I mounted this design on a breadboard and it worked, it's just a very basic push pull output but surprisingly it doesn't sound too bad at low volumes.

Can anyone suggest improvements to this design?


I replaced the Q1 and Q2 transistors with bc139/140, Q3 and 4 with BD907,908. I also put two 4.7 Ohm resistors between the push pull collectors.

 

The circuit has an output of only 18W. There are amp ICs that are more powerful and much better.

Connect the output and driver transistors as Sziklai pairs.
Use the good audio opamp (TLE2141) used in the original circuit at Red Circuits.
My modification shows Sziklai pairs:

 

There are amp ICs that are more powerful and much better.

Can you recommend a couple I could experiment with.

Connect the output and driver transistors as Sziklai pairs.

I did that, and changed the resistors to 0.22 Ohm, the reservoir caps to 2200uF and I'm quite happy with the amplifier, it's tremendously clear without having a boomy bass, when I turn it up it doesn't clip like cheap amps usually do.

What software did you use to edit/redraw the schematic?

 

Can you recommend a couple (of amp ICs) I could experiment with?

A few years ago there were 120 amp ICs available made by Philips, ST Micro and National Semi. Then Philips changed the name of their semiconductor division to NXP and stopped making many amp ICs. National also stopped making some.
The National LM1875 produces 20W at low distortion and their LM3875 produces up to 56W and their and LM3886 produces up to 50W at extremely low distortion.
ST Micro have their TDA2030A produces 16W and their TDA2050 produces 25W.

Buy from a proper electronics distributor because there are many counterfeit copies that do not work being sold by crooks.

I'm quite happy with the amplifier, it's tremendously clear without having a boomy bass

An amplifier with a high output impedance causes boomy bass because it does not damp the resonances of a speaker. The very high open-loop gain of your amp (220,000 at low frequencies) and of other good amps produces an extremely low output impedance.

When I turn it up it doesn't clip like cheap amps usually do.

Any amp clips badly when its volume control is turned up too high.

What software did you use to edit/redraw the schematic?

I use Microsoft Paint program to make and modify schematics.