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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
The Lunetta Voice
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synaesthesia



Joined: May 27, 2014
Posts: 291
Location: Germany
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PostPosted: Wed Jan 07, 2015 2:40 pm    Post subject: The Lunetta Voice
Subject description: A simple digitally controlled oscillator with a cool sound
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I am working on new modules for a semi-modular Lunetta right now and wanted to have a simple (as in low part count) digitally controlled sawtooth oscillator. At first I looked into a design using op-amps, but then remembered a version from Scott Gravenhorst that uses 4069 gates instead. That one wasn't controllable by a CV as easy as I wanted it to, but I managed to find a solution for that. The circuit is by no means exact, nor 1V/octave, nor generates note frequencies, but it does the job good enough for a Lunetta. Just before sharing I tried adding the PWM effect I mentioned in another thread (Pimp my square wave) and it works even better here. So I went back to experimentation mode for a while. The result is that I found a simple way to add even more punch to the sound it generates. So I consider it interesting enough to share the circuit as-is now.

In the left part there is your tried-and-trusted 4049 sawtooth generator (the original used 4069 gates). Adding the diode and the pull-up for the simple resistor network did the trick to make it digitally controllable. It feeds the signal into a passive resistor mixing stage. The result is turned into a square wave by an inverter and feeds a counter that takes the sub-octave and the sub-sub-octave using one half of a 4520, smoothes it with a cap, and feeds a small part of it back into the mixer stage. The result is a kind of resonance or tremolo that makes a really interesting sound. In my interpretation it comes from changing the amplitude height of the sawtooth wave, which in turn varies the pulse width of the final pulse wave. You can see that clearly as a jitter of the blue curve in the video. Nice sound, considered the few parts that it took. I tried to turn the sub-octave part of the circuit into a separate module, but that didn't work well. It seems that it really must have a sawtooth or triangle wave as an input. It doesn't affect square waves much.

I have added two control lines that can be used to disable the "resonant" and the "percussive" effects in the output, just in case. They are optional. Also, the percussive part using the LDR/LED vactrol is optional. As described in the schematic, the DCO generates frequencies between 190 and 880 Hz in approximately 40 Hz steps. The video shows the waveform captured from the sawtooth oscillator above and the waveform after the 4.7nF cap below. The final output is a square wave (pulse wave) again. Mind that the oscillator and mixer need a 4049UBE or 4069UBE, it won't work with 40106 inverters. Next step is a pattern generator to feed that thing Smile


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PHOBoS



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PostPosted: Wed Jan 07, 2015 2:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

Nice Smile

I wonder what happens if you place a pot parallel to U1e.

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synaesthesia



Joined: May 27, 2014
Posts: 291
Location: Germany
Audio files: 85

PostPosted: Fri Jan 09, 2015 2:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

PHOBoS said:
Quote:
I wonder what happens if you place a pot parallel to U1e.

It is still on breadboard, so I just tried that with a 50K and a 500K pot. However, the signal is lost then.

Regarding:
Quote:
it really must have a sawtooth or triangle wave as an input.

If you want to feed a square wave to the circuit, you need to turn it into a triangle or sawtooth wave first. Here is a simple way to do that using an integrator. The left version using an op-amp works well.
The right version using a 4049 inverter gate does not work so well. Vmin tends to go above the trigger level of the inverter gate for frequencies above 1KHz.


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synaesthesia



Joined: May 27, 2014
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PostPosted: Sun Jan 11, 2015 4:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

The oscillator won't work with 40106 inverters, but you can use op-amps instead. Haven't tried it with more than 5V, but it should work as well.


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