some really good things to buy for a pound.

ive bought a few different bits of gear off ebay over the last year or so, and heres my suggestions for things to look out for:

1. another oscilloscope. seriously, even if youve already got one, (and you are a geek right? thats why you're reading this) its a pain in the bum having to yank the 'scope out of the workshop and set it up with a camera for lissajous figures and wierdness and rescanning and things. and theyre really cheap. 99p on ebay if you can do the pickup yourself. i recommend a bicycle and a good backpack. it keeps you fit, is truly eco friendly and you can save on the bus fare. try and find one with a Z-axis input.


2. electrocraft 89 series RGB to PAL encoders. i picked up an electrocraft Component to PAL encoder as well, both brand new, from granada TV, both 99p. just plugging the outputs from the modular into these works with no voltage limiting or blanking or anything. ive tried some Abekas Cox ones that didnt work with any input that wasnt a valid RGB signal. meh. the electrocrafts appear to be able to take anything you can throw at them. they use a Sony encoder chip, and they rule. and the circuit board inside is tiny, easily small enough to fit behind a eurorack front panel, should you be that way inclined..


3. a Sync Pulse Generator. anything will do as long as it works. it should cost about 99p. i use an Amcron. i bought a couple of other random makes to try out and they all worked.



4. a Video Line Selector. this isnt essential, but is fun to have. allows a scope to accurately display the video signal on any arbitrary video line of your choosing, and also some of them generate positive 5 volt triggers for V sync (selectable between frame and field) and H sync, which is useful. ive got a philips, its excellent, and tiny. 99p.

5. a PAL to RGB/YUV converter. again, anything should work. if correctly listed, these generally go for more than 99p, because you can use them with big flatpanel TVs to plug in legacy things like VHS players &etc. but idiots sell things on ebay, and they dont always know what they have, or how to spell correctly.. 99p with some perseverance and trawling.



so there you have it. 5 shiny goldish coins and the worlds your oyster. hooray for the imminent changeover in Britain from analogue to digital broadcasting. all those local TV stations are unloading their meticulously maintained and initially very expensive analogue gear for 99p. because unless you're building a video synth, its all essentially useless. huzzah!


love and pez
S/P

I am a lazy git.

sorry for the lack of new things. work on just about everything has paused due to it being incredibly busy at work. the last thing i want to do when i get home is pick up another soldering iron at the moment. anyways, ill finish the docs for the VCOs with a BOM, corrected schematic, component overlay and some suggested parts suppliers this week.
love and pizza,
s/p

system flow diagram

heres a diagram explaining how the various signals are routed around the system. the synth is patched into two video encoders, which are both synchronised to the sync pulse generator which also supplies sync to everything else that needs it, like the camera. the outputs of the two encoders are fed into the main and camera inputs of the ave3. from there they go to a phillips line selector, a bit of test equipment that generates a signal suitable for an ordinary oscilloscope, and that also has positive 5 volt triggers for the horizontal and vertical timings. (more about them in a sec.) the output of the phillips goes to a hitachi scope, and the bridged input is fed of to a hitachi waveform monitor. you can point the camera at these and it looks quite cool.  a further bridging input is fed to the video monitor.

the five volt sync pulses from the philips are further processed by a box i built that contains a couple of comparators with variable thresholds from +12 to -12 volts. there are switches to change the comparator from inverting to non inverting so you  can process pretty much any analog sync waveform into a usable waveform for the oscillators to sync to. (negative going pulses from some random positive value to about minus 12 volts in the case of my oscs.)

the above diagram and description is a bit crude so ill be amending it as time progresses.
S/P

VCO schematic

here we go - take 1 of the video oscillator. its a pretty rough and ready schematic, but ill add to it, correct it and modify it from time to time to reflect the status of the current version im using in the synth. layout to follow.
front panel controls:

