Apex A40 fundamental improvement. (Sandy)

[SandyTodorov1]

I did not make boards for this improved version of A40.
I just wanted to show you how this CFA amp can be made significantly better than the original without changing its basic idea (CFA)

I prefer VFA amplifiers for audio they are significantly better.

 

[SandyTodorov1]

These are simulations with active load and speaker, at different output powers.

 

[Silvestre de moraes]

Sandy! Pessoas como você estão se tornando uma espécie rara no mundo. Obrigado por compartilhar suas melhorias, irei montar e postar sua obra de arte aqui.

 

[darek549]

Hi,
Thank you for so many responses. Initially I was thinking of building an A40 basic without the revisions. I liked the version in post #550 because the 10 ohm resistors in the rails are replaced with a multiplier ( if I recognised correctly ) . This is the version I was asking about but the Itco version also looks interesting.
In summary I would like to build either this version from post #550 or the Itco from #560 - if I understand correctly this is the revised version?

Generally I'll opt to build the version for which tiles or gerbers are available.

Sandy your P FET. looks interesting, I like amplifiers with a fet input.
Thanks for sharing the project on the forum.

 

[Joel Wesseling]

After making the original Apex and that one from post 550 I decide to build one of the Sandy versions of the CFA PA.
Here is the result:

How does it compare subjectively?

Please, do you have gerbers to share? Thank You!

 

[SandyTodorov1]

This is a more compact version of the same circuit (VFA) for lower power with 4 TO220 final transistors.

 

[SandyTodorov1]

And the designed P FET 1-1-3.4 V3.2 (Altium) from post #561

 

[dadod]

I prefer VFA amplifiers for audio they are significantly better.

This is just your opinion, both type could be equally good or bad, depends on designer capability.

 

[SandyTodorov1]

Of course a mediocre designer can make a worse than good CFA for an audio VFA amplifier.

But you cannot with the same number of transistors make a CFA amplifier better for audio than a VFA one.

And in order not to talk nonsense, propose your personal project of a CFA amplifier, and I will try to construct a VFA with better parameters and with the same number of transistors.
Or show a CFA amplifier with better parameters than the VFA shown here above, with approximately the same number of elements.

The only advantage of CFA amplifiers is the high rate of rise of the voltage, but this is only the case for strong signals.
But with VFA amplifiers, such (enough for audio) gain rates can also be achieved, and even for weak signals and not only for high-amplitude ones.

At the same time, the other important parameters: noise, THD, PSRR at VFA amplifiers are significantly better.

 

[dadod]

Ok here are my different designed and built CFA and VFA.
https://www.diyaudio.com/community/threads/200w-mosfet-cfa-amp.243481/
https://www.diyaudio.com/community/threads/200w-class-a-amp-with-high-efficency.304722/
https://www.diyaudio.com/community/threads/lateral-cfa-120w-bsa.338814/
https://www.diyaudio.com/community/threads/unique-cfa-120-230w-amp.253039/
https://www.diyaudio.com/community/threads/100w-cfa-mosfet-with-balanced-input.289933/
and VFA https://www.diyaudio.com/community/threads/thermaltrak-tmc-amp.182554/
Some of those threads are quite long.
Damir

 

[printnik]

Greetings. Please take a look at this.
https://www.diyaudio.com/community/...-input-stage-active-load.390084/#post-7119398
The amplifier turned out with very low distortion. Nice clipping. Little delay. Protection.

I used the scheme from here
https://www.diyaudio.com/community/threads/200w-mosfet-cfa-amp.243481/post-4857977

 

[hwckent]

Hello, Sandy! I would like to try build one !! Do you share layout or shall ? #410

 

[SandyTodorov1]

VFA P FET 1-1-3.4 V3.3
I recommend this fully finished project.
Its data is not worse than the one you are referring to, but it is easier to implement because it does not have complex positive feedback links.