Amplifier transistor matching?

Winfield Hill · Jun 6, 2005

Jim Thompson wrote...

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

Nobody should be bound to the podium. Solve the problem.

--
Thanks,
- Win

Midlant · Jun 6, 2005

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

"Joerg" <notthisjoergsch@removethispacbell.net> wrote in message
news:RFpoe.2123$IE7.1688@newssvr21.news.prodigy.com...

Hello Rich,

Five hours??? In CHURCH????!?!?!?!?!?!?!!! =:-O

No worries, our sermons aren't that long. But 1st service, education
hour (actually more than an hour) and 2nd service total about five
hours. All back-to-back with little time to swap batteries. How our
pastor manages that marathon, I don't know. It must be pretty tough.

Regards, Joerg

http://www.analogconsultants.com

Pooh Bear · Jun 6, 2005

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.

Some circuits almost don't care. It depends a lot on the driver stage.

True. Especially for low NFB, low gain designs. Still the better
the complimentary paiss match, the better will the amplifier be.

See above... I do tend to use quite a bit of local feedback and close the
loop gently as it happens. 'Low NFB' as commonly used by the audiotwats as a
generalisation is misleading. There'll be NFB somewhere ! It doesn't just
vanish.

Incidentally I can't really see how a failed output device can be
responsible for severe distortion. Normally it's a works or not
situation with output devices.

Well, when one side of a pair works while the other doesn't, you do
get signal out, but it's seriously (50% and up) distorted. Not just
'poor fidelity' but 'the amp is definitely bad' kind of sound.

As I mentioned elsewhere - when an output device fails, I've rarely known it
to be anything other than a short. That normally takes out the other output
device(s) and fuses etc and there's no sound.

The exception to that rule is the Hitachi style lateral mosfets. They
usually fail open. You see the effect when a big Mosfet amp amp doesn't clip
symmetrically any more !

I recently had a similar problem with an 2270 output block. I
replaced the bad output device with a matched (measured out of
about a dozen) transistor. The receiver sounds great, but the
repaird channel now measures better than the originally good
one.

That'll teach you !

Graham

Jim Thompson · Jun 6, 2005

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

480)460-2350 | |
| E-mail Address at Website Fax

Kevin Aylward · Jun 6, 2005

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.

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.

Johnny Thunder · Jun 6, 2005

jakdedert wrote:

Pooh Bear wrote:
Joerg wrote:

Hello Graham,

Usually it's current gain that's matched. ...

I'll second that, it's what I saw most in matched pairs or quads.
Except for FETs where the match is usually Vgs versus resistance.

Indeed.

... 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.

Yes, it is best to avoid matching. But when you can't avoid it and
then specify a transistor array it can be acceptable. That shouldn't
be some boutique part though. I have done a few matched designs
(where there was no other choice) based on SD5400 arrays. All RF
stuff though, not audio.

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.

Hmmm.. I'm not specifically into wireless mikes and I think both the
older VHF ( certainly ) and newer UHF ones are good old analogue.

A good place to ask would be alt.audio.pro.live-sound. The issue of
battery life with wireless mikes has come up a good many times.
That's where you'll find ppl who use this stuff all the time. I don't
think you'll avoid 9V batteries though from what I understand. You
might make your 5hrs with rechargeable NiMH but the pros seem to
prefer alkalines - just in case of a bad charge perhaps. The battery
( alkaline ) gets chucked at the end of the gig.

For most gigs, the price of a battery is negligible compared to the show
going 'down.' That said, the new Shures seem to do that long on a 9v. The
really nice ones have battery meters on the actual receiver, so that you can
monitor the battery condition remotely. I've seen a bunch of these lately.
They've performed flawlessly IME, but the included mic is a little large.
There's an ultra small mic option which is less noticable, but the (big)
stock mic sounds better than most lav's I've worked with....
http://www.musiciansfriend.com/srs7/search/detail/base_pid/270296?src=3WBZ4
DS

jak

Graham.

Matched pairs were nessary in the early days of transistor amps.
Manufacturing tolerances are tighter today and matching is not as big a
problem.

