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Old 30th December 2003, 07:09 AM   #1
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Default preamps, transistor testing, power amplifier yamaha

Hello all
The problem is a Yamaha p2200. One channel has 80vdc on the output and its not going away buy itself. I have checked the power supply and i belive it is getting the right amount of power. There is no visible damage to the board or any capacitors/resistors. Im wanting to know how to test the output transistors with a multimeter. My meter has a transistor tester on it however its designed for very small transistors and the output transistors wont fit in it.

II have another question which might get some people thinking.
The input of this amp is 4dbm i belive as it is a professional amp at 230w/8ohm a channel. Now my cd player output is something like -20dbm i belive. SO when i plug my cd player into it is really quiet. - Any suggestions.. . .
What i have done is plug my cd player into my hifi amp (around 30w) and pluged the speaker terminals of my hifi amp into the input of the yamaha power amp. . Can this do damage?? IT works but im not sure if it is correct? Does anyone no where to get a preamp or how to build a preamp with a 4dbm output??
Thankyou
Daniel
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Old 30th December 2003, 07:52 AM   #2
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Never connect speaker outputs to line inputs.
4db is 1.23V is the max voltage that can be applied to the input without clipping the output.
Speaker outputs are a magnitude more than that and will cause harm to your power amp input, if not blow it away completely. Maybe that's exactly what happened.
You need a preamp or a mixer to connect in between.
Look at the users manual
here
As for your first question: this is a good explanation how to measure transistors.
Keep in mind that such power amps will not be easy to repair yourself if I may assume your still a newbie to electronics

/Hugo
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Old 30th December 2003, 08:42 AM   #3
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As above, conencting speaker ouptuts to line inputs is a big nono unless you know the amp supports that form of bridging. Most do not, and I highly doubt yours does.

May I suggest purchasing a cheap DJ mixer to match levels, or constucting/purchasing a small active opamp circuit to match gain to the level needed.

Alternatively find a cd player with higher output

Power amps are not rivial to repair and can give you a nasty shock if youre not careful. Depending on your experience level you may just want to get someone else to look at it.
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Old 30th December 2003, 11:06 AM   #4
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Default umm... preamp???????

Gday,
Im yet to try testing the transistors. As far as the plugging amps into amps go, i wasnt totally sure if it was any good for it.. aparently not, it sounded good though. ANyway for the preamp thing, they seem to be hard to come buy. I bought a mixer off the net, and it is totally fully of siht. I recons 0db is coming out of it when there is no way that much power comes out of it. Where could i get a preamp or something from. I never heard of a cd player that could go that LOUD. cause when i was testing the power amp with my hifi amp i almost hand it cranked right up(30w into 8 ohm) Now heres another question, on the back of the amp it says " Input 100w 8ohm Unbalanced" What does that mean, it gave me the idea to plug in my hifi amp but im not doing that again. As for how it originally blew up, i have no idea, i bought this for 212.50 of ebay aus. and one channel wasnt working. It has a built in bi-amp system which is interesting and the channel that blew was the channel that was used for Low frequencies (no surprise there)
Thanks for your responses. Id like any info if anyone has it on preamps that have the 4dbm output cause the net is useless as far as preamps are concerned. Im wanting to plug my computer into this amp so i need some kind of amp inbetween. THanks
Daniel
priscared@hotmail.com
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Old 30th December 2003, 11:08 AM   #5
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Default usermanual

I have looked in that usermanual 60 pages!!! it doesnt tell u much. It just blabs on about how good it is. And so ive figured already that normal hifi equipment is about -20dbm and this amp needs 4dbm so i need an amp of some kind. Can anyone give me a company? A website? A kit? A circuit? Thanks
Daniel
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Old 30th December 2003, 11:32 AM   #6
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Ok thanks for the link to that transistor testing page. I found a f2n3055 transistor laying around and tested according to the page and it checked out. However my multimeter came up with 500 on the screen instead of 4-5volts. I dont know how my meter works. Its a q-1447 DSE if anyone has a similar model maybe they can tell me why my meter reads like this on diode mode. Anyway if anyone knows the specs on the output transistors on the p-2200 Yamaha power amp thatd be great. I dont even know if they are NpN or PNP , all i know is the Yamaha guy in melbourne told me they cost 30 bucks each!!!
CYA
Daniel
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Old 30th December 2003, 05:49 PM   #7
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Default Re: usermanual

Quote:
Originally posted by priscared
I have looked in that usermanual 60 pages!!! it doesnt tell u much. It just blabs on about how good it is. And so ive figured already that normal hifi equipment is about -20dbm and this amp needs 4dbm so i need an amp of some kind. Can anyone give me a company? A website? A kit? A circuit? Thanks
Daniel
IMHO the manual goes much further than a normal users manual should go. It's extremely well detailed and gives a lot of info about hook-up and is a great source of knowledge.
The preamp you're looking for depends on what the amp will be used. This is a typical PA-amp. Can be used in the house but it depends on your expectations. Much db's or a nice clean sound.
Or both

This amp deserves a good mixer, don't buy the cheap ones.
Ecler or Pioneer comes to mind as good value for money mixers. If you go for a normal preamp, browse the forum, you'll find tons of them.

Where does the 4-5 volt come from? Your meter indicate 500mV, thats 0.5V which is ok for a diode test.
What power transistors are inside?

/Hugo – would bring the amp to a repair center…
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Old 30th December 2003, 06:31 PM   #8
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Default Re: umm... preamp???????

Quote:
Originally posted by priscared
Input 100w 8ohm Unbalanced" What does that mean, it gave me the idea to plug in my hifi amp but im not doing that again.
Can't find it on the manual, you have a picture of that?

/Hugo
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Old 18th January 2004, 01:51 PM   #9
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Default heres a photo

Gday
i think ive solved my preamp problems , found an old yamaha soundcard lying around, sounds like **** but it works ok.
If anyone thinks they can help me out fixing my Yamaha amplifer, please search this forum for "priscared" as i have made 3 threads about it.
A website told me thats how to test transistors and that 4-5 volts should show up on the screen...
Also check out www.geocities.com/elphocfa/yamaha/
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Old 19th January 2004, 02:29 AM   #10
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Buy three pair of MJ21193/94 outputs and one pair of MJE15032/33 drivers per channel, throw away the junk in the amplifier without testing.

The cost per channel of the above parts is about USD$14

Flameproof and fusible resistors cost about $0.10 each for small ones and $0.50 for the 5W size. 1/4W and 1/2W films are about $0.05 each.

Just scape everything off and start over.
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