jrp Posted June 5, 2014 Report Share Posted June 5, 2014 (edited) edit june 6 - more sound examples ----------------------------------------- The Midibox-Project has been an inspiration to me for quite some time. While the most simple controller is possible, i normally cannot resist going big... Over the last years i have mainly been designing compressors and preamps for studio use. Before that i was working on a modular synth. That´s what i started with, that´s how i learned electronics. Mostly thanks to electro-music.com, music from outer space and some other places. CMOS was the only thing digital i could work with untill i discovered ucapps. This post is to discuss and present my take on an analog signal chain for the Midibox Sid. I composed this like i always design - using building blocks from datasheets, standard opamp circuitry, "known" designs, blocks borrowed from other people, well, sometimes i even invent something (sortof). It features - CEM3379 Filters (but these circuits could be implemented with any vcf) - voltage controlled Filter FM:fm sequence-.mp3fm 1-.mp3 These two clips use Filter FM controlled by LFO, tweaking the pitch of the modulating OSC. - voltage controlled Overdrive with volume compensation (needs improvement!):drive.mp3 - a wavefolder, designed by Ken Stone with some minor adaptions. http://www.cgs.synth.net/modules/cgs52_folder.htmlwaveshaper.mp3 there is a short bit of an clean sound and a bassline, then they are both shaped. At the end the bassline is doubled by the same patch, 1 octave up and with a saw instead of tri.folder single triangle lfo fade.mp3 This clip fades in an LFO controlling the folding of a single triangle osc. The folder is turned on after 4 barsfolder 3oscs lfo mod.mp3 Here three detuned OSCs are used. OSC3 is a saw one octave above the other two tri OSCs. Sustain was turned down a bit to get a good responce from the Folder. Again first 4 bars are clean.fm fade and folder.mp3 Single Tri OSC playing. Right side is tuned up 2 octaves and used as FM mod source. FM is controlled by envelope, depth is faded in over the first 12 bars. Then the folder controlled by an LFO on the other cv channel is switched in - fading from LP to HP of external filter Of course Sid already has a HP Filter mode, but this was just so easy to add... see schematic below.HP SAW 0-12-24.mp3 Saw OSCs pitched 0, -12, -24. High cutoff, HP is slowly faded inHP pulse +12-12-24.mp3 Same, but Pulse with PWM tuned +12, -12, -24 - external ins examples are a bit noisy couse i haven´t build the line reciever yet, so it´s just a signal hooked in with alligator clips...ext pad mod filter vca fm.mp3 A Drumloop is tweaked with the SID engine. OSC FM is used in the second half. Note that there is some bleedthrough of the modulation osc.ext pad mod filter vca fm.mp3 This time a pad sound was used. - additional noise + vca - Main VCAs, mixer and balanced line drivers Here are some basic waveforms. You hear three short clips with modulated wavefolding. Then there is a short sweep of distortion and then a couple of FM waveforms. All were generated using a single triangle oscillator. --sorry, file was to big, have to bounce it again---- Although this is still a work in progress i already have a bunch of schematics with tested values so i thought it´s about time to share a little. Soon after i hooked up my first Sid-Chip to a core module i was hooked up myself. I spend a lot of sparetime over the last 6 month, thinking what could be possible, what could be usefull, what could be fitted into the MB_SID concept. The analog CV-options and triggers are perfect. Thanks TK. I use analog filters and VCAs, they eat up 6 CV channels. Leaving 2 CVs and 8 triggers. Not much if you are used to modular synths. But that was part of the job- selecting the right blocks to get the most out of what is available. And i soon realiced that you would rarely need any more. Oh - and everything is saved with the patch!!!!!! I tried a bunch of circuits and ideas and came up with this collection of building blocks. Among the design goals were: Usefull addition soundwise (very subjective) Low parts count (more or less) Effective controll with one CV per stero side. All CVs are 0-5v, the DAC can drive 2k load so i dodn´t use any buffers. Of course a complete AOut Module can be used if you like to try any of these circuits, but if it is calibrated to 10,xx volts the cv inputs should be adapted. If you know what a voltage divider is this should be no problem. I use trimmers anyhow, but with series resistance to taylor the trimmer to a more precise action. Lowering or raising the