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Amplifier transistor matching?

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Anonymous
June 3, 2005 5:28:43 PM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

I am trying to fix an old Marantz 2245 stereo.
one of the amplifier blocks had severe distortion problems.
On inspection, two transistors were suspect. One I can find and fix.
The other transistor is part of two pairs of transistors on
the amplifier block. Apparently these two pairs of transistors
come in matched pairs. One is a 2SC960/LA43 the other one is
a 2SA607/LA43E. Replacement transistors have been reported not
to work satisfactorily on these Marantz circuits.
I was finally able to find 2SC960 transistors but not with the
same LA43 subscript.
My question is, what kind of transistors parameters do you guys
know should be matched among pairs of transistors to see if I got
a suitable matching pair before replacing them.

More about : amplifier transistor matching

June 3, 2005 5:49:24 PM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

Andy writes:

Without knowing their biasing circuitry, I don't think
a complete answer can be given. Some biasing circuits
are fairly forgiving, others seem like balancing a pencil
on it's end...

But, in my opinion, Vbe and hfe are primary parameters.

I would be interested in learning a better answer myself, tho.

You might consider sci.electronics.design also, if you
haven't already.

There are some competent IC designers there, who
deal with problems like this when they design their
miracle circuits.....

Andy
Anonymous
June 3, 2005 10:42:03 PM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

cor wrote:
> I am trying to fix an old Marantz 2245 stereo.
> one of the amplifier blocks had severe distortion problems.
> On inspection, two transistors were suspect. One I can find and fix.
> The other transistor is part of two pairs of transistors on
> the amplifier block. Apparently these two pairs of transistors
> come in matched pairs. One is a 2SC960/LA43 the other one is
> a 2SA607/LA43E. Replacement transistors have been reported not
> to work satisfactorily on these Marantz circuits.
> I was finally able to find 2SC960 transistors but not with the
> same LA43 subscript.
> My question is, what kind of transistors parameters do you guys
> know should be matched among pairs of transistors to see if I got
> a suitable matching pair before replacing them.

I've probably repaired many hundred such units, so here goes.....

We stocked generic parts for all of these repairs with minimal hFE=75
and VCE=100. Then parts were matched to the following characteristics:

1) Case style: TO-3, TO220, or small signal

2) NPN, or PNP

3) Regular transistor, or darlingtons.

4) Replace all transistor in the complete channels output circuit,
usually 5 to 7.

5) Turn the bias current adjustment to minimum resistance.

6) Plug the AC power cord thru a 40 watt lamp circuit in series with the
power.

7) Turn on the unit with no signal, and watch for a dimming light bulb.
If it goes full brightness, kill all power and go back to step 4
looking for more fried parts.

8) If the light goes dim, connect directly to AC power.

9) Feed 1kz sine wave in errant channel while driving a 100w 8ohm
resistive load. Run a very low power level to accentuate the 'notch'.
Watch the output on a scope and tweek the bias pot until this 'crossover
notch' dissappears.

10) Additional testing using a harmonic distortion analyzer may find a
more optimum setting for the bias at full power level.

You may or may not get original factory specs using generic parts, if
you can get 'factory' parts it may work better, or not.

Be aware, if you apply full AC power with even one of the transistors in
a failed mode, it will 'take down the whole show' all over again.

Good luck,
--
Luhan Monat: luhanis(at)yahoo(dot)com
http://members.cox.net/berniekm
"Any sufficiently advanced magick is
indistinguishable from technology."
Related resources
Can't find your answer ? Ask !
Anonymous
June 4, 2005 1:32:56 AM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

In article <42A0CB8B.227EE51F@exchangenet.net>, cor@exchangenet.net
says...
> My question is, what kind of transistors parameters do you guys
> know should be matched among pairs of transistors to see if I got
> a suitable matching pair before replacing them.

In the output stage, it's usually Beta (DC current gain) so that
they share the load.

For an input diff amp pair VBE may be more important.
Anonymous
June 4, 2005 2:10:02 AM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

cor wrote:

> I am trying to fix an old Marantz 2245 stereo.
> one of the amplifier blocks had severe distortion problems.
> On inspection, two transistors were suspect. One I can find and fix.
> The other transistor is part of two pairs of transistors on
> the amplifier block. Apparently these two pairs of transistors
> come in matched pairs. One is a 2SC960/LA43 the other one is
> a 2SA607/LA43E. Replacement transistors have been reported not
> to work satisfactorily on these Marantz circuits.
> I was finally able to find 2SC960 transistors but not with the
> same LA43 subscript.
> My question is, what kind of transistors parameters do you guys
> know should be matched among pairs of transistors to see if I got
> a suitable matching pair before replacing them.

