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donovas 7th April 2020 01:49 PM

bc550 LTP values
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.

Ketje 7th April 2020 02:14 PM

1 Attachment(s)
What is the use of that circuit? There are allready resistors inside the IC.

donovas 7th April 2020 02:21 PM

that solved it! thank you!

Salas 7th April 2020 02:25 PM

It jumps the internal LTP. Usually for substituting with very low noise external BJTs or JFETs. Collector resistors look like 1.25k or thereabouts.

sgrossklass 7th April 2020 05:02 PM


Originally Posted by donovas (
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.

donovas 10th May 2020 04:21 PM

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?

peranders 10th May 2020 04:37 PM

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

mchambin 11th May 2020 03:15 AM

Lowest noise bjt: ZTX 851.

peranders 11th May 2020 04:33 AM

Do you have any datasheet that tells that?

mchambin 11th May 2020 06:54 AM

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.

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