Tuesday, 13 October 2015

Overcycler2 demo track

All sounds were made with Overcycler2, my DIY 6 voice hybrid analog synthesizer, drums included.
Effects: reverb, equalizer, limiter.

By the way, I made several changes since the patches demo:
  • Oscillators sound improvements: 96KHz sampling, better interpolation (hermite) for improved treble response, major reduction of sound crackling (it can be heard in the last patch of previous demo).
  • Added the polyphonic 2 track step sequencer from P600fw. 20*2 sequences can be stored for now.
  • Added sequencer/arpeggiator and keyboard transpose.

Thursday, 1 October 2015

Overcycler2 patches demo

Here's a demo of a few patches on Overcycler2, showing some of its sound palette.
They tend to have lots of overdrive to get an idea of the raw synth sound but by adjusting the pre-filter mixer levels, it's perfectly possible to get tamer sounds.

By the way, I recently started implementing oscillator sync, I didn't demo it yet because I think I can improve the way it sounds (there's a bit of aliasing on the upper range right now).

Sunday, 27 September 2015

Overcycler 2 lives!

I finally received my PCB!

Unfortunately I found 2 bugs on the board revision I sent for production but it was too late, so there are a few small straps on it.

Anyway, I soldered all the components, did a bit of debugging and it finally worked, all 6 voices!
It works quite fine actually, better than on breadboard. Eg. the potentiometers ADC captured lots of noise while on breadboard which made adjusting values hard. Here the noise usually doesn't exceed 1 bit.
Overall much less noise on the PCB, which make the VCAs really quiet when closed.

Pic of the board (sorry, cellphone quality):

(The heatsink is temporary, I will use the case itself as a heatsink.)

Now I just need mount the board inside the case, solder the connectors (I have yet to receive them) and the synth will be done :)

Sunday, 20 September 2015

Overcycler 2, the return

Overcycler, my homemade polyphonic hybrid synthesizer, while being a working synth that I made music with, had quite a few caveats in its design, here are a few of them:

  • Being a 5 PCB design, I tought it was a good idea to have voice cards but it just complicated the design and made the enclosure a lot harder to build.
  • The enclosure was too small, not very practical, and overall badly built. The fact that it was too small also forced me to make a lot of hacks to fit everything inside.
  • The display was too small, which made parameters hard to read fast.
  • VCAs were noisy, bleeding audio even when fully closed and gain staging was wrong, which made the sound too tiny past the filter.
  • Using the VCA to compensate for resonance volume loss, it seemed like a good idea, saving the cost of one more VCA per voice but it made the synth sound small with resonance, as the SSM2044 lose its overdrive the more you added resonance.
  • DAC / sample & hold mechanism for CV control. Not a bad thing in itself but very sensitive to noise.
  • Link capacitors in some parts of the voice design had too small values, leading to poor bass response.
  • Overall just a prototype that was left unfinished.

So, as the title says, I'm making Overcycler 2, a full rebuild / redesign of Overcycler. Besides having a more enjoyable synth to make music with, I hope this will make it a properer DIY project that others can build. As you can guess all the previous issues were addressed:

  • Single PCB design, roughly A5 size (153mm x 209mm).
  • Bigger, better built, nicer enclosure, with wooden sides for that vintage vibe :)
  • Bigger display, 40x4 characters instead of 20x4.
  • Lots of work on gain staging, to try to make the synth always sound good.
  • Using the pre-filter mixer to compensate for resonance volume loss, requiring no additional parts and nicely doing the job. That was kind of an eureka moment when I thought about it :)
  • 8 channel DAC chip to handle the CVs. They are quite expensive so I chose to ditch multitimbrality (which never worked on overcycler) to keep the costs low.
  • Bigger and better quality link capacitors.
  • This time I really want to make it proper. 

By the way, I added a voltage controlled noise generator of my design and also removed the VC master volume to replace it by a dedicated potentiometer.

Right now I have a fully working voice on breadboard, a prototype PCB that is sent for production and I just finished drilling / preparing the enclosure, here are a few pics of it:

Now compare it to this and you will see what I mean by better built :)

To be continued when my PCB arrives!

