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.
the transistors are BC550
what R values should I go for?
thank you in advance.
It jumps the internal LTP. Usually for substituting with very low noise external BJTs or JFETs. Collector resistors look like 1.25k or thereabouts.
What exactly solved it? There wasn't actually anything changed in Ketje's circuit. 😕
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.
so the ccs in this circuit makes a loud turn on thump. changing the ccs to a resistor eliminates the thump but i want to keep the ccs.
how can i fix the thump?
how can i fix the thump?
Just wondering, but why do you use BC550 for this? Those transistors are not better than the internal in the 5534. You should look at MAT02, 03 or SSM2212, SSM2220
The data sheet does not.
This transistor is not sold for ultra low noise.
It happens it has a very low rbb, from the way it is manufactured.
Geeks, discovered it, measuring transistors rbb.
Do a search.
This transistor is not sold for ultra low noise.
It happens it has a very low rbb, from the way it is manufactured.
Geeks, discovered it, measuring transistors rbb.
Do a search.
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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.
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.