Unusual LM741 or UA741 Op-amp Power Amplifier Using Darlington Output Transistors
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- Опубликовано: 12 сен 2024
- Here I test a power amplifier made of 741 op-amp in unusual set up were the signal inputs of the Darlington transistors is derived from the supply current of the op-amp.
Very creative use of power rails, lol. I’m surprised it even works as well as it did - there must be all sorts of non-linearities between the signal and power line circuits in an op amp. Kudos for creativity.
Great video thanks. I love the spring steel clips on your heatsink very elegant idea. Also the clear view of the scope using the monitor.
Possibly a tighter layout would improve the distortion levels. Some decoupling caps nestled close to the op amp legs might clean the signal hitting your power amp. I am amazed you are getting a clean sine wave on the scope with such high distortion. John Audio Tech has some nice videos on good layout and decoupling for ok amps. Nice original amp design and your workspace is so well thought out. Keep going, really well done.
Nice video, this is redesigning class ab to be more like class a, but with less bias current, conventional class ab still have off time, even with higher bias current, but this design is not, both darlington is never off state, just idle
Cool idea! Did you try it with only local feedback for the op amp?
If you look at the voltage annotation on the schematic paper you can see that the input stage is at -1mV drive. So something is still wrong in simulation. Boosting over th eopamp supply has many drawbacks. Not every 741 is like the generic by tricking the supply current as booster drive. Second the PSRR get feedback to the input. So the positive and negative boost nodes couple to the input stage. You can boost by building the output stage of the opamp discrete. This is the way also to rise the voltage capabilities.
Omg you are a madman
This is really a nice tutorial video
Great video thank you
👍👍🇩🇿🇩🇿
Oops typo below: ok amps should say op amp. I used to love the sound of the cheaply built valve amps in my STEREO record player (a new thing in the 60s). Yes I am a bit ancient :) Lovely warm punchy, clear sound but it must have had loads of harmonics and distortion. Maybe this sounds like that in your room. Bit rough on a tiny phone speaker, maybe a good mic would render the sound better?
Very nice !
I do Agree with you the sound is not bad ,it is horrible.
Very nice video awesome..
Sir how to analysis this amp to design own, i mean how to select the component value for desired output ( say 100 watt @8 ohm)
Can you help me to design 100 watt amp @8 ohm load?? Or any website or book for reference
What is the minimum value of the DC biasing current in class A output stage? Explain you answer.
btw this is a nice vid ^_^ thank you so much! you saved my life lol
You can build a 'passive preamp' before sending it's output to the input of the opamp. It will vastly reduce the gain, so you may need two amplification stages.
For instance, if you want the knob to provide up to 16DB bump to a frequency range, the overall signal will need to drop by that amount to allow the headroom.
hi Mr Kerona, i am confused ,what i would like to know, if the 2n3904 input is only connected to the op-amp supply rail,how does the audio signal get into the 2n3904 base, and out of the 25c5198 output to the speaker, please forgive my lack of electronic knowlege
No need for apology friend! Basically the op-amp is loaded with a very low impedance at its output (47Ω in this case). Because of this, the op-amp will draw significant amount of current proportional to the input voltage through its supply pins when the input signal is non-zero. This supply current will cause a voltage drop across R5 and R6 which will turn on 2N3904 and 2SC5198 for positive going input signal and 2N3906 and 2SA1941 for negative going input signal. Also because of negative feedback, the magnitude of the output voltage is scaled up by a factor of R1/R7 = 220. FYI this amplifier configuration will not work with low power op-amps since the supply current to these op-amps is considerably lower than your standard op-amps.
I hope you are able to understand this amplifier configuration now. Let me know if it still doesn't make sense.
@@SmithKerona what i was thinking,that the audio signal has to go through the base of the 2n3904 driver transistor and into the output 25c198 into the speaker,but if i understand the two darlington pair just increase the current at the output of the op-amp and input of speaker or just increasing the amplification of the signal,now i my be compelely mistaking in myunderstanding of this,sorry
Why do we have two vOmin values in calss A amplifiers?
We need practical circuit for audio power amplifier
Btw, how can we change the treble and the bass for this schematic?
You can either change the value of C1 (higher value for bass response) or include either a high pass(treble control) or low pass (bass control) filter at the input of the power amplifier.
@@SmithKerona
Why do we have two vOmin values in calss A amplifiers?
Very nice. I have used nearly the same design, but in noninverting configuration ibb.co/NyLBzpL and a little bit simpler by application of an adjustable current source between the bases of the output transistors. So I just need to adjust one fine trimmer R8 in order to set the quiescent current through the output stage. I have also no connection between the opamp output and the amplifier output, because it is not necessary.
I was a little bit surprized to find the electrolytic capacitor C2 in your design. Why do you have it there? R8 and R9 are also not necessary, especially at this circuit position. It could make sense to have them in the emitter connections of Q3 and Q4 to the power rails in the case that thermal stability is an issue. You have a relatively large dc-output voltage, which is probably caused by the high closed loop gain, the mismatch of the input impedances between the inverting and noninverting inputs of the opamp and the offset voltage of the opamp. Therefore I have used the noninverting configuration. By use of the capacitor C3 I can make sure, that the dc-amplification of my circuit is always 1.