No current source. Q4/5 are hooked to a trimpot. If the wiper ever got dirty/failed - boom !
Since you are running the IRP240/9240 direct , the VAS needs to be run real HOT (12mA+) . better to use TO-126 MJE340/350.
PS - the simple "HH" I posted works well. People are selling these 30-40 YO amps on ebay - and they still work !
OS
Thanks. In a lot of respects that circuit is similar to the Silicon Chip SC480 amp from January 2003. That circuit uses a bipolar output stage based on TIP3055/TIP2955. The input, VAS and Bias stages are nearly the same as your design. So now we know where Leo Simpson (the ol' fella in Australia) got his inspiration from. The Maplin heritage lives on ...
Many years used this topo i see that using lateral MOSFET as output bring the best sounding.
I already tried bipolar + EF2 (2SC4793, 2SC5171, KSC2690A + 2SC2922, 2SC3519A, MJL3281A), Bipolar + EF3 (same EF2 but add KSC3503, 2SC3423 as pre-driver, bipolar driving HEXFRED, medium-power lateral MOSFET driving bipolar (2SK214 + 2SC2922, 2SC3519A, MJL3281A), medium audio vertical MOSFET driving bipolar (2SK2013 + 2SC2922/MJL3281A), bipolar driving lateral MOSFET.
I already tried bipolar + EF2 (2SC4793, 2SC5171, KSC2690A + 2SC2922, 2SC3519A, MJL3281A), Bipolar + EF3 (same EF2 but add KSC3503, 2SC3423 as pre-driver, bipolar driving HEXFRED, medium-power lateral MOSFET driving bipolar (2SK214 + 2SC2922, 2SC3519A, MJL3281A), medium audio vertical MOSFET driving bipolar (2SK2013 + 2SC2922/MJL3281A), bipolar driving lateral MOSFET.
