UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Sony-STR3800L. Output transistors.

orbanp1 · 28th Nov 2022, 7:53 pm

Double checked the spice model of the TIP41, it has an Ft of 4MHz to 6MHz, depending on the Vce voltage.
Checked the Ft of the MJE15032 model too, it has Ft around 30MHz.
Running the simulation with the MJE transistors the phase margin of the amp is only 16 degrees, which is clearly not enough!
Applying the 10pF compensating cap the phase margin increases to 73 degrees with the MJE transistors too.
So do use the compensating cap if you use better transistors!
Also, I would make both channels identical.

Regards, Peter

28th Nov 2022, 7:53 pm	#4
orbanp1 Heptode Join Date: Nov 2009 Location: London, Ontario, Canada Posts: 675	Re: Sony-STR3800L. Output transistors. Double checked the spice model of the TIP41, it has an Ft of 4MHz to 6MHz, depending on the Vce voltage. Checked the Ft of the MJE15032 model too, it has Ft around 30MHz. Running the simulation with the MJE transistors the phase margin of the amp is only 16 degrees, which is clearly not enough! Applying the 10pF compensating cap the phase margin increases to 73 degrees with the MJE transistors too. So do use the compensating cap if you use better transistors! Also, I would make both channels identical. Regards, Peter