Sony VFET Amps

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permaneder

Member
Joined 2009
Jon Lord said:
This is exactly the thing I originally wanted to criticize !

Many statements within this thread alone tell me, that Nelson Pass amplifier designs discussed here in the forum don't care much about nonlinearity of capacitances with associated time constants near or within the audio range. It is also said, that people even tend to like the sound of this ! I could also tell you that many people tend to like the sound of MP3.

If my warning may only be accepted in the Blowtorch thread doesn't mean that it is wrong or esoteric at all !

There are a few very well accepted audio and almonst all general analog designers, who are very careful about, what is classically referred to as "Differential Phase Distortion". This is a very well researched item in analog video for several decades, only the audio guild tends to ignore this and seems to think, that there is a kind of magic sonic barrier below 20kHz, which eliminates all kind of that stuff.

The fact, that loudspeakers are much worse in this respect than amplifiers and these are much worse than a jittery Audio DAC, doesn't mean that their impact is in the very same order, because the nature of the underlying sources is pretty different and gets more unnatural the more closer you get to the DAC.

Unfortunately many of the more recent (published) Nelson Pass amplifier designs shout out loud about this ignorance. And that was the reasoning behind my statement, that the (unpublished) topology of the 40th anniversary V-FET monster may tell us the very same story. And this led me to the provocative claim, that the good old TA-8650 may eat Nelson Pass' V-FET monster for lunch.

What was the impedance driving the V-FETs in this non (overall) feedback amplifier again ? I still don't know.

Why don't we find an opportunity to hear the SONY V-FET monster against a few selected (and refurbished) classic SONY V-FET amps ?

Btw.: Did you all know, that the good old feedback tends to reduce these effects ? Did you all read Bruno Putzeys' article and follow up about the "F word" in Linear Audio ?
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Father McKenzie
Writing the words of a sermon that no-one will hear
No-one comes near
Look at him working
Darning his socks in the night when there's nobody there
What does he care?
 
J

Jon Lord

Member
Joined 2005
You repeat yourself, as I do.

Last Verse:

"Eleanor Rigby died in the church
And was buried along with her name
Nobody came
Father McKenzie wiping the dirt
From his hands as he walks from the grave
No one was saved"

OK, bible closed, end of sermon ... :p
Amen :D
 
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poynt99

Member
Joined 2013
gk7 said:
It's sad that we are now on the level of personal attacks. The topic of nonlinear capitances of FETs (and MOSFets) and how to drive them, etc. would make an interesting and educational discussion, IMHO.
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Agreed. But it seems some people just can't sit by and let a technical discussion proceed if it doesn't agree with them.

I thoroughly enjoy reading both Nelson's and Jon's input, but when other folks interject with cranky, off-topic one-liners, I find it disruptive and offensive to be honest. I only responded in a disparaging manner because I've been hounded by this guy too, and it's getting tired real fast.

Let's keep up the good technical discussion guys. ;)
 
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Jon Lord

Member
Joined 2005
Thank you guys for giving me some support !

I'll prepare some simulations showing, what the impact of gate drive impedance is in an idealized, sample IRF150 based ZEN amplifier, both on amplitude modulation (classic non linear distortion) and level dependent group delay (or DPD).

The ZEN is probably the simplest and worst of them all, so a good candidate for impressive effects but also for quite impressive improvements.

OK ... Let me post this later this week ...
 
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kasey197

Member
Joined 2009
That would be useful..

Lots of hand waving lots of writing not much technical facts so far from Jon.

Non linear input capacitance of fets is pretty old. The fact that single stage zen amps evolved to have drivers also reflected this ....

Impact of drive impedance on fet distortion was graphed and showed by Nelson in an article written abt 10 years ago.

But maybe there is something new to be added here by Jon and if so I'm all ears.

Pictures tell a thousand words tho so how about some graphs, citations and things.... Like they do in technical writing,,,,
 
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