Depredation

modified 11 years ago

3 stage amp

144

03:28:40

I built this in lab, can't get it to work on here.  Help and Suggestions are appreciated

published 11 years ago

Chryseus

11 years ago

It appears your biasing is wrong, particularly with the first transistor, 14.7V is way too high

Depredation

11 years ago

I'm getting the 90 mV from the input at transistor 1

11 years ago

Hi, its almost perfect for audio preamp, but signal is too weak at the output, i noticed some unnecessary components at first and second stages

Depredation

11 years ago

I can't find aA or fA or some of the other units anywhere in the Fairchild or national semiconductor data sheets.

11 years ago

Would you know the maximum input voltage for this circuit?

hurz

11 years ago

In your first stage Re is much to high with 10k. Because Rc/Re gives you roughly the gain. Try about 500Ohm for Re. Seconde stage Re is much to low try about 200Ohm.

Depredation

11 years ago

I calculated re for all three transistors, as is the re for the transistors are 14 - 17 ohms. Not sure about the max input, this gain of this amp is only 20k-24k. 4.5 mV is suppose to output 10V, i built this on a breadboard.

hurz

11 years ago

Only 20000?? There are two stages which are for positive voltage gain, and if you have 20dB for each you get in total a gain of 100 with not to much distortion. I would recommand to set back all bjt properties to the EC default values.

rbrtkurtz

11 years ago

You say you built this in the lab. Then you should know what transistors you used and/or have a schematic for the circuit. So just Google search the datasheets for the transistors you used, and get the specs for them.

rbrtkurtz

11 years ago

Judging by the biasing, it doesn't look like high gain transistors were used.

Depredation

11 years ago

I used 2 2N3904 and a 2N3053, aA and fA don't exist in the databases. I have no idea what to set them too.

hurz

11 years ago

One fA is 1e-15Ampere. Or 0.000000000000001A

hurz

11 years ago

2N3904 is a NPN small signal general purpose transistor, 2n3053 is a PNP but you don't need that according to your schematic. Just take 3 x 2n3904 and keep EC default settings.

rbrtkurtz

11 years ago

The default values are pretty close to stimulating a 2N3904. If anything, set saturation current to 5fA - 10fA, and the reverse beta to 250mA/A. Leave the forward beta at 100A/A, and all the resistances at 1 ohm. Really, you can just leave all the values default, and it will closely approximate the transistor.

Depredation

11 years ago

Thank you very much!

Depredation

11 years ago

I am a dumb ass, the 10 v output from a 10 mv input was measured in peak to peak values. This app was giving the appropriate values.

Depredation

11 years ago

In rms

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