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/diy/ - Do It Yourself

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File: 1.04 MB, 1824x1368, keyboard.jpg [View same] [iqdb] [saucenao] [google]
224412 No.224412 [Reply] [Original]

Hey, I'm building a little keyboard/synth thing and I'm looking to do a "fade-out" effect. That might be called decay, sustain, whatever, I don't know shit about music (which is why I'm building this).
Basically what I want is when a key is released, the sound fades out over a fraction of a second.
The way this works is I have some old oscillator banks from an old 1951 Allen organ. They're Hartley oscillators, using triodes. To activate a note, you apply 250v B+ to its respective contact.
What I'm thinking is to use a capacitor on each note, from its contact to ground. When I push the key, the note plays and the capacitor charges (I have plenty of current in my B+ to charge it very quickly). When I release the key, current flows from the capacitor through the oscillator and keeps it going for that half a second. I can easily switch that effect in and out by tying the grounds of the capacitors together, and simply disconnecting them when I don't want the effect in. I can draw a diagram if I'm being too confusing.
Problem is, I can't adjust that at all, only by switching out the capacitors. What do you think I could do to have an adjustable decay/sustain/fade-out/whatever?
Pic related, it's my ghetto-ass 12 key keyboard and oscillators.

>> No.224418

capacitor discharge rate can be controlled by a resistance between terminals or to ground. try a 10k linear pot between - and ground. 1 per cap or tie all cap negatives together then through 10k pot.

You may have to play with the pot values.

>> No.224444
File: 137 KB, 834x542, 1325002094333.jpg [View same] [iqdb] [saucenao] [google]
224444

>> No.224448
File: 34 KB, 463x286, 110vca_645.jpg [View same] [iqdb] [saucenao] [google]
224448

>> No.224462

>>224412
Please tell me that's just a proof-of-concept prototype and not the actual production version of what you're building, because it makes the word "ghetto" look expensive by comparison.

>> No.224463

>>224412
You need one of the following:
o A modulator
o An analog multiplier
o A voltage-variable amplifier
..which as all really different forms of the same thing.

>> No.224478

>>224462
lol, it's just something I threw together from junk-bin parts in an hour. The final version is going to have proper keys with microswitches underneath.

>>224448
I will look into this.

>> No.224484

google "adsr circuits" and "vca circuits"