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#1
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Andy writes:
Without knowing their biasing circuitry, I don't think a complete answer can be given. Some biasing circuits are fairly forgiving, others seem like balancing a pencil on it's end... But, in my opinion, Vbe and hfe are primary parameters. I would be interested in learning a better answer myself, tho. You might consider sci.electronics.design also, if you haven't already. There are some competent IC designers there, who deal with problems like this when they design their miracle circuits..... Andy |
#2
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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. Some circuits almost don't care. It depends a lot on the driver stage. 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. Graham |
#3
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Amplifier transistor matching?
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. |
#4
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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. ... 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. Regards, Joerg http://www.analogconsultants.com |
#5
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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. Graham. |
#6
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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. |
#7
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#8
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#9
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#10
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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. I've probably repaired many hundred such units, so here goes..... We stocked generic parts for all of these repairs with minimal hFE=75 and VCE=100. Then parts were matched to the following characteristics: 1) Case style: TO-3, TO220, or small signal 2) NPN, or PNP 3) Regular transistor, or darlingtons. 4) Replace all transistor in the complete channels output circuit, usually 5 to 7. 5) Turn the bias current adjustment to minimum resistance. 6) Plug the AC power cord thru a 40 watt lamp circuit in series with the power. 7) Turn on the unit with no signal, and watch for a dimming light bulb. If it goes full brightness, kill all power and go back to step 4 looking for more fried parts. 8) If the light goes dim, connect directly to AC power. 9) Feed 1kz sine wave in errant channel while driving a 100w 8ohm resistive load. Run a very low power level to accentuate the 'notch'. Watch the output on a scope and tweek the bias pot until this 'crossover notch' dissappears. 10) Additional testing using a harmonic distortion analyzer may find a more optimum setting for the bias at full power level. You may or may not get original factory specs using generic parts, if you can get 'factory' parts it may work better, or not. Be aware, if you apply full AC power with even one of the transistors in a failed mode, it will 'take down the whole show' all over again. Good luck, -- Luhan Monat: luhanis(at)yahoo(dot)com http://members.cox.net/berniekm "Any sufficiently advanced magick is indistinguishable from technology." |
#12
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Ol' Duffer wrote:
In article , says... 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. An open device in a totem pole configuration makes the amp able to drive in only one direction, so you get only the positive or negative half of the waveform, i.e. 50% distortion. Good god ! I'd forgotten about non complementary outputs ( thankfully ). It's been that long. ;-) Graham |
#13
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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. Regards, Joerg http://www.analogconsultants.com |
#14
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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. 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. rec.audio.pro is good but mainly recording oriented. It's the live guys who use wireless mics most. Not today, the barbie is almost ready. Marinated ribs and potatoes tonight. Sounds very nice. Enjoy ! 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. Having the volts available is often handy, although I admit I don't know the exact answer. 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. Graham |
#15
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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. 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 But your system sems to be outdated. Here is a 2AA 6-8hrs transmitter http://www.sennheiser.com/sennheiser/icm.nsf/root/21531 -- ciao Ban Bordighera, Italy |
#16
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Ban wrote:
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. 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 But your system sems to be outdated. Here is a 2AA 6-8hrs transmitter http://www.sennheiser.com/sennheiser/icm.nsf/root/21531 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 |
#17
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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 -- ciao Ban Bordighera, Italy |
#18
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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 -- Ah - ok - tech spec here. http://www.sennheiser.co.uk/uk/icm.nsf/root/21405# Unfortunately not a lapel mic. I wonder if Sennheiser do a simple transmitter pack ? Graham |
#19
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"Pooh Bear" wrote in message
