C3,C4 and R7 and R6 were added in the final portion of the paper and the only note it has states "Impedence network comprised of R6, C2, R7, C3 provides a band-pass filter response with cutoff frequencies of approximately 16Hz and 16kHz, covering most of the audio frequency range." I did post the source, and they even included a picture of it set up on a breadboard. It seemed like it was a pretty tested solution to me but if it makes no sense then I guess not.What's up with R6 and C4? Maybe you've got other errors in your schematic as well.
And, upon further review, you've got the output connected right back to the input. I think you'd better go back and check your original source.
500 uA tail means 250 uA per transistor in balanced state. R1 dimensioned inapproriately, must be about doubled (or R2 halved). Back to stage 1 calculation.As per the specifications:
On the Differential Stage I set the resistors to provide 9.3v on the output and have 500uA going through the tail resistor.
Okay so I have made those changes and its almost working... I am not sure how to get the ac voltage reading you guys want, when I put a cap before the load resistor the whole circuit just stops working properly and its only uV range on my output. It also now appear to be clipping off the top half, If I understand that would be due to my CE currrent Source bias voltage being too high. Is that correct?After fixing the faults mentioned in post #2 and #5, I have no doubt that you get a functional audio amplifier, at least suited for educational purposes. Due to the class B output stage biasing, sound quality won't be mind blowing.
An ideal differential amplifier is often using current sources instead of resistors. But the project circuit isn't that bad. Suggest to correct the remaining fault and than try to improve the amplifier circuit.Also I am not sure what you meant by "That has current source and current sink around differential pair"
Okay I will try to figure out why the output is clipping. As I said, the reason I think it is clipping is the bias current/voltage on Q5 is set incorrectly, I will re do my calculations and see if I can fix it. Although that process has me very confused. I've seen online people use the Vbe Ic Graphs to find the spot with the most swing on it but i've also seen online people saying the manufacturers dont provide those graphs anymore and you never needed them to begin with.An ideal differential amplifier is often using current sources instead of resistors. But the project circuit isn't that bad. Suggest to correct the remaining fault and than try to improve the amplifier circuit.
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Circuit is designed for DC output coupling, no need for output capacitor. Have to check why positive halfwave is clipping.
Try reducing the value of R2.I will try to figure out why the output is clipping.
Thank you! I was barking up the wrong tree, trying to change the values of R3-5. After playing around with the value of R2 I found 510 ohms gave me a nice sine wave and the highest output and It is now definitely amplifying. Here is the output:Try reducing the value of R2.
That increases the drive to Q3.
Interesting, I did not realize R6/R7 had an effect on gain inside the passband frequency. So with the values of 20k/1k it is not possible to achieve anything over a gain of 20? How would one go about balancing the output?5W into 8 ohms is an output voltage swing into 8 ohms of 17.89Vp-p.
With your input of only 200mVp-p then the gain must be 17.89/0.2= 89.45 times. But your amplifier uses 20k for R6 and 1k for R7 then its gain should be 20/1= 20 times.
An audio amplifier should be balanced so that it has NO or VERY LITTLE output offset voltage.
Your gain is so low and your output offset voltage is so high that crossover distortion is not produced.
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