Pooh Bear wrote:
Ol' Duffer wrote:

In article ,
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/...rtno=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/widlarla...arlambert.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

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

"Midlant" 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

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" wrote in message
...
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 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

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Kevin Aylward wrote:

Pooh Bear wrote:

Ol' Duffer wrote:


In article ,
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/...rtno=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


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/widlarla...arlambert.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

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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Pooh Bear wrote:


Walter Harley wrote:


"Pooh Bear" wrote in message
...

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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Kevin Aylward wrote:

Pooh Bear wrote:
Ol' Duffer wrote:

In article ,
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/...rtno=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.

But rather more to the point, a driver stage that isn't low impedance will
also cause the same problem.

Graham

Hello Walter,

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.

That's right, except that 9V are a lot more expensive per Watt hour than
AA batteries. But the real concern I have with 9V is that even brand new
ones fail a lot. Happened again this week at church. After just a few
minutes a brand new battery went from 9V to zero. They are just too fickle.

So even if we don't find any digital system the next mikes must be AA
cells, no more 9V. Ideally they should be compatible with the Sennheiser
UHF diversity receivers since we have four of them already.

Regards, Joerg

http://www.analogconsultants.com

"Pooh Bear" wrote in message
...

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.

Hello Bob,

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.

Tone squelch is a great concept but even without it isn't such a big
deal to design it "pop free". I had an FM radio that never popped. It
looks at the noise content on the audio signal to determine squelch
action. I wonder why the wireless mikes couldn't do that.

When I repaired radios I sometimes looked at the schematics to see why
they popped. Usually the designers didn't fully study the DC levels.
There cannot be any DC shift or cap charge/discharge when the squelch
kicks in. Other times they ignored the charge injection of the FET path
used for muting.

Regards, Joerg

http://www.analogconsultants.com

On Fri, 3 Jun 2005 23:22:52 -0700, "Walter Harley"
wrote:

"Joerg" wrote in message
.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 Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

Joerg wrote:

Hello Walter,

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.

That's right, except that 9V are a lot more expensive per Watt hour than
AA batteries. But the real concern I have with 9V is that even brand new
ones fail a lot. Happened again this week at church. After just a few
minutes a brand new battery went from 9V to zero. They are just too fickle.

Did you see Ron's post in aapls ?

He's seen the same thing - battery packs up after a few mins. He 'tests' them now
for 10-15 mins before use.

So even if we don't find any digital system the next mikes must be AA
cells, no more 9V. Ideally they should be compatible with the Sennheiser
UHF diversity receivers since we have four of them already.

I was on ebay earlier and found some *280* mAh 9V NiMH cells. That's a little
better than your current ones.

http://cgi.ebay.co.uk/ws/eBayISAPI.d...9432 419&rd=1

Seller seems to know what he's talking about too !

Graham

Walter Harley wrote:

"Pooh Bear" wrote in message
...

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.

Oh - unusual but wth !

I ended up using flameproof power film resistors for emitter Rs so that in
the event of catastrophic failure - a cascade failure or 'burn up' as our
repair guys used to call it, the emitter Rs went open fast. Usually little
damage in that event. I do recall seing some TO-92s with their 'heads'
popped off though !

Graham

Jim Thompson wrote:

On Fri, 3 Jun 2005 23:22:52 -0700, "Walter Harley"
wrote:

"Joerg" wrote in message
.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?

About time to start a new thread ?

It all depends. Depends on your budget and the quality you're looking for.

I'm guessing that budget is low in your case. You *can* get cheap 'voice quality'
radio mics but these aren't a patch on the Sennheisers that Joerg is using.

You get what you pay for for the most part. The receiver should have no trouble
interfacing with any kind of PA gear btw.

I'm tempted to suggest looking on ebay for a cheap unit.

