Design of a Sawtooth wave generator

[Grumble]

I start to feel the need for a Sawtooth waveform generator because it has a distinct sound, very different from sine, triangle and square waveforms.
I could make one with my sequencer in audio mode, but this will only give about 8 levels of voltage maximal.
So, in the line of my other builds it will be a module with an Arduino, an AD9833 DDS in square mode to provide the clockpulses for 3x 4 bit up/down counters (74LS193) and a 10 bit DAC AD9760 from Analog Devices.
It wil have a midi(ish) input, a CV (and pot) for frequency shift and a sawtooth and squarewave out.

Question: I have noticed looking at the signals from the sawtooth wave of a Moog that at the steep edge of the waveform there is a very short negative goint glitch.
Is that important soundwise? Will it be audible? Because if it is I will add this glitch to the near perfect sawtooth constructed by the counters and DAC

When the design evolves I will put diagrams here.

edit= corrected the link to AD9760

[Grumble]

The SAW module is finished.
Sorry, have to go, later more...

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[Grumble]

This saw-tooth module basically consists of a counter that is clocked with a DDS. Lowest frequency is about 0.4Hz and max. frequency is about 10kHz.

The top knob holds a rotary encoder, and with every step the frequency is up or down one full note.
The second knob from the top holds a potmeter for fine tuning and will shift the frequency one octave up and one octave down, the same as the CV.
Than the two switches: the left switch will turn Midi-in on and off, the right switch is to choose between a positive or a negative saw-tooth signal.
Below the switches are 4 3.5mm jacks, from top to bottom:
- Saw-tooth output, 0 - 5 volt.
- Square output, 0 - 5 volt, this square wave voltage has the same frequency as the saw-tooth wave and is 50% duty cycle.
- CV input, may be used as CV or as an FM input , input frequency 0 - 500Hz.
-(hard) SYNC input, a negative transition will reset the counter to zero to 766.

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[Grumble]

The soundfile: first just the sawtooth, and than with some filtering and last but no least, with the reverb module.

You analog guys might think that this is somewhat overkill, but mind you: This module has perfect Midi tracking well over 7 octave

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[PHOBoS]

you're building some nice stuff with this modern approach to a modular synth, keep up the good work.

(the link to the DAC is incorrect btw)

[Grumble]

Thank you, and I corrected the link.

[Cfish]

Sounds great grumble

[Grumble]

Thanks Chris

[L´Andratté]

Hey grumble, I´m total analog guy, and I personally have no use for any midi tracking, still it´s inspiring to see some good stuff as yours.
Btw I plan for my actual synth project using a digital oscillator by electric druid (VCDO).Because it sounds soo good. Nice wavetables and good for drones. With a good vcf and vc delay you enter sitar territory /ramble off
Could you add such a thing (wavetable) easily to your digital oscillator? (as mentioned I´m happily lost with programming)

[Grumble]

Yes, it is possible, one way is to use the counter outputs as an address for an eeprom which data is fed to the dac.
In the eeprom you could store the wave table.
But its not a very user friendly type of generator that way.

The DVCO you are mentioning does sounds real good, considering its only 8 bits....

[L´Andratté]

[Grumble]

[mmagin]

Nifty design, and very clean output. (I have no idea whether the Moog imperfection is discernable to the ear.)

Is the 10 bit ADC in the arduino pro mini (atmega328) really sufficient resolution for pitch CV? I guess maybe so once the fine adjustment is set so it is in-tune on both high and low notes?

[Grumble]

I do not use that ADC for resolution of the pitch, for that I'm running a serial data thru my synth that represents the midi note and calculate the frequency when needed.
That way I have a very accurate and stable note, but am able to add some pitch with a potentiometer and/or a CV input.

[mmagin]

Oh, got it, I missed the midi input!

[cslammy]

[Grumble]

Yes, the AD9833 is a great little chip, usable for clock generation well in the MHz frequencies as well as sound generator using the sine wave ir triangle wave output.
I even was able to hard sync it!

[Grumble]

[gabbagabi]

wow, nice!
one would need superman to stop this grumble-train

[cslammy]

[Grumble]

If you would like to I can help you a bit with programming the max260.
Just pm me if you would like that.

[cslammy]

[ixtern]