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

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

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.

Graham
Anonymous
June 4, 2005 2:10:03 AM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

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.

> ... 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.

Regards, Joerg

http://www.analogconsultants.com
Anonymous
June 4, 2005 2:10:03 AM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

In article <42A0C72A.68DD168@hotmail.com>,
rabbitsfriendsandrelations@hotmail.com says...
> 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.

An open device in a totem pole configuration makes the amp able
to drive in only one direction, so you get only the positive or
negative half of the waveform, i.e. 50% distortion.
Anonymous
June 4, 2005 2:10:03 AM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

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...
Anonymous
June 4, 2005 3:14:11 AM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

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.

Graham.
Anonymous
June 4, 2005 3:14:12 AM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

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_...
DS>

jak
>
> Graham.
Anonymous
June 4, 2005 3:16:35 AM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

"Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:42A0C72A.68DD168@hotmail.com...
> 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.

If one of the pair fails, the result is severe distortion - a rectified
waveform, low-pass filtered by the speaker. Only about 30% THD... some
people don't even notice!
Anonymous
June 4, 2005 3:22:52 AM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

"Joerg" <notthisjoergsch@removethispacbell.net> wrote in message
news:D 14oe.24267$J12.18509@newssvr14.news.prodigy.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.
Anonymous
June 4, 2005 6:35:05 AM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

Hello Graham,

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

The analog ones are ok, except for a suboptimal squelch and a nasty pop
when muting it. In church you have to do that a lot.

> 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.

I had asked in rec.audio.pro but I'll try your suggestion tomorrow. Not
today, the barbie is almost ready. Marinated ribs and potatoes tonight.

We use Ansmann 9V NiMH which seem to be the only ones with 250mAh, plus
nifty uC charge stations. But even with top notch Alkalines our
Sennheiser EW system doesn't reach 5hrs. Actually the Ansmanns hold out
a bit better. Thing is, two AA cells pack a whole lot more energy than a
9V battery. I wonder why they didn't design for 3V or even better 2.4V.

Regards, Joerg

http://www.analogconsultants.com
Anonymous
June 4, 2005 7:22:01 AM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

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...

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 !

Graham
Anonymous
June 4, 2005 7:23:09 AM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

Ol' Duffer wrote:

> In article <42A0C72A.68DD168@hotmail.com>,
> rabbitsfriendsandrelations@hotmail.com says...
> > 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.
>
> An open device in a totem pole configuration makes the amp able
> to drive in only one direction, so you get only the positive or
> negative half of the waveform, i.e. 50% distortion.

Good god ! I'd forgotten about non complementary outputs ( thankfully ).

It's been that long. ;-)

Graham
June 4, 2005 7:51:20 AM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

Joerg wrote:
> Hello Graham,
>
>> Hmmm.. I'm not specifically into wireless mikes and I think both
>> the older VHF ( certainly ) and newer UHF ones are good old analogue.
>
> The analog ones are ok, except for a suboptimal squelch and a nasty
> pop when muting it. In church you have to do that a lot.
>
>> 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.
>
> I had asked in rec.audio.pro but I'll try your suggestion tomorrow.
> Not today, the barbie is almost ready. Marinated ribs and potatoes
> tonight.
> We use Ansmann 9V NiMH which seem to be the only ones with 250mAh,
> plus nifty uC charge stations. But even with top notch Alkalines our
> Sennheiser EW system doesn't reach 5hrs. Actually the Ansmanns hold
> out a bit better. Thing is, two AA cells pack a whole lot more energy
> than a 9V battery. I wonder why they didn't design for 3V or even
> better 2.4V.
> Regards, Joerg
>

But your system sems to be outdated. Here is a 2AA 6-8hrs transmitter
http://www.sennheiser.com/sennheiser/icm.nsf/root/21531
--
ciao Ban
Bordighera, Italy
Anonymous
June 4, 2005 8:21:52 AM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

Joerg wrote:

> Hello Graham,
>
> > Hmmm.. I'm not specifically into wireless mikes and I think both the older
> > VHF ( certainly ) and newer UHF ones are good old analogue.
>
> The analog ones are ok, except for a suboptimal squelch and a nasty pop
> when muting it. In church you have to do that a lot.
>
> > 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.
>
> I had asked in rec.audio.pro but I'll try your suggestion tomorrow.

rec.audio.pro is good but mainly recording oriented. It's the live guys who use
wireless mics most.


