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bc550 LTP values
bc550 LTP values
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Old 7th April 2020, 01:49 PM   #1
donovas is online now donovas  South Korea
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Default 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.

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Old 7th April 2020, 02:14 PM   #2
Ketje is offline Ketje  Belgium
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What is the use of that circuit? There are allready resistors inside the IC.
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Old 7th April 2020, 02:21 PM   #3
donovas is online now donovas  South Korea
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that solved it! thank you!
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Old 7th April 2020, 02:25 PM   #4
Salas is offline Salas  Greece
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bc550 LTP values
It jumps the internal LTP. Usually for substituting with very low noise external BJTs or JFETs. Collector resistors look like 1.25k or thereabouts.
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Old 7th April 2020, 05:02 PM   #5
sgrossklass is offline sgrossklass  Germany
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Quote:
Originally Posted by donovas View Post
that solved it! thank you!
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.
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Old 10th May 2020, 04:21 PM   #6
donovas is online now donovas  South Korea
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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?
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Old 10th May 2020, 04:37 PM   #7
peranders is offline peranders  Sweden
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bc550 LTP values
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
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Old 11th May 2020, 03:15 AM   #8
mchambin is offline mchambin  France
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Lowest noise bjt: ZTX 851.
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Transistor junction temperature is not transistor case temperature.
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Old 11th May 2020, 04:33 AM   #9
peranders is offline peranders  Sweden
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bc550 LTP values
Do you have any datasheet that tells that?
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Old 11th May 2020, 06:54 AM   #10
mchambin is offline mchambin  France
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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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Transistor junction temperature is not transistor case temperature.

Last edited by mchambin; 11th May 2020 at 07:23 AM.
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