Push Pull driver newbie question

Diogo

Member
2002-08-10 4:21 pm
Brazil
I'm only an student, and I have built a few push pull amps, all using BJT output devices with a single ended driver, I just want to learn how the push pull driver works and how to design an amp using this stage. i want it to drive a push pull output stage.

Thanks for everybody !!!
 
Nice to meet another student here!! Welcome to diyaudio.com!

What exactly do you want to know? I've put a schematic below of an amp I've just made. So which part you want us to tell you how it works?

best regards,

HB.
 

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I recommend you to take a look at the Leach amp

http://users.ece.gatech.edu:80/~mleach/lowtim/

There you have in many parts a classic design in the subject. Since you are new I gather that you haven't heard me nagging about my own stuff?

Check my monster phono amp and monster headphone amp. They are complex (according to some people) but still classic in many senses.

Se link below.
 
some info for Diogo:

R8 and R9 are there to limit the current through the diodes, they can also be replaced by a current source

the diodes are needed to avoid crossover diistortion, also other devices are common.

Q5 is the voltage amplifier stage (C3 reduces higher frequency oscillations), the gain is equal to R12/R13

Q3 and Q4 is a differential amplifier (R3 and R4 reduces little differences between Q3 and Q4). A differential amplifier only 'allow' different signals to go through. (i.e. if the same signal is applied to the base of Q4 and to the base of Q3 there won't go a signal to the base of Q5). When no signal applied, the diff. amp. is 'in balance' => the current through Q3 (I3) is equal to the current through Q4 (I4). I ~ (12V - 0.6V)/R5 = I3 + I4
I3 = I4 so I3 = I/2. Calculation of R7: R7 = 0.6V(Ube of Q5)/I3.

HB.