A place for thoughts as I think of them :
8 Aug 2009
Many people have asked about keyboards. I have written up some help here.
29 May 2009
Synthacon filter - the Synthacon filter is a brilliantly simple circuit from 1975 which sounds awesome. Read about this here.
11 May 2009
Geocities is closing down - welcome to the new website location picsynth.000space.com
15 April 2009
Q: There is a 6 PIN connector not connected to anything in the photo of PIC board, what is this for ?
A: This is for in-circuit serial programming of the PIC chip. I connect up my programmer to this connector to reprogram the PIC chip whilst it is in the synth, you don't need this connector as you will never be reprogramming the PIC chip !
13 April 2009
For a bit of fun I attempted arpeggiator part of Basshunter "Now you're gone", listen on youtube here. The high sound is deep PWM on OSC3 with 25% pulse being arpeggiated. Bass track is two triangles and deep PWM played by hand. Kristal chorus is used to make everything sound swirly and atmospheric. Love the real version of this, it has had 57 million hits !
3 April 2009
In some countries the 20 Mhz ceramic resonator may not be easily obtainable, this surprised me as in New Zealand they are very common. Anyway you can use a 20 Mhz quartz crystal instead of a ceramic resonator by adding two 15pf capacitors from pins to ground as shown below
26 March 2009
The PICSynth with its three oscillators can sound like a Minimoog, the real difference in sound is the Minimoog's filter. I have been experimenting with filters, there are many circuits that are available on the web. Either the Minimoog ladder filter or Steiner Parker Synthacon filter can provide that deep rumbling bass end and rich resonance. I built a Synthacon filter but it is not quite perfect yet...experimental filters can sit between output of VCF and input of VCA. Most circuits on the web use +/- supplies, so you will need to build a -12V supply to use them which is a disadvantage(or use 8 x 1.5V batteries!). They can also be quite difficult to get working well, in that you also need to worry about the envelope feeding the "Filter contour" as these filters react strongly to the control voltage.
7 Mar 2009
I have completed a multitrack recording which really showcases what the PICsynth is capable of, this is on youtube. I used Kristal multitrack recording software and multidelay effect that comes with Kristal. Listen here
7 Mar 2009
Nicely drawn layout for the waveshaper is on home page.
28 Feb 2009
PICSynth demo is up on Youtube - I had heaps of fun making this. If you liked the video give me a good rating. And thanks to Matrix Synth for featuring this only minutes after I put it up ! Mega hits ! By the way I used some great free software to do the voice over + arrange everything KRISTAL.
21 Feb 2009
I have been studying the Korg Mono/Poly as inspiration for future versions of PICSynth. Read about this here
15 Feb 2009
Very excited about the new sound from my Oscillator 3, this has a 256 step sawtooth or Pulse width modulation. Listen to the strings sound! Full details here.
9 Feb 2009
Updated the schematic to fix possible problems with loss of sawtooth wave from waveshaper into VCF - a number of resistors and 2 caps have changed value but the rest of the circuit is the same (please read errata).
I have drawn new veroboard layout for VCF/VCA - it is much better layout!
Also photographed step by step.
I hope to do the same with the other boards too.
30 Jan 2009
Here is my design for a waveshaper to produce a 256 step sawtooth.
This sounds as good as an analog sawtooth and has all higher harmonics.
I connected it as an extra waveshaper so this is like having another 3rd oscillator
It has the added bonus of allowing you to play C6-B6 highest octave output from PICsynth. When combined with existing oscillators you get a
very fat sound (390 kb wma)
22 Jan 2009
Taking a break from programming for a while after the release of V3 chip.
I have been busy designing a new waveshaper. One thing I should point out is that the sound of the PICSynth is really dependant on the waveshaper and filter circuits not the PICSynth chip: the PICSynth chip controls the pitch of the notes and the detune amounts but not the waveform. The new waveshaper could be used instead of (or together with) the current design to enhance the sound. More details to come.
17 Jan 2009
So how do you actually make a PICSynth ? I have presumed a level of knowledge of how to build electronics circuits eg being able to read a schematic, being able to tell one part from another and how to insert them the right way around how to read a veroboard layout etc etc... Many people are interested in building a Synth but lack the basic practical skills in circuit building. I hope to include more practical information on how to build the circuit.
Starting with an excellent site I found on
building a circuit on veroboard.
I strongly think that veroboard is the way to go - just because it is such an easy way to get the PICsynth built, although PCB layouts are also in the pipeline for people who are that way inclined.
16 Jan 2009
Playing the arpeggiator is fun and opens up a whole world of chords to the synth. I like to find cool patterns by holding down chords and extra note keys, the only problem is once you have found a pattern is how to press the HOLD button as both hands are on the keyboard.
The solution : I connected a foot switch (salvaged from old sewing machine!) as my hold button. So you press this with your foot then you can release all the keys - the synth will carry on playing the pattern. Fun!
11 Jan 09
V3 chip is out !
This has a cool new arpeggiator and portamento. Listen to the sounds - the arpeggiator is lots of fun and produces cool retro sequences.
1 Jan 09
I have had a few people ask for source code, this will not be available but here are a few clues as to how the PICSynth chip works for people who want to program their own chip...
The PICSynth code consists of two main parts :
Mainline - sets up ports, scans keyboard, measures analog pitch adjust input, sets up timers for the two oscillators
Interrupt service routine - responds to timer overflow and toggles oscillator outputs
The advantage of this approach is that the mainline can do anything you want without effecting note pitch because note pitch is determined by interrupt frequency not mainline code execution times.