> Not today, the barbie is almost ready. Marinated ribs and potatoes tonight.

Sounds very nice. Enjoy !


> We use Ansmann 9V NiMH which seem to be the only ones with 250mAh, plus
> nifty uC charge stations. But even with top notch Alkalines our
> Sennheiser EW system doesn't reach 5hrs. Actually the Ansmanns hold out
> a bit better. Thing is, two AA cells pack a whole lot more energy than a
> 9V battery. I wonder why they didn't design for 3V or even better 2.4V.

Having the volts available is often handy, although I admit I don't know the
exact answer.

250mAh is good though. What's the terminal voltage when charged ? If it's only
8.4V that seems to be problematic. I gather some NiMHs have an extra cell.

Graham
Anonymous
June 4, 2005 8:59:39 AM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

Ban wrote:

> Joerg wrote:
> > Hello Graham,
> >
> >> Hmmm.. I'm not specifically into wireless mikes and I think both
> >> the older VHF ( certainly ) and newer UHF ones are good old analogue.
> >
> > The analog ones are ok, except for a suboptimal squelch and a nasty
> > pop when muting it. In church you have to do that a lot.
> >
> >> 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.
> >
> > I had asked in rec.audio.pro but I'll try your suggestion tomorrow.
> > Not today, the barbie is almost ready. Marinated ribs and potatoes
> > tonight.
> > We use Ansmann 9V NiMH which seem to be the only ones with 250mAh,
> > plus nifty uC charge stations. But even with top notch Alkalines our
> > Sennheiser EW system doesn't reach 5hrs. Actually the Ansmanns hold
> > out a bit better. Thing is, two AA cells pack a whole lot more energy
> > than a 9V battery. I wonder why they didn't design for 3V or even
> > better 2.4V.
> > Regards, Joerg
> >
>
> But your system sems to be outdated. Here is a 2AA 6-8hrs transmitter
> http://www.sennheiser.com/sennheiser/icm.nsf/root/21531

You mean ?

http://www.sennheiser.co.uk/uk/icm.nsf/root/21531

Which is an in ear monitoring ( IEM ) *receiver* !

Not the same thing at all !


Graham
June 4, 2005 8:59:40 AM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

Pooh Bear wrote:
> You mean ?
>
> http://www.sennheiser.co.uk/uk/icm.nsf/root/21531
>
> Which is an in ear monitoring ( IEM ) *receiver* !
>
> Not the same thing at all !
>
>
> Graham

Sorry, there was still another page in my clipboard, I meant this one (in
German for Joerg)
http://www.sennheiser.com/sennheiser/icm.nsf/root/21405
--
ciao Ban
Bordighera, Italy
Anonymous
June 4, 2005 10:47:21 AM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

Ban wrote:

> Pooh Bear wrote:
> > You mean ?
> >
> > http://www.sennheiser.co.uk/uk/icm.nsf/root/21531
> >
> > Which is an in ear monitoring ( IEM ) *receiver* !
> >
> > Not the same thing at all !
> >
> >
> > Graham
>
> Sorry, there was still another page in my clipboard, I meant this one (in
> German for Joerg)
> http://www.sennheiser.com/sennheiser/icm.nsf/root/21405
> --

Ah - ok - tech spec here.

http://www.sennheiser.co.uk/uk/icm.nsf/root/21405#

Unfortunately not a lapel mic. I wonder if Sennheiser do a simple transmitter
pack ?

Graham
Anonymous
June 4, 2005 11:22:11 AM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

Walter Harley wrote:

> "Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> wrote in message
> news:42A0C72A.68DD168@hotmail.com...
> > 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.
>
> If one of the pair fails, the result is severe distortion - a rectified
> waveform, low-pass filtered by the speaker. Only about 30% THD... some
> people don't even notice!

Since failure IME is invariably short circuit, I tend to find that it goes
'bang'. Fuse blown etc.