Graham

On Sun, 05 Jun 2005 23:00:52 +0100, Pooh Bear
wrote:

Jim Thompson wrote:

On Fri, 3 Jun 2005 23:22:52 -0700, "Walter Harley"
wrote:

"Joerg" wrote in message
.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?

About time to start a new thread ?

It all depends. Depends on your budget and the quality you're looking for.

I'm guessing that budget is low in your case.

Now why would you guess that? I recently spent more than $1K on
stencil-cutting and sandblasting equipment for one of her projects.

You *can* get cheap 'voice quality'
radio mics but these aren't a patch on the Sennheisers that Joerg is using.

You get what you pay for for the most part. The receiver should have no trouble
interfacing with any kind of PA gear btw.

I'm tempted to suggest looking on ebay for a cheap unit.

Graham

Joerg, What would you recommend?

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

Hello Graham,

Did you see Ron's post in aapls ?

He's seen the same thing - battery packs up after a few mins. He 'tests' them now
for 10-15 mins before use.

Yes, I saw his post. That is just one more argument for abandoning 9V
batteries. I am not at all satisfied with their quality levels and that
is also a reason why I try to encourage my clients to design for AA
batteries.

At our church we are also ushers so testing for 10 minutes just isn't
easy to do. Also, we had batteries fail at all kinds of time frames.
Some would die within minutes, others would go for 30-40 minutes and
then die, and so on. From the 9V NiMH half of them died within months,
some within weeks. Not good at all.

I was on ebay earlier and found some *280* mAh 9V NiMH cells. That's a little
better than your current ones.

http://cgi.ebay.co.uk/ws/eBayISAPI.d...9432 419&rd=1

Seller seems to know what he's talking about too !

Indeed, but I have never heard the brand Vapextech. Anyway, I just don't
want to continue with 9V anymore for any new mikes. For the existing one
we continue do need them though so I'll check this one out. So thank you
for that hint, it could help us get more mileage out of a charge.

Regards, Joerg

http://www.analogconsultants.com

Hello Jim,

Joerg, What would you recommend?

Assuming that you don't want to spend a whole lot and that it doesn't
have to be hifi I would look at a Radio Shack setup. That is what we had
when our church was just starting (aka lower in budget...). We also used
an RS wireless mike for large meetings with production employees at my
last company. We had to hold those in the cantina since it was the only
place where the fire marshall allowed enough occupancy.

The units are different now but still cheap:

http://www.radioshack.com/category.asp?catalog%5Fname=CTLG&category%5Fname=C TLG%5F007%5F008%5F003%5F002&Page=1&find=wireless%2 0microphone(keyword)&hp=search

One of them is a complete set, mike and receiver. Then you only have to
plug the receiver's line out into the PA system. The older one we had
could also be operated from batteries and from a car battery which would
be really nice for scout meetings in the outbacks.

Regards, Joerg

http://www.analogconsultants.com

Jim Thompson wrote:

On Sun, 05 Jun 2005 23:00:52 +0100, Pooh Bear
wrote:

I'm guessing that budget is low in your case.

Now why would you guess that?

You mentioned Girl Scouts !

Graham

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

"Joerg" wrote in message
. com...
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.


Try the new G2 series Sennheisers. They use AA batteries and have 9hr
battery life w/alkalines. With the new high capacity NiMh AA's out there
you should get close to that or even longer life. They are not digital, but
they do sound great. Why do you need true digital?

Mike D.

Regards, Joerg

http://www.analogconsultants.com

On Fri, 03 Jun 2005 22:10:02 +0100, Pooh Bear
wrote:

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.

I think the original post is misleading you a bit. The 2245 amp
will run just fine with non-matched output transistors, without
'sever distortion problems'. However, to achieve the lowest possible
distortion and stability, matched pairs are advisable. This is true
for *any* symmetrical audio amplifier design.

