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Bill and Will's Synth
April 2009 - In February of 2009, Jürgen Haible posted a message on the MOTM list server announcing what he referred to as his "Living VCOs" Module. It is essentially three separate VCOs and a "driver" circuit. The Idea, in part, is to re-create the sound of slightly de-tuned EMS oscillators. As a former Synthi-AKS owner, I find this particularly attractive. The reason Will and I embarked on this synth building endeavor in the first place was to replace the Synthi that got away. (Actually, she's on tour - in more able hands than mine - hands that deserve her more than me and so she's right where she belongs. Still I pine for her.) The Synthi has 3 VCOs and, per my recollection, as they're almost never perfectly in tune, they create a characteristic sound when they're nearly in unison - I think this is what Jurgen describes as "beating." The idea of the three VCOs is the reason Will and I got three of Paul's "Ultra VCOs" (MOTM-300) and we love them. The EMS VCOs, however, have a characteristic sound and as an addition to our three 300s and two 310s of Paul's, we're very intrigued. In his documentation, Jürgen mentions providing a raw output from each VCO core to feed to a waveshaper to create Sine, Saw, Triangle, and Square outputs and so we did some research and figured out how to use part of the MFOS VCO circuit as a waveshaper. Our first plan was to build a simple 1U sister-module with three of the MFOS PCBs for shaped outputs for each of the three "Living VCOs." But more recently, we've decided to include the waveshapers in a deluxe, 7U version of the module. By way of cross reference, please check out Dave Brown's page. Here we go... |
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Table of Contents |
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Here's a table of contents that we hope will make it easier to traverse this page: Background - presents Jurgen's initial description of the module Recapitulation of Construction/Feature Options - presents a simple list of different implementation considerations Option Details - presents the details of our implementation with some discussion of alternate ideas - you'll probably want to consider these in deciding how to build yours. It's not a complete list but, rather, focuses on our own implementation. Parts - presents a Bill of Materials and notes about it Panel - presents how we, in collaboration with Jürgen and others, came up with our panels' design - Construction Phase 1 - Resistors, Capacitors, IC Sockets, Power Plugs, MTA headers Construction Phase 2 - Trimmers, Panel connections |
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Background |
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Jürgen's site describes the module: "I already have a lot of different VCOs, from the ultra precise MOTM-300 to the lush, but not so well-tracking VCOs of my EMS-Synthi clone. Each VCO has it's benefits, the CEM3340's (partly under autotune control) are the "workhorses" in the OB-8, the Prophet 5 and my own JH-3, the Yamaha CS-oscillators are more on the "temperamental" side, but still playable without autotune (the 4 ones in my CS-50 stay better in tune than the 8 ones in my CS-60 ...). The precision of the MOTM VCO is invaluable for complex audio range modulation patches. I've never heard better drones than from three EMS VCOs running at almost the same frequency, and beating against each other in an ever changing pattern. "My goal was to build a set of VCOs that have the untamed bass range power of early EMS and Moog VCOs, but which are tracking a keyboard voltage over 5 or more octaves nevertheless. I found that "untamed" Beating in the bass range and controlled beating in higher octaves is not possible with standard exponential 1V/Oct oscillators. A good part of that special sound of early Moog and EMS oscillators is not because of any "randomness", "unstability", "instability" or "noisyness", as so often is said. A good deal of their behavior is because of that, but it is not the whole story. There are also some very deterministic factors in these old circuits which have been unpleasant side effects for the designers back then, but which are worth a closer analysis when we're designing a musical VCO today. This is implemented in form of three "linear detune" potentiometers on the JH-5A VCOs. "Features
Jürgen's site has many more details on it - but we want to include this part here too because it speaks to the heart of why, in particular, we want to build this module. "Drift and Noise and all that stuff "Every few years there seems to be a heated debate how "stable" a good-sounding VCO should be, or shouldn't be. "I never quite understood how one can make an almost religious question out of this. IMO, the situation is quite easy: Find which factors cause these random changes in a VCO (there aren't many possibilities!), and then decide if you either: 1. want to get rid of them, or 2. add them externally, or 3. deliberately keep them in your VCO. "VCOs with design philosophy 1 are more expensive, can be used in applications where stability is important, and you can always do Number 2. "I could have built a VCO like this, and added the linear detune feature there. But I decided to go for Number 3 in the "Living VCOs" project. Asuming those who buy them want to play animated 3-VCO-sounds in the first place, I kept everything as simple and unexpensive as possible, and I've chosen the same noisy 4-transitor exponential converter that EMS used in the VCS3. I'm not overly scientific about it - I just like the sound of it." Exactly. You know, I suppose you could base a synth on these three VCOs - especially if you include a wave-shaper Sister-module. But we wouldn't want to. We like Paul's super-accurate 300s too much - and we're happy to have them. But as an addition, it looks like these will be very good. So - you really got to check his full description out, but we included all of his text above to describe the features and design philosophy behind the module.
