Hello to all! In need some advice regarding this amp , is it valid? Needs a slight change ? Over all to make it a good working amp, what power supply will it need ? Maybe a protect / input sensitivity selector . My old amp is dead And its time for a new one ! Any help is apricietad . Cheers!
Project 117
Project 117
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The schemat in question is available here: Project 117
Your first problem is going to be finding suitable transistors that can withstand 270V rail-to-rail swing. The output transistors indicated on Rod's sch break down at 250V so clearly unsuitable. The mighty MJL4281/MJL4302 break down at 350V so on the face of it they might work, but the SOA at these operating voltages is terrible so realistically I think you have two options:
1. Cascode the outputs to reduce the voltage across each transistor (have a look at the Leach SuperAmp for inspiration) or
2. Use Power MOSFET outputs instead, which are going to better withstand those voltages.
The benefit of Option 2 is that you can possibly dispense with the need for pre-drivers. There is no way this EF3 output stage is going to be stable as drawn. Good decoupling of the driver and pre-driver collectors is mandatory for good stability as is judicious use of base stoppers.
Good luck.
Your first problem is going to be finding suitable transistors that can withstand 270V rail-to-rail swing. The output transistors indicated on Rod's sch break down at 250V so clearly unsuitable. The mighty MJL4281/MJL4302 break down at 350V so on the face of it they might work, but the SOA at these operating voltages is terrible so realistically I think you have two options:
1. Cascode the outputs to reduce the voltage across each transistor (have a look at the Leach SuperAmp for inspiration) or
2. Use Power MOSFET outputs instead, which are going to better withstand those voltages.
The benefit of Option 2 is that you can possibly dispense with the need for pre-drivers. There is no way this EF3 output stage is going to be stable as drawn. Good decoupling of the driver and pre-driver collectors is mandatory for good stability as is judicious use of base stoppers.
Good luck.
I doubt you "can" if you're asking such basic questions. Project 117 is intended to be a framework only, if you need something more canned look at Apexaudio's class H amplifier threads. You will find complete schematics, pcb layouts, and all the protection circuits and stuff you need to make it safe. At those voltages class H makes a lot more sense, and is about as easy to implement as the S-Leach cascode.
Every year or two somebody new brings up 117, and it gets shot down in about 15 minutes, often with the thread getting closed by moderators.
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