What exactly solved it? There wasn't actually anything changed in Ketje's circuit.that solved it! thank you!
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.
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 ZTX951Do you have any datasheet that tells that?
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.
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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