Share what you love or don't love about the Dynaco 400 and whether you prefer or don't prefer the Leach Super Amp
Leach = EF3, Dyna = EF2 with TIP drivers. Sometimes one can go too cheap and the results speak for themselves.
One of the driver boards was fried in mine. The output transistors in that side measured poorly (but weren’t actually blown/shorted). I don‘t know about causality there. I gutted it, replaced the big caps, drilled the heatsink for four more outputs. Put in a standard 3X parallel MJ15024/5 output stage. Built some new driver boards with more oomph (EF3, and gobs of open loop gain). With that heat sink, it would run up to 3 pairs of speakers w/o issue. With four it would start slamming the SOA protection.
Very good insightful feedback. Can we salvage the amplifier with minor improvements without completely replacing it?
Per post #2, 6 mhz Ft drivers (TIP31c/32c) sounded bad in my ST120. Dull highs on cymbal, bells, top octave piano. The original surviving 50 mhz drivers in the ST120 were fine. I believe the later nomenclature of those in EBC are 2n5320/5322. If you can't find those, 30 mhz Ft MJE15028/29 sound good on my AX6 stuffed in the ST120. Install heatsinks, 2 pairs outputs on TO5 is quite a load. I did on the MJE15028/29 too even though my unit only has one pair outputs. Check for ultrasonic oscillation when installing faster parts.
MJE15032/15033. Easy-peasy painless.
Convert to triple EF by adding a pair of modern high speed predrivers (TO-126). Then replace the slave transistor bias resistor stack with 10x the value (and ditch the carbon comps). Add a speed up network to the main predriver pair (200 ohm between emitters, and small bypass cap). Add a speed up network to the slave predriver pair as well (this will actually prevent switch off entirely). There is room on the PCB to do this. This is helpful even if you keep the TIP41/42.
Heres how the simulation holds up without much alteration, seems this amp didnt want to be altered in the first place, thats just how it was
But its clear so far in the feedback that it left several with a bad taste in the mouth, were there any wins?