What happens if you touch one of the differential pair transistors of op-amp?

00:00 Touching the + input side transistor of the differential pair.
00:32 Touching the - input side transistor of the differential pair.
01:08 Touching the both transistors of the differential pair.
The input stage of the operational amplifier (op-amp) consists of differential pair transistors. If the temperature rises by touching one of these pairs, an offset occurs at the output. However, if the temperature of both of the pairs changes the same, there will be no offset in the output.
This is an experiment to understand the internal working of an op-amp. This homemade op-amp is composed of five transistors. For this experiment, the differential pairs were not thermally coupled.
See more information, hackaday.io/project/176860-ho...

[@malcolmholmes115]

I think I should try to make an opamp from Soviet germanium transistors. Challenge accepted! Thank you for amazing project, looking forward to build it.

[@mitsuruyamada]

Thank you for watching! Even with such a simple circuit, the principle of op-amp operation can be quite enjoyable. If you try to make one, be sure to incorporate a variable resistor that balances the first-stage differential pair. Unlike commercially available op-amp, it cannot operate without it. I hope you will try !

[@malcolmholmes115]

@@mitsuruyamada thank you for a hint. I already checked your original article. I will tune it with a precision potentiometer first, then pick the resistor of the same value as set in the potentiometer. I want to build a couple of modules for education purposes. I have big plans and a large stock of electronic components waiting for me when I come back from the vacation

[@mitsuruyamada]

​@@malcolmholmes115 Thanks. Since my circuit is very simplified, the potentiometer was necessary because the first stage balance also shifts when the supply voltage value changes. It's great that commercial op-amps have almost no offset shift even when the supply voltage changes significantly. When I used this circuit for educational training, I first had the members make only the differential pair part to experience the principle. Next, I asked them to devise their own way to add the amplification stage and emitter follower. This training was designed to give the members the experience of thinking up their own circuits, which is something they tend to neglect these days.

[@malcolmholmes115]

@@mitsuruyamada I wish I had as good teacher as you when I started learning electronics. Still there is many things to learn for me, it’s my dream to learn electronics since I was young, but only recently I started to actually learn and build anything.

[@ezengondolkozom3700]

Cool video! What kind of oscilloscope do you have if I may ask?

[@mitsuruyamada]

Thank you for watching! This oscilloscope is a Tektronix TDS-320. This model is from the 1990s, and it was the first general-purpose digital sampling oscilloscope capable of observing high-speed single-shot phenomena. The display is a CRT instead of the current LCD, but the rest of the operation is almost the same as the current one. I bought this as a second-hand item.

[@gregandark8571]

Wooow !!! Antigravitational tech is coming :)

[@mitsuruyamada]

Thank you for watching ! It's a temperature change inside the transistors, but I actually get quite a throb feeling doing this. I've had other people do it and they were impressed.