The formula for calculating timer value to load to get an interrupt every 1/2 period is
n = 1/(f x 0.2E-6 x 2)
f = frequency of note
0.2E-6 = 0.2 usec (timer period at 20 Mhz = 1 instruction cycle = 4 clock cycles)
assumes prescaler = 0 produces note C6-B6
I stick to square wave output - the waveshaper circuit handles the job of getting out of the square. Some other people have attempted to do more or all of the analog parts in a microcontroller. I leave the analog jobs to analog circuits. The PIC replaces the keyboard control voltages/resistors chains and VCOs but still leaves lots of scope for the electronics hobbiest to alter the sound using analog electronics.
15 Dec 08
You may have noticed that there are 4 spare pins on the 74HC154 (pins 14-17). I plan to matrix these with octave sense lines to create another 16 possible on/off switches to control future functions. I have many exciting ideas for new functions for a PICSynth V3 chip - which will still be a PIC18F1220 and pin compatible. Programming some new functions is what I am planning to do over xmas break.
12 Dec 08
Schematic available on the site.
8 Dec 08
I have been busy drawing the schematic in a package instead of hand drawn version. This should be released shortly.
2 Dec 08
I have been thinking about the waveshaper, the staircase sounds great but not as authentic as a real sawtooth waveform. A real analog sawtooth is a linear rising waveform with all harmonics present, and most other waveforms can be constructed from it. In an early mockup of PICSynth I had a many step stairstep (kind of like what a DAC - digital to analog converter would output) I actually found this no more pleasing to the ear than the simple staircase - the many small steps sounded worse than a few big ones!
I have been studying the M110 chip from the 70s used in Jen synths. It is a digital chip but manages to generate a real analog sawtooth by outputting two things :
1. Square wave
2. Voltage proportional to frequency
The following circuit is then used to form a sawtooth :
The voltage proportion to frequency is needed otherwise the sawtooth would get smaller the higher the note became - the circuit to compensate for this is difficult. An interesting waveshaper idea none the less.
2 Dec 08
Am getting a lot of hits because of the following, just like to say thanks!
http://www.synthtopia.com/content/2008/11/02/new-synth-diy-project-picsynth/
http://blog.makezine.com/archive/2008/11/the_picsynth_project.html
23 Nov 08
PICSYNTH V2 chip is available. This allows variable pitch adjustment of oscillator 1 as well as having very accurate higher note frequencies. I have uploaded variation1.wma recorded tonight. This was made by varying pitch of oscillator 1 using the new detune control, a little inspiration followed around the beating notes. Oscillator 1 is also being fed into filter cutoff frequency for interesting peaky filter effects. The new pic18f1220 chip is cool!
14 Nov 08
PICSynth V2 chip is under development. I am working on a new pitch adjust PIN which is fed by analog voltage from 0-5V to adjust the pitch of Oscillator 1.
5 nov 08
Other possible modules :
LFO - Low Frequency Oscillator. This can modulate the filter or VCA currently. It wont be able to modulate the Oscillators (ie Vibrato) until PICSynth V2 - see below.
ADSR Envelope Generator- instead of simple AD module. I am fond of the simple one though!
Second ADSR - to module the filter. This would allow tone colouring independent of VCA attack and decay.
Noise - could be mixed into VCF input.
Portamento - now that would be a programming challenge ! Maybe in PICSynth V2.
More oscillators - you could add more dividers/waveshapers to get sub octave oscillators.
There is no end of inspiration on the web, I like looking at synths like
ARP 2600 to get ideas for new modules.
The PICSynth chip and waveshaper could be used instead of a VCO and combined with Music from Outer Space/Sound Lab etc... circuits found on the web.
3 Nov 08
Aims of the project :
Make things as simple as possible, this project needs to be within the reach of someone who has only dabbled a little in electronics.
Stick to monophonic with top key priority, easy to construct and fun to play.
Modular flavour - more advanced constructors can swap in and out modules.
Stick with single supply operation.
29 Oct 08
Oscillator mod filter. Got this idea from looking at a picture of Micro Moog. Feed oscillator 1 into filter modulation like so :
Cool ring modulation like sound - see sounds.
The diode is absolutely necessary. I managed to blow up a PIC chip when 12V from analog section spiked into PIC pin!
29 Oct 08
Have just got a PIC18F1320 chip which is a more capable chip for experiments with frequency modulation. My idea is to use the analog input capability of this chip which could be fed by a LFO, this is just an idea currently. It will be interesting to see whether the PIC has enough speed to do this AND do everything it does already.
Also I'd lose 1 PIN - and they are all used currently! Maybe there needs to be another way to tell the chip to detune. I'd like to keep any new chips PIN compatible - lots of challenges.
21 Oct 08
Note that the two back-to-back transistors in the VCA section should be a matched pair. Don't worry too much about a perfect match because that is what the 1k timmer is for - adjust it for perfect VCA operation.
The main AD capacitor is 10uF tantalum - a tantalum capacitors fast response time provides a sharper attack than an electrolytic. You can hear the difference.
Total current drawn is 11 ma thanks to ultra low power PIC and CMOS. This means the synth will work from batteries! (I did try a 9V battery and everything works except VCA - it needs 12V - working on this)
Carrying on the battery theme how about someone building a tiny portable picsynth using a toy organ keyboard - with a fat synth sound !