... Incidentally I can't really see how a failed output device can be responsible for severe distortion. Normally it's a works or not situation with output devices. If one of the pair fails, the result is severe distortion - a rectified waveform, low-pass filtered by the speaker. Only about 30% THD... some people don't even notice! |
#20
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Walter Harley wrote:
"Pooh Bear" wrote in message ... Incidentally I can't really see how a failed output device can be responsible for severe distortion. Normally it's a works or not situation with output devices. If one of the pair fails, the result is severe distortion - a rectified waveform, low-pass filtered by the speaker. Only about 30% THD... some people don't even notice! Since failure IME is invariably short circuit, I tend to find that it goes 'bang'. Fuse blown etc. Graham |
#21
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"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. |
#22
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Pooh Bear wrote:
http://www.sennheiser.co.uk/uk/icm.nsf/root/21405# Unfortunately not a lapel mic. I wonder if Sennheiser do a simple transmitter pack ? Graham http://www.sennheiser.co.uk/uk/icm.n...ries500_21640# they also make the SKP100G2 which should be cheaper (no phantom power), but it is new and not yet in the catalogue. The existing receiver should work with these too. -- ciao Ban Bordighera, Italy |
#23
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Pooh Bear wrote:
Walter Harley wrote: "Pooh Bear" wrote in message ... Incidentally I can't really see how a failed output device can be responsible for severe distortion. Normally it's a works or not situation with output devices. If one of the pair fails, the result is severe distortion - a rectified waveform, low-pass filtered by the speaker. Only about 30% THD... some people don't even notice! Since failure IME is invariably short circuit, I tend to find that it goes 'bang'. Fuse blown etc. Graham I also have made this experience. Both BJT and FETs go short-circuit and blow the mains fuse. Maybe in a bridged output configuration it could be a DC-value, but then the protection kicks in and disconnects the relays. -- ciao Ban Bordighera, Italy |
#24
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Ban wrote:
Pooh Bear wrote: http://www.sennheiser.co.uk/uk/icm.nsf/root/21405# Unfortunately not a lapel mic. I wonder if Sennheiser do a simple transmitter pack ? Graham http://www.sennheiser.co.uk/uk/icm.n...ries500_21640# That looks good, although possibly a little chunky to put in one's pocket ! they also make the SKP100G2 which should be cheaper (no phantom power), but it is new and not yet in the catalogue. The existing receiver should work with these too. I also found this one sold as a 'kit' with a clip on mic - but it's back to 9V batteries. http://www.sennheiser.co.uk/uk/icm.n...101?Open&row=2 Graham |
#25
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Cor, I too have one of these. Is yours a made in California real Marantz
or a later one made in Japan. I have a scratchy right channel. I've cleaned the pots, especially the volume pot, but it doesn't seem to have helped. Have you had this problem? If so what did you do to rectify it? John "cor" 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. |
#26
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My bad. Mine is a Japan model. I have it pulled out as I'm rearranging
the office. In small print under Marantz Sun Valley USA is made in Japan. This clears up the incongruity as I thought this series was long after his USA run. "Midlant" wrote in message news:R0joe.65359$sy6.30149@lakeread04... Cor, I too have one of these. Is yours a made in California real Marantz or a later one made in Japan. I have a scratchy right channel. I've cleaned the pots, especially the volume pot, but it doesn't seem to have helped. Have you had this problem? If so what did you do to rectify it? John "cor" 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. |
#27
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Hello Graham,
250mAh is good though. What's the terminal voltage when charged ? If it's only 8.4V that seems to be problematic. I gather some NiMHs have an extra cell. They are seven cell so it is slightly above 9V. Of course it will drop to 8.4V rapidly but then they stay there almost until exhaustion. Alkalines show a more steep voltage decline. You can use them down to 6V and below but the mike's circuitry won't work properly when they are this low. That is one reason why we changed to NiMH. The other was cost as 9V alkalines are really expensive. They rarely go on sale like AA batteries sometimes do. Regards, Joerg http://www.analogconsultants.com |
#28
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Hello Ban,
Sorry, there was still another page in my clipboard, I meant this one (in German for Joerg) http://www.sennheiser.com/sennheiser/icm.nsf/root/21405 Thanks! This could even work with our existing bank of UHF diversity receivers. I'll have to find out whether they would operate on NiMH at 2.4V. But even if not, AA batteries are cheap except that this leaves the environmental concern of disposal. Regards, Joerg http://www.analogconsultants.com |
#29
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Hello Graham,
I also found this one sold as a 'kit' with a clip on mic - but it's back to 9V batteries. I really want to discourage our church to buy any more 9V gear. It just doesn't hold up well enough. But Ban's hint regarding the handheld is great, too, because we also use handhelds and have the same issues there (battery quits or just fails). Also, Sennheiser should have no problem designing a similar transmitter for lapel use. I mean, it's not rocket science. I have built transmitters that worked off 2.4V decades ago. They could run for days. Regards, Joerg http://www.analogconsultants.com |