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Plan 1 - 4 & 5 Unit Version w/o Waveshapers |
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This is the 4U and 5U panel design placed next to a MOTM-310 layout to illustrate the horizontal alignment. In order to maintain the LVCO Module in four units' space, we decided to do a design using very small, Tyco PKG50B1/4 .551in. knobs for fourteen of the controls. This is radical for us, but we wanted to include all the controls - and if we used standard MOTM 1" knobs, the module would expand to a seven-unit wide module. (That 7U module is the one we'll build) So for the 4U module design we're going to go ahead with the very small knobs aligning them on the standard horizontal Knob Grid, and vertically aligning them with the jacks. It really looks pretty good. If we use the Tyco 506-PKES-70B-1/4 .74in. dia. small knobs like on some of the Tellun Modules, it takes up five units. We can use a larger (and less expensive) counting dial. The horizontal Knob Grid is maintained to an extent, but especially in the "Driver" section and the VCO link switches, the grid deviates. But it's not so bad. We'll use very good pots for the ten-turn FREQUENCY control of each VCO and hence correct what I, like so many EMS owners, felt was a drawback of the Synthi design - the kinda lousy Frequency pots of the original Synthi. And we'll use really nice counting dials. For the 4U they're 1.2" dia, for the 5U they're larger, M46 ones. Aside from the difference in the size of the counting dial and the small knobs, the essential layout of the 4U and 5U versions are essentially the same. It will be expensive just for these parts - let alone everything else - but we feel that if we're going to build the damned thing at all, put in all the effort, well, we might as well go for broke. If we're a little strapped, we can leave off the counting dials and use just plain knobs at first. The counting dials are the most expensive part and we can add them on later. Jürgen's posting doesn't fully describe the details of the different configurations possible but he does provide three .pdf diagrams of possible connections.
Wiring Option 1 The possible options are too numerous to outline fully, so we're going to primarily focus on the features as we intend to implement them - based on Wiring Option 3:
Our idea is to provide controls to allow the VCOs to operate reasonably independent of each other and also to so they can be controlled commonly by the "Driver" and by the Pulse Width and PWM controls of VCO 1. Here's how we propose to accomplish this: The Driver TUNE and OCTAVE controls all VCOs -
But the VCOs can be un-linked like this -
The VCO Outputs are switchable between the 0...10V saw provided by the CORE output (for use by a waveshaper) and the output of the VCO's AMP (can be wired up either as +/- 1.2V or +/- 5V) The shape of the wave provided by the AMP can be switched between a saw wave and pulse wave. |
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Plan 2 - 7 Unit Version with Waveshapers |
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This is the 7U panel design placed next to a MOTM-300 layout to illustrate the horizontal alignment. Everything horizontally aligns - except for the counting dials. In the "Driver" and the lower 60% of every VCO, everything is on a standard vertical alignment as well. Primo! The 7U module includes 3 waveshapers fashioned from 3 MFOS VCO PCBs. All controls are included and are the standard MTOM Tyco 506-PKES-90B1/4 1.01in. dia. knobs. We use the larger (and less expensive) counting dial. The horizontal grid is maintained except for the counting dials. We'll use the same very good pots for the ten-turn FREQUENCY control of each VCO. And we'll the bigger, really nice counting dials - the larger, M46 ones. This layout differs from the 4 & 5U modules. Super-importantly, there are 4 extra jacks per VCO - the waveshaper outputs - SIN, TRI, SAW, SQR outputs (just like on the MOTM-300). Also, the PW & PWM "Link" switches are in the "Driver" section. This, actually seems even more intuitive to us. The features represented are the same as for the 4 & 5U versions (except for the addition of the waveshaper outputs), but they're configured differently. We'll explain more later. Here's how they stack up:
Because of the inclusion of waveshapers, The VCO Outputs need only be switchable between saw and pulse outputs of the VCO's AMP. The core output of each VCO is fed into a waveshaper (MFOS VCO Waveshaper Section) - its outputs provide the SIN, TRI, SAW, and SQR outputs. It could be that a MOTM-300 PCB could provide these waveshapers too... we just haven't explored this possibility. |
