Amplifier transistor matching?

[Ban]

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_sennheiser_wireless-systems_evolution_series500_21640#

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

 

[Ban]

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

 

[Pooh Bear]

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_sennheiser_wireless-systems_evolution_series500_21640#

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&row=2

Graham

 

[Midlant]

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.

 

[Midlant]

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.

 

[Joerg]

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

 

[Joerg]

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

 

[Joerg]

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

 

[Rich The Newsgroup Wacko]

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?"

 

[Walter Harley]

"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.

 

[Joerg]

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

 

[Joerg]

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]

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

 

[Pooh Bear]

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_sennheiser_wireless-systems_evolution_series500_21640

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

 

[Joerg]

Hello Graham,

http://www.sennheiser.co.uk/uk/icm.nsf/root/products_sennheiser_wireless-systems_evolution_series500_21640

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

 

[Pooh Bear]

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

 

[Pooh Bear]

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

 

[cor]

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.

 

[Trevor Wilson]

"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

 

[Kevin Aylward]

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!

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.html, 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.