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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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Pooh Bear wrote:
| Quote: |
Walter Harley wrote:
"Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:42A14893.CCCC3243@hotmail.com...
Since failure IME is invariably short circuit, I tend to find that it goes
'bang'. Fuse blown etc.
I've seen failures where the initial failure was probably a short, but the
resulting current fused the leads of the device (TO220) causing an open. In
gear that has a fuse on the mains but not on the power supply, there's
plenty of juice in the filter capacitors to turn a TO220 into melted bits
without tripping the mains fuse.
TO-220s ! Those are driver transistors ! ;-)
I think i still have a Harmon Kardon 330 in the attic that uses TO 220's |
for outputs..... WOnder why its still siting there??? ;)
I seem to remember some home type amps that would have output distortion
problems when the 1/2 watt emitter resistors in the driver stages went open.
Bob
| 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 ?
But I agree, it's unusual.
Yup, Graham
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Pooh Bear
Guest
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| Posted: Sun Jun 05, 2005 9:03 pm Post subject: Re: Amplifier transistor matching? |
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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!
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 |
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Joerg
Guest
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| Posted: Sun Jun 05, 2005 10:03 pm Post subject: Re: Amplifier transistor matching? |
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Hello Walter,
| Quote: | 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 |
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Walter Harley
Guest
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| Posted: Sun Jun 05, 2005 10:03 pm Post subject: Re: Amplifier transistor matching? |
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"Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:42A24DFA.81CAF05D@hotmail.com...
| Quote: | 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. |
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Joerg
Guest
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| Posted: Sun Jun 05, 2005 10:03 pm Post subject: Re: Amplifier transistor matching? |
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Hello Bob,
| Quote: | 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 |
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Jim Thompson
Guest
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| Posted: Sun Jun 05, 2005 10:03 pm Post subject: Re: Amplifier transistor matching? |
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On Fri, 3 Jun 2005 23:22:52 -0700, "Walter Harley"
<walterh@cafewalterNOSPAM.com> wrote:
| Quote: | "Joerg" <notthisjoergsch@removethispacbell.net> wrote in message
news:d14oe.24267$J12.18509@newssvr14.news.prodigy.com...
BTW, since you seem to be an audio guru: Is there any truly digital
wireless mike system with a reasonable battery life (like >5hrs for the
lapel mikes)? Preferably with AA and not with 9V batteries.
Dunno about digital. The Shure analog UHF packs, with lav mics, last more
than 6 hours with a pair of alkaline AAs. One of my gigs uses a dozen or
more channels of them; we put fresh batteries in at 4:30pm, and at 10:30pm
when the show ends they're usually still showing three or four out of five
bars on the battery life indicator. We replace them every night anyway - if
we went for two nights, by the end of the second night we'd be too nervous.
As jak said, the price of batteries is small compared to the price of the
show going down.
|
Can I interject and ask some advice?
My wife has lots of Girl Scout speaking presentations, but she's a
walker... walks away from the podium and the microphone.
Did it again last week with me frantically waving, "Go back to the
microphone."
These presentations are usually in not-very-well or anciently equipped
locations... last week was in an old Catholic Church Parish Center.
What should I buy in the way of a wireless microphone, with facility
to plug the receiver into almost any PA equipment I might encounter?
Thanks!
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food. |
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Pooh Bear
Guest
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| Posted: Sun Jun 05, 2005 10:03 pm Post subject: Re: Amplifier transistor matching? |
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Joerg wrote:
| Quote: | 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.
| Quote: | 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.dll?ViewItem&category=50622&item=5779432419&rd=1
Seller seems to know what he's talking about too !
Graham |
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Pooh Bear
Guest
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| Posted: Sun Jun 05, 2005 10:03 pm Post subject: Re: Amplifier transistor matching? |
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Walter Harley wrote:
| Quote: | "Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:42A24DFA.81CAF05D@hotmail.com...
It was a film resistor that failed rather than wire wound I assume ?
