drawing of a cmoss based synth...

jamiewoody · May 30, 2010, 09:53:03 PM

i could take the led out, though i was hoping to use it to tell if the battery is on.

there is no speaker, it is a phone jack out to amp/mixer.

jamiewoody · November 06, 2010, 12:02:23 PM

i built this as i was learning about shmitt triggers. i feel just as confused today about them! lol

a couple of things i've taken notice of, is that they are harder to use than 555 or 556. i can throw together some components and make noise. but, there are some problems.

1. i can just make random noise, no real musical scale.then again, why is this a problem? it depends on how you look at it.
2. it's hard to make sounds constant. i can twist a knob, and there is sound, keep twisting, there isn't. it could have to do with the wrong potentiometer for the job.
3. some sounds/tones are louder, some are softer. it would be nice, especially for recording purposes, to have them all on the same level.

any thoughts on these issues?

Timodon · November 10, 2010, 11:58:13 AM

weird that you say that, I've found schmitts easier to get my head round than 555s. They just seem a bit less cluttered:- battery -live, ground - capacitor, input- resistor - output, bosh. As far as your points go -

1. well you can control the frequency with a pot so you can tune your oscillator to any note you like for a drone and combine oscs for a chord. If you want to change notes with something other than a pot then you're getting into keyboard/ ribbon territory. Complicated to build but fairly easy to work out how it would fit into the circuit I think.

2. Not sure why this is - if you're talking frequency pot then it could be that you're going above and below the audible range so maybe use a smaller pot/ higher capacitor. If it's a different pot then let us know which one in your ciruit it is.

3. Compression! But seriously - I'm really not an expert but on your diagram you only seem to have one of the oscillator outputs hooked up to the speaker. from my own tinkering with schmitt triggers I would think that means you'll only really hear that output with any clarity but you might still hear bleed from the other oscs (the "quieter" sounds you're hearing maybe)? Maybe you could design a simple mixer circuit before the speaker to combine more of your outputs (you can get some funky modulation effects if you combine outputs using diodes instead of resistors btw)

Course I could be wrong as I still haven't heard it yet!

jamiewoody · November 10, 2010, 09:45:07 PM

initially making sound with cmoss is not hard, and in fact easier (for the beginner).
the problems for me is, yes, there are a million tones on one of these chips. but, making all these tones output at a consistent volume is another can of worms! who wants to sit there with a volume knob turning it up and down?

there is a wealth of weird tones, but it is hard to play a consistent musical scale with a potentiometer, to me. it is easy to figure that one out with 555. as a matter of fact, earlier this year, when i had never touched a 555 in my life, i was able to INSTANTLY make an oscillator!

again, i speak out of lack of experience.

Timodon · November 12, 2010, 02:21:26 PM

Quote from: jamiewoody on November 10, 2010, 09:45:07 PM
who wants to sit there with a volume knob turning it up and down?

This made me chuckle as I am a sound engineer by trade so I do it for a living

Seriously though I've not experienced the issue that you're having. Did you read the part in my reply about building a basic mixer circuit and combining all your outputs to one? it doesn't have to be a complicated design, you don't even need to use pots, just resistors of the same value before the speaker/ line out.

Yeah it's impossible to play a scale on a pot - but that's also true of a 555. The principles behind both oscillators are the same - vary the resistance, vary the frequency, vary the note. Whatever method you choose to vary the resistance with will dictate how close to a playable musical instrument you get!

jamiewoody · November 12, 2010, 03:40:41 PM

i don't think that 's true of a 555...make a VCO, and you can play a melody.

then again, like i mentioned earlier, limitations can also be endearing qualities. i kinda like the weirdness of the atonal sounds this makes. even though this was not a "circuit bent" project (well, being someone ELSE'S circuit anyway...), it is still kind of about randomness,,,

Gordonjcp · November 12, 2010, 04:00:13 PM

The trick is not making it voltage-controlled - that bit is easy. The trick is making it so that the control voltage bears a sensible relationship to the pitch you get out ;-)

Timodon · November 14, 2010, 12:28:05 PM

Quote from: jamiewoody on November 12, 2010, 03:40:41 PM
i don't think that 's true of a 555...make a VCO, and you can play a melody.

but if you look at it like that this isn't it also true of a schmitt trigger? the principal of varying the voltage/ resistance to change the frequency of the oscillator holds true for both chips doesn't it? the 555 just needs 1 more cap to get going and you only get 1 osc (2 with a 556) instead of a possible 6.