JAM

Bob Urz · Jun 6, 2005

Pooh Bear wrote:

Midlant wrote:

Cor, I too have one of these. Is yours a made in California real Marantz
or a later one made in Japan. I have a scratchy right channel. I've
cleaned the pots, especially the volume pot, but it doesn't seem to have
helped. Have you had this problem? If so what did you do to rectify it?
John

I've heard US contributors to the audio groups mention 'Caig' as good for
switches - maybe pots too.

Caig stuff works great. Cramolin D5 or pro gold.
Its not cheap, but it will work better than anything else
i have tried.

One problem in the old Marantz is the tape monitor switches.
Its common to have them get oxidized internally and cause a channel
to cut out. These switches are sealed. My patented way to revive them
is to carefully burn a hole in the back with a thin solder pencil.
You have to be careful to work the switch in and out when you do
this so the plastic does not jam up the switch internally. You then
use some D5 or such and work the switch in and our for a minute or
so. Then seal it back up.

Bob

I have no expereince of it though as it doesn't appear to be sold in the UK.

Graham

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jakdedert · Jun 6, 2005

Joerg wrote:

<snip>

We really don't. But spread spectrum is so much lower maintenance.
Most RF mikes including the Sennheiser SK series operate as UHF
secondary user. That has several disadvantages. One is that UHF
channels get kicked around a lot these days with new temporary DTV
channels being assigned and so on. Another issue is noise. When a
large bank of fluorescents gets turned on this is audible on pretty
much any FM based system. Not so with spread spectrum.

Other problems could have been avoided with clever engineering.
Examples are the pop noise when a mike is turned off, and sometimes
even when it is muted. The answer I got regarding the mute pop was
like "pastors use that switch too often and it wears out". Well, then
why is there a mute switch? And why isn't it properly debounced?
After all, these systems are also advertised for use in churches and
smaller congregations do not have an audio or mixer operator. So I'd
expect proper mute switching.

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. If there is
an operator controlling the sound system, there's a lockout function which
takes the performer out of the loop in terms of unintended switch punches.
You must open the battery panel, press and hold *two* switches to re-enable
the user controls. Sure beats gaffing over the buttons...which I always do
when handing talent a mic not so equipped.

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.

jak

Regards, Joerg

http://www.analogconsultants.com

Joerg · Jun 6, 2005

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.

Regards, Joerg

http://www.analogconsultants.com

Joerg · Jun 6, 2005

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.

Regards, Joerg

http://www.analogconsultants.com

Joerg · Jun 6, 2005

Hello Winfield,

Nobody should be bound to the podium. Solve the problem.

When a friend was speaking I saw the field strength meter on the
wireless receiver for his mike go from near full scale to zilch. Oh no,
not now... The battery had given out. He has such a thunderous voice
that I could not notice a difference and I was way in the back, behind
the audience.

So it may just be a matter of training ;-)

Regards, Joerg

http://www.analogconsultants.com

BOB URZ · Jun 6, 2005

Kevin Aylward wrote:

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

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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Jim Thompson · Jun 6, 2005

On Mon, 06 Jun 2005 19:31:02 GMT, Joerg
<notthisjoergsch@removethispacbell.net> wrote:

Hello Winfield,

Nobody should be bound to the podium. Solve the problem.

When a friend was speaking I saw the field strength meter on the
wireless receiver for his mike go from near full scale to zilch. Oh no,
not now... The battery had given out. He has such a thunderous voice
that I could not notice a difference and I was way in the back, behind
the audience.

So it may just be a matter of training ;-)

Regards, Joerg

http://www.analogconsultants.com

480)460-2350 | |
| E-mail Address at Website Fax

Jim Thompson · Jun 6, 2005

On Mon, 06 Jun 2005 14:34:24 -0500, BOB URZ
<"sound(remove)"@inetnebr.com> wrote:

Kevin Aylward wrote:

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

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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480)460-2350 | |
| E-mail Address at Website Fax

Joerg · Jun 6, 2005

Hello Jim,

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 · Jun 6, 2005

Kevin Aylward wrote:

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 · Jun 6, 2005

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

Pooh Bear · Jun 6, 2005

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

Mike Dobony · Jun 6, 2005

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

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

Joerg · Jun 6, 2005

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

Amplifier transistor matching?

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