Maker Pro
Maker Pro

Amplifier transistor matching?

W

Walter Harley

Jan 1, 1970
0
Joerg said:
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.
 
B

Ban

Jan 1, 1970
0
Pooh said:
Since failure IME is invariably short circuit, I tend to find that it
goes 'bang'. Fuse blown etc.

Graham

I also have made this experience. Both BJT and FETs go short-circuit and
blow the mains fuse. Maybe in a bridged output configuration it could be a
DC-value, but then the protection kicks in and disconnects the relays.
 
P

Pooh Bear

Jan 1, 1970
0
Ban said:

That looks good, although possibly a little chunky to put in one's pocket !

they also make the SKP100G2 which should be cheaper (no phantom power), but it is new and not yet in the
catalogue. The existing receiver should work with these too.

I also found this one sold as a 'kit' with a clip on mic - but it's back to 9V batteries.

http://www.sennheiser.co.uk/uk/icm.nsf/root/21101?Open&row=2

Graham
 
M

Midlant

Jan 1, 1970
0
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
 
M

Midlant

Jan 1, 1970
0
My bad. Mine is a Japan model. I have it pulled out as I'm rearranging
the office. In small print under Marantz Sun Valley USA is made in
Japan.
This clears up the incongruity as I thought this series was long after
his USA run.
 
J

Joerg

Jan 1, 1970
0
Hello Graham,
250mAh is good though. What's the terminal voltage when charged ? If it's only
8.4V that seems to be problematic. I gather some NiMHs have an extra cell.

They are seven cell so it is slightly above 9V. Of course it will drop
to 8.4V rapidly but then they stay there almost until exhaustion.
Alkalines show a more steep voltage decline. You can use them down to 6V
and below but the mike's circuitry won't work properly when they are
this low. That is one reason why we changed to NiMH. The other was cost
as 9V alkalines are really expensive. They rarely go on sale like AA
batteries sometimes do.

Regards, Joerg
 
J

Joerg

Jan 1, 1970
0
Hello Ban,
Sorry, there was still another page in my clipboard, I meant this one (in
German for Joerg)
http://www.sennheiser.com/sennheiser/icm.nsf/root/21405

Thanks! This could even work with our existing bank of UHF diversity
receivers. I'll have to find out whether they would operate on NiMH at
2.4V. But even if not, AA batteries are cheap except that this leaves
the environmental concern of disposal.

Regards, Joerg
 
J

Joerg

Jan 1, 1970
0
Hello Graham,
I also found this one sold as a 'kit' with a clip on mic - but it's back to 9V batteries.

I really want to discourage our church to buy any more 9V gear. It just
doesn't hold up well enough. But Ban's hint regarding the handheld is
great, too, because we also use handhelds and have the same issues there
(battery quits or just fails). Also, Sennheiser should have no problem
designing a similar transmitter for lapel use. I mean, it's not rocket
science. I have built transmitters that worked off 2.4V decades ago.
They could run for days.

Regards, Joerg
 
R

Rich The Newsgroup Wacko

Jan 1, 1970
0
Hello Graham,

The analog ones are ok, except for a suboptimal squelch and a nasty pop
when muting it. In church you have to do that a lot. ....
We use Ansmann 9V NiMH which seem to be the only ones with 250mAh, plus
nifty uC charge stations. But even with top notch Alkalines our
Sennheiser EW system doesn't reach 5hrs. ...

Five hours??? In CHURCH????!?!?!?!?!?!?!!! =:-O
 
R

Rich Grise

Jan 1, 1970
0
Hello Graham,


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?

Thanks,
Rich
 
W

Walter Harley

Jan 1, 1970
0
Pooh Bear said:
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.
 
J

Joerg

Jan 1, 1970
0
Hello Rich,
Uh, stupid questions department here - why not just use that one?

Because that one was for ham radio and the stuff for secondary user UHF
needs FCC blessing.

Regards, Joerg
 
J

Joerg

Jan 1, 1970
0
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
 
P

Pooh Bear

Jan 1, 1970
0
Joerg said:
Hello Graham,


They are seven cell so it is slightly above 9V. Of course it will drop
to 8.4V rapidly but then they stay there almost until exhaustion.
Alkalines show a more steep voltage decline. You can use them down to 6V
and below but the mike's circuitry won't work properly when they are
this low. That is one reason why we changed to NiMH. The other was cost
as 9V alkalines are really expensive. They rarely go on sale like AA
batteries sometimes do.

The guys in aapls mention that big live shows buy 9V alkakines by the case from
direct distribution. That makes it rather less costly.

Regds, Graham
 
P

Pooh Bear

Jan 1, 1970
0
Joerg said:
Hello Graham,


I really want to discourage our church to buy any more 9V gear. It just
doesn't hold up well enough. But Ban's hint regarding the handheld is
great, too, because we also use handhelds and have the same issues there
(battery quits or just fails). Also, Sennheiser should have no problem
designing a similar transmitter for lapel use. I mean, it's not rocket
science. I have built transmitters that worked off 2.4V decades ago.

I just checked the full datasheet for this one - the 'transmitter module' and it says nominal
battery voltage 2.4V ! Good for 8 hrs they say.

http://www.sennheiser.co.uk/uk/icm....er_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
 
P

Pooh Bear

Jan 1, 1970
0
Midlant said:
Cor, I too have one of these. Is yours a made in California real Marantz
or a later one made in Japan. I have a scratchy right channel. I've
cleaned the pots, especially the volume pot, but it doesn't seem to have
helped. Have you had this problem? If so what did you do to rectify it?
John

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

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

Graham
 
P

Pooh Bear

Jan 1, 1970
0
Walter said:
I've seen failures where the initial failure was probably a short, but the
resulting current fused the leads of the device (TO220) causing an open. In
gear that has a fuse on the mains but not on the power supply, there's
plenty of juice in the filter capacitors to turn a TO220 into melted bits
without tripping the mains fuse.

TO-220s ! Those are driver transistors ! ;-)

Many years ago I bought a bass amp in which the emitter resistor of one side
of the push/pull output had gone open, with the transistors still intact -
not sure how. Got a great deal on the amp from the seller, who assumed it
was totaled. One resistor later, I had a fine amp that I used for a couple
of years and eventually sold at a profit.

It was a film resistor that failed rather than wire wound I assume ?
But I agree, it's unusual.

Yup, Graham
 
T

Trevor Wilson

Jan 1, 1970
0
cor said:
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.
 
Top