#30
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On Sat, 04 Jun 2005 02:35:05 +0000, Joerg wrote:
Hello Graham, Hmmm.. I'm not specifically into wireless mikes and I think both the older VHF ( certainly ) and newer UHF ones are good old analogue. The analog ones are ok, except for a suboptimal squelch and a nasty pop when muting it. In church you have to do that a lot. .... We use Ansmann 9V NiMH which seem to be the only ones with 250mAh, plus nifty uC charge stations. But even with top notch Alkalines our Sennheiser EW system doesn't reach 5hrs. ... Five hours??? In CHURCH????!?!?!?!?!?!?!!! =:-O -- Cheers! Rich ------ "Hear about... the fellow who was descended from a long line his mother heard?" |
#31
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On Sat, 04 Jun 2005 18:42:56 +0000, Joerg wrote:
Hello Graham, I also found this one sold as a 'kit' with a clip on mic - but it's back to 9V batteries. I really want to discourage our church to buy any more 9V gear. It just doesn't hold up well enough. But Ban's hint regarding the handheld is great, too, because we also use handhelds and have the same issues there (battery quits or just fails). Also, Sennheiser should have no problem designing a similar transmitter for lapel use. I mean, it's not rocket science. I have built transmitters that worked off 2.4V decades ago. They could run for days. Uh, stupid questions department here - why not just use that one? Thanks, Rich |
#32
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"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. 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. |
#33
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Hello Rich,
I really want to discourage our church to buy any more 9V gear. It just doesn't hold up well enough. But Ban's hint regarding the handheld is great, too, because we also use handhelds and have the same issues there (battery quits or just fails). Also, Sennheiser should have no problem designing a similar transmitter for lapel use. I mean, it's not rocket science. I have built transmitters that worked off 2.4V decades ago. They could run for days. Uh, stupid questions department here - why not just use that one? Because that one was for ham radio and the stuff for secondary user UHF needs FCC blessing. Regards, Joerg http://www.analogconsultants.com |
#34
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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 |
#35
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Joerg wrote:
Hello Graham, 250mAh is good though. What's the terminal voltage when charged ? If it's only 8.4V that seems to be problematic. I gather some NiMHs have an extra cell. They are seven cell so it is slightly above 9V. Of course it will drop to 8.4V rapidly but then they stay there almost until exhaustion. Alkalines show a more steep voltage decline. You can use them down to 6V and below but the mike's circuitry won't work properly when they are this low. That is one reason why we changed to NiMH. The other was cost as 9V alkalines are really expensive. They rarely go on sale like AA batteries sometimes do. The guys in aapls mention that big live shows buy 9V alkakines by the case from direct distribution. That makes it rather less costly. Regds, Graham |
#36
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Joerg wrote:
Hello Graham, I also found this one sold as a 'kit' with a clip on mic - but it's back to 9V batteries. I really want to discourage our church to buy any more 9V gear. It just doesn't hold up well enough. But Ban's hint regarding the handheld is great, too, because we also use handhelds and have the same issues there (battery quits or just fails). Also, Sennheiser should have no problem designing a similar transmitter for lapel use. I mean, it's not rocket science. I have built transmitters that worked off 2.4V decades ago. I just checked the full datasheet for this one - the 'transmitter module' and it says nominal battery voltage 2.4V ! Good for 8 hrs they say. http://www.sennheiser.co.uk/uk/icm.n...eries500_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 |
#37
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Hello Graham,
http://www.sennheiser.co.uk/uk/icm.n...eries500_21640 Trouble is, it measures 4" x 1-3/4 " sq. Only has an XLR input so you'd need a conversion cable from your lapel mic. That is a bit bulky. But it still gives hope that they'd come out with a 2.4V lapel wireless some day. The electronics in there can't be this big. Regards, Joerg http://www.analogconsultants.com |
#38
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Midlant wrote:
Cor, I too have one of these. Is yours a made in California real Marantz or a later one made in Japan. I have a scratchy right channel. I've cleaned the pots, especially the volume pot, but it doesn't seem to have helped. Have you had this problem? If so what did you do to rectify it? John I've heard US contributors to the audio groups mention 'Caig' as good for switches - maybe pots too. I have no expereince of it though as it doesn't appear to be sold in the UK. Graham |
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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 ! ;-) 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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"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. **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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