Jim Thompson wrote:

Kevin has a hair up his butt about voltage control, a really long hair
;-)

Especially considering he was explaining why beta matching is important !

Graham

Joerg wrote:

Hello John,

He relies on Christ. If He brings you to it, He will see you through it.

Yes, and that is part of many of the sermons. We have a group of
missionaries going to Russia tomorrow morning. They don't have their
tickets yet, none speaks Russian.... but they trust it's going to work
out ok.

I'm curious why you'd send missionaries to Russia. They already have the
Orthodox Church there which is making something of a comeback after decades of
communism ( although it never ever truly died out ).

Have your missionaries previously met the Russian Mafia btw ? ;-)

Graham

"Joerg" wrote in message
. ..
Hello Jak,

You'll like the Shures mentioned before. No such problems in my
experience.
No pops, no noise when the receiver is operating without a transmitter,
extremely wide choice of frequencies...auto frequency search. ...

That would be an alternative. This time though we'd insist on a serious
test drive before a purchase. The additional Shure system we have is
more than 10 years old but the noise tolerance (lamp switches etc.) is
not stellar, to put it mildly. The Sennheisers are a lot better.

On rare occasions we had mikes "forget" their programmed frequency. In
the middle of a worship service there is not much you can do about
that when it happens. At least not fast enough.

Not seen any of that, either. In any case, the problem can be minimized
by
having a wired backup. Again, an operator is desirable so that the
backup
doesn't need to be left 'open.' If none is available, a switched
mic--turned off, but left potted up--is a fair alternative. The talent
needs to be aware of the plan, of course.

Frequency memory losses were rare, maybe a couple times a year. Yes, we
do have wired backups and the choir people are well trained. But some
performances require lots of movement and the cables would become a
hazard.


We have had our EW100 (not the new G2) for over a year and never had one
single frequency memory loss. It is used for 3 services a week and then for
special occasions. The only down side is the short rechargable memory life
with the 9v. My experience wiht the new AA's is comparable to alkaline,
close enough that if we get a new system we would definately use the
rechargable AA's. I think you shoudl have your system checked out.

Mike D.

Regards, Joerg

http://www.analogconsultants.com

Hello Mike,

We have had our EW100 (not the new G2) for over a year and never had one
single frequency memory loss. It is used for 3 services a week and then for
special occasions. The only down side is the short rechargable memory life
with the 9v. My experience wiht the new AA's is comparable to alkaline,
close enough that if we get a new system we would definately use the
rechargable AA's. I think you shoudl have your system checked out.

We had sent them in a while ago. The frequency info losses aren't really
a big concern, battery life is the problem. Also, we have four
mikes/receivers so that waters down the statistical significance of the
memory failure events.

The mute buttons are a bit weak, too. We had one croak and another
become rickety. The handhelds have better quality mute buttons but they
are hard to operate because you have to turn a cover wheel and then
fumble around behind the mike to find it. So we usually just turn the
mike away from the pulpit after the scripture readings (our pastor wears
a lapel mike).

Regards, Joerg

http://www.analogconsultants.com

Hello Graham,

I'm curious why you'd send missionaries to Russia. They already have the
Orthodox Church there which is making something of a comeback after decades of
communism ( although it never ever truly died out ).

From what I know there was a school principal from Petrozavodsk who
visited a Christian school in the US. This was AFAIK back in the commie
times and he was not so much interested in the bible (I guess his gvt
didn't like that at all) but in why students were better motivated,
among other things, and what he could do about that back in Russia. That
is where the idea came up to send people over from here to teach the
students in Russia English, using the bible as a text book. So, now
there are regular missions to that city, not just from our church but
also lots of others.

Participation is voluntary for students. Usually 100-200 sign up from
what I heard. This year blew us away, a whopping 1000 signed up.

Have your missionaries previously met the Russian Mafia btw ? ;-)

No, but I guess they wouldn't be interested much in missionaries.

Regards, Joerg

http://www.analogconsultants.com

Jim Thompson wrote:

On Sun, 05 Jun 2005 23:58:53 +0100, Pooh Bear
wrote:


Jim Thompson wrote:

On Sun, 05 Jun 2005 23:00:52 +0100, Pooh Bear
wrote:

I'm guessing that budget is low in your case.

Now why would you guess that?

You mentioned Girl Scouts !

Graham

My wife has been a Girl Scout leader for 40 years ;-)

...Jim Thompson

Lol ! Nothing wrong with that Jim !

