Amplifier transistor matching?

[Guest]

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.

 

[Andy]

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

 

[Guest]

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."

 

[Guest]

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.

 

[Guest]

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

 

[Guest]

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

 

[Guest]

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.

 

[Guest]

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...

 

[Guest]

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.

 

[Guest]

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_pid/270296?src=3WBZ4
DS>

jak
>
> Graham.

 

[Guest]

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!

 

[Guest]

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:d14oe.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.

 

[Guest]

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

 

[Guest]

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=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 !

Graham

 

[Guest]

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

 

[ban]

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

 

[Guest]

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

 

[Guest]

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

 

[ban]

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

 

[Guest]

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