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Old 19th April 2001, 10:16 PM   #1
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Last edited by k.junold; 23rd July 2014 at 11:22 AM.
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Old 19th April 2001, 11:12 PM   #2
blmn is offline blmn  Brazil
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k.junold,

I don´t have Douglas Self´s book with me now, but, you can find at Douglas Self´s site (www.dself.demon.co.uk) articles about power amps using japanese series of low power transistores with low noise and high Ft. (2SA970 etc.)

regards
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Old 12th February 2004, 01:31 PM   #3
Electrons are yellow and more is better!
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What are your application? Transistors don't have to have low noise. It depends where they are. Normally only the input transistors are important. BC546, 547 548 549 550 556 557 558 559 560 etc are normal and OK in most situations. BD135 136 137 138 139 140 don't have to have low noise in most situations.

The speed is also OK 100-300 Mhz for the BC types and aorund 100 MHz for the BD types.
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Old 13th February 2004, 02:42 PM   #4
Pedja is offline Pedja  Serbia
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Hi P-A, nice, quick answer.
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Old 13th February 2004, 02:47 PM   #5
Electrons are yellow and more is better!
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Very low noise transistors have drawbacks (not so fast, higher capacitances, not so high Hfe in some cases) so that means (as allways) that you must choose transistor type with taste. Each transistor must be chosen considering what it should do.
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Old 13th February 2004, 03:13 PM   #6
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Besides that Per, ultra low noise only makes sense in low signal apps AND low source resistance. I.e. MM pre amps and even then … The BC446 – BC 560 small signal transistors can be considered low noise for nearly all audio apps.

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Old 13th February 2004, 03:46 PM   #7
Pedja is offline Pedja  Serbia
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…and besides all that, the question was asked 3 years ago.
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Old 13th February 2004, 04:10 PM   #8
Electrons are yellow and more is better!
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Quote:
Originally posted by Pedja
…and besides all that, the question was asked 3 years ago.
Hm, but why was the thread so high up....?
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Old 13th February 2004, 05:24 PM   #9
Pedja is offline Pedja  Serbia
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No idea. It was high before you have answered?

As about the thread topic, since the question was what is lower noise replacement for BC547, the answer can be BC549/550 (549/550 are lower noise than 546/547/548).

Pedja
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Old 13th February 2004, 05:32 PM   #10
pjacobi is offline pjacobi  Germany
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Anyway, just imagine the pure guy asking the original question:

Sitting in front of the PC, soldering iron switched on, desperately pressing 'refresh'.

And no answer for three years.

And to be not 100% off topic: 3 BC547 would have lower noise than one BC547, but you must have well matched devices to get fair current shating without further measures.

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Peter Jacobi
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