Project page: https://github.com/gligli/overcycler

Wednesday, 5 August 2015

P600fw 2.10 second release candidate

A change in the behavior of the "PolyMod OscB" knob was made during the development of 2.1. While this change fixed a bug, I have decided to revert to 2.0 behavior to keep the patches sounding exactly the same when using poly mod.
This is the only change in this RC.

Download links:

Sunday, 19 July 2015

P600fw 2.10 first release candidate

Only one small bug with the "free" osc frequency mode mas fixed since last alpha.

As usual the manual needs an update, and this time I won't be doing it so if anyone wants to work on it, please contact me!

Also, please report any problem you could find.

Download links:

Saturday, 2 May 2015

New P600fw alpha (may 2)

Notable changes:
- Sequencer is now polyphonic, it works by pressing more than one key at once on a step, once all keys are unpressed, you can enter a new chord / note. Compatibility with sequences from previous alphas is lost.
- In the sequencer, the "2" key is now used for both rest and tie. It adds a rest when no note is pressed and a tie when a note is pressed.
- Implementation of MIDI tuning Standard.
- Possibility to change per note tuning. Pressing FROM TAPE + TUNE enters a mode where the last pressed note tuning can be edited using the modwheel. Pressing FROM TAPE + TUNE again exits this mode. Tuning is stored per patch and affects each octave the same.
- Pressing FROM TAPE twice quickly now enters a mode where seq/arp transposition can be made by pressing the corresponding note alone. Pressing FROM TAPE again exits this mode.
- FROM TAPE + keypad number options now show their value on first press. One time actions such as reverting to basic patch now require 2 presses.
- LFO to VCA modulation ("AB-VCA" option of the "LFO TGT" parameter, by pressing "1" twice).
- Adding SYSEX format documentation ( https://github.com/gligli/p600fw/raw/master/documentation/sysex_format.ods )
- Adding SYSEX patch dump request command.
- Many changes to seq/arp clock management.
- Sequencer now responding properly do MIDI stop.
- Many bug fixes.

Thanks go to Ricard Wanderlof and Seth Nickell for many of these changes.

Download links:

Sunday, 22 February 2015

New P600fw alpha (febuary 22)

Notable changes:
- Fix for some occasional MIDI overruns that could cause hanging notes.
- Fix for wrong OscA pitch when when polymod routes OscB to FreqA.
- Adding an option to limit VCF cutoff frequency to 22Khz, enabled by pressing FROM TAPE + 9 (now shared with the "spread" option). Basically, it helps avoid some sound harshness due to strange filter behavior in the ultrasound range (see this post for more info).

Download links:

Sunday, 8 February 2015

New P600fw alpha (febuary 8)

I think I'm getting close to a 2.1 release, if any tester has issues with its P600 with the latest alphas, it would be a good time to report them, thanks!

Notable changes:
- Adding a workaround for the abrupt way the VCA envelope release stage ends, please report if you get any strange behavior with this fix.
- Arpeggiator hold fixes.
- Arpeggiator and sequencer now restart on first note when receiving a MIDI start message.
- A sequence can now be cleared by pressing 0 while recording it.
- Working unison track through MIDI.
- Misc. optimisations.

Download links:

Saturday, 24 January 2015

New P600fw alpha (january 24)

Notable changes:
- Fixed various bugs / github issues.
- Major changes to the sequencer (mostly suggested by ricard):
        - Pressing SEQx immediately starts playing the respective sequence. Pressing it (them) again stops it.
        - To record, first press RECORD, then SEQx. This is analogous to saving a patch, where you press RECORD, then the patch number on the numeric keys.
        - In record mode, use the numeric keypad 1,2 and 3 keys to do back/tie/rest.
        - Sequencer waits for input before playing when FROM TAPE + SEQx is pressed.
- Adding scaling adjustment mode:
        - Enabled by powering the synth with "TP301 SCALE" shorted.
        - Will alternatively display the current oscillator/filter (A1..A6,B1..B6,F1..F6) and a value that needs to be made close or equal to zero by tweaking the corresponding adjustable.
        - Press 1 to go to next oscillator/filter, press 2 to go the previous one.
        - When done, turn off the synth and unshort TP301, next start will be in normal mode.

Download links: