My best discrete preamp with 3 transistors

[EdGr]

THD compare:
0.00182% opamp version
0.00008% my best

Distortion is caused by the non-linear relationship between voltage and current. Your three-transistor circuit is doing well because the current remains nearly constant. The op-amp version can do well with two more transistors for current-source biasing.
Ed

 

[No ideas]

If we stick to 3 transistors and 12V supply,
here is the classical opamp version.

THD compare:
0.00182% opamp version
0.00008% my best

View attachment 1450054

Whats the max output voltage?

 

[lineup]

@No ideas
For the opamp version with load 4.7k Ohm load and at THD 1.0%
the max output is 3.48Vrms which is 4.86Vpeak.

 

[lineup]

Distortion is caused by the non-linear relationship between voltage and current. Your three-transistor circuit is doing well because the current remains nearly constant. The op-amp version can do well with two more transistors for current-source biasing.
Ed

Thanks for your tip.
But the idea of this thread is 3 transistors.
With higher number of transistors it is possible to get even lower THD. I am almost sure.
I want to see 3 transistor circuits.

 

[lineup]

Here is an improved version of the original circuit.
Uses a BC337-40 output transistor.
Now output is at 6.00V and this gives a max output 5.8Vpeak at THD 0.1%.
The THD at 1Vrms out is now slightly higher 0.00011%.

 

[Joel Wesseling]

This is the circuit in post 25 above.
0.84Vrms in and 4Vrms out just shy of clipping
20khz square wave

 

[Mark Tillotson]

It is a rather noisy with 28nV/√Hz from the input resistor, I'm sure its possible to do a lot better from a noise perspective. Have you compared the THD+N to the THD?

 

[Joel Wesseling]

I would love to have the ability to measure THD - one more audio related thing I need to figure out, at the lowest cost that's available

 

[stv]

measure THD

Have a look: https://www.diyaudio.com/community/threads/how-to-distortion-measurements-with-rew.338511/