It runs from plus and minus 12 volts, and has a range of dc(ish) to over 100-200khz (as far as i can tell). it has a linearish cv response (within some ill defined and i suspect probably quite wierd limits that i havent looked into yet). it sounds quite good too at the audio end of things, and is a nice vcLFO for any type of modular. just adjust the timing cap values on the range switch to taste. big ones make it slower, smaller ones make it go faster.
all parts are chosen to have as much similarity in values as is practically possible. its lots cheaper to buy 100 quality pots of the same value than to buy 100 cheap pots in various odd values and sizes. so for the most part, the pots are all 100k linear, the resistors are mostly 100k 1% metal film, and if you want it to work well, all wiring is with RG178 shielded coax except the power supply which is thickish hookup wire. it has attenuverting inputs, and also level controls on the outputs. as in the sandin (which the sync circuit is blatantly borrowed from!) you can disconnect the CV inputs from the oscillator core to improve stability for oscillators that dont need modulating. signal levels are pretty high, and it seems to tolerate ten volt bipolar CV input .levels too. bonus. the CV trim control sets the offset to the modulation voltages, which means you can get some fairly precise control over the modulation points. its not easy to explain, and confused the crap out of me the first time i used it, but it seems to work quite well for trimming out (or adding in) distortions in the modulated waveforms..
if you want to build it, email me and ill let you have any further updates that arent on this site yet. i recommend prototyping it on a breadboard first.
here is the PCB layout i used. i havent done a component overlay yet, ill get on it. there are probably errors. YMMV.

UPDATE march 2011 - heres a wiring diagram for the offboard connections that i found in my files..

Cheers, have fun, and please point out the glaring omissions and mistakes ive undoubtedly made.
S/P

edit: i just noticed that i didnt put the value for the mark-space ratio pot in. its a 10k linear pot with two 2k2 resistors wired between each end and the wiper. ill put it in the next revision, im going down the pub now.
edit2: the resistors in series with the sine and triangle outputs from the 8038 that go into the output amps shouldnt be there. replace them with a link wire.

and now for something completely different..

i started building this from scratch a couple of weeks ago. its a semi-acoustic (chambered) SG junior body made from Indian Rosewood. ive got the body about 80% done and the necks about 30% done. yay wood. the fretboard shown above is just for the photo. the one its actually going to get is a waaaay more psychedelic piece of brazilian rosewood. the necks brazilian too.. heavy, but should sound pretty weighty too.

anyways - the next few posts will be back to video synths, i need to sort out the bandsaw before i do any more on this.

s/p

It Lives.....

well, here it is as of tonight..its on its side compared to the system layout diagram posted previously, so the modules on the  rightmost column are the oscilators. the other one is the matrix mixer. in the rack is a patchbay and two RGB-pal and YUV-pal encoders and sync pulse generators. sitting just on top of the rack is a panasonic AVE-3 effects generator, which TOTALLY RULES. i recommend buying one. ill draw up a system flow diagram at some point soon, to show how its all synced up. heres another pic of it being modulated in parallel with some drones from the audio modular.

it kind of goes without saying that i am currently as happy as a dog with two di.. er.. tails.
anyways.. ive started drawing up the schematics, and am trying to make them legible. the pcb layouts of the modules ive already built are done, but i may redesign them to use standard maplins stylee pots rather than the surplus ones i used which have a funny pinout.. ive also done some component layout diagrams. i reckon there should be a forum for this kind of thing somewhere. anyone know anything about setting up forum servers or list servers etc? my email addressl is cunningly disguised on the right...---> please get in touch.

s/p

Progress!

Ive been away/busy/lazy for the last month, but i have made progress. theres a cabinet, and the first three modules are wired up and working. more pics and screenshots to follow. oh, and schematics for the three modules too.

System Layout diagram

heres the current big picture as to what goes where in the system.as time goes on ill draw up the schematics for each module on a computer (theyre all scrawled in a notebook atm) and post them up here.

A post about the chassis design.

the chassis for all the modules is very simple: its a piece of plywood with these aluminium boxes from Maplin's screwed to them. the PCBs and controls are mounted in the removable lid, thus making it fully modular. power cabling runs along the back of the plywood which also gives extra mounting space for power supplies, sync distro, etc. i put it together of a couple of hours, so its really very easy to build too. i guess i should draw up some proper plans and post them somewhen soon.

its a very strong but lightweight system, and as all the modules are sheilded from each other with at least 2 thicknesses of well grounded aluminium between them im hoping it should also provide excellent RF shielding. my 12 module unit cost me less than £100 to put together, including a load of 40mm aluminium angle (3mm thick) that ill make rack ears out of. it doesnt fit in a standard 19 inch rack, but i can make whatever wooden case to go around the main unit as and when i feel like it and use standard rack mounting strips to hold it in place.

i have many audio analog synth pcb's that have been waiting to be cased. ill use this method with them as well.