coresponding resistor does the trick. Effects can be switched in individually, but share the same CV so the same modulation will be applied. Can sound very cool, but normally one at a time is enough for a certain sound. There is also a mode that controlls two sets of effects - in mono. Have i said i love the modulation matrix? Sorry, i have schematics, but no board layout. I am a veroboard guy... I refuse to learn any layout software... I am happy i found a good way to solder SMD. I carefully bend every second leg upwards. The remaining pins can be soldered nicely to a veroboard. The bend pins will be soldered using short bridges (cut resistor legs). I use this a lot to perform crossings (like multilayer) or connect ic pins, etc. Quite sturdy, of course you musn´t apply preasure, so whatch out when changing chips. It´s definitly quick compared to strapping wire. Anyways, i like working like this when there is a good audio book around. Kind of fun looking for the shortest signal path as you go along filling the board. In the current state i have implemented and build (in stereo): - CGS Simple Wavefolder with some adaptions - Filter FM - Highpass blend for external LP-Filters using same VCA as Filter FM - Voltage controlled Overdrive with volume compensation. Needs improvement. - Switching of modulation Signal for FM sounds. Making Sid L the source for both signal channels, Sid R the modulation source for Filter FM. - Stereo/dual mono CV mode Only checked out, under construction: - Noise for external Filter Todo: - Tweak the overdrive for less noise and better Bass-responce - build signal switching circuitry - design frontpannel and CS - decide if F2A should be used. This is a problem in conjunction with the 8580 requiring calibrated log mode. Alternative would be to include independent controll for CV 1 and 3 - put everything in a box with psus - decide what could be ommitted - Build Stereo Sid 2,3,4.... Here you see a block diagramm of the signal flow. -A buffering amplifier brings the sid output to a more roboust level. -Folder, Filter and Overdrive are chained and can be switched in and out (see extra diagram below). - FM and Highpass are part of the Filter-schematic Signal and CV switching Most of this is propably self explaining. Switches controlled by the Gates from MB_SID. Stored with the patch. Very nice! Switches are not selected yet, but i´ll propably go CMOS 4066 or 4053 for CVs and some Maxim Chip for Audio-Signals. Max 333 ACPP might be the choice. For 5.20 € at reichelt you get 4 SPDT switches that can be powered with up to 30v. For a compressor i would always use a relay, but this is a synth... Maybe powering the 4000 series cmos chips from +-7,5v would be smart. makes the PSU more complex though. I still have to test how they perform with AC-coupled signals when powered from 12v single rail. SW 2 is different for L and R channel. This will route the left Sid to both audio channels, making the right Sid the MOD source for FIlter FM of both channels. SW 1,4,5 are controlled by a center off, DPDT switch on the panel. They provide three modes for external signals: EXT to SID_input EXT to CEM3379 filter directly EXT to CEM3379, Sid disconnected from filter (but still available for FM!) To be honest, this should work, but i might not build it. If i really build 4 stereo voices, they could be fitted differently. SW 11,12, 13 are also hardware controlled for routing Voices 2-4 to the Main out. A Gate is used to split CV 7 and 8 between L and R channel (each cv controlling every active effect) - or - direct CV 7 to Wavefolder and distortion, CV 8 to the other effects - on both channels. Wavefolder: I found this little circuit on CGS. Really fascinating what it can do.http://www.cgs.synth.net/modules/cgs52_folder.html I found that, although this will react very much on different input levels, it sounds best when a defined level is used (so no VCA is required). I calibrated mine to work perfect with a single oscillator. Using multiple OSCs sounds interesting as well, but some sounds are "broken". Luckilly oscillators can be turned down with the Sustain. Instead CV is applied as an offset. On the schematic i tried a drawing of the waveform at different CV levels. It sounds a bit like a phaser and a bit like pwm for triangle and saw. Filter, FM and Highpass: Depending on Switch SW 2 L, R a modulation signal is routed to an inverter and VCA. FM is generated by switching the VCA output to the Filter Cutoff pin. HP by summing the VCA output with the filter Output. Since the VCA delivers an inverted signal it will cancle out below Cutoff - creating a