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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
Massive 3 Oscillator Per Key Synth
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AnalogComputer



Joined: Aug 04, 2013
Posts: 1
Location: Cary, NC

PostPosted: Sun Aug 04, 2013 4:19 am    Post subject: Massive 3 Oscillator Per Key Synth
Subject description: Yes --- I'm Crazy...
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Hi all,

So I saw Jacob Watters C-MOnSter Synth about a year ago and thought "What a clever idea" --- http://www.jacobwatters.com/c-monster.php

I thought I would try a verison on my own but a little more complex.

So I want to have three banks of oscillators each with it's own division. This will be achieved using a total of 6 40106's. Oscillators would be individually tuned using .1% resistors. I found a nice calculator online to help me order resistors. Having stable tuning well prevent resistors from drifting during voltage spikes and temperature changes.

http://www.talkingelectronics.com/pay/BEC-2/Page49.html

I'm using this reference to help me do the tuning. ---

http://4.bp.blogspot.com/-ctu3NCaUAjA/UK4vnC0xHlI/AAAAAAAAFqI/HtqkUvP4lxc/s1600/equal-tempered-music-scale.jpg

After this, I plan to do the same as Jacob a divide each bank using 4040's. The output of each note will be turned on and off using the keyboard. I plan to salvage a 5 octave keyboard from either an organ or a cheap plastic keyboard.

My trouble is from here. How would I exactly go about switching each set of oscillators on and off? Would I use a group of 4066's? I basically want to have it so I can switch off/on each group of oscillators.

Next, I know I want to have waveforms on each group of produced square waves. I have been looking at schematics to create
- Triangle
- Sawtooth
- Sine
waveforms. I am trying to keep it as simple as possible because I will need to do this for each key. From there I would like to create a simple low-pass/hi-pass filter. And finally, I would like to create a super simple envelope. The output of each key would then be actively mixed using an opamp.

I know this is a tall order but I'm in no rush. This is also counter-culture to lunettas being free form, but having an oscillator for 6 cents a piece is nice too... The goal here is to create a string/synth hybrid. I thought about create PCB's at first, but it seems stripboard will be easier to modify and costs alot less...

I am going to design a 10A 5V power supply to provide clean power. This will be done using a nice 9VAC 50VA transformer. I am going to be experimenting with some 40106's and the signal path. But for now I have lots of work to do.

Chris
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Cynosure
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Joined: Dec 11, 2010
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PostPosted: Sun Aug 04, 2013 6:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hello Chris. Welcome to the forums. Here are some answers:

Quote:
Oscillators would be individually tuned using .1% resistors.

I highly recommend trimpots. Your calculations are never going to be exact, and an error of just 2 cents can be easily heard by musicians. Plus, if you change to a dual power supply then your calculations will be all off.

Quote:
How would I exactly go about switching each set of oscillators on and off?

I think on mine I used a few 4066's to turn off the clock input to the dividers and had a pull-down resistor to ground on the clock inputs.

The ideal method would be to premix each group of oscillators and then mix the final outputs, but then you are going to have to deal with a lot of switching. That method would require a 4066 switch to be used for every note, multiplied by three for each set of oscillators.

Quote:
Next, I know I want to have waveforms on each group of produced square waves.

This might be difficult if you plan on doing more than generic filtering. In order to do any actual wave shaping, it will need to be done for every note from each of the oscillator groups.

Quote:
And finally, I would like to create a super simple envelope. The output of each key would then be actively mixed using an opamp.

It sounds like you want an envelope that will be applied to each key individually. That will be a lot of envelopes. Look up the 7555 CMOS AD/R envelope. It is the most simple one that I know, but it is still going to be a lot of work to make 61 of them, plus the 61 filters and/or vca's to go with them.

There is a reason this method of sound synthesis was mostly limited to organs. To do what you are describing would require you to make 61 monosynths.

For mine, I added reverb before the filter to try to fake a bit of release. I passed all the sound through the same two filters (not a filter for each note). I then added a very simple decay circuit (an RC filter on the CV line on a 4066 that is triggered by the audio). This gives a decay, but you need to release all the keys in order for it to retrigger the envelope. This action is similar to the percussion sound on many old organs.

You might need to make some compromises - either that or be prepared to do a lot of soldering.

Quote:
I am going to design a 10A 5V power supply to provide clean power. This will be done using a nice 9VAC 50VA transformer.


You are going to want a stable ground reference for such a complex system. You can use your 9VAC transformer to do this, although 50A seems a little bit overkill.

http://electro-music.com/forum/topic-50293.html

I started that thread after I had half my project done and started to run into all kinds of problems. Changing it made everything a lot more stable.
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JingleJoe



Joined: Nov 10, 2011
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PostPosted: Tue Aug 06, 2013 3:10 am    Post subject: Reply with quote  Mark this post and the followings unread

Haven't read this thread in full, feeling a bit attention-spanless Laughing but if you don't mind perhaps sacrificing the traditional gate signal from your keys you can use them to turn the signal on and off, not a 4066, the key itself does a better job;

text circuit diagram time

____________ key contacts
[mixed oscs]------o o-------[resistor to main signal bus for all keys]
repeat.

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astroman



Joined: Sep 13, 2012
Posts: 44
Location: UK

PostPosted: Thu Aug 08, 2013 7:13 am    Post subject: Reply with quote  Mark this post and the followings unread

I admire you for taking this big project on but personally I wouldn't want a square wave keyboard like this. I know people do this sort of thing 'cos u can' and please don't regard my comment as critical
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