Re: Negative Feedback and the Criminal Assets Recovery Bureau

Can you get some comments in on FETs here, any of you guys? There are
quite a number of audio amplifiers that use both JFETs and MOSFETs so I
think it warrants some discussion.


"Trevor Wilson" <trevor@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in
news:44c7ec10$0$12690$88260bb3@xxxxxxxxxxxxxxxxx:


"Patrick Turner" <info@xxxxxxxxxxxxxxxxxx> wrote in message
news:44C6B5A9.6FEC281@xxxxxxxxxxxxxxxxxxxxx


Trevor Wilson wrote:

"Patrick Turner" <info@xxxxxxxxxxxxxxxxxx> wrote in message
news:44C5F4D1.EA43F22A@xxxxxxxxxxxxxxxxxxxxx
Modern transistors are more linear than even the best Triodes.

You have said this misleading statement before.

**It's not misleading. It's fact.

Nothing is a fact until all sides agree it is, and you have to proove
what you
say.

**Just look at the curves.






Unfortunately for your arguments this is not the case with regard
to voltage
gain.
Transistors need only a small range of turn on voltage applied
between their
base and emitter,
and their gm varies enormously between being on the threshold of
turn on
of
collector-emitter current and saturation.

**Transistors are controlled by CURRENT, not Voltage. The CURRENT
gain of modern transistors is extremely linear, over a wide range of
Collector currents and Voltages.

Current relationships between base and collector currents are
substantially
linear.

**EXTREMELY linear.

The voltage relationship is not.

**Irrelevant.

You don't have the concepts correctly in your mind.

**Sure I do. Modern BJTs are extremely linear amplification devices.





Only enormous amounts of externally applied NFB corrects the
inherent voltage
non-linearity
of all BJTs where there is substantial current change as in the
case of all
power transistors.

**Transistors (BJTs) are CURRENT amplification devices.

Sure, we all know that, but their voltage linearity is intrinsically
poor.

**Er, that's because they're current amplifiers. And in that sense,
they are exceptionally linear.






Try setting up any bjt in common emitter mode without any emitter
resistor
and
apply
a voltage from a very low impedance to the base. The bjt is
disgustingly
non
linear
compared to a triode using no external applied NFB.

**Transistors (BJTs) are CURRENT amplification devices. Apply a
current to
the Base and measure the change in Collector current. Get back to me
when you've done this.

The current applied to the base is propelled by the applied voltage.
No voltage = no current.

**Duh. No current flow = no Voltage. What's your point?


Set up a small bjt in bread board as a an SE device in class A with
zero NFB and
record the
voltage linearity.

**Points:
* No amplifier on the planet uses zero NFB. Why would you want to
attempt to build one?
* Se amplifiers are dumb. Push pull makes more sense.

Its terrible.
Lots of NFB is needed to linearize the bjt, which is easy, because
they have a
lot of gain...


Even most pentodes which do not have internal electrostatic NFB
like a triode
can easily
out perform a bjt.

**Not even close. Pentodes are vastly less linear than even average
BJTs. Triodes, at least, are reasonably linear.

Your ignorance of tube behaviour is breathtaking.

Try reading RDH4 about the comparison of triode connected pentodes
and the same tube running as a pentode.
At low levels the pentode was more linear than the triode.

**Are we discussing POWER amps, or something else?





I am not here to discuss whether the bjt amp can sound well, or
measure well.
Both are known to be possible so it is believed by most folks.

**Me either. I'm here to correct Jute's lies.


Without external loops of NFB including the emitter follower
connection which is a high amount of applied series voltage NFB,
the BJT is a hopeless
voltage amp

**Transistors (BJTs) are CURRENT amplification devices.

No need to emulate a trained galah.

**It seems you've forgotten this point.




unless we try to restrict the current change in the device, and
then the
gain is

enormous and subject to the perils of the high collector
resistance and circuit slowness due to capacitances, and the non
linear input resistances
of
other
devices in the signal path.

A class A single bjt voltage amp stage with a single MJE340 with
another
for a
constant current source
collector load can have a gain of maybe 1,000, or like a pentode
with a CCS load
in its anode circuit.
If external loops of shunt NFB are applied around either device,
then the
linearity can be quite good for
either device, because for a gain reduction of 100, from 1,000 to
10, the
thd is
also reduced about
100 fold.

The linearity is dependant on the NFB applied, and not on the
basic VOLTAGE
linearity
of the device without NFB, which for a bjt is relatively poor, and
poorest
when
considerable
current change occurs in the device.

**Transistors (BJTs) are CURRENT amplification devices.

Gee, I think I heard that parrot again.

**Until you figure that out, I need to repeat it.


Maybe you could confirm what i am saying if you
went right back to basics with a breadboard and a CRO
and examined the basic workings of the basic devices that mankind has
invented over the last 100 years.

**Sure. Right after you recall that BJTs are current amplification
devices and cannot be used in identical topologies to tubes. They
operate in a fundamentally different way and need to be treated
accordingly.



.

Relevant Pages

  • Re: Negative Feedback and the Criminal Assets Recovery Bureau
    ... Transistors need only a small range of turn on voltage applied between ... modern transistors is extremely linear, over a wide range of Collector ... Modern BJTs are extremely linear amplification devices. ...
    (rec.audio.tubes)
  • Re: Negative Feedback and the Criminal Assets Recovery Bureau
    ... Transistors need only a small range of turn on voltage applied ... gain of modern transistors is extremely linear, ... Modern BJTs are extremely linear amplification devices. ...
    (rec.audio.tubes)
  • Re: Negative Feedback and the Criminal Assets Recovery Bureau
    ... no. BJTs are current amplification devices and need to be treated as ... The turn on voltage between base and emitter for bjts when plotted against the ... is not a linear relationship while the ratio of base input current to collector ... **That's because BJTs are current amplification devices. ...
    (rec.audio.tubes)
  • Re: MOSFET power amp..???
    ... against overload, by 'throttling back' their amplification, if ... temperatures of the chip become elevated. ... BJTs deliver around 1/10th the ...
    (uk.rec.audio)
  • Re: The Catch-22 of Negative Feedback aka NFB
    ... I didn't say a 300B is more linear than a 2SC whatever. ... EASILY AVAILABLE amplification devices (there were ... by a pushy, ill-manned gatecrasher like Wilson. ... In real life, as distinct from simplified theory, NFB adds artifacts ...
    (rec.audio.tubes)