Hello and Synth design

[Tenine]

Hi everyone,
I've been around here for a month or more now, but this is my first proper introduction.
Hello!

I did post a topic before about syncing Nanoloop 1.3 to a single pulse per 16th clock signal from my Boss Dr-55, but no-one seemed to know/comment.


I've been planning to build a little monophonic synth for bass lines for a while now.
After getting over my initial disliking of IC's [I don't think I enjoyed using them when I studied electronics either], I found that LM13700s are excellent for making voltage controlled devices.

I've never wanted to use the 1V/oct protocols,
so I developed my own variation.

Basically, it's like a monophonic top octave divide-down synth.

The first stage of control is a CV input.
That CV controls the osc 's pitch [1 Octave / 12 semitones].
The osc is fed into a multiplexor but is also used to drive a 4013.
The 4013 is fed into a different input on the multiplexor and is also used to drive another 4013.
The 3rd 4013 is fed into the last multiplexor input.

The second stage of control is a stereo jack to send 1s and 0s to the multiplexor.
00
01
10
11
Using the above 4 states, you can select which of the 4 octaves the synth plays in.

[Obviously, the 3rd stage of control is a Gate signal like other CV/Gate synths.]

After the multiplexor, I'm thinking about adding another 4013 for manual octave-down-shifting.
This is all then fed into a Waveshaper [Saw - to - Triangle].


The features are shaping up to look like there will be the following...

Keyboard - 32 Mini-Keys [F - C]
Oscillator - Pitch, Octave [Normal / -1 Octave], Waveform Symmetry [Saw-to-Triangle]
Mixer - Oscillator Volume, External Audio Input Gain
Filter [LP] - Frequency, Resonance [Low / Mid / High], Envelope
Envelope Generator - Decay
VCA - Mode [Envelope / Gate], Volume

Control -
Pitch CV Input
2-Bit Octave Data Input [Stereo Jack, 4 Octave Control Range]
Gate Input

Modulation -
Filter CV Input
VCA CV Input

Audio -
Oscillator Pulse Output [For external processing, sub-osc generation etc]
External Audio Input
Master Audio Output




I'd love to hear what you all think of it please.
Any suggestions or ways to simplify the design will be greatly appreciated.
Also any ways to use minimal amounts of transistors instead of IC's where possible would be nice [I imagine that this can be done at least with the Wave shaper...]
Would it be possible to run the circuits on +/- 4.5 V [from a DC 9V supply]?


Another thing I have been thinking about is ditching the keyboard and including a sequencer.
If I did this, I'd like to be able to programme at least 16 steps without having physical controls for pitch etc per step.
By this, I mean, just entering the pitch data, glide on/off data and note/rest/reset data, then being able to press a button and move onto entering the data into the next step of the loop.
Is there a practical way to do this? I can only think of ways involving some sort of memory chip...
Perhaps the sequencer idea is more trouble than it's worth, would you say?


I'm looking forward to any replies.

Thanks for reading.

Alex

[Uncle Krunkus]

Sounds like a great project. I'd love to see some schematics if you've got any. The sequencer does sound fairly elaborate, not so much in it's function, but in the implementation. I know you can get programmable resistor arrays etc. but you'd still have to take it back to some type of memory. I think you'd be better off sequencing from a computer and using a midi->CV converter. But I know that is not in the spirit of what you want to create.

[Tenine]

Thanks:) Hopefully it will be a great project and won't present too many problems- I don't fancy pulling all my hair out this early on in life!

The schematics [for the Voltage Controlled parts at least] are mostly from the LM13700 datasheet.
I'd use 2 LM13700 ICs. 1 for VCO [Pulse] and VCA and the scond one for VCF. I could make an MS-20 like filter instead though, I guess.


I think the many reason I decided to use the 4013 to build the divide-down bank and the 4052 to siwtch between them, is for the purposes of sequencing. I like analogue CV sequencers, but I'd like to be able to gig with this so tuning the notes for each song is hardly practical!

We'll see what others think, but I fear you've already summed up the sequencer pretty well, without having physical controls for each step, you end up relying on memory ICs and it gets a bit much especially for just 16 steps.


If that's the case, I might abandon the idea of using the 4013s, just manually tuning each key to the correct pitch.
I can always add a single 4013 IC to allow manual octave shifting over 2 octaves.
Or I could limit it to one octave manual shifting, but include a sub-osc.
It would certainly simplify the oscillator section and allow me to focus more on the CV/Audio patching side of things.

Maybe I've been approaching this in the wrong way...
If I think of the synth more as something I play live and a signal processor, I'm less worried about the sequencing.
I guess I just wanted the functionality of a MC-202 on the cheap
I love ths sound and it has that all-important Clock input.
I don't really want to use MIDI in this music project.

Thanks again, Uncle K.

Alex