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

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

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

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

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

-- Ron


Graham

Hello Mike,

Try the new G2 series Sennheisers. They use AA batteries and have 9hr
battery life w/alkalines. With the new high capacity NiMh AA's out there
you should get close to that or even longer life. They are not digital, but
they do sound great. ...

Yes, we'll certainly look into those. Especially if they are compatible
with our existing Sennheiser UHF gear.

... Why do you need true digital?

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

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

On rare occasions we had mikes "forget" their programmed frequency. In
the middle of a worship service there is not much you can do about that
when it happens. At least not fast enough.

Regards, Joerg

http://www.analogconsultants.com

Jim Thompson wrote:

On Fri, 3 Jun 2005 23:22:52 -0700, "Walter Harley"
wrote:

"Joerg" wrote in message
.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


MCM http://www.mcminone.com has a number of wireless mic systems,
starting at $39 and going up to $499.

--
Former professional electron wrangler.

Michael A. Terrell
Central Florida

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

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

"Joerg" wrote in message
m...
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

Ron wrote:

On Fri, 03 Jun 2005 22:10:02 +0100, Pooh Bear
wrote:

snip

I think the original post is misleading you a bit. The 2245 amp
will run just fine with non-matched output transistors, without
'sever distortion problems'. However, to achieve the lowest possible
distortion and stability, matched pairs are advisable.

For a design of that era I would tend to agree.

This is true for *any* symmetrical audio amplifier design.

I have to differ with you here. Poor beta match is only an issue when the
output devices load a moderate impedance driver stage. This gives rise to
unequal open loop gain for positive and negative half cycles. NFB will only
*reduce* this assymetry.

The effect can be eliminated by use of a *low* impedance driver stage or a
high gain pre-driver stage, as I have always used. Remember the Quad
'triples' in the 303 ? My amp design in the Vision that spawned the D series
amps actually used quadruples - but the big devices were actually off under
quiescent conditions - so for low level it was essentially similar to a
'triples' design at low power.

High ac gain in the driver - pre-driver stages also improves load related
stability as the load impedance doesn't reflect back in any significant way
to the previous voltage gain stage.

Note *ac* gain. I was briefly misled in the development of that amp by using
DC gain requirements and it was unstable with some loads. Then I ran a gain
/ phase plot and the result became obvious.


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

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

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


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

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

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

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

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

That'll teach you !

Graham

On Sun, 05 Jun 2005 23:58:53 +0100, Pooh Bear
wrote:


Jim Thompson wrote:

On Sun, 05 Jun 2005 23:00:52 +0100, Pooh Bear
wrote:

I'm guessing that budget is low in your case.

Now why would you guess that?

You mentioned Girl Scouts !

Graham

My wife has been a Girl Scout leader for 40 years ;-)

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

Pooh Bear wrote:
Ron wrote:

On Fri, 03 Jun 2005 22:10:02 +0100, Pooh Bear
wrote:

snip

I think the original post is misleading you a bit. The 2245 amp
will run just fine with non-matched output transistors, without
'sever distortion problems'. However, to achieve the lowest possible
distortion and stability, matched pairs are advisable.

For a design of that era I would tend to agree.

This is true for *any* symmetrical audio amplifier design.

I have to differ with you here. Poor beta match is only an issue when
the output devices load a moderate impedance driver stage. This gives
rise to unequal open loop gain for positive and negative half cycles.
NFB will only *reduce* this assymetry.

The effect can be eliminated by use of a *low* impedance driver stage
or a high gain pre-driver stage, as I have always used. Remember the
Quad 'triples' in the 303 ? My amp design in the Vision that spawned
the D series amps actually used quadruples - but the big devices were
actually off under quiescent conditions - so for low level it was
essentially similar to a 'triples' design at low power.

High ac gain in the driver - pre-driver stages also improves load
related stability as the load impedance doesn't reflect back in any
significant way to the previous voltage gain stage.

Note *ac* gain. I was briefly misled in the development of that amp
by using DC gain requirements and it was unstable with some loads.
Then I ran a gain / phase plot and the result became obvious.

Could you explain what you actually mean here by "misled"? DC gain has
never had any relevance to amplifier stability. No one is going to
design an amp feedback loop based on DC conditions. Its only the phase
at the unity gain frequency that matters.

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

Bob Urz wrote:
Kevin Aylward wrote:

Pooh Bear wrote:

Ol' Duffer wrote:


In article ,
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/...rtno=2SC5200-O

A simple low value emitter ballast resistor overcomes the bulk of
beta mismatch anyway and I would never fail to use them. You can't
depend on paralled device temps being identical - in fact quite the
reverse - never mind thermal runaway !



Well, it might be useful to explain just why beta/hfe matching is
important, considering that that the bipolar transistor is a voltage
controlled device!

A bi polar transistor is a current controlled device actually.

Here we go, yet again...

I see that you have succumbed to the Bantam paperback popular
misconceptions Bob. A Bipolar transistor is indeed a voltage controlled
device.

For example, see
http://www.anasoft.co.uk/EE/voltagec...edbipolar.html

and for a simple pictorial description of the actual physics, see:

http://www.mtmi.vu.lt/pfk/funkc_dari...transistor.htm

There is simply no mechanism as how a flow of base charge can instigate
a flow of emitter/collector charge. Its applied voltage that that cause
the injection of charge.

The relevent simplified equation is:

Ic ~ Is.exp(Vbe/Vt)

Note the lack of a base current term.

I would suggest obtaining good academic semiconductor physics text book
if you want more details on the correct operation of bipolar
transistors.

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

jakdedert wrote:

Pooh Bear wrote:
Joerg wrote:

Hello Graham,

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

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

Indeed.


... I've never specified matched
pairs in any design ( pro-audio btw ) in my entire life despite
being responsible for some 10s of thousands of amplifiers out
there. It seems like poor design to need matched pairs to me.

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

BTW, since you seem to be an audio guru: Is there any truly digital
wireless mike system with a reasonable battery life (like 5hrs for
the lapel mikes)? Preferably with AA and not with 9V batteries.

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

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

For most gigs, the price of a battery is negligible compared to the show
going 'down.' That said, the new Shures seem to do that long on a 9v. The
really nice ones have battery meters on the actual receiver, so that you can
monitor the battery condition remotely. I've seen a bunch of these lately.
They've performed flawlessly IME, but the included mic is a little large.
There's an ultra small mic option which is less noticable, but the (big)
stock mic sounds better than most lav's I've worked with....
http://www.musiciansfriend.com/srs7/...0296?src=3WBZ4
DS

jak

Graham.

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

JAM

Pooh Bear wrote:

Midlant wrote:


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


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


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

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

Bob

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

Graham


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Joerg wrote:

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

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

You'll like the Shures mentioned before. No such problems in my experience.
No pops, no noise when the receiver is operating without a transmitter,
extremely wide choice of frequencies...auto frequency search. If there is
an operator controlling the sound system, there's a lockout function which
takes the performer out of the loop in terms of unintended switch punches.
You must open the battery panel, press and hold *two* switches to re-enable
the user controls. Sure beats gaffing over the buttons...which I always do
when handing talent a mic not so equipped.

On rare occasions we had mikes "forget" their programmed frequency. In
the middle of a worship service there is not much you can do about
that when it happens. At least not fast enough.

Not seen any of that, either. In any case, the problem can be minimized by
having a wired backup. Again, an operator is desirable so that the backup
doesn't need to be left 'open.' If none is available, a switched
mic--turned off, but left potted up--is a fair alternative. The talent
needs to be aware of the plan, of course.

jak

Regards, Joerg

http://www.analogconsultants.com

Hello Jak,

You'll like the Shures mentioned before. No such problems in my experience.
No pops, no noise when the receiver is operating without a transmitter,
extremely wide choice of frequencies...auto frequency search. ...