I just imagined that the Scouts don't normally have a great budget for
tech stuff. I've helped out the UK Scouts in the past btw. They're damn
fine with ropes and had my PA rig mounted on scaffolding towers in no
time at all !

Graham

Johnny Thunder wrote:

Matched pairs were nessary in the early days of transistor amps.

Due to poorer design of driver stages. Parts cost more back then and it wasn't
normal practice to 'overdesign'.

Manufacturing tolerances are tighter today and matching is not as big a
problem.

There's still quite a big spread in hfe. Better design of the driver stage
eliminates the problem.


Graham

On Tue, 07 Jun 2005 01:04:02 +0100, Pooh Bear
wrote:

Jim Thompson wrote:

On Sun, 05 Jun 2005 23:58:53 +0100, Pooh Bear
wrote:


Jim Thompson wrote:

On Sun, 05 Jun 2005 23:00:52 +0100, Pooh Bear
wrote:

I'm guessing that budget is low in your case.

Now why would you guess that?

You mentioned Girl Scouts !

Graham

My wife has been a Girl Scout leader for 40 years ;-)

...Jim Thompson

Lol ! Nothing wrong with that Jim !

I just imagined that the Scouts don't normally have a great budget for
tech stuff. I've helped out the UK Scouts in the past btw. They're damn
fine with ropes and had my PA rig mounted on scaffolding towers in no
time at all !

Graham

They have a great budget when a certain benefactor makes equipment,
and vans, etc., available for free ;-)

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

Hello Jim,

They have a great budget when a certain benefactor makes equipment,
and vans, etc., available for free ;-)

A lot of things in our country rely on generosity and that is good. It
shows the next generation where the real values are.

Once you buy a system maybe your wife could train a few girl scouts to
become the "technology team". Then they can set it all up and learn how
stuff like a wireless system works. And what to do when it doesn't. What
was that motto? "Be prepared". So they could check for free UHF channels
at the planned location, figure out the frequency, make sure all the
gear is packed and so on.

Regards, Joerg

http://www.analogconsultants.com

On Tue, 07 Jun 2005 00:18:21 GMT, Joerg
wrote:

Hello Jim,

They have a great budget when a certain benefactor makes equipment,
and vans, etc., available for free ;-)

A lot of things in our country rely on generosity and that is good. It
shows the next generation where the real values are.

Once you buy a system maybe your wife could train a few girl scouts to
become the "technology team". Then they can set it all up and learn how
stuff like a wireless system works. And what to do when it doesn't. What
was that motto? "Be prepared". So they could check for free UHF channels
at the planned location, figure out the frequency, make sure all the
gear is packed and so on.

Regards, Joerg

http://www.analogconsultants.com

My inclination is to a multiple-microphone version for later
expansion, since they do a lot of Flag Ceremonies with multiple
speaking parts.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

On Tue, 07 Jun 2005 00:18:21 GMT, Joerg
wrote:

Hello Jim,

They have a great budget when a certain benefactor makes equipment,
and vans, etc., available for free ;-)

A lot of things in our country rely on generosity and that is good. It
shows the next generation where the real values are.

Once you buy a system maybe your wife could train a few girl scouts to
become the "technology team". Then they can set it all up and learn how
stuff like a wireless system works. And what to do when it doesn't. What
was that motto? "Be prepared". So they could check for free UHF channels
at the planned location, figure out the frequency, make sure all the
gear is packed and so on.

Regards, Joerg

http://www.analogconsultants.com

Be prepared!
That's the Boy Scout marching song
Be prepared!
If you should meet a Girl Scout who is suitably inclined
Be prepared!

;-)

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

There is simply no mechanism as how a flow of base charge can
instigate a flow of emitter/collector charge. Its applied voltage
that that cause the injection of charge.

The relevent simplified equation is:

Ic ~ Is.exp(Vbe/Vt)

Note the lack of a base current term.

I would suggest obtaining good academic semiconductor physics text
book if you want more details on the correct operation of bipolar
transistors.

Kevin Aylward

But Kevin is right, Ebers-Moll is defined via Vbe and Vbc. And beta_f or
beta_r are only derived from the alpha terms. I think it is just a point of
view, in practical circuits you use hfe and don't care much for Vbe since it
is almost constant in comparison to the current.
--
ciao Ban
Bordighera, Italy

Ban wrote:
There is simply no mechanism as how a flow of base charge can
instigate a flow of emitter/collector charge. Its applied voltage
that that cause the injection of charge.

The relevent simplified equation is:

Ic ~ Is.exp(Vbe/Vt)

Note the lack of a base current term.

