Vacoder part I: MFOS Vocoder PCB Assembly

Music From Outer Space. MFOS, as it is known to it’s fans. Ray Wilson’s stunning contribution to the immortal pile of stuff we all leave behind when we pass away. Ray has passed on, and as I shed a single tear of sadness at the loss, I am comforted to know that perhaps he is now an electron somewhere, doing work for the universe as he moves from valence to valence and atom to atom. We all miss Ray Wilson.

Ray is one of my heros: he fell in love with electronics and through reading Electronotes, a magazine dedicated to DIY synthesizers, he taught himself to think like an engineer and design like an artist. He has created a more or less new modular system. He’s done kits by the ton. He contributed a great deal to my early enthusiasm and excitement about both electronics and electronic music. I was honored and surprised when Ben Mandberg gave me the kit he’d had sitting in his closet for 6 years. I received it earlier this month. What a PCB!! She’s monstrous!

+/-300 resistors, over 100 caps, lots of IC’s, and filters galore (twelve in all!)

I will populate the board with the BOM provided by my homie Ben. It’s a mix of ceramic TDK capacitors and nice film caps, milled IC sockets, Kayama 5% carbon resistors (all but 4 in the circuit,) 1N914 diodes instead of 1N4148s, and some pretty generic unmatched (as far as I can tell) PNP/NPN transistors. The ICs are a mixed bunch: Operational Transconductance Amplifiers (OTAs) from National Semiconductor, Farnell made LM324s, and the ubiquitous TL072 from Texas Instruments too. The CD40106 Hex Inverting Schmidt Trigger IC is from TI also. TI used to make oil field hardware- until they invested in this new fangled “sillycon” in the 60s. Now they are “King Shit of Fuck Mountain,” to quote Bob Odenkirk from Mr. Show.

One of the ssoftware utilities Ray used in the design process was actually software from TI called “Texas Instruments FilterPro.” I plan to explore this software when I design new expansion PCBs for the MFOS vocoder. He also used Webbench Filter Designer. I plan to do some expansion boards with 4-12 channels each after I modify the output mixer bus with individual volume knobs and outputs for each band. Thankfully, Ray anticipated this, and gave the ability to tap into and out of critical busses on the PCB quite easily. I’ll need that software I’m sure, though, as filters are all math! I’m looking forward to playing with some new tools.

I did my least frequent components on the BOM first, starting with resistors as they were the shortest in height. I actually did the small signal diodes first as they were the shortest, but there was no method necessary. They were all the same. The BOM had been ordered with no customer part number in the Customer Part# field for Mouser, so I had to look at the spreadsheet BOM for placing each part of each value. If the CP# field had been filled in for some of the parts, I could have placed them without going back n forth from the BOM. Many parts though wouldn’t have had room in the field for all the designators though, so it’s a moot point. So all the resistors that were only used once were first. Then the resistor values only used twice. And so forth. This meant that by the end I was able to confidently put the most numerous part into the PCB without looking at each resistor designator because I knew that there was only one value left and that any open resistor pads had to be for that value.

I then did the IC sockets, anchoring one pin at a time to make sure the whole thing was flat against the PCB before soldering. And so on up in ascending order of height, so caps, then transistors, and finally trimpots. Something like that, more or less. I like to pretend I’m logical and methodical when I assemble stuff. Yeah, right. Like anyone really is. Plus, ya want to know when I’m least logical and careful? When I’m excited. And be warned, people, I am really excited so I did rush a lil bit to get ‘er soldered up. So it looks a little home-made, but hey, I stuffed and soldered it in under 6 hours.

Some of the capacitor selection here on the PCB looks to me to be pretty arbitrary, but I’m just gonna get ‘er goin and make modifications later. Ben may not have gotten film caps consistently for the filters on the PCB so some might be ceramic- oh well. If need be, I’ll change some caps later. I’m so fucking grateful to Ben Mandberg, who is a true homie, for the gift. Any caps he bought are just fine by me!

I’ll get into the details of what capacitors do what, which filter strips on the PCB are what bands, how the filters work from an electrical point of view, and how Ray designed this magnificent device to work in another post. Then, with any luck, we will do some serious modification. Along the lines of the Moog Vocoder and some of the Kraftwerk vocoders: possibly modular I/O for each band, possibly potentiometers to control the volume of each band fed to the output mixer bus, and in the end, let’s face it, probably both. God help me, it’s gonna get comically complicated. I was born a circuit bender, I’ll die a circuit bender. Or was that a Snake Handler? Don’t matter. Below is a pic of what it looks like before I solder and cut all the leads from a big ass PCB like this. You can see it’s not super precise or technical. I just bend the leads enough for them not to fall out when I flip the PCB. Then I bend em back a little when I solder them. I makes them easier to cut and less likely to short to another lead during solder application.

