F4 Beast Builders

[Zen Mod]

as it seems to me , that article is one big mishmash

few good pieces , rest fifi fog

in best case - poor transcribe of PL boy'z words

 

[Zen Mod]

.

 

[Nelson Pass]

Yes I was thinking also many times about this and came to the conclusion that it was possibly not well expressed......

Mr. Pass did you write this?

It is an error by someone else.

 

[generg]

Many thanks!

 

[Nelson Pass]

I have checked, and I cannot find any documents from us that give that
description. I did find the XA25 referred to as a "VFET" amp in a magazine...

 

[generg]

That is really worth a laughter and there was so much smoke and fog coming out of our brains what the master wants to say .....😀😀😀

 

[Zen Mod]

well , if yo're interested , I can Photoshop few ( in fact , odd number of them , even better) VT4C on top of it

 

[generg]

Pleaaaase do it, so I get to know what VT4C is...... :--))

 

[Nelson Pass]

What puzzles me is the word "gain" in "stabilizing gain and bias". I do not understand what is being stabilized or possible mechanisms to perform the stabilization.

The circuitry is push-pull complementary. If you build such a thing with no
degeneration, you contend with high variable open loop gain and bias
figures. These should be stabilized.

You can imagine it as you like, but you can assume it's fairly simple.

 

[Zen Mod]

.......what VT4C is...... :--))

perfect for Photoshoppping

 

[generg]

yeah, valve heads!

😀😀😀

 

[lhquam]

The circuitry is push-pull complementary. If you build such a thing with no
degeneration, you contend with high variable open loop gain and bias
figures. These should be stabilized.

You can imagine it as you like, but you can assume it's fairly simple.

A conceptually simple approach might be 1 Farad cap across a 0.2R degeneration resistor, but that would be impractical. Or would it? AVX SCMR22C155MSBA0 is 1.5F, 5V, ESR=9mOhms and has a relatively small 16mm x 24mm radial package.

 

[generg]

Because I still cannot really grab the phase margin problem I want to warn people seeing or even building F4 beasts similar to the circuits I posted that they could be unstable.
On the other side all builds I did showed never any oscillation tendency.

So I relax now a bit......:--))

 

[lhquam]

Because I still cannot really grab the phase margin problem I want to warn people seeing or even building F4 beasts similar to the circuits I posted that they could be unstable.
On the other side all builds I did showed never any oscillation tendency.

So I relax now a bit......:--))

Yes, I do not know if low values phase and gain margin are a problem when the OLG is relatively low. Perhaps Nelson's setting of the -3dB frequency well below the frequencies where there might be an oscillation addresses the issue.

 

[2 picoDumbs]

I have no issues with any of this, but I'm evil so I'm enjoying watching you blokes suffer in your jocks.
Hahaha

 

[Zen Mod]

An externally hosted image should be here but it was not working when we last tested it.

 

[2 picoDumbs]

Hahaha

 

[lhquam]

I have no issues with any of this, but I'm evil so I'm enjoying watching you blokes suffer in your jocks.
Hahaha

Perhaps you can educate us poor blokes with either facts or opinions. Perhaps point us at some relevant theory.

 

[2 picoDumbs]

You already have the knowledge, you just need to persist.
I don't want to rob you blokes of a nice long suffering learning process.
Hahaha

Here is my tip. Think like a cave man.

 

[lhquam]

Fair enough. Yes, the fun is in the hunt and eating the kill. Sometimes one is confronted with a highly elusive, but delicious beast.