I would suggest obtaining good academic semiconductor physics text
book if you want more details on the correct operation of bipolar
transistors.

Kevin Aylward

But Kevin is right, Ebers-Moll is defined via Vbe and Vbc.

Its not just the Ebers-Moll, its the *device* *physics*. Its how a
transistor actually works from a phyiscal point of view. There is simply
no way that flow of base charge induces a flow of collector charge.

If one don't understand that it is Vbe that determines and injects
carries into the base that are then swept up into the collector, then
one doesn't understand transistor operation at all. Its that simple.

And beta_f
or beta_r are only derived from the alpha terms. I think it is just a
point of view,

No it isnt.

in practical circuits you use hfe and don't care much

This is simply not true. The only practical way to effectivly design
transister amplifiers is to treat the transistor as a voltage controlled
current source. Period. e.g.

di = dv.gm

Av max = Va/Vt etc.

http://www.anasoft.co.uk/EE/bipolard...ardesign1.html

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

Pooh Bear wrote:
Jim Thompson wrote:

Kevin has a hair up his butt about voltage control, a really long
hair ;-)

Especially considering he was explaining why beta matching is
important !

Indeed. The explanation was why hfe matching mattered despite the fact
that the bipolar transistor is a voltage controlled device. To wit, its
the voltage drop across rbb' that is the killer.

Why don't you use spice and put two power transistors in parallel. Have
two separate models, with only Bf different. Do runs with and without RB
set to zero. Then put in emitter resisters. Its a good exercise.

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

Jim Thompson wrote:
On Mon, 06 Jun 2005 14:34:24 -0500, BOB URZ
wrote:



Kevin Aylward wrote:

Bob Urz wrote:
Kevin Aylward wrote:

Pooh Bear wrote:

Ol' Duffer wrote:


In article ,
says...

I've never specified matched pairs in any design ( pro-audio
btw ) in my entire life despite being responsible for some 10s
of thousands of amplifiers out there. It seems like poor
design to need matched pairs to me.

You should check a batch of power transistors on a curve tracer
sometime. The results may scare you. I routinely see a factor
of three variation in Beta within batches. Of course you can
use big, wasteful swamper resistors, or a bank of 5 unmatched
devices where 2 matched would be sufficient. Or you can let
the amps blow up and they I buy more transistors than I need and
select a good grouping from the middle of the range and fix them
so they don't blow up anymore...

These devices which I currently use for example are pre-graded by
the manufacturer. Worst case match is 2:1 in either gain grade.

http://www.profusionplc.com/cgi-bin/...rtno=2SC5200-O

A simple low value emitter ballast resistor overcomes the bulk of
beta mismatch anyway and I would never fail to use them. You
can't depend on paralled device temps being identical - in fact
quite the reverse - never mind thermal runaway !



Well, it might be useful to explain just why beta/hfe matching is
important, considering that that the bipolar transistor is a
voltage controlled device!

A bi polar transistor is a current controlled device actually.

Here we go, yet again...

I see that you have succumbed to the Bantam paperback popular
misconceptions Bob. A Bipolar transistor is indeed a voltage
controlled device.


So, the manuals with transistor curve tracers which state
a change a base current and plot collector current and voltage
are wrong? With bipolar beta B=Ic/Ib?

And for FET's its a change in gate voltage vs Drain/source?

Bob



For example, see
http://www.anasoft.co.uk/EE/voltagec...edbipolar.html

and for a simple pictorial description of the actual physics, see:

http://www.mtmi.vu.lt/pfk/funkc_dari...transistor.htm

There is simply no mechanism as how a flow of base charge can
instigate a flow of emitter/collector charge. Its applied voltage
that that cause the injection of charge.

The relevent simplified equation is:

Ic ~ Is.exp(Vbe/Vt)

Note the lack of a base current term.

I would suggest obtaining good academic semiconductor physics text
book if you want more details on the correct operation of bipolar
transistors.

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.


----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet
News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the
World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via
Encryption =----

Kevin has a hair up his butt about voltage control, a really long hair
;-)

Indeed. It is they way they work. Only the illinformed consider that the
transister is current controlled.

What we have here is an enormous amount of erroneous waffle on the
bipolar transistor. Its quite amazing really. There is no point in
perpetuating this daft myth. It only leads to confusion.

Any *actual* *understanding* of the standard 3 junction pictorial
descriptions of basic transistor operation should leave people with no
doubt as to the correct operation of a bipolar transistor. Base current
don't "cause" the flow of collector/emitter current. Its Vbe that
injects charge into the emitter, irrespective of base current. End of
story.