Graham
June 4, 2005 11:57:58 AM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

Pooh Bear wrote:
>
> http://www.sennheiser.co.uk/uk/icm.nsf/root/21405#
>
> Unfortunately not a lapel mic. I wonder if Sennheiser do a simple
> transmitter pack ?
>
> Graham
http://www.sennheiser.co.uk/uk/icm.nsf/root/products_se...
they also make the SKP100G2 which should be cheaper (no phantom power), but
it is new and not yet in the catalogue. The existing receiver should work
with these too.
--
ciao Ban
Bordighera, Italy
June 4, 2005 12:17:38 PM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

Pooh Bear wrote:
> Walter Harley wrote:
>
>> "Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> wrote in message
>> news:42A0C72A.68DD168@hotmail.com...
>>> 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.
>>
>> If one of the pair fails, the result is severe distortion - a
>> rectified waveform, low-pass filtered by the speaker. Only about
>> 30% THD... some people don't even notice!
>
> Since failure IME is invariably short circuit, I tend to find that it
> goes 'bang'. Fuse blown etc.
>
> Graham

I also have made this experience. Both BJT and FETs go short-circuit and
blow the mains fuse. Maybe in a bridged output configuration it could be a
DC-value, but then the protection kicks in and disconnects the relays.
--
ciao Ban
Bordighera, Italy
Anonymous
June 4, 2005 2:37:24 PM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

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

"cor" <cor@exchangenet.net> wrote in message
news:42A0CB8B.227EE51F@exchangenet.net...
>I am trying to fix an old Marantz 2245 stereo.
> one of the amplifier blocks had severe distortion problems.
> On inspection, two transistors were suspect. One I can find and fix.
> The other transistor is part of two pairs of transistors on
> the amplifier block. Apparently these two pairs of transistors
> come in matched pairs. One is a 2SC960/LA43 the other one is
> a 2SA607/LA43E. Replacement transistors have been reported not
> to work satisfactorily on these Marantz circuits.
> I was finally able to find 2SC960 transistors but not with the
> same LA43 subscript.
> My question is, what kind of transistors parameters do you guys
> know should be matched among pairs of transistors to see if I got
> a suitable matching pair before replacing them.
Anonymous
June 4, 2005 4:09:06 PM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

My bad. Mine is a Japan model. I have it pulled out as I'm rearranging
the office. In small print under Marantz Sun Valley USA is made in
Japan.
This clears up the incongruity as I thought this series was long after
his USA run.

"Midlant" <washrag71@hotmail.com> wrote in message
news:R0joe.65359$sy6.30149@lakeread04...
> 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
>
> "cor" <cor@exchangenet.net> wrote in message
> news:42A0CB8B.227EE51F@exchangenet.net...
>>I am trying to fix an old Marantz 2245 stereo.
>> one of the amplifier blocks had severe distortion problems.
>> On inspection, two transistors were suspect. One I can find and fix.
>> The other transistor is part of two pairs of transistors on
>> the amplifier block. Apparently these two pairs of transistors
>> come in matched pairs. One is a 2SC960/LA43 the other one is
>> a 2SA607/LA43E. Replacement transistors have been reported not
>> to work satisfactorily on these Marantz circuits.
>> I was finally able to find 2SC960 transistors but not with the
>> same LA43 subscript.
>> My question is, what kind of transistors parameters do you guys
>> know should be matched among pairs of transistors to see if I got
>> a suitable matching pair before replacing them.
>
>
Anonymous
June 4, 2005 5:15:07 PM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

Ban wrote:

> Pooh Bear wrote:
> >
> > http://www.sennheiser.co.uk/uk/icm.nsf/root/21405#
> >
> > Unfortunately not a lapel mic. I wonder if Sennheiser do a simple
> > transmitter pack ?
> >
> > Graham
> http://www.sennheiser.co.uk/uk/icm.nsf/root/products_se...

That looks good, although possibly a little chunky to put in one's pocket !


> they also make the SKP100G2 which should be cheaper (no phantom power), but it is new and not yet in the
> catalogue. The existing receiver should work with these too.

I also found this one sold as a 'kit' with a clip on mic - but it's back to 9V batteries.

http://www.sennheiser.co.uk/uk/icm.nsf/root/21101?Open&...

Graham
Anonymous
June 4, 2005 6:14:55 PM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

"Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:42A14893.CCCC3243@hotmail.com...
> Since failure IME is invariably short circuit, I tend to find that it goes
> 'bang'. Fuse blown etc.

