Hmmmm... Is the Q4 and Q9 really necessary? I think that the IRF610/9610 has very low input capacitance, and the VAS can drive them easily, especially with the 47kohm resistors...
sajti
sajti
Upupa Epops said:
I understand it, but I have two problems with it:
1, Due the low internal capacitors of the 610/9610, there is no heavy load on the VAS. I checked the most interesting Cgd, which is 15pF for the 610, and for the 9610 too. This means 30pF, which results 236kHz pole between the stages. I think it's fast enough.
2, The emitter followers can oscillate with pure capacitive loads. And the MOSFETs are pure capacitors, if You see them from the input. I found this oscillation in some amplifiers I made.
sajti
To sajti : By my opinion 236 kHz is not enough ( 😎 ). Oscilation by capacitive load you can cut by small value serial resistor, connected in gate ( same as by output fets ).
Ok, if You need higher pole, the followers will help. In my amplifier I use higher current VAS (not folded cascade).
sajti
sajti
Upupa Epops said:
I made ampifier with 80mA bias for VAS, to drive 4pairs of IRFP240/9240. It gives 150W/8ohms, and 500W/2ohms...
sajti
sajti, did you post your amlifier schematic at forum already? can you give me the link to it? Or post here if no, is it possible? Let's share experience.
there in my first schematic variant, VAS current is about 20mA (THD at high frequency depends on it, as measurement shows); in second variant it is much lower, about 1.5mA, and buffer used there.
there in my first schematic variant, VAS current is about 20mA (THD at high frequency depends on it, as measurement shows); in second variant it is much lower, about 1.5mA, and buffer used there.
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