PIC-based fraktal synth

State Machine · Posted: Sat May 03, 2008 6:41 am Post subject:

Ole,

Nice job ..... I love the display cryptics .... adds much appeal. Nice additions also (filter, etc ...).

I have 3 of the PIC IC's in the wait so I can build one myself. Just have to finish up on a product release.

I assume sound samples are next ... Wink

Bill

Joel · Joined: Sep 12, 2006 Posts: 97 Location: London, UK

okvern · Posted: Sat May 03, 2008 1:36 pm Post subject:

Hi Joel, Bill,

First, the state variable filter design and board--you can find the basic circuit at MFOS (http://www.musicfromouterspace.com/analogsynth/statevariablefilter.html) or at Takeda-san's site (http://www.aleph.co.jp/~takeda/radio/SVVCF.html). I've attached my version of the schematic (this board also included a small audio amp--after I made the board, I decided that the amp should go in the mask, so I sawed that part of the board off). My version of the schematic is based on Takeda-san's layout--I had slightly different parts, so I created an Eagle version to match. (His board layouts are great, by the way, and well worth studying!)

Attached files:

PICSynthBoards.zip: The main board and filter board, as 600ppi bilevel TIFFs. You'll need to look at the Eagle layouts for parts placement.

PICSynthFilterAmp.zip: Eagle .brd and .sch files for the state variable filter/amp board.

PICSynthBoard.zip: Eagle .brd and .sch files for the main board. Note that the LED display I used is pretty weird--you'll probably want to edit to add something more standard (I had some of these lying around).

PICSynth_AddOnBoard.jpg: schematic of the LFO/CV summer circuit (I built this on a breadboard--didn't do an Eagle layout)

PICSynthFilterAmp.jpg: Schematic of my version of the state variable filter/amp board.

Note on the Eagle boards: When you open them, you'll need to hit the "Ratsnest" button to get the ground planes to fill in (if you don't, it'll look like a lot of things that should connect to GND don't connect).

Hope these are useful! I also want to thank catweazle/Eric for his incredible synth design!

I'll post sounds and other stuff soon.

Thanks,

Ole

PICSynth_FilterAmp.jpg

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PICSynthBoard.zip

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PICSynthFilterAmp.zip

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PICSynthBoards.zip

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okvern · Posted: Sat May 03, 2008 1:40 pm Post subject:

Fellow Builders,

I meant to mention--the +15v and -15v. supplies shown in the schematics are really +9v/-9v--everything is powered from two nine volt batteries, and battery life seems pretty good so far (now that I've exiled the LM383 to its own supply).

Thanks,

Ole

okvern · Posted: Sun May 04, 2008 1:06 am Post subject:

Fellow Builders,

Here are a few samples. These are all straight out of the filter into Audition 3.0, no effects, nothing fancy. Envelopes are provided by me turning the volume knob (have to add an envelope generator and VCA next time!). The only other manual intervention is a bit of keyboard "playing" in one of the WSG examples.

Thanks,

Ole

Fractal2_a.mp3

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WSG_MiniKeyboard.mp3

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Fractal1.mp3

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FRactal1_b.mp3

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Fractal2_b.mp3

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State Machine · Posted: Sun May 04, 2008 6:43 am Post subject:

Very cool ! Thanks for sharing all of this. Very Happy

The SVF really adds the final touch to the project and provides some real nice movement to this sound generator. Perhaps a voltage controlled panner would also make a nice addition so that now you could have spatial FX as well. You can pan slowly or quickly for some nice "ping-pong" FX Wink

I listened to all the samples and the last one has some semblance of a melody Wink

This synthesizer could have some real appeal with the "chip music" crowd and "noise" artists. It also could add great ambiance for classic electronic "space music" by adding some reverberation. Very Happy

Thanks for posting the samples and other information. I have decided that mine will have such a filter and I will add a panning circuit also to the mix of additions. Thats as far as I will go with it just in case I want it to be battery powered and want to keep it simple. Very Happy

Bill

okvern · Posted: Sun May 04, 2008 11:13 am Post subject:

Hi Bill,

I really like the WSG algorithm--you could probably reproduce most of the soundtrack for "Forbidden Planet" with it (and rest in peace Bebe Barron, one of the composers of that brilliant score--she died recently). It's definitely the "solo" instrument of the four synths in the design. It's also interesting to me because it still has two parameter pots to use up--I have to look at Eric's source code to see if more features could be added.

Yesterday I added an external CV in to the frequency input summing circuitry so that I can drive it from an external sequencer. I'm running out of places to add switches/jacks at this point--I think I'll add a jack for an external power supply and call it done.

Again, all credit to Eric for sharing this design with the community!

Thanks,

Ole

LeftHandControls.jpg

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Controls from top to bottom: filter frequency, filter resonance, filter LFO depth, low pass/bandpass switch, audio out

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RightHandControls.jpg

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From top to bottom: external CV input, LFO freqeuncy, reverse switch, space for external power jack, on/off switch

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YoSynthi · Joined: Aug 29, 2006 Posts: 26 Location: UK

Oh dear,

I've just got hold of the appropriate PIC chips so that I can experiment with this project, but I've been unable to access the links at the start of the thread, with the source code and project description:

http://etecnic.fh-pforzheim.de/~catweazle/F-Synth/

Is the site / link dead? Does anyone have any of this stuff archived?

Catweazle? Anyone...?

