ECE4450 L14: Triangle-to-Sine Waveshaping (Analog Circuits for Music Synthesis, Georgia Tech course)
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- Опубліковано 24 сер 2024
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I recorded this during the Spring 2021 offering of ECE4450: Analog Circuits for Music Synthesis, but this material will likely be appropriate for future offerings as well.
The circuit in the green box at 6:00 is a well-known discrete implementation of a Schmitt trigger (effectively a comparator with positive feedback to give it hysteresis).
8:50 Reminiscent of the ICL8038 sine shaping network.
Whoa. Thank you for explaining the 901B triangle converter. That's the circuit that got me into this mess in 2005.
It's the gateway circuit to a life of sin. ;)
huh! the diode-resistor-voltage divider thingy in the moog schematic is a circuit i learned in school as a linearisation circuit. of course this can be used to do the opposite, as is done here. awesome! thank you for pointing that out and helping me make another connection in my brain.
Thanks for explaining what's going on in these circuits! I will try to design my own sine wave from AS3340 triangle wave.
Great explanation!
The title is a little misleading. Shouldn't it be Triangle-to-Sine instead of Triangle-to-Sawtooth?
All those S-curves are the same! :D
@@TranscendentBen Hard to disagree. But I personally was like 'hmm, again?'. I cant wait for the logarythmic current driver, every time I think this has to be next
@@krolu The exponential voltage->current conversion with temperature compensation is pretty complicated so I've been putting it off. ;)
Whoops! The title isn't just misleading, it's flat out wrong. I had copied the title over but forgot to change the S-word! I will fix that now...
@@Lantertronics I know, it's the part that making me nervous. I'm just wandering how temperature compensation will be done. Will it be based on 3300K PTC as its the most fundamental but the most difficult to get, or maybe some temperature shift for transistor array in one die. Just curious
Great explanation 👌 Thanks.
I suspect that a mosfet differential pair would actually give a better approximation to the sine function than a bipolar differential pair, since the mosfet pair saturates at a definite voltage, giving a zero derivative at the peak. In contrast, the tanh nonlinearity of the differential pair never reaches zero derivative, so the sine approximation will have somewhat pointed peaks.
If my calculations are correct, the ideal mosfet differential pair has a nonlinearity
f(x) = x*sqrt(2-x^2), |x|
But I also realized that unlike the bipolar differential pair, the scale of the input voltage needed get to a certain point along the mosfet differential pair's nonlinearity varies with the (square root of) the ratio of the source current and the mosfets' gain. This probably makes it quite a lot harder to set the operating point of a mosfet differential pair to get the desired scale of the nonlinearity.
Thanks
it’s fascinating that basically the same circuit used to add harmonics to a signal in a distortion pedal can also be used effectively remove harmonics from a triangle wave to make a sine(-ish!) wave
Amazing:)
@2:30 you say you do not know what R44 is for .... yet @13:45 you mention the very same inverting aplif with gain set to equiv of minus R43/R44
Also would be nice to see a tusl sine wave output vs triangle input, I bet it would have been more distorted than if triangle to sine was done via opamp based Miller integrator
5:54 You mentioned "The Art of Electronics" and that two-transistor comparator is not on that page in my 3rd Edition, and looking through, I don't think it's there at all (a good reason to save earlier editions). I double-checked, it's there in the venerable (30 years old!) 2nd Edition, but the 3rd has been out five years or so, and I think everyone should have it!. I even have the "X Chapters" book that came out only a year ago. Please when you reference a book mention the edition!
But that's a neat and tiny minimal comparator circuit, I don't know why I haven't come across it before. Apparently I didn't read through the 2nd Edition carefully enough!
There's a circuit that looks similar in the 2nd ed, but it's described as a Discrete Schmitt Trigger, and it has things that are significantly different (e.g. there's a resistor between the collector of Q1 and the base of Q2). I also looked in the index, and the pages around it, and couldn't find this particular circuit as a comparator....
@@elmegil Ah, yeah... I was hand waving there a bit...
Seems like the VCS3 might be combining the nonlinearity from the differential pair and the diode network? Hard to see the voltage swing at the input of the differential pair from the schematic though.
Nice video......Hello, will you be exploring the Oberheim SEM? Im in the process of troubleshooting one and could use a little insite.
We'll take a peek at the SEM VCF later.
Check it my analysis of the SEM VCF here: ua-cam.com/video/jAokGV71MEw/v-deo.html
Sine like? How close to an actual sine are the outputs?
Close enough for music. ;)
hi! ...
Could you explain the circuit of the wavetek 130 function generator?
by !..
Are you trying to fix one?
See p. 5 of the service manual: bitsavers.informatik.uni-stuttgart.de/test_equipment/wavetek/130_Aug72.pdf
@@Lantertronics hi! ,In college we are looking at quadrature oscillators, and we are interested in knowing how to obtain a sinusoidal signal from a triangular one, and we found the wavetek 130, but we did not understand the sinusoidal converter circuit.
@@Lantertronics gracias !!