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

BOB URZ" "sound(remove) wrote:
Kevin Aylward wrote:

Bob Urz wrote:
Kevin Aylward wrote:

Pooh Bear wrote:

Ol' Duffer wrote:


In article ,
says...

I've never specified matched pairs in any design ( pro-audio
btw ) in my entire life despite being responsible for some 10s
of thousands of amplifiers out there. It seems like poor design
to need matched pairs to me.

You should check a batch of power transistors on a curve tracer
sometime. The results may scare you. I routinely see a factor
of three variation in Beta within batches. Of course you can
use big, wasteful swamper resistors, or a bank of 5 unmatched
devices where 2 matched would be sufficient. Or you can let
the amps blow up and they I buy more transistors than I need and
select a good grouping from the middle of the range and fix them
so they don't blow up anymore...

These devices which I currently use for example are pre-graded by
the manufacturer. Worst case match is 2:1 in either gain grade.

http://www.profusionplc.com/cgi-bin/...rtno=2SC5200-O

A simple low value emitter ballast resistor overcomes the bulk of
beta mismatch anyway and I would never fail to use them. You can't
depend on paralled device temps being identical - in fact quite
the reverse - never mind thermal runaway !



Well, it might be useful to explain just why beta/hfe matching is
important, considering that that the bipolar transistor is a
voltage controlled device!

A bi polar transistor is a current controlled device actually.

Here we go, yet again...

I see that you have succumbed to the Bantam paperback popular
misconceptions Bob. A Bipolar transistor is indeed a voltage
controlled device.


So, the manuals with transistor curve tracers which state
a change a base current and plot collector current and voltage
are wrong? With bipolar beta B=Ic/Ib?

This is a functional relation not a causal one.

We can use a watch and produce a relation (graph) between the positions
of the planets and the positions of the watch hands. Does this mean that
the watch hands are controlling the planets motion, or that the planets
motion is controlling the watch hands?


And for FET's its a change in gate voltage vs Drain/source?


Yes.

Its voltage that makes charge move.

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

"Jim Thompson" wrote in message
...
Be prepared!
That's the Boy Scout marching song
Be prepared!
If you should meet a Girl Scout who is suitably inclined
Be prepared!

What, no attribution for Tom Lehrer?

MrT.

Mr.T MrT@home wrote in sci.electronics.design:

"Jim Thompson" wrote in message
...
Be prepared!
That's the Boy Scout marching song
Be prepared!
If you should meet a Girl Scout who is suitably inclined
Be prepared!

What, no attribution for Tom Lehrer?

Perhaps because Tom Lehrer's text is different:

...
If you're looking for adventure of a new and different kind
And you come across a girl scout who is similarly inclined,
Don't be nervous, don't be flustered(?), don't be scaaaared!
Be prepared!

Anno

On Tue, 7 Jun 2005 18:16:58 +1000, "Mr.T" MrT@home wrote:


"Jim Thompson" wrote in message
.. .
Be prepared!
That's the Boy Scout marching song
Be prepared!
If you should meet a Girl Scout who is suitably inclined
Be prepared!

What, no attribution for Tom Lehrer?

MrT.


Actually I had forgotten that it was Tom Lehrer. I should have
remembered since he was a performer at the junior prom at MIT in 1961,
along with, IIRC, my memory is fuzzy here... Jenny Richie ??

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

On Sat, 04 Jun 2005 22:08:06 +0000, Joerg wrote:

Hello Rich,

I really want to discourage our church to buy any more 9V gear. It just
doesn't hold up well enough. But Ban's hint regarding the handheld is
great, too, because we also use handhelds and have the same issues there
(battery quits or just fails). Also, Sennheiser should have no problem
designing a similar transmitter for lapel use. I mean, it's not rocket
science. I have built transmitters that worked off 2.4V decades ago.
They could run for days.

Uh, stupid questions department here - why not just use that one?

Because that one was for ham radio and the stuff for secondary user UHF
needs FCC blessing.

Ah.

Thanks,
Rich

On Sun, 05 Jun 2005 10:56:30 -0500, Bob Urz wrote:
Kevin Aylward wrote:

Well, it might be useful to explain just why beta/hfe matching is
important, considering that that the bipolar transistor is a voltage
controlled device!

Tastes Great!

A bi polar transistor is a current controlled device actually.
A small base current is used to control a larger collector current.
A FET is a voltage controlled device.