fade to a more or less Highpass responce. Note that, if switch SW2 is on, or the wavefolder is active, things look a little different. The rest of the Filter is more or less off the CEM3378/3379 datasheet. I settled for a slightly higher drive, giving this filter a little more grit. Of course the same circuitry could be added to any VCF. I have not yet implemented the Noise. I tried it once and liked having white noise as an alternative to the sid noise sound. Also having an extra VCA for noise is nice to have. Schematics for analog white noise (using a transistor with open collector) are on the web. Overdrive This can be seen as first design concept. I have to do something about the noise, propably by chaining more clipping diodes, thereby raising overall level. It could also use some basic filtering at the output. The overdrive itself is made by the opamp with the diodes in the feedback path - forming an unsymetrical sof clipper. You know this from the guitar stompboxes... The first VCA acts as a voltage controlled drive-pot. The trimmer around the CV opamp will set a bias at low level so with no CV applied there will be close to none distortion. Volume compensation is archieved by applying a portion of the CV controlling the Drive (first VCA) to a second SSM2164 VCA but without the inverting opamp, turning it down as volume raises. Remember SSM2164 is at unity gain at 0v cv and will turn down with a CV going positive. This works very well, it can be trimmed to taste so that the percived Volume is constant or if you like, slightly raising. If i had a 9th gate i would make it switchable pre or post filter. But that could also be solved by building different Voices. Pre filter is nice as you can controll the harmonics, Post filter has a more agressive touch and gives cool clipping of filter selfoscillation. VCA and Mix Nothing special here, only maybe that i use an unbuffered CV that is inverted in the ensamble settings. Nice feature! Since my Studio is all balanced this is what i added for outputs. compensation caps (47pf) across the output opamps feedback resistor are required and missing in the schematic. I use NE5532 for it´s 600 R drive capability. Sorry if this was confusing, i am a bit hit by how much info this is myself... Edited June 6, 2014 by jrp Quote Link to comment Share on other sites More sharing options...
jrp Posted June 6, 2014 Author Report Share Posted June 6, 2014 does anyone know if it´s possible to put audio examples in the forum post as miniplayers instead of downloads? Quote Link to comment Share on other sites More sharing options...
yogi Posted October 17, 2014 Report Share Posted October 17, 2014 Wow, interesting designs. Just recently I got the bug to explore some analog ideas. I'd like to hear more about your experience with the AOUT capabilities of the SID V2 softs. I'm thinking about a simple mono synth design combining an Electric Druid VCDO (4 CVs) fed into a Shruthi-1 SSM2044 VCF/VCA (4 CVs) board, controlled with a MB AOUT-NG/Core8. These choices are based on the parts/boards I have on hand and am trying to minimize the parts count. Judging from your notes I think I may be able to strip down the AOUT-NG to just the DAC; the SSM VCF board is designed for raw 5V PWM inputs (from the AVR). So there doesn't seem like there is a need to condition the DAC outs to 0-10V then div the signal back to 0-5V. As well, the VCDO outputs 5V PWMs that should be fine with the VCF board ( designed for the AVR's raw PWM). The CVs into this chip are 0-5V so I think there only needs to be 1:1 buffers that allows some minor calibration between the DAC and the VCO chip. One question I have is what, if any, benefit there would be with more filtering on the PWM signals in this user case? Very much 'up in the air' as to what softs to run on the Core; MBCV 1 or Analog Toolbox or SID V2. It seems like the SID firmware offers the most features, but I'm unsure if it will work as a 'analog synth' controller or if it is more for external filter handling. Can it route Note pitch to CVs in addition to the LFO/modulation CVs? Seems like the Analog Toolbox offers a basic front end - Pitch, LFOs and EGs Another option I have considered, would it be possible to use 2 AOUT/Cores somewhat like the MB6582? One for VCO/LFOs and the second for 2 VCF/VCA control. In other words, does MB6582 allow for CV control from each core? Sorry for all the questions, you just seem to have dug deep into the analog control options in the SID software. Yogi Quote Link to comment Share on other sites More sharing options...
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