The simplest class A power amplifier on the planet?

The Pleiades 1 (one) transistor emitter follower.


At your risk. Take all safety precautions including a fuse in series with a battery, protecting wars against high Sound presure levels etc.


Attention: There is a mistake in this post. The signal input ground is not connected to battery minus but to emitter. So the circuit may not be an emmiter follower in the ordinary sense. Speaker output is taken from emmiter. In fact when music signal was connected to battery minus instead of emmiter sound from speaker dramatically decreased. See later additions.


Why was it not thought of 40 years ago? Perhaps not being ready.


The idea came today by looking for a long time, calmly, not in a rush the schematic of the JVC Nivico 70's radio. 2 complimentary emmited follwers driving the 3.2Ω speaker.


So why not just one transistor operating in class A (electrons flowing all the time)?


The Pleiades 2N3055 one transistor power amplifier was modified in a few seconds. Alligator cable clips disconnected the 4Ω speaker from the collector and connected it directly to the emitter.


Bingo.


Loud sound, no distortion. Great treble. Efficiency.


Oh my God.


Just one 12V battery in series with a fuse for safety, a 10KΩ biasing resistor from collector to base. Battery plus at collector. Speaker terminal connected to emitter. The other speaker terminal to battery minus. Music connected from a CD Walkman line out through a series resistor to transistor base.


That's all folks.


Signal path:


Fame soundtrack CD - Sony Walkman line out mono bridged, 150Ω Zout? - Pleiades R,C filter in parallel for cuting some treble eg (40Ω,2.2μF) - Pleiades 2N3055 emitter follower - linoleum Pleiades Auratone 5C type cube monitoring speaker with Tesla 5 inch 4Ω drive unit - reverberant room - listeners' brain


It sounds running like a transient Ferrari.


Later addition. Just while waking up in the morning it was realized that the ground from CD player connection had been accidentally left to emitter. So the circuit although output is taken from emmiter may be the same circuit as before, ie collector follower but bias resistor from battery plus to bas instead of from collector to base. So there is no signal negative feedback. More investigation needed.


Later addition: With this circuit voltage across 4Ω speaker is 1.2V. Reconnecting to collector follower voltage is 1.2V and 1.4V if bias resistor is connected to Vb. so the emitter follower circuit does not behave as amcollector follower with base restore connected from Vb to base. And it sounds more clear and loud that the other 2 (collector follower circuits).