Less Filling!
--
Cheers!
Rich
------
"There was a young lady of fashion
Who had oodles and oodles of passion.
To her lover she said,
As they climbed into bed,
"Here's one thing the *******s can't ration!""

Kevin has a hair up his butt about voltage control, a really long hair
;-)

Indeed. It is they way they work. Only the illinformed consider that the
transister is current controlled.


No, being 'informed' doesn't make an engineer pick a more difficult
analytical approach to quantitative circuit design; quite the
opposite. 90% of the time, a simple 0.6Vbe-plus-Beta model is the
easiest and *most reliable* way to design transistor circuits.

This is sci.electronics.design, not sci.device.physics. If I had to
analyze the physics of every component I use, I wouldn't get anything
done. What matters is how they behave.


What we have here is an enormous amount of erroneous waffle on the
bipolar transistor. Its quite amazing really. There is no point in
perpetuating this daft myth. It only leads to confusion.

Any *actual* *understanding* of the standard 3 junction pictorial
descriptions of basic transistor operation should leave people with no
doubt as to the correct operation of a bipolar transistor. Base current
don't "cause" the flow of collector/emitter current.

That's like saying that poison doesn't cause death because only heart
failure *really* causes death.

John

Hello Jim,

My inclination is to a multiple-microphone version for later
expansion, since they do a lot of Flag Ceremonies with multiple
speaking parts.

The Sennheiser system does that nicely. Currently we have four but I can
see it going to 6-8. However, we'll only do that with AA battery powered
gear, no more 9V.

On our current gear the transmitters show their frequency on a little
LCD, same for the receivers. Receivers also show RF level and audio
level. The latter makes it really easy to see if a mike is active
without the mixer pot turned on.

Regards, Joerg

http://www.analogconsultants.com

John Larkin wrote:
Kevin has a hair up his butt about voltage control, a really long
hair ;-)

Indeed. It is they way they work. Only the illinformed consider that
the transister is current controlled.


No, being 'informed' doesn't make an engineer pick a more difficult
analytical approach to quantitative circuit design; quite the
opposite.

The voltage controlled model is the simple model, and the correct one.

90% of the time, a simple 0.6Vbe-plus-Beta model is the
easiest and *most reliable* way to design transistor circuits.

Not at all. This is not true in the slightest.

Please explain, as discussed in this thread, from a beta perspective,
why a hfe mismatch of 2 can result in say, 10 times mismatch in current
(or more) for || devices. Why is it not just a factor of 2?

Hint: Rbb' drops a voltage to Vibe, Ic = Io.exp(Vbi/Vt)


This is sci.electronics.design, not sci.device.physics. If I had to
analyze the physics of every component I use, I wouldn't get anything
done. What matters is how they behave.

Its not about the physics is about understanding how to design
transistor circuits correctly. To do this, one must understand that the
transistor is a voltage controlled device. The why is irrelevant. Sure,
for a simply switch one might just work out the base current needed to
saturate the device, but for any design that isnt trivial, the beta
model is, essentially, useless. The first order model for gain doesn't
even have a beta term.

http://www.anasoft.co.uk/EE/bipolard...ardesign1.html

To wit,

Av = RL/re = 40Vdc

Av max = Va/Vt.



What we have here is an enormous amount of erroneous waffle on the
bipolar transistor. Its quite amazing really. There is no point in
perpetuating this daft myth. It only leads to confusion.

Any *actual* *understanding* of the standard 3 junction pictorial
descriptions of basic transistor operation should leave people with
no doubt as to the correct operation of a bipolar transistor. Base
current don't "cause" the flow of collector/emitter current.

That's like saying that poison doesn't cause death because only heart
failure *really* causes death.

No it isn't. Base current is not equivalent to poison, its equivalent to
the body stinking after the heart failure. i.e. its just a nuisance.

This is really all getting a bit tiresome. I have explained this many
times. Base current is an effect caused by an application of voltage.
Without understanding this basic fact, it is impossible to *design* an
amplifier correctly. All one can do is **** about under the illusion
that there was a "design" performed. Period.

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

On Tue, 07 Jun 2005 18:37:56 GMT, "Kevin Aylward"
wrote:

John Larkin wrote:
Kevin has a hair up his butt about voltage control, a really long
hair ;-)

Indeed. It is they way they work. Only the illinformed consider that
the transister is current controlled.


No, being 'informed' doesn't make an engineer pick a more difficult
analytical approach to quantitative circuit design; quite the
opposite.

