Yeah, the 10K/200K improved many schemes (but not enough) until I lowered the VAS degeneration -- then 2K4/47K works better.
500R gate stopper on the VAS still oscillates, although if I go back to the BJT CCS then it's the stuttering oscillation instead of the constant fuzz or motorboating.
500R gate stopper on the VAS still oscillates, although if I go back to the BJT CCS then it's the stuttering oscillation instead of the constant fuzz or motorboating.
Slower cascodes (2N5087) make the gain curve nice and smooth (particularly with 10K/200K dividers), but the &*$*@ still oscillates.
No cascodes at all oscillates much later (making it through 4ms of nice clean signal).
Is there anything wrong with the LTP phase comp? It does seem to work....
No cascodes at all oscillates much later (making it through 4ms of nice clean signal).
Is there anything wrong with the LTP phase comp? It does seem to work....
None of the suggestions between #772 and #788 made you happy before
... but ...
maybe you are thinking, perhaps I ought try them all again using the new analysis procedure?
My engineering tech used to say "even a BLIND pig finds an acorn, from time to time" and perhaps he meant, a random shot in the dark occasionally hits something worthwhile, if you make enough attempts.
... but ...
maybe you are thinking, perhaps I ought try them all again using the new analysis procedure?
My engineering tech used to say "even a BLIND pig finds an acorn, from time to time" and perhaps he meant, a random shot in the dark occasionally hits something worthwhile, if you make enough attempts.
Armed with my new tools I've massaged the compensation on all three front ends. Margins are up across the board, as are slew rates, and frequency response in the CFA case.
The Hitachi front end is really starting to strut its stuff driving laterals:
-3dB FR DC to 250KHz
160 V/usec slew rate
0.008% 20kTHD @ 100 watts
Remember when it was called BuzzBomb? It now has 70º phase margin and 15dB gain margin.
The Hitachi front end is really starting to strut its stuff driving laterals:
-3dB FR DC to 250KHz
160 V/usec slew rate
0.008% 20kTHD @ 100 watts
Remember when it was called BuzzBomb? It now has 70º phase margin and 15dB gain margin.
You'd need another current limiting strategy; even with 30V rails the flying catch diodes either clip too aggressively or don't keep the FETs from smoking with a short.
Ignoring that, I set the rails at 36V, dropped the drivers, flying catch diodes, and source resistors, reduced the currents in both differentials and set the bias at 110mA for 50W class A/B. It seems to perform admirably:
Ignoring that, I set the rails at 36V, dropped the drivers, flying catch diodes, and source resistors, reduced the currents in both differentials and set the bias at 110mA for 50W class A/B. It seems to perform admirably:
I made a change yesterday to better-correct some square-wave overshoot, so they're "settling" again. (I like to have them make it through a week or so with no changes before I declare them "done".)
After that the plan is to order a pair of the KISS boards first to test the regulators since they're shared between all the front-end boards.
After that the plan is to order a pair of the KISS boards first to test the regulators since they're shared between all the front-end boards.