bc550 LTP values

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hi guys ive breadboarded this circuit and it works but the offset is too high (0.5v) and im thinking i used the wrong resistor values, for R1 and R2.

the transistors are BC550

what R values should I go for?

thank you in advance.

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that solved it! thank you!
What exactly solved it? There wasn't actually anything changed in Ketje's circuit. :confused:

Also, what kind of external circuitry were you using? The circuit as shown substitutes an opamp (with super low Vnoise - BC337 may be a better bet than BC550 actually) so needs the usual external components to do anything useful. You could build an MC prepre, for example.
 
Do you have any datasheet that tells that?
Well I've built a test preamp using those transistors that detects the difference in Johnson noise between a 1 ohm and 3.3 ohm resistor as source, ie 0.2nV/√Hz of source voltage noise is not swamped by a ZTX851 or ZTX951

The transistors are actually designed as switching transistors with very low saturation voltage, which also happens to require very low Rbb.
 
Horowitz/Hill 3rd ed. lists a sub-2 ohm Rbb' for both... they're pretty much the closest thing to the legendary 2SB737 left for super low impedance work, if without the same high beta. Super low Rbb' high beta transistors all seem to have gone the way of the dodo these days.

If a sub-10 ohm Rbb' will do in your application, ZTX450 and 550 seem like a more sensible alternative. There's a whole range of parts if ca. 30 ohms will do.
 
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