The voltage controlled model is the simple model, and the correct one.

90% of the time, a simple 0.6Vbe-plus-Beta model is the
easiest and *most reliable* way to design transistor circuits.

Not at all. This is not true in the slightest.


Then I owe somebody about $200 million.


Please explain, as discussed in this thread, from a beta perspective,
why a hfe mismatch of 2 can result in say, 10 times mismatch in current
(or more) for || devices. Why is it not just a factor of 2?

Because the beta model doesn't address current sharing of base
currents when transistors are paralleled. Discrete circuit designers
rarely (as in, never) hard-parallel bipolar transistors anyhow. If
they ever elected to do so, they would have to analyze the situation
properly.

Nobody can afford to design without regard to min/max beta specs. Not
even you.

Its not about the physics is about understanding how to design
transistor circuits correctly. To do this, one must understand that the
transistor is a voltage controlled device. The why is irrelevant. Sure,
for a simply switch one might just work out the base current needed to
saturate the device, but for any design that isnt trivial, the beta
model is, essentially, useless. The first order model for gain doesn't
even have a beta term.

Well, maybe yours doesn't, but that's just the equations you prefer,
to make your point.

This is really all getting a bit tiresome. I have explained this many
times. Base current is an effect caused by an application of voltage.
Without understanding this basic fact, it is impossible to *design* an
amplifier correctly. All one can do is **** about under the illusion
that there was a "design" performed. Period.

So, if A causes B, and B causes C, you conclude that A does *not*
cause C. OK, can't argue any more about that.

John

John Larkin wrote:
On Tue, 07 Jun 2005 18:37:56 GMT, "Kevin Aylward"
wrote:

John Larkin wrote:
Kevin has a hair up his butt about voltage control, a really long
hair ;-)

Indeed. It is they way they work. Only the illinformed consider
that the transister is current controlled.


No, being 'informed' doesn't make an engineer pick a more difficult
analytical approach to quantitative circuit design; quite the
opposite.

The voltage controlled model is the simple model, and the correct
one.

90% of the time, a simple 0.6Vbe-plus-Beta model is the
easiest and *most reliable* way to design transistor circuits.

Not at all. This is not true in the slightest.


Then I owe somebody about $200 million.

You must be switching a lot of relays;-)



Please explain, as discussed in this thread, from a beta perspective,
why a hfe mismatch of 2 can result in say, 10 times mismatch in
current (or more) for || devices. Why is it not just a factor of 2?

Because the beta model doesn't address current sharing of base
currents when transistors are paralleled. Discrete circuit designers
rarely (as in, never) hard-parallel bipolar transistors anyhow.

Thats still missing the point. No one is suggesting this.

If
they ever elected to do so, they would have to analyze the situation
properly.

But you cant do this without using the exponential nature of Ic verses
vbe, i.e. the inherent voltage controlled nature of bipolar transistors.
That's why the matching goes off tremendously. As I noted, 50ma at 5
ohms is 250mv. This is huge as the exponent of the exponential is
250/25.


Nobody can afford to design without regard to min/max beta specs. Not
even you.

That misses point as well. The voltage controlled model does not ignore
beta in the slightest, so no, I don't ignore it. I have already pointed
these interested to the relevant paper that shows how beta is included.

Indeed, in SS, worst case analyses is automatic with button presses. It
has decent defaults for all main parameter variations, including max/min
beta. http://www.anasoft.co.uk/WCSETUP.GIF



Its not about the physics is about understanding how to design
transistor circuits correctly. To do this, one must understand that
the transistor is a voltage controlled device. The why is
irrelevant. Sure, for a simply switch one might just work out the
base current needed to saturate the device, but for any design that
isnt trivial, the beta model is, essentially, useless. The first
order model for gain doesn't even have a beta term.

Well, maybe yours doesn't, but that's just the equations you prefer,
to make your point.

Its the way the transistor works, and its what you need to do if you are
designing non switching circuits.


This is really all getting a bit tiresome. I have explained this many
times. Base current is an effect caused by an application of voltage.
Without understanding this basic fact, it is impossible to *design*
an amplifier correctly. All one can do is **** about under the
illusion that there was a "design" performed. Period.

So, if A causes B, and B causes C, you conclude that A does *not*
cause C. OK, can't argue any more about that.

Wrong analogy. I have explained many times that is *electric field* that
causes charges to move. Period. It is why it is often referred to as an
*accelerating* potential. It tries to accelerate charges. Base current
does not in any way try to cause an acceleration of emitter charge. This
is so bloody simply. F=qE. End of story.

