The last circuit, in steady state, behaves exactly as R2, but when the signal changes, the current through the capacitor is the derivative of the signal, reducing the amount by which the circuit is just R2.
I speculate it acts like an inductor because that would be a logically silly thing for it to do but I'm not doing the math at 1am on my phone.
Similarly, this capacitance multiplier is more likely to be seen on a chip than outside one. Capacitance inside an IC takes up a lot of chip area, while transistors are small.
It fascinates me how many utterly critical foundational technologies have become specialist niches (while only ever growing more foundational and critical) over the past century. 8I
"I keep coming back to this topic for two reasons. First, I think these components are usually explained poorly, making them a major stumbling block for folks trying to learn the craft. Second, op-amps have gotten really good, inexpensive, and small, so I think they should be used more."
No offense, but these are words typically spoken by someone who has never taken any electrical engineering courses or read any of Walter Jungs books, after having some electronics background.
"gotten really good"? Really, like in the 1970s?? (the 741, still widely used today was released in 1968). I recall in the 1980s in the electronics that were once completely discrete, they were _everywhere_ and still are today.
I've done a few EE courses across two countries on the path to masters. The opamps were used at most for small signal processing in those. No more creative uses like frequency/capacitance multipliers. Comparing notes with friends in other unis, it wasn't that different there. You'd have to go into degrees much more focused on electonics to go to that level.
Eh there are also decades worth of audio electronics designs which use the 741 and the decision of which actual part to use is often an aesthetic one. (i.e., assuming all other parameters are compatible then just use your ears). There are always new (hobbyist) designs being drafted around specific parts that are otherwise obsolete simply due to the musical character of certain parts
Capacitance multipliers are how wah-wah pedals work.
The classic Vox / Dunlop/ Cry Baby wah-wah pedal used by Hendrix, Gilmour, Clapton, Harrison, and so many others, is built from a resonant LC filter.
How do you change the resonant frequency of an LC filter with a pedal mechanism? The pedal turns a pot, and that controls a capacitance multiplier circuit.
19 comments
[ 3.6 ms ] story [ 24.2 ms ] threadI speculate it acts like an inductor because that would be a logically silly thing for it to do but I'm not doing the math at 1am on my phone.
I've always admired lcamtuf.
No offense, but these are words typically spoken by someone who has never taken any electrical engineering courses or read any of Walter Jungs books, after having some electronics background.
"gotten really good"? Really, like in the 1970s?? (the 741, still widely used today was released in 1968). I recall in the 1980s in the electronics that were once completely discrete, they were _everywhere_ and still are today.
I've done a few EE courses across two countries on the path to masters. The opamps were used at most for small signal processing in those. No more creative uses like frequency/capacitance multipliers. Comparing notes with friends in other unis, it wasn't that different there. You'd have to go into degrees much more focused on electonics to go to that level.
The classic Vox / Dunlop/ Cry Baby wah-wah pedal used by Hendrix, Gilmour, Clapton, Harrison, and so many others, is built from a resonant LC filter.
How do you change the resonant frequency of an LC filter with a pedal mechanism? The pedal turns a pot, and that controls a capacitance multiplier circuit.
Simple and elegant.