I've seen failures where the initial failure was probably a short, but the
resulting current fused the leads of the device (TO220) causing an open. In
gear that has a fuse on the mains but not on the power supply, there's
plenty of juice in the filter capacitors to turn a TO220 into melted bits
without tripping the mains fuse.

Many years ago I bought a bass amp in which the emitter resistor of one side
of the push/pull output had gone open, with the transistors still intact -
not sure how. Got a great deal on the amp from the seller, who assumed it
was totaled. One resistor later, I had a fine amp that I used for a couple
of years and eventually sold at a profit.

But I agree, it's unusual.
Anonymous
June 4, 2005 9:39:31 PM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

Hello Graham,

> 250mAh is good though. What's the terminal voltage when charged ? If it's only
> 8.4V that seems to be problematic. I gather some NiMHs have an extra cell.

They are seven cell so it is slightly above 9V. Of course it will drop
to 8.4V rapidly but then they stay there almost until exhaustion.
Alkalines show a more steep voltage decline. You can use them down to 6V
and below but the mike's circuitry won't work properly when they are
this low. 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.

Regards, Joerg

http://www.analogconsultants.com
Anonymous
June 4, 2005 10:37:49 PM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

Hello Ban,

> Sorry, there was still another page in my clipboard, I meant this one (in
> German for Joerg)
> http://www.sennheiser.com/sennheiser/icm.nsf/root/21405

Thanks! This could even work with our existing bank of UHF diversity
receivers. I'll have to find out whether they would operate on NiMH at
2.4V. But even if not, AA batteries are cheap except that this leaves
the environmental concern of disposal.

Regards, Joerg

http://www.analogconsultants.com
Anonymous
June 4, 2005 10:42:56 PM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

Hello Graham,

> I also found this one sold as a 'kit' with a clip on mic - but it's back to 9V batteries.

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.

Regards, Joerg

http://www.analogconsultants.com
Anonymous
June 5, 2005 12:56:58 AM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

On Sat, 04 Jun 2005 02:35:05 +0000, Joerg wrote:
> Hello Graham,
>> Hmmm.. I'm not specifically into wireless mikes and I think both the older
>> VHF ( certainly ) and newer UHF ones are good old analogue.
>
> The analog ones are ok, except for a suboptimal squelch and a nasty pop
> when muting it. In church you have to do that a lot.
....
> We use Ansmann 9V NiMH which seem to be the only ones with 250mAh, plus
> nifty uC charge stations. But even with top notch Alkalines our
> Sennheiser EW system doesn't reach 5hrs. ...

Five hours??? In CHURCH????!?!?!?!?!?!?!!! =:-O
--
Cheers!
Rich
------
"Hear about... the fellow who was descended from a long line his mother
heard?"
Anonymous
June 5, 2005 1:06:09 AM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

On Sat, 04 Jun 2005 18:42:56 +0000, Joerg wrote:

> Hello Graham,
>
>> I also found this one sold as a 'kit' with a clip on mic - but it's back to 9V batteries.
>
> 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?

Thanks,
Rich
Anonymous
June 5, 2005 2:08:06 AM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

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.

Regards, Joerg

http://www.analogconsultants.com
Anonymous
June 5, 2005 2:10:57 AM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

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
Anonymous
June 5, 2005 3:37:45 AM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

Joerg wrote:

> Hello Graham,
>
> > 250mAh is good though. What's the terminal voltage when charged ? If it's only
> > 8.4V that seems to be problematic. I gather some NiMHs have an extra cell.
>
> They are seven cell so it is slightly above 9V. Of course it will drop
> to 8.4V rapidly but then they stay there almost until exhaustion.
> Alkalines show a more steep voltage decline. You can use them down to 6V
> and below but the mike's circuitry won't work properly when they are
> this low. 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 guys in aapls mention that big live shows buy 9V alkakines by the case from
direct distribution. That makes it rather less costly.

Regds, Graham
Anonymous
June 5, 2005 4:22:02 AM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

Joerg wrote:

> Hello Graham,
>
> > I also found this one sold as a 'kit' with a clip on mic - but it's back to 9V batteries.
>
> 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.

