A protection diode in series with the base or in anti-parallel with the emitter junction is a customary solution to that problem. A better protection is found in the Bolshevik amp @ RCL-electro.ru (the linked forum is Russian-speaking):
Continuation of the amp presented in post #1737:
https://www.diyaudio.com/community/threads/unusual-amp-from-1987.357369/post-7515758
with logic level NMOS output devices.
The amp/chassis is finished and playing music.
Great sound, no problems with the build, no surprises. Little (TO-220) HUF75842 transistors (2 pairs per channel) seem to be
perfect choice for a small (25W) amp. This is also 1st time for me to use 1inch black nylon slab for a chassis, with thinner Alu
top. Easier and faster to machine than metal.
https://www.diyaudio.com/community/threads/unusual-amp-from-1987.357369/post-7515758
with logic level NMOS output devices.
The amp/chassis is finished and playing music.
Great sound, no problems with the build, no surprises. Little (TO-220) HUF75842 transistors (2 pairs per channel) seem to be
perfect choice for a small (25W) amp. This is also 1st time for me to use 1inch black nylon slab for a chassis, with thinner Alu
top. Easier and faster to machine than metal.
Attachments
Continuation of the Hafler P7000 inspired amp from post 1709
https://www.diyaudio.com/community/threads/unusual-amp-from-1987.357369/post-7492293
I had an idea to 'improve' it slightly - see attached schematic, by using Hawksford cascode for VAS.
I gave it a try, and while in the sim it was showing faster rise times, but the reality didn't follow the sim.
From the initial tests, it behaves exactly the same a first amp; the only possible improvement I see is its stability.
I experimented with different transistors, feedback RC values, and this amp shows rock solid stability in all conditions.
https://www.diyaudio.com/community/threads/unusual-amp-from-1987.357369/post-7492293
I had an idea to 'improve' it slightly - see attached schematic, by using Hawksford cascode for VAS.
I gave it a try, and while in the sim it was showing faster rise times, but the reality didn't follow the sim.
From the initial tests, it behaves exactly the same a first amp; the only possible improvement I see is its stability.
I experimented with different transistors, feedback RC values, and this amp shows rock solid stability in all conditions.
Attachments
I'm not planning to design a PCB dedicated to this amp. I only have small daughter board for the input/Vas circuitry, that is plugged into my
'amp platform' with Output Stage. This whole concept doesn't really make sense to someone who wants to build just 1 amp.
If you want to build it as a standalone amp, you will need to design a PCB by yourself, perhaps using examples of similar boards built
for previous amps in this thread.
Daughter board of the 1st Hafler amp:
Of course I can share PCB design for it.
'amp platform' with Output Stage. This whole concept doesn't really make sense to someone who wants to build just 1 amp.
If you want to build it as a standalone amp, you will need to design a PCB by yourself, perhaps using examples of similar boards built
for previous amps in this thread.
Daughter board of the 1st Hafler amp:
Of course I can share PCB design for it.
