F5 power amplifier

[KSTR]

Hi Patrick,

I completly agree to your definition of "X", indeed one doesn't restrict oneself to inverting gain stages. It's all about wether or not the error signal of one half is feed into the other with the correct polarity and level.

I simulated all three variants, the simple Bridge (the nodes in question grounded), Zinsula (nodes connected directly) and yours (nodes cross-connected only). But I couldn't find any significant change in distortion, both looking at the single-ended outputs (ref'd to GND) and the differential ouput, the third harmonic always dominated THD with its stable value. Therefore I guess that the error signal is not cross-fed in the way needed to get the cancellation in the diffential output.

Quoting the Master, an indicator if "X" is at work should be:

Original by Nelson Pass
By actual measurement, this circuit does very little to reduce the
distortion and noise of each half. Distortion curves before and after the application of Su-Sy are nearly identical. The distortion curves for the circuit shown in the patent cover sheet are: (A) the intrinsic distortion of each half of the real example circuit, (B) the distortion of the differential output lowered due to the intrinsic matching between the circuits, (C) the distortion of each half with Su-Sy applied, and (D) the differential distortion with Su-Sy applied.

This does not seem to be case in either of the floating node configs. We have to think harder

- Klaus

[EUVL]

Test Setup :

[EUVL]

Measurements :

There is a very small peak of +0.5dB at about 600kHz, but since it was not proper power supply and wiring, I did not bother and left it as is.

Full complements to the original circuit creator that it works first time without a hitch, even with all the changes from the original schematics.




Patrick

[Manu]

Slightly OT :
Micromega? Witch one?
Any comment on sound?
Manu

[EUVL]

> Micromega? Witch one?
>Any comment on sound?

As stated above "Stage 1".
11 years old, but too good to throw away.

Analogue section completely modified with discrete filter / amplifier stage with balanced output.
Sound is OK, but not my reference.


Patrick

[KSTR]

Patrick,

pretty cool job you did, congratulations! And thumbs up to Nelson of course, there aren't many simple 4-Transistor amps around that seem to be as good and as robust as this one.

BTW, did you run tests with cap loads yet?. I'd be very interessted to see how the step response looks like...

- Klaus

[EUVL]

Load is reactive (Stereophile dummy speaker).
I posted the link and photos before on the Solid State Forum.
Please search.

And no, I do not test with pure capacitive load.
It is not realistic, and for me only of academic interests.


Patrick

[steenoe]

Originally posted by EUVL
[B

Here are a few photos. [/B]

Darn man, that is simply too neat, to be true.....
Lovely stuff..

[steenoe]

Originally posted by EUVL
Fully assembled :

Thats even better; I think I see 4 power J-fets in there?? Wrong pic?

[Variac]

balanced