I just checked the full datasheet for this one - the 'transmitter module' and it says nominal
battery voltage 2.4V ! Good for 8 hrs they say.

http://www.sennheiser.co.uk/uk/icm.nsf/root/products_se...

Trouble is, it measures 4" x 1-3/4 " sq. Only has an XLR input so you'd need a conversion cable
from your lapel mic.

Graham
Anonymous
June 5, 2005 4:22:03 AM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

Hello Graham,

> http://www.sennheiser.co.uk/uk/icm.nsf/root/products_se...
>
> Trouble is, it measures 4" x 1-3/4 " sq. Only has an XLR input so you'd need a conversion cable
> from your lapel mic.

That is a bit bulky. But it still gives hope that they'd come out with a
2.4V lapel wireless some day. The electronics in there can't be this big.

Regards, Joerg

http://www.analogconsultants.com
Anonymous
June 5, 2005 5:32:06 AM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

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.

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

Graham
Anonymous
June 5, 2005 5:57:30 AM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

Walter Harley wrote:

> "Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> wrote in message
> news:42A14893.CCCC3243@hotmail.com...
> > Since failure IME is invariably short circuit, I tend to find that it goes
> > 'bang'. Fuse blown etc.
>
> I've seen failures where the initial failure was probably a short, but the
> resulting current fused the leads of the device (TO220) causing an open. In
> gear that has a fuse on the mains but not on the power supply, there's
> plenty of juice in the filter capacitors to turn a TO220 into melted bits
> without tripping the mains fuse.

TO-220s ! Those are driver transistors ! ;-)


> Many years ago I bought a bass amp in which the emitter resistor of one side
> of the push/pull output had gone open, with the transistors still intact -
> not sure how. Got a great deal on the amp from the seller, who assumed it
> was totaled. One resistor later, I had a fine amp that I used for a couple
> of years and eventually sold at a profit.

It was a film resistor that failed rather than wire wound I assume ?

> But I agree, it's unusual.

Yup, Graham
Anonymous
June 5, 2005 6:32:12 AM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

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

Mine is made in Japan. Ser 27960.
Maybe that it why the manual I got does not exactly match the components I have.

My pots seem to be ok. I only noticed that the on button is slow in the way out.

Are you sure its the pots? If you switch sides at the preamp plugins does the
scratchiness switch sides?



> "cor" <cor@exchangenet.net> wrote in message
> news:42A0CB8B.227EE51F@exchangenet.net...
> >I am trying to fix an old Marantz 2245 stereo.
> > one of the amplifier blocks had severe distortion problems.
> > On inspection, two transistors were suspect. One I can find and fix.
> > The other transistor is part of two pairs of transistors on
> > the amplifier block. Apparently these two pairs of transistors
> > come in matched pairs. One is a 2SC960/LA43 the other one is
> > a 2SA607/LA43E. Replacement transistors have been reported not
> > to work satisfactorily on these Marantz circuits.
> > I was finally able to find 2SC960 transistors but not with the
> > same LA43 subscript.
> > My question is, what kind of transistors parameters do you guys
> > know should be matched among pairs of transistors to see if I got
> > a suitable matching pair before replacing them.
Anonymous
June 5, 2005 2:07:43 PM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

"cor" <cor@exchangenet.net> wrote in message
news:42A0CB8B.227EE51F@exchangenet.net...
>I am trying to fix an old Marantz 2245 stereo.
> one of the amplifier blocks had severe distortion problems.
> On inspection, two transistors were suspect. One I can find and fix.
> The other transistor is part of two pairs of transistors on
> the amplifier block. Apparently these two pairs of transistors
> come in matched pairs. One is a 2SC960/LA43 the other one is
> a 2SA607/LA43E. Replacement transistors have been reported not
> to work satisfactorily on these Marantz circuits.
> I was finally able to find 2SC960 transistors but not with the
> same LA43 subscript.
> My question is, what kind of transistors parameters do you guys
> know should be matched among pairs of transistors to see if I got
> a suitable matching pair before replacing them.

**All old Marantz amps required the use of hFE matched devices, for optimum
distortion levels. Matching needs to be within around 30%. I only ever used
unmatched devices with one Marantz amp and I found THD levels rise from
around 0.01% to around 0.1%. I never bothered using non-matched devices in
any other Marantz amps, since that day.


--
Trevor Wilson
www.rageaudio.com.au
Anonymous
June 5, 2005 2:08:19 PM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

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...
>
> 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!