State Machine · Posted: Sat May 10, 2008 6:27 am Post subject:

catweazle · Posted: Sat May 10, 2008 12:34 pm Post subject:

Hi
server is down... I'm sorry...
That would be cool if you can make a backup of the documentation (schematic, software) on a another server.
If any information/pics and so on is needed I can post it of course.

Very cool work okvern !!! thumb up

That filter rocks - great samples!

Maybe I find some time to do some work on this.
i'm glad you have fun with it.

Gtz
Eric

PICsynth_V11.zip

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Schematic and Sourcecode / Hex Files

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okvern · Posted: Sat May 10, 2008 2:39 pm Post subject:

Fellow Builders,

The party/rave/whatever is tonight! Everything is working, and (amazingly) I have not yet chickened out--the superhero named "The Oscillator" is ready to rock. Smile

I ditched the LM383 version of the mini-amp, though, and advise everyone to not bother with that chip--it's unstable, hot, and just a nuisance. I built a Little Gem (http://runoffgroove.com/littlegem.html) instead, and it's great.

Glad you like the samples, Eric!

Thanks,

Ole

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State Machine · Posted: Sat May 10, 2008 8:59 pm Post subject:

OK, here is a link to the PIC Based Fraktal Synth projatc files in case you cant get to the others. Just look for the file "picsynth_v11_191" in the list .....

http://statemachine.freehomepage.com/

Bill

hanley · Joined: May 24, 2006 Posts: 27 Location: London

okvern · Posted: Mon May 12, 2008 3:32 pm Post subject:

Hi hanley,

They're just voltage dividers--I used 100K when I built it.

Thanks,

Ole

hanley · Joined: May 24, 2006 Posts: 27 Location: London

thanks the the info okvern

built this last week and other that confusing myself with some wiring it turned out great

i have a question for anyone who made/looked at the circuit design

the PWM output from the PIC has a resistor and cap on it
Posted Image, might have been reduced in size. Click Image to view fullscreen.

Posted Image, might have been reduced in size. Click Image to view fullscreen.

when i tried to send a signal though this it was almost inaudiable
without the resistor and cap is sounds fine

whats the purpose of this part of the circuit?

catweazle · Posted: Fri Jun 20, 2008 3:51 am Post subject:

R7 and C1 form a RC-lowpass filter to filter out the PWM frequency.
C2 (~0.1uF) filter DC contents (audio inputs don't like DC voltages)

The R8 (470k) limits the signal (on my test the output signal was a bit strong for my mixer. you don't need the R8 really.

catweazle · Posted: Sat Jun 21, 2008 2:52 pm Post subject:

@okvern: how was the rave???

my server is running again ... my sound samples and pics
are available here http://etecnic.fh-pforzheim.de/~catweazle/F-Synth/

okvern · Posted: Sat Jun 21, 2008 10:51 pm Post subject:

Hi Eric,

The party was so loud that I couldn't hear myself, most of the time, even when I was *wearing the mask*. When we put it through a guitar amp and the PA, though, it was cool, and people dug it. It was quite the party. It's been a month, and I might still be hung over. Smile

"The Oscillator" lives, and is currently set up next to my dining room table. We often consult him for advice, weather forecasts, etc. I am still exploring all of the stuff you built into that synth, and still discovering wonderful sounds. Again, excellent work! You rock.

Thanks,

Ole

oootini · Joined: Oct 15, 2007 Posts: 80 Location: ireland

don't suppose anyone has a veroboard layout of this?

looks like it might be time for me to build from a schematic...
*gulp.

catweazle · Posted: Mon Jun 23, 2008 2:03 pm Post subject:

hi oootini,
if you use a veroboard (stripe type board) then you have to
cut a lot more traces than using a Perfboard (with dots instead of stripes).
There are not much connections between to points, ok supply voltages...

Here is the minimal configuration (excluding display),
on the pic you see the first version of the picsynth, but the
2 additional switches and the led display are not really complex to attach.
Voltage regulator (+5V, 7805) is mounted at the case and
the remaining components (caps and protection
diode) are soldered "flying" directly to the supply-jack and the 7805.

The output filter (resistor and cap) are soldered directly to the output jack.

gtz
eric

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oootini · Joined: Oct 15, 2007 Posts: 80 Location: ireland

cool, thanks catweazle. reckon i'll invest in some perfboard then. can't wait to get stuck into this...

State Machine · Posted: Tue Jun 24, 2008 3:42 pm Post subject:

oootini · Joined: Oct 15, 2007 Posts: 80 Location: ireland

have all my parts and a loaded pic chip and am gonna start on this today. questions:

r30 - r21 (the resistors on the numierical display - the schematic says they should be 200- 470 R. i presume this means that any res between these values will work yeah?

also, i've read in descriptions for other projects that the pot bodies should be grounded to prevent audible hum. i am going to be putting the completed citcuit into a plastic container. will this be a problem? woould a piece of tinfoil across all the pots be sufficient to stop this hum?

catweazle · Posted: Sat Jul 12, 2008 11:04 am Post subject:

the resistors for the led display depends on the display used.
(on lower values the leds will be brighter)
if you power the device with batteries I recommend using higher values
(less current consumtion)

I never had problems with unshielded pots in other projects.
they are only voltage deviders so I think there is no shielding needed.

oootini · Joined: Oct 15, 2007 Posts: 80 Location: ireland

thanks catweazle. Smile

one more question: would this circuit work with a 9 volt battery? i have a 9v battery clip handy...