It’s time for me to get mad mathematical as I delve into the world of analog filters and frequency manipulation. That will all be upcoming. So will be a post on the chassis, finished unit, some more stuff about power supplies for bi-polar circuits.

E-Mu Morpheus Prototype?

I have a friend in Santa Cruz who is always finding strange toys to play with. She recently called me to have me service her E-Mu Proteus. She gave me an extra Proteus Custom she had sitting around (yay!) and I also got a weird ass rack with no faceplate decals on it. It looked to me like a piece of beat up hardware with nothing remarkable about it. Until she turned it over and I saw the business card for Dana Massey, the DSP engineer at E-mu systems during the ’90s. It suddenly dawned on me that I was looking at a factory E-Mu test bed. I was excited to get it home to see what kind of patches were saved on the unit from the lab. I figured I might be able to find some cool patches and stuff.

Alas, upon inspecting it while plugged into my soundsystem with a MIDI controller, I realized the patches were just the same shitty factory patches Dave Rossum had shipped with the original units. I was unable to find anything impressive or interesting about it while I played it. It seems like most of Rossum’s rack products: useful when it came out, and then within months or a year, each model became a thing of the past as newer and easier to use systems hit the market. The other thing about the Morpheus and Proteus modules are that they are ROM-plers, as in “samplers you can’t sample with,” as all of their sounds are just ROMs sampled at the factory. I personally like synthesizers and samplers much better, but ROM-plers like the E-Mu Proteus are still used all the time to make HipHop and Electronica.

Z-plane filters, which are Rossum’s unique contribution to the field of sound synthesis, are pretty cool. The Z-plane is a type of digital filter whose cutoff frequencies change over time. They’re usually 18 poles, as opposed to the 4 pole analog filter that Moog popularized. The Z-planes sound spacious and very pretty. The tones they produce can be bell like or very ambient and pretty. The Z-plane filter itself was always the domain of rack mounted E-Mu systems modules in 19 inch racks, until Rossum released the Eurorack Z-plane filter for modular synths. The Z-plane filter module for Eurorack is clearly his best iteration of this software, as it is the most versatile, useful with other hardware, and you can drive the module to do crazy shit the original rack synths couldn’t do. I also should note: I really don’t care for digital filters in general, so take my synopsis with a grain of salt.

From what I can tell, it looks like Dana Massey or whoever at E-Mu, was blowing up some ICs from time to time inside the unit. I can see where the quad flat pack ICs for interfacing with the slot inside have been resoldered. I can also see that the GAL/PAL ICs are socketed and most are unlabeled with the usual sticker. There are also several EPROM ICs with their windows uncovered on the PCB. I surmise that this unit was used as a test platform for Morpheus EPROMs or as a test bed for the slot on the PCB. The slot looks like it could be a slot for an E-Mu ROM expansion, but I looked into it and nowhere does it advertise the Morpheus as expandable, so I assume it could have been the programming or testing interface for mass production. I’m not sure.

Starving Musician in Santa Cruz apparently gave my friend Christina this unit for free, as it did not have a label on the face and also seemed to have Dana Massey’s business card on the bottom. The guys at the shop said they couldn’t sell it, so it went to Christina, and now to me. A fun little project, but altogether a little disappointing. The Morpheus sounds whack in my opinion, and who in God’s name wants to menu dive for 5 minutes for each parameter tweak. The Z-plane is interesting, and pretty cool. I was hoping to find some really crazy ass patches onboard, but no such luck, all patches were factory standard. If I were to get a Z-Plane device for my studio I’d be interested in the Eurorack module but not much else. This test bed goes back to Christina!

Below are some more photos:

You can see everything is Rev. A, 1.0, etc. Pretty cool. EPROMs still have the original labels and stickers. Everything looks great inside despite it’s beat up exterior.

Above are more Atmel programmable devices in their sockets, with their windows exposing the bare IC dies inside of the ICs.

Above is the Analog Devices ADSP-2115 DSP IC on it’s breakout board with it’s complimentary programmable devices on the right and what I assume is flash on the left.

Above is the output section, with it’s Analog Designs DACs, low noise N-FET output op-amps, big thick SMT resistors and caps, a Zettler relay (just like in an electric car!) and finally the E-mu ASICs on the bottom of the shot. Pretty cool.

A friend of mine recently went to work for Dave Rossum. He’s very very happy, as anyone who’s ever used an E-Mu product would be. Dave’s work with samplers gave the world hiphop. Basically, all on his own (aided by the team of professionals who enabled his vision.) Thank you, Dave Rossum. We are in your debt.