The issue is the internal base resistance, rbb', from the external base
terminal to the actual junction.

Lets say, the output in a device is 5A, with a hfe of 100. This is 50ma
base current. Typically, rbb' might be 5 ohms for a power device (or
less). This
results in 250 mv across rbb', that is, the applied voltage is
reduced by 250mv. If the hfe was half due to mismatch, there would be a
net 250mv difference in applied base emitter voltage *iff* the current
stayed the same. It don't, as the current will be reduced resulting in
less drop. The calculation actually gets a bit messy.

Essentially, we have:

IB1.RB1 + Vt.ln(IC1/Io1) = IB2.RB2 + Vt.ln(IC2/Io2)

simplifying with RB1=RB2 and Io1=Io2 we get

Vt.ln(IC1/IC2) = (IC2/Hfe2 - IC1/Hfe1).R

or

IC1/IC2 = exp((IC2/Hfe2 - IC2/Hfe1)R/Vt)

Which is still a bit tricky to solve, hence the introduction of
SuperSpice:-)

We can actually do something more with the above with a bit of
rearranging:

IC1.exp(IC1.R/Hfe1.Vt) = IC2.exp(IC2.R/Hfe2.Vt)

Which the more astute readers will recognise can be expresed in terms of
our friend the Lambert W function,
http://www.anasoft.co.uk/EE/widlarlambert/widlarlambert..., to wit:

IC1 = Vt.hfe1/R . W( R/(Vt.hfe1) . IC2.exp(IC2.R/Hfe2.Vt) )

So given, IC2 we can calculate IC1.

Emitter resisters introduce negative feedback, but I think I will stick
to SS for the sums...

It should be noted that 2:1 hfe variations, without emitter degeneration
can typically be of the order of 10:1 in current ratios.

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.
Anonymous
June 5, 2005 2:10:15 PM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

"Midlant" <washrag71@hotmail.com> wrote in message
news:R0joe.65359$sy6.30149@lakeread04...
> 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

**No Marantz 2245 was made in the US. ALL 4 digit models were of Japanese
origin. Check for low level DC Voltage on the pot. If present, you have a
coupling cap fault. If not, you have a 'dirty' pot. Clean it.


--
Trevor Wilson
www.rageaudio.com.au
Anonymous
June 5, 2005 2:47:35 PM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

Joerg wrote:
> Hello Graham,
>
>> Hmmm.. I'm not specifically into wireless mikes and I think both the
>> older
>> VHF ( certainly ) and newer UHF ones are good old analogue.
>
>
> The analog ones are ok, except for a suboptimal squelch and a nasty pop
> when muting it. In church you have to do that a lot.
>
The modern Shure units have tone code squelch. When the mike is "muted"
there is no pop or noise. There will be noise possibly when its first
turned on. You should be be looking at the ULX series in SHure.

Bob


>> 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.
>
>
> I had asked in rec.audio.pro but I'll try your suggestion tomorrow. Not
> today, the barbie is almost ready. Marinated ribs and potatoes tonight.
>
> We use Ansmann 9V NiMH which seem to be the only ones with 250mAh, plus
> nifty uC charge stations. But even with top notch Alkalines our
> Sennheiser EW system doesn't reach 5hrs. Actually the Ansmanns hold out
> a bit better. Thing is, two AA cells pack a whole lot more energy than a
> 9V battery. I wonder why they didn't design for 3V or even better 2.4V.
>
> Regards, Joerg
>
> http://www.analogconsultants.com

----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
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Anonymous
June 5, 2005 2:56:30 PM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

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...
>>
>>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.
A small base current is used to control a larger collector current.
A FET is a voltage controlled device.

