Joined: Nov 20, 2007 Posts: 1988 Location: West Red Spot, Jupiter
Audio files: 224
Posted: Mon Dec 17, 2018 9:28 am Post subject:
MOSFETs (at least those in 4069ub and 4007) have an odd relationship between gate voltage and output. Using a 4007 or 4069 as a linear amplifier, gain is highest when the gate voltage is halfway between the rails and goes lower as the gate voltage approaches either rail. This can allow it to round out a triangle input, but I've no idea what harmonics are added/subtracted. The WASP filter uses 4069 as a distortion element which gives the WASP filter its crunch. _________________ FPGA, dsPIC and Fatman Synth Stuff
Time flies like a banana. Fruit flies when you're having fun. BTW, Do these genes make my ass look fat?corruptio optimi pessima
Joined: Nov 20, 2007 Posts: 1988 Location: West Red Spot, Jupiter
Audio files: 224
Posted: Mon Dec 17, 2018 3:36 pm Post subject:
wow caps rated in mF - takes me way back. When I was a kid, I looked for TVs to scavenge on the curb on trash day. These were vacuum tube TVs. The caps were in mF or mmF which one doesn't see much these days. _________________ FPGA, dsPIC and Fatman Synth Stuff
Time flies like a banana. Fruit flies when you're having fun. BTW, Do these genes make my ass look fat?corruptio optimi pessima
But I got in the mail 100k digital potentiometers X9C104. 4069 SVF with this potentiometers sounds clean. But the resonance is too weak.. Will try with low pass gate.
TL431 used as 2,5V comparator. In this curcuit envelope is exponentional. But if you will make inverting amp with digital pot. in feedback loop, envelope will be linear.
If you will use CD4069 as inverting amp with digital pot. in feedback loop, envelope will be also linear, but shape of signal may be distorted. For example, triangle wave will look like lines bended into arches.
Pot. can switch in non zero crossing point, and I don't know why, maybe because of TL431 is not the best decision. Maybe it's breadboard feature.
That's why I used the 470 pF capacitor. It removes the peaks from switching. Two oscillograms, with and without capacitor. Code also included.
Digital_VCA.jpg
Description:
5V digital VCA
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169.33 KB
Viewed:
553 Time(s)
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VCA.jpg
Description:
Without cap.
Filesize:
76.2 KB
Viewed:
497 Time(s)
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VCA_470pF.jpg
Description:
With cap.
Filesize:
99.23 KB
Viewed:
485 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.
And after one more month I got my vtl5c1 vactrols)))
And they are so slow... It's not necessary to use second ATTiny85 for PWM, i'ts sounds very intuitive if just change a length of note. Very clean and tasteful sound! I like it a lot!
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