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Simple Amp problems

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The 3rd transistor has a voltage gain of 33 so the slightest difference in its base to emitter voltage will cause it to be cutoff or saturated.
I think its base voltage is 1.15V, its emitter voltage is 0.5V and its collector voltage is saturated at 0.6V.

Increase the value of the 150 ohm emitter resistor to make the 3rd transistor less sensitive.
 
Hey there thanks for the reply.

As it stands my output is smaller than my input. If i make the 150 Ohm resistor on the first amp stage it doesnt seem to make any difference though if i make it smaller (100 Ohms) the voltage out for the first amp stage gets closer to what it should be and i start producing gain on my output though the amp now clips and teh voltages on the other stages are wrong.

Is it for the same reason?

Thanks

Tom
 
3k5, 650k, 860k etc. are not standard values, use real resistor values.
 
Cheers again for the help but using propper resistor values didnt work.

On the first stage, you are assuming that the Darlington transistor arrangement is dropping 1.4V across the two base-emitter junctions. However, it is probably better to assume about 1 V or 1.1 Vdrop. This is because the first junction has lower base current than the second (hence lower Vbe).

In any event, your circuit has a bias sensitivity issue, because the bias voltages of each stage all propagate from the first stage bias resistors. Any error from the early stages, propagate to the latter stages.

Also, audioguru has a valid point about the sensitivity of the second stage. The small errors in the assumed Darlington Vbe drop, can have a big effect on this second stage.
 
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Cheers again for the help but using propper resistor values didnt work.
Of course using proper resistor values alone won't make your circuit work, you need to design it properly for that. Using real resistor values just means you'll be able to build it without having to connect loads of resistors in series or parallel to get the correct values.
 
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