Amplifier transistor matching?

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Amplifier transistor matching?
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BOB URZ
Guest

Posted: Mon Jun 06, 2005 8:03 pm Post subject: Re: Amplifier transistor matching?

Kevin Aylward wrote:

Quote:

Bob Urz wrote:
Kevin Aylward wrote:

Pooh Bear wrote:

Ol' Duffer wrote:

In article <42A0C72A.68DD168@hotmail.com>,
rabbitsfriendsandrelations@hotmail.com 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/gex/pcatdtl?ipartno=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

Quote:

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

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

http://www.mtmi.vu.lt/pfk/funkc_dariniai/transistor/bipolar_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
informationEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

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Joerg
Guest

Posted: Mon Jun 06, 2005 8:03 pm Post subject: Re: Amplifier transistor matching?

Hello John,

Quote:

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.

Regards, Joerg

http://www.analogconsultants.com

Joerg
Guest

Posted: Mon Jun 06, 2005 8:03 pm Post subject: Re: Amplifier transistor matching?

Hello Jak,

Quote:

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.

Quote:

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.

Regards, Joerg

http://www.analogconsultants.com

Joerg
Guest

Posted: Mon Jun 06, 2005 9:02 pm Post subject: Re: Amplifier transistor matching?

Hello Jim,

Quote:

Joerg, Can you recommend a Sennheiser model, with lapel microphone?

My experience is limited to their 9V wireless gear which I would not
recommend because of limited battery life and premature battery
failures. There is a new "SK 100 G2" unit which looks very interesting
and that is the one I am going to check out once we upgrade:

http://www.sennheiser.com/sennheiser/icm_eng.nsf/root/21411

The corresponding receivers are typically 19" rack mount and I believe
they do sell kits that contain transmitter, mike, receiver, diversity
antennas, power supply and the cables. The Sennheiser web site is not
very good so you may have to call them to see what the best deal would
be for the whole set. Believe it or not, their "search function" didn't
find their own SK100 mike transmitters, Google did...

Since this is professional gear the output is usually differential, for
connection to a large mixer panel.

To be honest, this professional gear takes more time to set up in the
field when compared to cheaper systems like the Radio Shack I mentioned
before.

My only gripe besides the 9V with our existing Sennheisers is the pop
noise upon turn-off and mute. But if your wife's scout presentations are
typically uninterrupted that won't matter. Also, these systems can be
upgraded to umpteen mikes if that was ever needed.

Regards, Joerg

http://www.analogconsultants.com

Pooh Bear
Guest

Posted: Mon Jun 06, 2005 10:02 pm Post subject: Re: Amplifier transistor matching?

Kevin Aylward wrote:

Quote:

Pooh Bear wrote:
Ron wrote:

On Fri, 03 Jun 2005 22:10:02 +0100, Pooh Bear
rabbitsfriendsandrelations@hotmail.com> wrote:

snip

I think the original post is misleading you a bit. The 2245 amp
will run just fine with non-matched output transistors, without
'sever distortion problems'. However, to achieve the lowest possible
distortion and stability, matched pairs are advisable.

For a design of that era I would tend to agree.

This is true for *any* symmetrical audio amplifier design.

I have to differ with you here. Poor beta match is only an issue when
the output devices load a moderate impedance driver stage. This gives
rise to unequal open loop gain for positive and negative half cycles.
NFB will only *reduce* this assymetry.

The effect can be eliminated by use of a *low* impedance driver stage
or a high gain pre-driver stage, as I have always used. Remember the
Quad 'triples' in the 303 ? My amp design in the Vision that spawned
the D series amps actually used quadruples - but the big devices were
actually off under quiescent conditions - so for low level it was
essentially similar to a 'triples' design at low power.

High ac gain in the driver - pre-driver stages also improves load
related stability as the load impedance doesn't reflect back in any
significant way to the previous voltage gain stage.

Note *ac* gain. I was briefly misled in the development of that amp
by using DC gain requirements and it was unstable with some loads.
Then I ran a gain / phase plot and the result became obvious.

Could you explain what you actually mean here by "misled"? DC gain has
never had any relevance to amplifier stability. No one is going to
design an amp feedback loop based on DC conditions. Its only the phase
at the unity gain frequency that matters.

I misled myself I'm afraid. It's that long ago that I forget the exact
details.

Graham

Pooh Bear
Guest

Posted: Mon Jun 06, 2005 10:02 pm Post subject: Re: Amplifier transistor matching?

Jim Thompson wrote:

Quote:

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

Pooh Bear
Guest

Posted: Mon Jun 06, 2005 11:02 pm Post subject: Re: Amplifier transistor matching?

Joerg wrote:

Quote:

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

Mike Dobony
Guest

Posted: Tue Jun 07, 2005 12:03 am Post subject: Re: Amplifier transistor matching?

"Joerg" <notthisjoergsch@removethispacbell.net> wrote in message
news:4o1pe.612$Z44.509@newssvr13.news.prodigy.com...

Quote:

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.

Quote:

Regards, Joerg

http://www.analogconsultants.com

Joerg
Guest

Posted: Tue Jun 07, 2005 12:03 am Post subject: Re: Amplifier transistor matching?

Hello Mike,

Quote:

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

Joerg
Guest

Posted: Tue Jun 07, 2005 1:03 am Post subject: Re: Amplifier transistor matching?

Hello Graham,

Quote:

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.

Quote:

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

Pooh Bear
Guest

Posted: Tue Jun 07, 2005 1:03 am Post subject: Re: Amplifier transistor matching?

Jim Thompson wrote:

Quote:

On Sun, 05 Jun 2005 23:58:53 +0100, Pooh Bear
rabbitsfriendsandrelations@hotmail.com> wrote:

Jim Thompson wrote:

On Sun, 05 Jun 2005 23:00:52 +0100, Pooh Bear
rabbitsfriendsandrelations@hotmail.com> 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 ***
fine with ropes and had my PA rig mounted on scaffolding towers in no
time at all !

Graham

Jim Thompson
Guest

Posted: Tue Jun 07, 2005 1:03 am Post subject: Re: Amplifier transistor matching?

On Tue, 07 Jun 2005 01:04:02 +0100, Pooh Bear
<rabbitsfriendsandrelations@hotmail.com> wrote:

Quote:

Jim Thompson wrote:

On Sun, 05 Jun 2005 23:58:53 +0100, Pooh Bear
rabbitsfriendsandrelations@hotmail.com> wrote:

Jim Thompson wrote:

On Sun, 05 Jun 2005 23:00:52 +0100, Pooh Bear
rabbitsfriendsandrelations@hotmail.com> 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 ***
fine with ropes and had my PA rig mounted on scaffolding towers in no
time at all !

Graham

Pooh Bear
Guest

Posted: Tue Jun 07, 2005 1:03 am Post subject: Re: Amplifier transistor matching?

Johnny Thunder wrote:

Quote:

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'.

Quote:

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

Joerg
Guest

Posted: Tue Jun 07, 2005 1:03 am Post subject: Re: Amplifier transistor matching?

Hello Jim,

Quote:

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

Jim Thompson
Guest

Posted: Tue Jun 07, 2005 2:03 am Post subject: Re: Amplifier transistor matching?

On Tue, 07 Jun 2005 00:18:21 GMT, Joerg
<notthisjoergsch@removethispacbell.net> wrote:

Quote:

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

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