Work in Progress: Digital/Analog Hybrid Synthesizer

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syso2342

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Hello,

I would like to introduce you a bit of my DIY project based on the Teensy. Although I am not using
the normal Teensyduino-Environment and Libraries, but customized versions, I would like to share
the current status of it with you. Parts of the Libraries are made by Roel here from the Forums
or at least based on his code.

The Synth consists of a Digital Part (which is Teensy powered) and implements the following:
- Currently 3 Oscillators (Direct Digital Synthesis / DDS) with FM-Modulation,
coarse Detune, fine Detune, Unison Amount, Sawtooth, Sine, Square & Wavetable (custom
Waveforms per Oscillator
- Own Envelope Generator per Oscillator to allow complex sound-schemes
- Oscillator Mixer which allows to fade between waveforms.
- Patch Manager - Allows you to save and load all synthesizer settings (osc detune, envelope etc.)
to any of the 128 available patch storage spaces. More space is usable by switching banks.
All patches and banks are stored on an SD-Card!
- Full MIDI control of any setting (currently only USB-MIDI, but thats a minimal change)
- NoteStack - A smart note "allocator" which allows us to easily extend the system to polyphonic mode,
implement arpeggiators etc.

There are also more "digital" or at least half-digital components connected to the Teensy:
- CD4051 Analog Multiplexers (4 of them) attached to 4 inputs of the Teensy ADC
using to provide 32 Analog Inputs for Potentiometers (control surface)

- AD5668 16-Bit 8x DAC - is used to provide control voltages for analog VCA and VCF for bigger
precision than PWM.

The Analog Components are:
- Currently SSM2044-based Resonant Low-Pass Filter
- 2164-based Dual VCA
- WiP Filter is a more complex Multi-Mode Filter
 
syso2342, the sound files are amazing! I'm grinning from ear to ear. Thanks!

Thank you! That are the old demos. There has been done a lot of improvement since I recorded those samples.
It sounds much much much better now. Today my new filter boards arrived. I think I will post some updates later!
 
Awesome! This is surprisingly similar to a project I'm working on, though I'm using an STM32F4 Discovery board and hope to use CEM3389 filters (I say hope to because I am not very good at analog circuitry so I haven't actually got any of the filters working yet). You can have a look at my code here (I'm afraid it's not very well documented, but I'd be happy to answer any questions) and listen to some demos of the (unfiltered) oscillators here and here.

I'd like to make it fully polyphonic (8 voices, as I have 8 CEM3389 chips) eventually, though I'm having trouble enough getting one filter to work (also I haven't had all that much time recently so the project's been on hold for the last 2 months or so) so that will probably be a while.

I am actually looking for alternatives to the STM32F4 Discovery board since it isn't very conveniently sized and the teensy has definitely been on my mind (it's so nice and small!). I'm a little worried about power though, do you find the teensy is fast enough? How many oscillators do you predict you will be able to run?

Good to see other people doing similar things with different approaches :)
 
Hey, quick update! My self made SSM2044 boards that arrive today have just been soldered and fired up!
All works! No PWM noise at all! All perfect! You cannot imagine how fat this thing sounds now.

pPRodD3yR1jk.jpg
 
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Here is by the way a part of the control surface. It has 40 potentiometers
and uses only 8 teensy pins for that!

pcb2.png
 
Wow, nice. 40 pots. Where do you buy them? Pots that I've been using so far have been a bit too costly to buy that many of..
 
Wow, nice. 40 pots. Where do you buy them? Pots that I've been using so far have been a bit too costly to buy that many of..

I'm not the OP, but it depends on what type of potentiometer, trimpot, etc. you get. Some cheaper pots include:

I find both dipmicro and tayda to have fast turn around times in spite of being based in Canada and Thailand respectively. Dipmicro is in Niagara Falls, and has a courier come to the US 3 times a week to mail US orders, while Tayda has a warehouse in Colorado, that stocks most things.

However, in the case of a potentiometer that you would want to turn by hand (as opposed to a screwdriver in the above pots) that fits on a breadboard, the cheapest I've found is Alaska Electronics, which sells 5 potentiometers for $4 (i.e. $0.80 for one): http://www.ebay.com/itm/Trimpot-3386U-w-knob-U103-10k-10000-OHM-5-PIECES-/321395468258 (Adafruit wants $1.25 per trimpot).
 
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I've found trimpots not to be durable enough to use in this sort of situation, they're not meant to be twisted over and over and over again. Cheapest ones I've found in my area that I actually trust for this sort of application cost like €1.35 a piece, which adds up pretty fast.
 
I am using standard ALPS Potentiometers (between 1K and 10K values) linear for around $.50€ per piece.
 
Man, it really sounds awesome. I like the dirt.

As for kits, wouldn't that be a bit difficult due to the rarity of those classic SSM chips nowadays?
 
Man, it really sounds awesome. I like the dirt.

As for kits, wouldn't that be a bit difficult due to the rarity of those classic SSM chips nowadays?

Thank you! The new version is no longer based on rare components and sounds also good! I'll keep
you updated
 
Interesting project :) i'm embarking on a mini-mpc (simpler than iMPC for ipad, but that sort of thing) project for sequencing beat samples, once its done it would be very cool to create a midi sync/record linkup between my project on one of these synths :)
 
Hi there,

Great project !

Is it possible to post the code you used to get all those analog inputs to work with the 4051s ?

That would be hugely appreciated.

I'm trying to get 10 sliding pots and 12 pots to work through 3 4051s.

Thanks a mil !!
 
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