Another Video

feedback, live camera feed (black and white security cam found in a bin) and oscillators and mixing from the synth. the sync feed to the camera has been pulled which gives it the scrolling across the screen effect.

More VidSynth Pictures

heres a shot of the video synth as it is today - its leaning against the effects rack with the old modular synth on top.

the three modules running across the top of the cabinet are the oscillators. they are based on the venerable and much loathed XR8038 chip. i like it. the flux capacitor shaped module in the centre is a 3 channel arbitrary function generator and the one to the left is a 3 by 3 mixer matrix. heres a pic of the guts of one of the VCOs

a note about the jacks - they're not BNCs but frankly i dont care. it works. the hookup wire is RG178 super skinny video coax. pots and switches are surplus from somewhere or other, and the pcb is home made. note the extra capacitors tacked on the board for more power supply goodness. yay prototypes...

Video Demo

heres a short video - live input from a black and white camera, processed and mixed with some abstract video from the synth.

Prototyping

heres a shot of the synth that made the previous screenshots ..

its a large format modular synth that has been built over the last ten years. its mostly based on EFM circuits and CEM chip applications notes. the EFM modules are remarkably adept at working at frequencies far exceeding the audio bands... well, the ones that didnt explode due to user error are anyways...
the video encoding hardware is in a seperate rack that consists of various 99p ebay bargains - broadcast grade rgb to pal, component to pal and pal to everything encoders and decoders, 2 sync pulse generators, various genlocks, mixers, switchers, VDA's and an oscilloscope. ebay rocks.
its a great time to pick stuff like this up on ebay. all the pro broadcast facilities in the UK are dumping their analogue gear as the digital switch-over approaches. a lot of it ends up on ebay, where it generally goes for bugger all & buyer collects. as most of the facilities are based in London, its not hard to cycle down to Soho with a backpack and a shiny one pound coin to pick up, for instance, an NTSC sync generator full of Sandin IP MC1445 video multiplier chips....

more screenshots

these are from december 2009/january 2010. the machine that made these was macgyvered out of my homebuilt modular synth by upping the frequencies of the oscillators, making a few 'glue modules' like sync processors and feeding the output to a broadcast grade RGB to PAL converter i bought on ebay for 99p. i learned a lot, too.. i let the Magic Smoke out of pretty much every module at least once before i worked out why video levels are 1 volt max... electronics explodes when trying to handle 10 volt swings at video frequencies unless you are actually trying to build a transmitter, in which case youll probably have a sufficiently large powersupply, good cooling, a radio license and a much better understanding of high speed analogue electronics than me..
weeee!
BANG!....damn.

1st post. analogue modular video synth stuff.

the above picture is a still from the video synthesizer ive been designing and building over the last year or so. its a fully modular system, mostly inspired by the Sandin Image Processor from the early seventies and the Supernova 12 system built for Australian band Severed Heads. its been prototyped and is currently in the construction phase. i plan on sharing the progress i make on this build (and whatever else i happen to be working on thats fun or interesting) in this blog.

hopefully other people will be inspired to make an analogue video synth too- i reckon that analogue image manipulation techniques never really got the chance they needed back in the seventies to really mature creatively by becoming accessible to a wide spectrum of visual artists (in the way analogue synthesizers did for musicians) before digital processing came in and replaced them completely. boo.

musicians in 2010 have their pick of both analogue and digital tools, and can choose the right one for the right job. video is now pretty much exclusively trapped inside a laptop. damn. i hate laptops...

to this end, ill be sharing various circuits and pcb layouts and construction tips as and when they are tested, working and im happy with them. i like the idea behind the original Sandin IP's 'Distribution Religion' and many of the modules in my system are inspired by Sandin modules, so i reckon its only fair to share the fun. Hopefully other people will get involved and share new circuits too. stay tuned.