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ski
08-02-2003, 03:19 PM
Any engineers or electronics enthusiasts in the crowd? :P

By Tuesday, I have to design an audio frequency (AF) amplifier. They gave me the diagram...

And the specs:
Rin (input resistance): between 23 and 27 Ohms
Av (Voltage gain): between 100 and 130
Vo (output voltage): 3 Volts peak to peak (ideally sine wave from -1.5V to 1.5V)

And some crap about 3dB points, I'll figure that out later :)

So it's basically finding the values of the resistors in that diagram by looking at each BJT (Bipolar Junction Transistor). Now, I'm stuck on the first transistor, because it's in there all funny (all the examples in my notes and the book are given in the orientation of the right transistor).

Has anyone...
1) Had to do a similar assignment?
2) Worked with these?
3) Acquired knowledge of transistor-based amplifiers?

The only help I really need is the method of madness to solve it. Chances are if you're still reading this, you might know what all of this stuff is! So right now I'm taking the left half of the circuit and trying to make it into its small scale equivalent to find input/output voltage, resistance, etc. Don't know why I'm doing it, but I am :heh:

Commom Base Amplifier (http://filebox.vt.edu/users/kedooley/work/cbe_amps.pdf)... although I expect no one to be able to help me (due to it not being fun :P), if you do, that's a helpful document.

Thanks, if anything, I provided some humor for being stuck on this!

EDIT: See below!

ramazank2
08-02-2003, 04:15 PM
All I remember is V=IR but there is one other golden rule...

PrObLy
08-02-2003, 04:24 PM
wish I could help but I'm taking Electrical Circuits next semester

maybe this link (http://www.angelfire.com/ab3/mjramp/pagefour.html) could help ya though

ski
08-02-2003, 05:08 PM
Thanks probly -- I'm glad you could help a little bit with that link!

This is one project that I'm actually interested in, because I messed around with car audio junkus in high school (from a distant level, I just knew terms and what sounded good :D) and now I'm starting to see how a car or home audio amplifier works (just take in your source, run it through the basic concept of the amp I'm making, then load it with the speakers. It's finally coming together!

Making slow but steady progress - not sure where I'm going, but I'm solving like a madman for some of the resistor values.

Does anyone have any background using PSpice? just wanted to check :)

Sir_Froggy
08-02-2003, 06:15 PM
man I hated that resistor stuff in physics...I could never understand it, everything else was fine though....

ski
08-02-2003, 06:43 PM
Originally posted by ramazank2
All I remember is V=IR but there is one other golden rule...

Probably Norton/Thevenin equivalents :cool:

InfiniteNothing
08-02-2003, 06:49 PM
Probably loop rule. Isn't there a junction rule too?

coleslaw
08-02-2003, 10:47 PM
Convert each BJT into its equivalent hybrid-pi model and then go from there.

ski
08-03-2003, 10:04 AM
hmmm, you mean it's AC bias model? when you change it the way I'm thinking of, you get an R-sub-pi (one of the resistors coming out of the BJT).

Thanks slaw :)

ski
08-03-2003, 07:08 PM
I decided to withdraw from this course. 8 hours of class each day has finally caught up to me, and I won't be able to get a good grade on the project or final (50% combined of my total grade). No more of this for me until Spring of next year, but I'll be a year behind :eek:

<sigh>