You know, I don't remember any more; it was around 15 years ago. To the
extent I can dredge up any memories, it was a 5W ceramic cinderblock, so
presumably wirewound.
|
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 |
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Pooh Bear
Guest
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| Posted: Sun Jun 05, 2005 10:03 pm Post subject: Re: Amplifier transistor matching? |
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Jim Thompson wrote:
| Quote: | On Fri, 3 Jun 2005 23:22:52 -0700, "Walter Harley"
walterh@cafewalterNOSPAM.com> wrote:
"Joerg" <notthisjoergsch@removethispacbell.net> wrote in message
news:d14oe.24267$J12.18509@newssvr14.news.prodigy.com...
BTW, since you seem to be an audio guru: Is there any truly digital
wireless mike system with a reasonable battery life (like >5hrs for the
lapel mikes)? Preferably with AA and not with 9V batteries.
Dunno about digital. The Shure analog UHF packs, with lav mics, last more
than 6 hours with a pair of alkaline AAs. One of my gigs uses a dozen or
more channels of them; we put fresh batteries in at 4:30pm, and at 10:30pm
when the show ends they're usually still showing three or four out of five
bars on the battery life indicator. We replace them every night anyway - if
we went for two nights, by the end of the second night we'd be too nervous.
As jak said, the price of batteries is small compared to the price of the
show going down.
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 |
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Jim Thompson
Guest
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| Posted: Sun Jun 05, 2005 11:02 pm Post subject: Re: Amplifier transistor matching? |
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On Sun, 05 Jun 2005 23:00:52 +0100, Pooh Bear
<rabbitsfriendsandrelations@hotmail.com> wrote:
| Quote: | Jim Thompson wrote:
On Fri, 3 Jun 2005 23:22:52 -0700, "Walter Harley"
walterh@cafewalterNOSPAM.com> wrote:
"Joerg" <notthisjoergsch@removethispacbell.net> wrote in message
news:d14oe.24267$J12.18509@newssvr14.news.prodigy.com...
BTW, since you seem to be an audio guru: Is there any truly digital
wireless mike system with a reasonable battery life (like >5hrs for the
lapel mikes)? Preferably with AA and not with 9V batteries.
Dunno about digital. The Shure analog UHF packs, with lav mics, last more
than 6 hours with a pair of alkaline AAs. One of my gigs uses a dozen or
more channels of them; we put fresh batteries in at 4:30pm, and at 10:30pm
when the show ends they're usually still showing three or four out of five
bars on the battery life indicator. We replace them every night anyway - if
we went for two nights, by the end of the second night we'd be too nervous.
As jak said, the price of batteries is small compared to the price of the
show going down.
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.
| Quote: | 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 Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food. |
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Joerg
Guest
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| Posted: Sun Jun 05, 2005 11:02 pm Post subject: Re: Amplifier transistor matching? |
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Hello Graham,
| Quote: | 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.
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 |
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Joerg
Guest
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| Posted: Sun Jun 05, 2005 11:02 pm Post subject: Re: Amplifier transistor matching? |
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Hello Jim,
| Quote: | 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=CTLG%5F007%5F008%5F003%5F002&Page=1&find=wireless%20microphone(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 |
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Pooh Bear
Guest
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| Posted: Sun Jun 05, 2005 11:02 pm Post subject: Re: Amplifier transistor matching? |
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Jim Thompson wrote:
You mentioned Girl Scouts !
Graham |
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jakdedert
Guest
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| Posted: Mon Jun 06, 2005 12:04 am Post subject: Re: Amplifier transistor matching? |
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Ban wrote:
I've used and can recommend the Sennies as well....
jak |
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Mike Dobony
Guest
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| Posted: Mon Jun 06, 2005 12:04 am Post subject: Re: Amplifier transistor matching? |
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"Joerg" <notthisjoergsch@removethispacbell.net> wrote in message
news:tr8oe.24319$J12.15889@newssvr14.news.prodigy.com...
| 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.
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.
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