Look, this *is* how it is.

Apply a voltage to a diode. A current is generated, to wit:

Id = Io.exp(Vd/Vt)

This current will flow through that junction irrespective of how that
voltage gets to the junction.

Now add a junction for the collector. *Nothing* bloody well changes. The
voltage at the base is the same voltage as it was in the stand alone
diode, therefore that junction current will still be set by that
voltage. However, in this case, most of the emitter diode current gets
sucked up into the collector, not the base. The base terminal is just a
convenient way to impress a voltage across a diode junction, but without
actually supplying the current for that junction.

The above is how one really needs to think about basic transistor
operation.

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

On Sat, 04 Jun 2005 17:39:31 GMT, Joerg
wrote:

That is one reason why we changed to NiMH. The other was cost
as 9V alkalines are really expensive. They rarely go on sale like AA
batteries sometimes do.

The theatre technicians here in London UK seem to be able to source
alkaline 9v batteries at about a third of the retail price of a
Duracell.

Hello Laurence,

The theatre technicians here in London UK seem to be able to source
alkaline 9v batteries at about a third of the retail price of a
Duracell.

That would be 30c US. Really?

Regards, Joerg

http://www.analogconsultants.com

Joerg wrote:

Hello Laurence,

The theatre technicians here in London UK seem to be able to source
alkaline 9v batteries at about a third of the retail price of a
Duracell.

That would be 30c US. Really?

Regards, Joerg

http://www.analogconsultants.com

Also, try to develop a connection with local hospitals and clinics. A
friend of mine used to get cases of alkalines (9V, AA, whatever) free.

Apparently, for medical use, they must be discarded by law when they meet
the expiry date. They were still good as new.

Mike Monett

Hello Mike,

Also, try to develop a connection with local hospitals and clinics. A
friend of mine used to get cases of alkalines (9V, AA, whatever) free.

Apparently, for medical use, they must be discarded by law when they meet
the expiry date. They were still good as new.

That is a good idea. Although nowdays they can have over 5 years of
shelf life. Yesterday I replenished the lab with AA and they expire in
May 2012.

Another source that was mentioned here or on a.b.s.e. are photo
processors. Apparently disposable cameras often contain an AA or AAA
cell with lots of life left in it.

Regards, Joerg

http://www.analogconsultants.com

"Joerg" wrote in message
.. .
That's right, except that 9V are a lot more expensive per Watt hour than
AA batteries. But the real concern I have with 9V is that even brand new
ones fail a lot. Happened again this week at church. After just a few
minutes a brand new battery went from 9V to zero. They are just too
fickle.


Agree. At the same gig where we've gone through literally tens of thousands
of AAs in wireless mics with not a single problem, we've had probably a 1%
failure rate in 9V batteries for the few wireless units we have that take
those. Same thing as what you describe - they test okay, and then drain
within minutes.

I assume it's because of the multi-cell internal construction of a 9V.

Hello Walter,

Agree. At the same gig where we've gone through literally tens of thousands
of AAs in wireless mics with not a single problem, we've had probably a 1%
failure rate in 9V batteries for the few wireless units we have that take
those. Same thing as what you describe - they test okay, and then drain
within minutes.

I assume it's because of the multi-cell internal construction of a 9V.

That may well be the reason. The first time I looked at how they are
internally connected my confidence level dropped a lot. Statistically
the six cells of a 9V must have a higher combined failure rate than two
AA cells. But not by this much, there must be something else that causes
failures.

The contacts on a 9V are a pain as well. How many times has something
ripped out when disconnecting a 9V battery? A lot...

Regards, Joerg

http://www.analogconsultants.com

"Anno Siegel" wrote in message
...
Mr.T MrT@home wrote in sci.electronics.design:

"Jim Thompson" wrote in message
...
Be prepared!
That's the Boy Scout marching song
Be prepared!
If you should meet a Girl Scout who is suitably inclined
Be prepared!

What, no attribution for Tom Lehrer?

Perhaps because Tom Lehrer's text is different:

Which word?

MrT.

A good reason is because a 9V can't source as much current as even a single
AA cell for the same duration due to their much smaller individual cells.
There are six seperate 1.5V cells connected in series to produce the 9
volts. The cells internal electrodes have significantly less surface area to
interact with a much reduced quantity of electrolyte. If you still need 9
volts for a circuit try ganging six AA's in series. If weight is a concern,
even AAA cells aranged in a battery of 9 volts will outlast most 9V's.

