LM3886F, discreet with MOSFET outputs

[solderdude]

TI called amplifiers with such output stage ,Overture series. Overture is a trademark. Maybe I call, Fet Overture or F.Overture.
Overture, in French means opening, and Fête, pronounced FET, means festive. I can call it Ouverture en FET.

Anything is better than LM3886F.

QCMFA ?
(Quasi Complementary MosFet Amp)

Below another QCMFA design.

and another one (no bootstrap)

and N. Pass design but with FET's :

or this one

They are all just variations of your basic quasi complementary output stage amplifier design.

 

[Hayk]

What is complimentary in it?

 

[solderdude]

Quasi complementary ... the output stage.
Q5 turns the (not complementary) output devices in quasi- (or semi)-complementary output devices.

Just like Q4 in the upper schematic, U4 in the 2nd circuit, Q5 in the Pass circuit and Q8 in the bottom circuit.

The rest of the circuits is all just a slightly different design all based on the same principle... just different executions.
This makes all of these circuits 'unique' (as in no direct copies) and all of them will perform differently as well.

 

[Hayk]

The amp is now called "Overture en Fêt".
I still have lot of space to implement other features and a detachable speaker protection by SSR.

 

[Hayk]

I will show you how my distortion measurement is precise.
I showed with this amp, the Overture en Fêt, it measures 0.00009%.
I did the same with M67b which measured by Tina has 0.0007%.
I again subtract the input from the output and get 7.4% for 1.8mv with output 20v.
If 7.4 x1.8/20000=0.00066% THD. The shape of the residual is patatoidal, rich with 3rd harmonic

 

[solderdude]

0.0007% (if practice is the same as this also depends on the PCB layout) then any distortion is -100dB so well below possible audible levels (-70dB) so whether or not the distortion is even or odd dominant it is all inconsequential.
The audiophiles seem to prefer asymmetrical distortion (2nd harm) over symmetrical (3rd harmonic)... go figure.

Curious how the actual amp will measure under actual loads.

 

[Hayk]

Indeed, the PCB layout is important factor for the distortion. The main cause is the class B character that results half way rectified currents. These currents emit electromagnetic waves that can be captured by the input stage.
The remedy was proposed by Edward Cherry in late 80's, to add 470uf bypassing capacitors on the rails and use a clean ground for the inputs.
An amplifier can measure very low distortion but can sound dirty by complex music, it is the case for "Wolverine" amp that aligns 4 zeros in THD+N on DIYaudio.
One can see my technique in the PCB pics bellow. The rectified ground currents of the capacitors on the bottom side are connected to the left of the ground power supply connector, whereas the speaker receives the ground from the right side. The supply tracks isolate the capacitors grounds. The output track is in this isolated region to cancel the radiation by the supply tracks. The tracks between the capacitors and the transistors are the big problems as they have high frequency rectified currents. My solution is to apply a magnetic steel wire upon these tracks and it can be done by soldering acoustic guitar brass wound strings or capacitor leads, this why they are on the top side.
There is also the feedback path, it is on the bottom side to be shielded by the ground and opposite to the load side to be away from sensing output currents.
You also noticed that I don't use air inductor for the Thiel to avoid electromagnetic radiation and use wide flat wires. This inductor of 2.2uh falls 10% at 20A, but a second one can be installed upon it on parallel, it costs $0.25. The high current resistors should be non inductive, they don't emit radiation.
The most difficult music to reproduce by class B amps is the Dies Irae of Verdi.

 

[Hayk]

I got banned from engineering discussions on this website, so this thread is discontinued.

 

[Power Pop 23]

I got banned from engineering discussions on this website, so this thread is discontinued.

Per Amir,

4 transistor class A very low THD 40w amp.

I have designed long ago, a type of SRPP MOSFET output amplifier, that has ended after several models to https://www.eevblog.com/forum/projects/4-transistor-40w-class-a-0-0004-thd-amplifier/ How it works. The Q1,Q2,Q4 don't need explanation. Q3 is biased by a voltage across 470uf capacitor Vc...

www.audiosciencereview.com