Quote from: Gordonjcp on November 12, 2010, 04:00:13 PM
The trick is not making it voltage-controlled - that bit is easy. The trick is making it so that the control voltage bears a sensible relationship to the pitch you get out ;-)

Too true. That's why I kept the number of buttons on my BetaSynth down to three. I don't mind tuning up every time I play it (I own a hammered dulcimer with around 30 strings that needs tuning for every gig) but tuning oscillators can get tricky at higher frequencies because of the (ahem) logarithmic relationship between frequency and pitch.

jamiewoody · November 14, 2010, 03:45:49 PM

my whole point, tim, was that it is harder to make a "musical" synth with cmoss. if you find it easy, put one together and upload an image...

Timodon · November 14, 2010, 08:08:58 PM

Sorry for any confusion - I get that your saying it's tricky to build a musical synth with Cmos - I agree, and you can check out the video of my attempt in this thread http://www.circuitbenders.co.uk/forum/index.php/topic,1573.0.html

- but I'm saying isn't that also true of the 555? I don't see (or hear) a great deal of difference between the oscillators one can create using either chips (beyond the different types of modulation you can achieve).

It seems to me the difficulty isn't with which chip you pick, it's with the method you choose to vary the resistance/ voltage that controls the frequency of the oscillator. Whatever you choose to do (ribbon, buttons, keyboard etc etc) that part of the circuit is by necessity going to be fairly complicated (compared to our atonal APC's and Lunettas controlled by pots) and will require higher grade components than us hobbyists usually buy to keep things stable.

I'd bloody love to make one though. Maybe harvest a keyboard and resistance ladder from a broken keboard and use it to control a DIY synth!

Gordonjcp · November 15, 2010, 09:08:04 AM

I'd bloody love to make one though. Maybe harvest a keyboard and resistance ladder from a broken keboard and use it to control a DIY synth!

These days I'd be inclined to use a microcontroller to scan the keys and generate the output voltage using PWM. That way you can guarantee that your steps are all the same size, and scale it to get 1V/octave.

jamiewoody · November 15, 2010, 05:27:55 PM

who knows...i've had people tell me cmoss was easier to work with than 555. not for me. the first time i ever sat down with a 555, handful of caps and resistors, i was able to make a vco, which i could get to play a musical scale. it didn't require jumpers like a 556 does, etc...of course, i need an education to go along with what i am doing. i understand the theory behind cmoss, though. and what digital is...

jamiewoody · November 15, 2010, 05:33:29 PM

tim, after revisiting your "my first diy synth" thread, i can understand your experience with cmoss. that little keyboard you made is awesome! i need to get that book you learned that from...

Timodon · November 15, 2010, 08:00:09 PM

Quote from: jamiewoody on November 15, 2010, 05:33:29 PM
tim, after revisiting your "my first diy synth" thread, i can understand your experience with cmoss. that little keyboard you made is awesome! i need to get that book you learned that from...

Dude, Jamie, DO IT! I guarantee you will feel a lot more assured about what you're doing with basic circuits, cmos or otherwise - it's written in clear, understandable language and each chapter builds on the concepts you learnt in the last one. And both the circuits I've built from that book were based on the design but with my own personal flourishes added (discovered by wiring it up wrong on the breadboard, what genius!) so it gives you plenty of room for your own creativity to come bubbling out!

Plus you'll enjoy the CD. and there are a bunch of interesting chapters that have nothing to do with cmos in there with fun experiments/ projects to build as well.

Quote from: Gordonjcp on November 15, 2010, 09:08:04 AM
I'd bloody love to make one though. Maybe harvest a keyboard and resistance ladder from a broken keboard and use it to control a DIY synth!

These days I'd be inclined to use a microcontroller to scan the keys and generate the output voltage using PWM. That way you can guarantee that your steps are all the same size, and scale it to get 1V/octave.

Very interesting tip Gordon thanks! I have absolutely zero knowledge of microcontrollers, how they work, where I could hack one from etc. any good resources you can point me at? Course I know about google so I could always use that...