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Rich Grise
Guest
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 Posted: Sat Jun 04, 2005 10:03 pm Post subject: Re: Amplifier transistor matching? |
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On Sat, 04 Jun 2005 18:42:56 +0000, Joerg wrote:
| Quote: | 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.
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Uh, stupid questions department here - why not just use that one?
Thanks,
Rich |
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Walter Harley
Guest
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| Posted: Sat Jun 04, 2005 10:03 pm Post subject: Re: Amplifier transistor matching? |
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"Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:42A14893.CCCC3243@hotmail.com...
| Quote: | 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. |
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Joerg
Guest
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| Posted: Sat Jun 04, 2005 11:03 pm Post subject: Re: Amplifier transistor matching? |
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Hello Rich,
| Quote: | 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?
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Because that one was for ham radio and the stuff for secondary user UHF
needs FCC blessing.
Regards, Joerg
http://www.analogconsultants.com |
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Joerg
Guest
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| Posted: Sat Jun 04, 2005 11:03 pm Post subject: Re: Amplifier transistor matching? |
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Hello Rich,
| Quote: | Five hours??? In CHURCH????!?!?!?!?!?!?!!! =:-O
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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 |
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Pooh Bear
Guest
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| Posted: Sat Jun 04, 2005 11:03 pm Post subject: Re: Amplifier transistor matching? |
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Joerg wrote:
| Quote: | 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.
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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 |
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Pooh Bear
Guest
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| Posted: Sun Jun 05, 2005 12:04 am Post subject: Re: Amplifier transistor matching? |
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Joerg wrote:
| Quote: | 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.
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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 |
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Joerg
Guest
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| Posted: Sun Jun 05, 2005 12:04 am Post subject: Re: Amplifier transistor matching? |
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Hello Graham,
| Quote: | 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.
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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 |
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Pooh Bear
Guest
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| Posted: Sun Jun 05, 2005 1:07 am Post subject: Re: Amplifier transistor matching? |
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Midlant wrote:
| Quote: | 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
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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 |
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Pooh Bear
Guest
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| Posted: Sun Jun 05, 2005 1:07 am Post subject: Re: Amplifier transistor matching? |
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Walter Harley wrote:
| Quote: | "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 ! ;-)
| Quote: | 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 ?
| Quote: | But I agree, it's unusual.
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Yup, Graham |
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Trevor Wilson
Guest
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| Posted: Sun Jun 05, 2005 11:02 am Post subject: Re: Amplifier transistor matching? |
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"Midlant" <washrag71@hotmail.com> wrote in message
news:R0joe.65359$sy6.30149@lakeread04...
| Quote: | 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 |
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Kevin Aylward
Guest
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| Posted: Sun Jun 05, 2005 11:02 am Post subject: Re: Amplifier transistor matching? |
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Pooh Bear wrote:
| Quote: | 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. |
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Trevor Wilson
Guest
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| Posted: Sun Jun 05, 2005 11:02 am Post subject: Re: Amplifier transistor matching? |
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"cor" <cor@exchangenet.net> wrote in message
news:42A0CB8B.227EE51F@exchangenet.net...
| Quote: | 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 |
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cor
Guest
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| Posted: Sun Jun 05, 2005 11:02 am Post subject: Re: Amplifier transistor matching? |
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Midlant wrote:
| Quote: |
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?
| Quote: | "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. |
|
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| Back to top |
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Bob Urz
Guest
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| Posted: Sun Jun 05, 2005 4:03 pm Post subject: Re: Amplifier transistor matching? |
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Joerg wrote:
| Quote: | 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
| Quote: | 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
|
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Bob Urz
Guest
|
| Posted: Sun Jun 05, 2005 4:03 pm Post subject: Re: Amplifier transistor matching? |
|
|
Kevin Aylward wrote:
| Quote: | Pooh Bear wrote:
Ol' Duffer wrote:
In article <42A0C72A.68DD168@hotmail.com>,
rabbitsfriendsandrelations@hotmail.com says...
I've never specified matched pairs in any design ( pro-audio btw )
in my entire life despite being responsible for some 10s of
thousands of amplifiers out there. It seems like poor design to
need matched pairs to me.
You should check a batch of power transistors on a curve tracer
sometime. The results may scare you. I routinely see a factor
of three variation in Beta within batches. Of course you can
use big, wasteful swamper resistors, or a bank of 5 unmatched
devices where 2 matched would be sufficient. Or you can let
the amps blow up and they I buy more transistors than I need and
select a good grouping from the middle of the range and fix them
so they don't blow up anymore...
These devices which I currently use for example are pre-graded by the
manufacturer. Worst case match is 2:1 in either gain grade.
http://www.profusionplc.com/cgi-bin/gex/pcatdtl?ipartno=2SC5200-O
A simple low value emitter ballast resistor overcomes the bulk of beta
mismatch anyway and I would never fail to use them. You can't depend
on paralled device temps being identical - in fact quite the reverse
- never mind thermal runaway !
Well, it might be useful to explain just why beta/hfe matching is
important, considering that that the bipolar transistor is a voltage
controlled device!
A bi polar transistor is a current controlled device actually. |
A small base current is used to control a larger collector current.
A FET is a voltage controlled device.
Bob
| Quote: | 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.
|
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