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More differential amplifier questions

Started by NPreston, April 23, 2017, 05:05:35 PM

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NPreston

I have been really trying to understand differential pairs lately in the hopes to build a real power amp someday.. I have read through the subject in Art of Electronics as well as looked up some diy discreet transistor op amp examples..  I'm starting to get how it works and tried it out today with mixed results.. It appeared to work for a while, then I tried to add a capacitor to the feedback path to increase AC gain and it started popping transistors..

Was wondering if anyone could help me understand a few resistor values and tell me what I could have set up better??

1)I arbitrarily set R1 at 33k..  not sure how this should be set..
2)I chose R3 for a 2ma constant current source for Q1/Q2.  then assumed 1ma in Q1 and set R2 to 680 for roughly .65 volts to bias Q4. I believe this is how R2 and R3 are chosen??  Also not sure if maybe Im running too much current?
3)I chose R4 based on a value I saw somewhere in an example..   How do you choose a value for this resistor?
4)I believe R5 and R6 can be used to set gain as in an op amp??

Also not in the schematic.. I had a random capacitor from the collector to base of Q4.   

Anyways I hope the attached schematic shows up.. 

Thanks.

Enzo

Look on the index page for this forum, in the stickies up top,  See "teemuk's book"?  He posted it here for free download.  I suggest and recomkend you do that, read it.

J M Fahey

Excellent book.

But if you want to design, start with this:  http://www.rason.org/Projects/bipolamp/bipolamp.htm

You canĀ“t use 2 or 3 transistore until you learn how to use one :)
Go step by step.

phatt


Another option,
Try Rod Elliott's pages,, they are well written and give in depth explanations without being Too tecky. :tu:

Audio Index; http://sound.whsites.net/articles.htm#ampl

Power Amplifier Design Guide here;
http://sound.whsites.net/amp_design.htm

Trouble shooting Amps
http://sound.whsites.net/troubleshooting.htm

The site is VAST so be prepared to spend many weeks reading. 8|
Phil.