That would be an alternative. This time though we'd insist on a serious
test drive before a purchase. The additional Shure system we have is
more than 10 years old but the noise tolerance (lamp switches etc.) is
not stellar, to put it mildly. The Sennheisers are a lot better.

On rare occasions we had mikes "forget" their programmed frequency. In
the middle of a worship service there is not much you can do about
that when it happens. At least not fast enough.

Not seen any of that, either. In any case, the problem can be minimized by
having a wired backup. Again, an operator is desirable so that the backup
doesn't need to be left 'open.' If none is available, a switched
mic--turned off, but left potted up--is a fair alternative. The talent
needs to be aware of the plan, of course.

Frequency memory losses were rare, maybe a couple times a year. Yes, we
do have wired backups and the choir people are well trained. But some
performances require lots of movement and the cables would become a hazard.

Regards, Joerg

http://www.analogconsultants.com

Hello John,

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

Yes, and that is part of many of the sermons. We have a group of
missionaries going to Russia tomorrow morning. They don't have their
tickets yet, none speaks Russian.... but they trust it's going to work
out ok.

Regards, Joerg

http://www.analogconsultants.com

Hello Winfield,

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

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

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

Regards, Joerg

http://www.analogconsultants.com

Kevin Aylward wrote:

Bob Urz wrote:
Kevin Aylward wrote:

Pooh Bear wrote:

Ol' Duffer wrote:


In article ,
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/...rtno=2SC5200-O

A simple low value emitter ballast resistor overcomes the bulk of
beta mismatch anyway and I would never fail to use them. You can't
depend on paralled device temps being identical - in fact quite the
reverse - never mind thermal runaway !



Well, it might be useful to explain just why beta/hfe matching is
important, considering that that the bipolar transistor is a voltage
controlled device!

A bi polar transistor is a current controlled device actually.

Here we go, yet again...

I see that you have succumbed to the Bantam paperback popular
misconceptions Bob. A Bipolar transistor is indeed a voltage controlled
device.


So, the manuals with transistor curve tracers which state
a change a base current and plot collector current and voltage
are wrong? With bipolar beta B=Ic/Ib?

And for FET's its a change in gate voltage vs Drain/source?

Bob



For example, see
http://www.anasoft.co.uk/EE/voltagec...edbipolar.html

and for a simple pictorial description of the actual physics, see:

http://www.mtmi.vu.lt/pfk/funkc_dari...transistor.htm

There is simply no mechanism as how a flow of base charge can instigate
a flow of emitter/collector charge. Its applied voltage that that cause
the injection of charge.

The relevent simplified equation is:

Ic ~ Is.exp(Vbe/Vt)

Note the lack of a base current term.

I would suggest obtaining good academic semiconductor physics text book
if you want more details on the correct operation of bipolar
transistors.

Kevin Aylward

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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On Mon, 06 Jun 2005 19:31:02 GMT, Joerg
wrote:

Hello Winfield,

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

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

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

Regards, Joerg

http://www.analogconsultants.com

Joerg, Can you recommend a Sennheiser model, with lapel microphone?
Thanks!

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

On Mon, 06 Jun 2005 14:34:24 -0500, BOB URZ
wrote:



Kevin Aylward wrote:

Bob Urz wrote:
Kevin Aylward wrote:

Pooh Bear wrote:

Ol' Duffer wrote:


In article ,
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/...rtno=2SC5200-O

A simple low value emitter ballast resistor overcomes the bulk of
beta mismatch anyway and I would never fail to use them. You can't
depend on paralled device temps being identical - in fact quite the
reverse - never mind thermal runaway !



Well, it might be useful to explain just why beta/hfe matching is
important, considering that that the bipolar transistor is a voltage
controlled device!

A bi polar transistor is a current controlled device actually.

Here we go, yet again...

