Inside Electronic Gain Control
Normally, if you want to control the gain of an amplifier, you’ll use a variable resistor. You know, like a volume control. But what if you want to control the …read more Continue reading Inside Electronic Gain Control
Category Archives: jfet
JFET Stands in For Triode in This Infinite Impedance Detector
An “Infinite Impedance Detector” might sound a little like something that [Zaphod Beeblebrox] would use to zip around the galaxy. It’s not, of course, but it is an interesting and …read more Continue reading JFET Stands in For Triode in This Infinite Impedance Detector
Practical Transistors: JFETs
Transistors come in different flavors. Tubes used an electric field to regulate current flow, and researchers wanted to find something that worked the same way without the drawbacks like vacuum …read more Continue reading Practical Transistors: JFETs
Ken Shirriff Found Butterflies In His Op-Amp
In 1976, Texas Instruments came out with the TL084, a four JFET op-amp IC each with similar circuitry to Fairchild’s very popular single op-amp 741. But even though the 741 has been covered in detailed, when [Ken Shirriff] focused his microscope on a TL084, he found some very interesting things.
To avoid using acid to get at the die, he instead found a ceramic packaged TL084 and pried off the cover. The first things he saw were four stabilizing capacitors, by far the largest structures on the die and visible to the naked eye.
When he peered into his microscope …read more
Continue reading Ken Shirriff Found Butterflies In His Op-Amp
Theremin in Detail
[Keystone Science] recently posted a video about building a theremin — you know, the instrument that makes those strange whistles when you move your hands around it. The circuit is pretty simple (and borrowed) but we liked the way the video explains the theory and even dives into some of the math behind resonant frequencies.
The circuit uses two FETs for the oscillators. An LM386 amplifier (a Hackaday favorite) drives a speaker so you can use the instrument without external equipment. The initial build is on a breadboard, but the final build is on a PCB and has a case. …read more
