About two Output Stage

[Havenwood]

Hi, what output stage you consider optimal or best for a low power amplifier (<20W)?
Distorsion / Sound / Thermal Estability / Zout / optimal Iq / . . .

figure2 need 2 preset (R30/R31) to set the same Iq on power transistor?

 

[satoru]

The first one, which is rather a standard Darlington configuration. The second one is for low power output and you'll need a lot of changes to adopt it for 20W output.

The first one may oscillate dependent on the choice of output transistors, layout, VAS, characteristics of the speaker and cable connected, etc. So, watch out!

Have fun!

Regards,
Satoru

 

[Steve Dunlap]

The only changes you will make to the second one is to use proper outputs and increase the the current sources. I have seen commercial amps with 100W output using the same basic circuit with more output pairs.