I see that you have succumbed to the Bantam paperback popular
misconceptions Bob. A Bipolar transistor is indeed a voltage controlled
device.


So, the manuals with transistor curve tracers which state
a change a base current and plot collector current and voltage
are wrong? With bipolar beta B=Ic/Ib?

And for FET's its a change in gate voltage vs Drain/source?

Bob



For example, see
http://www.anasoft.co.uk/EE/voltagec...edbipolar.html

and for a simple pictorial description of the actual physics, see:

http://www.mtmi.vu.lt/pfk/funkc_dari...transistor.htm

There is simply no mechanism as how a flow of base charge can instigate
a flow of emitter/collector charge. Its applied voltage that that cause
the injection of charge.

The relevent simplified equation is:

Ic ~ Is.exp(Vbe/Vt)

Note the lack of a base current term.

I would suggest obtaining good academic semiconductor physics text book
if you want more details on the correct operation of bipolar
transistors.

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.


----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
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----= East and West-Coast Server Farms - Total Privacy via Encryption =----

Kevin has a hair up his butt about voltage control, a really long hair
;-)

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

Hello Jim,

Joerg, Can you recommend a Sennheiser model, with lapel microphone?

My experience is limited to their 9V wireless gear which I would not
recommend because of limited battery life and premature battery
failures. There is a new "SK 100 G2" unit which looks very interesting
and that is the one I am going to check out once we upgrade:

http://www.sennheiser.com/sennheiser...nsf/root/21411

The corresponding receivers are typically 19" rack mount and I believe
they do sell kits that contain transmitter, mike, receiver, diversity
antennas, power supply and the cables. The Sennheiser web site is not
very good so you may have to call them to see what the best deal would
be for the whole set. Believe it or not, their "search function" didn't
find their own SK100 mike transmitters, Google did...

Since this is professional gear the output is usually differential, for
connection to a large mixer panel.

To be honest, this professional gear takes more time to set up in the
field when compared to cheaper systems like the Radio Shack I mentioned
before.

My only gripe besides the 9V with our existing Sennheisers is the pop
noise upon turn-off and mute. But if your wife's scout presentations are
typically uninterrupted that won't matter. Also, these systems can be
upgraded to umpteen mikes if that was ever needed.

Regards, Joerg

http://www.analogconsultants.com

Kevin Aylward wrote:

Pooh Bear wrote:
Ron wrote:

On Fri, 03 Jun 2005 22:10:02 +0100, Pooh Bear
wrote:

snip

I think the original post is misleading you a bit. The 2245 amp
will run just fine with non-matched output transistors, without
'sever distortion problems'. However, to achieve the lowest possible
distortion and stability, matched pairs are advisable.

For a design of that era I would tend to agree.

This is true for *any* symmetrical audio amplifier design.

I have to differ with you here. Poor beta match is only an issue when
the output devices load a moderate impedance driver stage. This gives
rise to unequal open loop gain for positive and negative half cycles.
NFB will only *reduce* this assymetry.

The effect can be eliminated by use of a *low* impedance driver stage
or a high gain pre-driver stage, as I have always used. Remember the
Quad 'triples' in the 303 ? My amp design in the Vision that spawned
the D series amps actually used quadruples - but the big devices were
actually off under quiescent conditions - so for low level it was
essentially similar to a 'triples' design at low power.

High ac gain in the driver - pre-driver stages also improves load
related stability as the load impedance doesn't reflect back in any
significant way to the previous voltage gain stage.

Note *ac* gain. I was briefly misled in the development of that amp
by using DC gain requirements and it was unstable with some loads.
Then I ran a gain / phase plot and the result became obvious.

Could you explain what you actually mean here by "misled"? DC gain has
never had any relevance to amplifier stability. No one is going to
design an amp feedback loop based on DC conditions. Its only the phase
at the unity gain frequency that matters.

I misled myself I'm afraid. It's that long ago that I forget the exact
details.

Graham