Bob


> The issue is the internal base resistance, rbb', from the external base
> terminal to the actual junction.
>
> Lets say, the output in a device is 5A, with a hfe of 100. This is 50ma
> base current. Typically, rbb' might be 5 ohms for a power device (or
> less). This
> results in 250 mv across rbb', that is, the applied voltage is
> reduced by 250mv. If the hfe was half due to mismatch, there would be a
> net 250mv difference in applied base emitter voltage *iff* the current
> stayed the same. It don't, as the current will be reduced resulting in
> less drop. The calculation actually gets a bit messy.
>
> Essentially, we have:
>
> IB1.RB1 + Vt.ln(IC1/Io1) = IB2.RB2 + Vt.ln(IC2/Io2)
>
> simplifying with RB1=RB2 and Io1=Io2 we get
>
> Vt.ln(IC1/IC2) = (IC2/Hfe2 - IC1/Hfe1).R
>
> or
>
> IC1/IC2 = exp((IC2/Hfe2 - IC2/Hfe1)R/Vt)
>
> Which is still a bit tricky to solve, hence the introduction of
> SuperSpice:-)
>
> We can actually do something more with the above with a bit of
> rearranging:
>
> IC1.exp(IC1.R/Hfe1.Vt) = IC2.exp(IC2.R/Hfe2.Vt)
>
> Which the more astute readers will recognise can be expresed in terms of
> our friend the Lambert W function,
> http://www.anasoft.co.uk/EE/widlarlambert/widlarlambert..., to wit:
>
> IC1 = Vt.hfe1/R . W( R/(Vt.hfe1) . IC2.exp(IC2.R/Hfe2.Vt) )
>
> So given, IC2 we can calculate IC1.
>
> Emitter resisters introduce negative feedback, but I think I will stick
> to SS for the sums...
>
> It should be noted that 2:1 hfe variations, without emitter degeneration
> can typically be of the order of 10:1 in current ratios.
>
> 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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Anonymous
June 5, 2005 3:01:44 PM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

Pooh Bear wrote:

>
> Walter Harley wrote:
>
>
>>"Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> wrote in message
>>news:42A14893.CCCC3243@hotmail.com...
>>
>>>Since failure IME is invariably short circuit, I tend to find that it goes
>>>'bang'. Fuse blown etc.
>>
>>I've seen failures where the initial failure was probably a short, but the
>>resulting current fused the leads of the device (TO220) causing an open. In
>>gear that has a fuse on the mains but not on the power supply, there's
>>plenty of juice in the filter capacitors to turn a TO220 into melted bits
>>without tripping the mains fuse.
>
>
> TO-220s ! Those are driver transistors ! ;-)
>
>
I think i still have a Harmon Kardon 330 in the attic that uses TO 220's
for outputs..... WOnder why its still siting there??? ;) 

I seem to remember some home type amps that would have output distortion
problems when the 1/2 watt emitter resistors in the driver stages went open.

Bob

>
>>Many years ago I bought a bass amp in which the emitter resistor of one side
>>of the push/pull output had gone open, with the transistors still intact -
>>not sure how. Got a great deal on the amp from the seller, who assumed it
>>was totaled. One resistor later, I had a fine amp that I used for a couple
>>of years and eventually sold at a profit.
>
>
> It was a film resistor that failed rather than wire wound I assume ?
>
>
>>But I agree, it's unusual.
>
>
> Yup, Graham
>
>

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Anonymous
June 5, 2005 6:32:24 PM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

"Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:42A24DFA.81CAF05D@hotmail.com...

> It was a film resistor that failed rather than wire wound I assume ?

You know, I don't remember any more; it was around 15 years ago. To the
extent I can dredge up any memories, it was a 5W ceramic cinderblock, so
presumably wirewound.
Anonymous
June 5, 2005 6:38:47 PM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

On Fri, 3 Jun 2005 23:22:52 -0700, "Walter Harley"
<walterh@cafewalterNOSPAM.com> wrote:

>"Joerg" <notthisjoergsch@removethispacbell.net> wrote in message
>news:D 14oe.24267$J12.18509@newssvr14.news.prodigy.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?

Thanks!

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:( 480)460-2350 | |
| E-mail Address at Website Fax:( 480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.
Anonymous
June 5, 2005 10:02:44 PM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

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
Anonymous
June 5, 2005 10:07:01 PM

Archived from groups: sci.electronics.basics,sci.electronics.design,rec.audio.tech,alt.audio.equipment (More info?)

Ban wrote:
> Pooh Bear wrote:
>> You mean ?
>>
>> http://www.sennheiser.co.uk/uk/icm.nsf/root/21531
>>
>> Which is an in ear monitoring ( IEM ) *receiver* !
>>
>> Not the same thing at all !
>>
>>
>> Graham
>
> Sorry, there was still another page in my clipboard, I meant this one
> (in German for Joerg)
> http://www.sennheiser.com/sennheiser/icm.nsf/root/21405

I've used and can recommend the Sennies as well....

jak
!