Dave is certainly an OG in Audio design, and love or hate the products, he’s worthy of praise as a designer, marketeer, and visionary in electronic audio. Just like Dave Smith, Tom Oberheim, Don Buchla, Bob Moog, and all the myriad of new designers who are now creating tomorrow’s classic hardware. But the when and where of Dave’s samplers, especially, had a very very deep impact on music production and changed the whole world. He was capable of seeing samplers as a new instrument, not a computer. An instrument that I believe still has not had it’s limits properly philosophically tested.

ARP 4035 Filterbank

I worked for a gentleman here in the Bay Area for a period of time in 2016 when I moved back here from Eureka after being gone for 10 years. He was a cool guy to work with, but he drank a lot and was always complaining about having drama between his mistresses. He used to work for the Dead. I learned a ton about electrical engineering from him though, and got a chance to repair a ton of hardware from Fender Rhodes-es, Rhodes CHROMAs and a Wurlitzer to Roland Fantoms and ARP Odysseys. It was fun, but he payed me 8-10$ an hour while I plowed through the backlog of repairs. Love the guy, but he definitely didn’t know how to take care of employees or monetize his expertise very well. Case in point: ARP4035 filters. New fabrication.I hand assembled several, 14, I believe, while I worked there. He let me keep 4 PCBs and their components separate and put them aside so I could build them on my own time to recuperate the loss from the hours and hours spent soldering the ones he sold on the website. I actually really appreciate that. It was generous, and he knew I was feinding for synthesizer modules to play with. I also built him a rather ratty test rig. So I have four of these, 2 of each assembly type (capacitors I think were the only difference between them.) I plan to make a small PCB with the necessary I/O and voltage trimming to make these drop in replacements for the ARP 4035 filter module into either 5U or Eurorack panels, 1 for each filter. I’ma callz it the “ARP 4035 Quad-Filterbank.” I know, right? Totally unique and interesting naming scheme!If anyone has any interest, I actually figured out how to use new OEMs to get the circuit for the 4035 filter pretty much perfect. The tempco (temperature compensation) resistors, although hard to find, are out there. And they can be made by the 100-1000 at a time by resistor manufacturers here in the USA, if someone wants OEM information. Replacing the matched FETs in the schematic isn’t difficult, but it takes a little thought. Let me know if anyone would care to see what kind of solution we employed.

Synthesizer tools: passive (unpowered) gate trig

Dogshow! A while back I was playing with my Yamaha CS-5 as I was in the process of modifying and restoring it. As I did so I wanted to hear the LFO running free on the oscillators, but there was no way to hold the note without holding a key down. I later that week was looking at the old Moog System 55 modular (y’know, from before they started to suck) and I found it enlightening as far as how he had triggered his gates, but still no stroke of dogshow. I am also modifying and restoring a Moog Prodigy, and I was trying to figure out what some of the silkscreens meant. I saw trig, and gate, and a few others I found odd all to be on the same unit. Trig couldn’t refer to filter, as there was already a filter CV input. After doing some digging, I found out Bob had used short to ground triggers made from doorbell switches in the original Moogs. I then got distracted from the Moog jive:Why don’t I just put a couple of switches and jacks together to make a trig to ground? Here it is:Yes, it’s made of a plastic housing from a crappy Chinese wall-wart supply. Why not use Chinese craftsmanship for something useful, afterall? Sorry. That’s brutal. The red switch is normally open. The black push toggle is latching to either pole, one not connected. There is a Switchcraft jack of both Eurorack and 5U modular standard size. They share a ground. The pushbutton switch shorts the “input” lug on the jacks to the “common” or ground lug. You can use it with pretty much any synthesizer that has a short to ground trigger for the gate. Push the toggle to hold the gate open. Tap the button to temporarily trigger the device. Afterthought: I need to find a way to invert it so that the triggers sit at ground and short to positive, but that’s a little more thought intensive. Haven’t gotten round to it yet.Used with the CS-5, Moog Lil’ Phatty, modular, Arp Odyssey, and KORG Ms-20 it works a dream. Got a synth without a gate trig switch? Just add one. Circuit bend that shit in there! The best company to source temporary and pushbutton switches from is Grayhill, but there other great companies out there too. The switches pictured were Chinese crap I had sitting in The Pile. When I do permanent mods on synthesizers, I use Grayhill components. Expensive? Yes. Supreme quality? Yes. In my experience.My KORG MS-20 Desktop unit, with it’s very not stock spec rounded candy red Grayhill switch installed. Pardon the dust- California is on fire and it is currently raining ash in San Francisco. Everything is covered in dust. The Chinese trig switch that came stock literally only worked 1/3 of the time it was pressed. The Grayhill works every time, never had a press that didn’t trigger. A worthy and simple mod. Doing it to a Yamaha CS or an ARP would be easy, but more thought would certainly be required. Happy modding!