Regards,
Chris

On Sun, 05 Jun 2005 23:00:52 +0100, Pooh Bear
wrote:

Jim Thompson wrote:

On Fri, 3 Jun 2005 23:22:52 -0700, "Walter Harley"
wrote:

"Joerg" wrote in message
.com...
BTW, since you seem to be an audio guru: Is there any truly digital
wireless mike system with a reasonable battery life (like 5hrs for the
lapel mikes)? Preferably with AA and not with 9V batteries.

Dunno about digital. The Shure analog UHF packs, with lav mics, last more
than 6 hours with a pair of alkaline AAs. One of my gigs uses a dozen or
more channels of them; we put fresh batteries in at 4:30pm, and at 10:30pm
when the show ends they're usually still showing three or four out of five
bars on the battery life indicator. We replace them every night anyway - if
we went for two nights, by the end of the second night we'd be too nervous.
As jak said, the price of batteries is small compared to the price of the
show going down.


Can I interject and ask some advice?

My wife has lots of Girl Scout speaking presentations, but she's a
walker... walks away from the podium and the microphone.

Did it again last week with me frantically waving, "Go back to the
microphone."

These presentations are usually in not-very-well or anciently equipped
locations... last week was in an old Catholic Church Parish Center.

What should I buy in the way of a wireless microphone, with facility
to plug the receiver into almost any PA equipment I might encounter?

About time to start a new thread ?

It all depends. Depends on your budget and the quality you're looking for.

I'm guessing that budget is low in your case. You *can* get cheap 'voice quality'
radio mics but these aren't a patch on the Sennheisers that Joerg is using.

You get what you pay for for the most part. The receiver should have no trouble
interfacing with any kind of PA gear btw.

I'm tempted to suggest looking on ebay for a cheap unit.

I remember reading years ago that the spoken human voice could be
intelligible at a quite high distortion level. I think the amplifier
in question was 30% or somesuch, but that sounds high even to me now.
Depending on the venue, even room acoustics may outweigh any
distortion issues, I'd guess. Think of the US National Anthem sung at
a sports venue...


"for th or e la and e nd of...you get my drift. :-)

Tom


Graham

On Fri, 10 Jun 2005 19:32:17 GMT, the renowned Tom MacIntyre
wrote:



I remember reading years ago that the spoken human voice could be
intelligible at a quite high distortion level. I think the amplifier
in question was 30% or somesuch, but that sounds high even to me now.
Depending on the venue, even room acoustics may outweigh any
distortion issues, I'd guess. Think of the US National Anthem sung at
a sports venue...


"for th or e la and e nd of...you get my drift. :-)

Tom


Years ago, I heard a demo of the human voice with 1-bit resolution. It
was understandable, but not at all pleasant.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

On Fri, 10 Jun 2005 15:53:01 -0400, Spehro Pefhany
wrote:

On Fri, 10 Jun 2005 19:32:17 GMT, the renowned Tom MacIntyre
wrote:



I remember reading years ago that the spoken human voice could be
intelligible at a quite high distortion level. I think the amplifier
in question was 30% or somesuch, but that sounds high even to me now.
Depending on the venue, even room acoustics may outweigh any
distortion issues, I'd guess. Think of the US National Anthem sung at
a sports venue...


"for th or e la and e nd of...you get my drift. :-)

Tom


Years ago, I heard a demo of the human voice with 1-bit resolution. It
was understandable, but not at all pleasant.


So I think our point is the same, or at least similar...the human
voice, when spoken, possibly doesn't require the same low distortion
for reasonable intelligibility.

Tom


Best regards,
Spehro Pefhany

Hello Spehro,

Depending on the venue, even room acoustics may outweigh any
distortion issues, I'd guess. ...

In a sports arena it will also have to do with the amount of booze that
was consumed.

Regards, Joerg

http://www.analogconsultants.com

"Tom MacIntyre" wrote ...
So I think our point is the same, or at least similar...the human
voice, when spoken, possibly doesn't require the same low distortion
for reasonable intelligibility.

And cell-phone manufacturers regularly plumb the depths of
low-res to see how much we will put up with! :-)

Hello Richard,

And cell-phone manufacturers regularly plumb the depths of
low-res to see how much we will put up with! :-)

Yes, it seems so. It could be the carriers since their currency is
kb/sec. Yesterday a long time friend called me on his cell phone. I
could not even recognize who it was until several seconds into the
conversation, and initially only by what he was talking about.

Regards, Joerg

http://www.analogconsultants.com