from scratch?!
here is an idea i have...please dialogue with me, as i haven't tried it yet.
harvest some plastic mini-keys from a dead casio...
i could plant some normally closed switches under the keys, you get the picture, press the key, and the switch is activated.
i could experiment with different caps, since they seem to produce lower tones in the higher values, and wire each cap to a resistor and a trimmer.
the series of cap-resistor-trimmer on all of the keys would be wired in parallel to the synth circuit. i could do a circuit with different synth types i have been learning to build, cmoss, 555, 556...
my theory (or lack of! lol!) is that i could perhaps "tune" each key with the trimmer pots, so there will be a set pitch for each key. i would prolly only do a two octave keyboard.
of course, the box would be very "moog" looking, with wood on the sides, etc!
so, what do you think? any problems with this idea?
It wouldn't really stay in tune. Analogue synths used to use very high-precision resistors in series, with the pressed key shorting a proportion of them. The resistor ladder formed part of a potential divider that went into a very carefully-adjusted amplifier and gave a linear output voltage proportional to the note pressed. This then got fed into a logarithmic amplifier (fiddly as hell) and then into a voltage-controlled oscillator (actually, current-controlled but we can gloss over that - also fiddly as hell).
Dig out the circuit diagram for an analogue monosynth for an example. The Powertran Transcendent 2000 had a circuit like that for the keyboard.
thanks. may go out of tune huh?
all i can do is try things and see if they work. the more i experiment, the more intuitive i become!
look for the "toy organ" schematic here:
Engineer's Mini-Notebook - 555 Timer IC Circuits (http://www.scribd.com/doc/6475770/Engineers-MiniNotebook-555-Timer-IC-Circuits#key1fdb6qdi66tvlxcrjl3q)
Nice one for posting that notebook. I've been after that for a while.
no doubt! forrest mims is a futuristic folk artist! ;-)
this WILL be my next book purchase!!!
i saw a youtube vid of a homemade electronic keyboard, and i exchanged some email with the one who made it. he made a basic VCO, and came out with a capacitor, then from the capacitor, did a parallel circuit of trimmers andN/O switches. of course the push button switches were the keys, and the trimmers tuned the keys.
it seems the MIMS model is a little different, there are different values of capacitors for the keys.
which seems better?
Thought about it then thought it would be shit if I did it.
(Apologies for pointless rubbish post but needed to post something so Admin didn't delete my dusty account)
Good idea!
I made a very rudimentary 3 tuneable key (or 3 button) version of a keyboard on my Betasynth. The pots were all in parallel on the same oscillator of a hex schmitt trigger. As well as tuning eacfh key for a simple three note melody or bassline the fun thing about that was that the pots have a weird relationship with each other when pressed at the same time. Different notes are produced by pressing different combinations of keys - not great if you wanted a precision instrument but good for the kind of music I wanted to make with it!
using a schmitt trigger seems like a good idea, since there are a quadzillion different sounds that can come from one!
i threw together a stepped tone generator with a 556 on the breadboard. i hooked up a switch (normally closed, i need normally open instead), and i learned i was able to trigger a tone using the button. but, when i would twist a potentiometer, the pitch would change.
i would love to make a "mini-keyboard" and make an oscillator for it, which would effect the waveform yet not change the tuning...