Bjt/jfet?

Thread Starter

Zeeus

Joined Apr 17, 2019
616
Jfet? :mistake

Please enlighten TS

Firstly, was using 70k in place of Q4 and Q5, was testing DC "Quiescent point" (watching the emitter of Q4, expecting about 6v there) and noticed that if scope probe was at collector of Q1 then the output voltage (emitter of Q4) went up to about 11v. strange (why's this?) when changed the 70k to current source, and probe was still there then it went up to around 7v

Now..This circuit does not work..was expecting a large gain but 'nothing' showed up on scope

R7 is boostrap resistor right? which is current source on Q3, yh?

What am I missing?
 

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Thread Starter

Zeeus

Joined Apr 17, 2019
616
Thanks..Just re did it (with and without changing R2 and R1 and C)and it seems to be working (although not working on spice)

gain starts reducing early

That what you want me to see?

edit : I see

I actually have 33uf 33uf and 100pf...100pf makes the difference between work and not work
 
Last edited:

Bordodynov

Joined May 20, 2015
3,431
I changed the ratings to more reasonable ones.
I wanted to show you that you ruined the gain with an excessively large gain correction capacity. I did a frequency response calculation for two capacitor values. This is 100 pF and 0.1 microfarad. You can see everything in the picture. I used the "step param" command. I also used the "measure" command. The results of measuring the gain at a frequency of 1 kHz are at the bottom of the circuit.
Summarizing what has been said: you created a circuit that does not amplify the signal at a frequency of 1 kHz, and you used this frequency at the input.
 
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