Two Stage Amplifier with Mosfet in class A

[diegomj1973]

Hi:

Here is my new design of a two stage amplifier with output mosfet run in class A. Output power is 4,8 W into 12 ohms for input of 2 V RMS. Máx Output power is 30 W into 8 ohms. Z input is 5k9 aprox.
In the attached file are the curves of total distortion vs. frecuency into 6, 8 and 12 ohms and for input of 0,001 V until 5 V RMS.
Sorry for my english!

[diegomj1973]

In my real life project, i´d put stopper resistors with every IRF150N in the schematic: maybe around 100 to 390 ohms.

The sound with my monitors is wonderful!.

Thanks

[padamiecki]

Originally Posted by diegomj1973

Hi:Here is my new design of a two stage amplifier with output mosfet run in class A.

Hi, what is a voltage source 21,7V to the gate of cascoded IRF150? How did you make this?

[diegomj1973]

I didn´t put the cascode voltaje made with one fix resistor + potentiometer + zener + diode in series between negative rail and ground, only for a bit clear schematic.

The power supply is made with 4 transformers: 4 units x 220 V/24 V/240 VA (two for channel). Total of 960 VA for 30 W + 30 W RMS aprox máx in class A.

28200 uF per rail and per channel. Total of 112800 uF.

4 bridges diodes of 15A.

PSRR is around 93,7 dB.

Any sugestion?

[diegomj1973]

Normally, i run the amp at 4,8 W + 4,8 W RMS into 12 ohms with a greater dynamic range than 8 ohms.

[Bigun]

Very nice circuit - your output stage is very close to something I am considering to use with tube driver, except I was not (until now) thinking of using the Aleph current source that you have employed. The Aleph is very well thought of, not surprised you find it sounds so good.

What is the purpose of the capacitor between emitters of the LTP input pair ?

[diegomj1973]

Hi Bigun:

The objective of this capacitor is to help lower the distortions mainly to the low frequency side.

It's something I checked in my many simulations.

Thanks

[homemodder]

Shouldnt you be more concerned about the high frequency distortion. Try a inductor of around 7 to 10 uH.

[AndrewT]

Can a bc560 drive the gate of an irf150? How much does cascoding help?

[Bonsai]

That capacitor connected across the emitters forms a low impedance at high frequency and raises the gain of the diff pair. This may get you Lowe distortion, but you will have then probably have to deal with reduced stability margins and possible TIM. I'd leave it out - its always better to trade a bit of distortion for stability in my view.