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Parts |
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BOM Will and I have developed a parts-list / bill-of-materials based on the feature set described above in the form of an XL spreadsheet. Today, August 18, 2009, it's pretty complete. We've used the BOM to arrange for our parts order and corrected some mistakes in the process. In the BOM, the left-most column is the "part." The parts we've checked and double-checked and used to build a mouser "Project" have an orange background. These parts we have a high (but not perfect) level of confidence that we've specified correctly - we caught a mistake or two in part numbers / prices as we were building the "Project." Please double-check us and let us know of mistakes you find. Click here to see Jürgen's Bill of Materials. Corrections to BOM: None yet - Notes: None yet - Click here to download the spreadsheet (apx. 48K).
Buckaroos The bottom-line price is a bit of a shocker. Using inexpensive alpha pots wherever possible, but still the expensive 10-turn 10Ks with the $40 verniers for the FREQUENCY controls, the parts come out to about $500.00 without the pcb (add another $75) and the panel (assuming Bridechamber makes it, we're guessing around $100). Now - this blows the mind until one considers that this is really four modules in one. We estimate that if you select a smaller feature set and didn't use the counting dials you could easily chop $200 off the parts. But again, Will and I are going to do the go-for-broke implementation with cermet pots rather than Alphas and ordering extra parts along the way too. Our parts will cost in the neighborhood of $650 - that's around $825 including pcb and panel - about $275 per oscillator. What would three MOTM-300s cost in 2.0 form? Around $300ea or $900. How about three MOTM-310s in 2.0? Around $250ea or $750. For that matter, what's one one Zeroscillator cost - around a grand assembled right? So this made us realize that the Living VCO is in the same ballpark, really... you just have to see it as four-modules-in-one. But this means we'll be building it over a longer period of time. As money comes available we'll buy the next phase of stuff probably like this: Phase 1 - pcb $75 Phase 2 - Construction Phase 1 components - $90 Phase 3 - Construction Phase 2 components - $390 Phase 4 - panel and fancy dials - $350 Counting Dials OK - here are the Bornes Counting Dials (Mouser #652-H-550-6A). Gotta say, although they look just fine, their plastic is kinda thin and they seem a tad flimsy at first. They are lightweight, though - and for many applications this would be an advantage. So you know what? - they'll be fine. On one of them, the ring that holds the knob-part onto the base-part had come off the back. But we got out our Retaining Ring Pliers and fixed it with a little extra coaxing from a screwdriver.
Wave-Shapers It's perverse and excessive, but we're going to use three MFOS VCO PCBs as waveshapers for the module. So we've been looking at the MFOS VCO schematics and at the PCB and here's some early thinking about which components are involved. But we'll update this soon.
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Panel |
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Following Jürgen's examples, Will and I developed the Panel designs at the top of the page. Here's the 7U design we'll be building:
For our FPD panel design, click here. If you decide to use it, you'll want to modify it a bit - take out the red circles that mark the location of the counting dials - double-check everything about your particular counting dial specs, etc.
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Construction Phase 1 All the stuff in Phase 1 gets soldered using "Organic" Solder. At every break in the action, we wash the board off to get rid of the flux. |
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Construction Phase 2 All the stuff in Phase 2 gets soldered using "No-Clean" Solder and the PCB doesn't get washed off from here on. |
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Set up / Testing |
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Use Notes |
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The fine Print: Use this site at your own risk. We are self-proclaimed idiots and any use of this site and any materials presented herein should be taken with a grain of Kosher salt. If the info is useful - more's the better. Bill and Will © 2005-2010 all frilling rights reserved
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