low noise replacement for BC547, BC557, BD135, BD136

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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
 
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.
 
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.

Regards,
Peter Jacobi
 
ok

I ment in this circuit,thanks!:confused:
 

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The base resistors are OK left at 51 ohm. They isolate the opamp output from the B-C and B-E junction capacitance of the transistor and prevent any stability issues. The absolute value won't be very critical.

Absolutely no problem with the different ft of the transistors either.
 
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