gates effectively address note 2, subnote 2 in the quote of post #38, (b) is that even a necessary LPF with Mosfets rather than the original architecture from post #1, and (c) is a gate cap to ground not the best way to accomplish this?
4. How’s 47u for 600 ohm loads here - more needed, or less, or just right? I’ve never really dialed in calcs for that cap position, but I am aware that it relates to rail voltage, possible output level, transient speed, and of course load.
5. Shall we look at potential failure modes now? One dual supply starts up before the other, one side of one supply fails, various latchup concerns (addressed I think!), anything else that comes to mind that should be addressed?
6. If an OPA1656 is chosen and the circuit output is shorted to ground, what is the source-drain current on each side of the complementary pair? That Diodes part with max 1V threshold should be considered 200mA maximum, but there are 400-500mA parts with higher Vth and similar capacitances available.