I've watched a lot of long tailed pair instructional videos and this one is the best because it opens with a question and answers it while showing all work. It is a long video in comparison, but the details it expands on are the most important. Thank you!
Please keep making more of these videos - please keep 'them coming and thank you so much for taking the time to make them and share your knowledge with us!!!
Excellent teacher, I'm learning a lot by the step by step procedures you take for each component, its really nice how you explain the details of the math involved to get the values, thanks for doing these types of videos.
it is similar to an OP-amp in inverter mode. But what to control the gain with voltage, many ideas come to me, incredible. Could you tell me if there is any IC that has this configuration? And pairs of transistors of the same type, NPN or PNP, that are in the same package? I find it difficult to have pairs of identical transistors, I would have to buy many and see if they are identical in the same conditions of temperature and current. Is the second stage to minimize the differences? I have to watch the video several times, my English is very bad. Greetings.
A bit late for reply but you can look into an Operational Transconductance Amplifier like the old LM13700 Dual OTA. Still available. Same trick but with current bias, not voltage You change with the bias and the gain changes proportionnally.
@@Bob-1802 Thanks, I am learning little by little, I have looked at OTAs but I do not control any of that, I have seen that they use it a lot in VCO, VCA and filters in the world of Rack synths, the kind that has many cables. I know you can convert voltage to current with an OPamp but I haven't practiced it yet. I'm with the basics of an OPamp, current sources and current mirrors for a differential amplifier. I have seen that an OPamp can be used directly for the second stage. When I have more time I will study it more thoroughly, I am determined to make an audio compressor, in the process I will learn a lot.
Hello Mandy, there are several gain parameters that can be calculated for the two stage differential amplifier that is shown in the video such as differential gain, single ended gain and common mode gain. Since you haven't specified which gain you wanted to calculate I am going to assume single ended gain. The magnitude of the second stage gain is (gm*Rc)/2 just like the first stage with Rc being 7.5k and is the transconductance of the second stage transistor at Ic=1mA. Since the second stage doesn't load the first stage (Zin of second stage is more than 10 times Zout of first stage) we can simply multiply the fist stage gain and the second stage gain directly to get the over all gain. I will leave the mathematics to you as an exercise! Cheers and sorry for the late replay :)
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I've watched a lot of long tailed pair instructional videos and this one is the best because it opens with a question and answers it while showing all work. It is a long video in comparison, but the details it expands on are the most important. Thank you!
Excellent. Theory calculations, practical demonstrations are very help full to understand. thank you
Please keep making more of these videos - please keep 'them coming and thank you so much for taking the time to make them and share your knowledge with us!!!
Excellent teacher, I'm learning a lot by the step by step procedures you take for each component, its really nice how you explain the details of the math involved to get the values, thanks for doing these types of videos.
The only one VCA is working on my LTSpice :-) great video! Great Video and Explanation. TOP. YOu deserve a subscription definitely.
That was a really good walk through your circuit. :)
totally perfect!
Fantastic explanation! You cleared up things for me so I SUBBED and rang the bell. Great job. Thanks.
Is there any off-the-shef part, which could be used as VCA?
it is similar to an OP-amp in inverter mode. But what to control the gain with voltage, many ideas come to me, incredible.
Could you tell me if there is any IC that has this configuration?
And pairs of transistors of the same type, NPN or PNP, that are in the same package? I find it difficult to have pairs of identical transistors, I would have to buy many and see if they are identical in the same conditions of temperature and current.
Is the second stage to minimize the differences? I have to watch the video several times, my English is very bad.
Greetings.
A bit late for reply but you can look into an Operational Transconductance Amplifier like the old LM13700 Dual OTA. Still available.
Same trick but with current bias, not voltage You change with the bias and the gain changes proportionnally.
@@Bob-1802 Thanks, I am learning little by little, I have looked at OTAs but I do not control any of that, I have seen that they use it a lot in VCO, VCA and filters in the world of Rack synths, the kind that has many cables.
I know you can convert voltage to current with an OPamp but I haven't practiced it yet.
I'm with the basics of an OPamp, current sources and current mirrors for a differential amplifier.
I have seen that an OPamp can be used directly for the second stage.
When I have more time I will study it more thoroughly, I am determined to make an audio compressor, in the process I will learn a lot.
Hi, how do you calculate the gain of the 2nd stage? And what is the gain range of the whole circuit?
Buy the person.
Hello Mandy, there are several gain parameters that can be calculated for the two stage differential amplifier that is shown in the video such as differential gain, single ended gain and common mode gain. Since you haven't specified which gain you wanted to calculate I am going to assume single ended gain. The magnitude of the second stage gain is (gm*Rc)/2 just like the first stage with Rc being 7.5k and is the transconductance of the second stage transistor at Ic=1mA. Since the second stage doesn't load the first stage (Zin of second stage is more than 10 times Zout of first stage) we can simply multiply the fist stage gain and the second stage gain directly to get the over all gain. I will leave the mathematics to you as an exercise! Cheers and sorry for the late replay :)