I found some more files – this appears to be the PCB image i made mine from. the quote on the PCB is a Coil lyric. most of my PCBs have a Coil reference on them.. I generally design freehand PCB images in MS Paint whilst i think up the schematic in my head, then build them, then draw a schematic. ill have to reverse engineer my own synth in order to draw up a parts placement pic which might take a while, sorry…
a jolly useful circuit in my experience, and one im pretty pleased i came up with. another nice feature is you can set the threshold so that its output sync pulses can lag behind the input slightly, which seems to give some control over colour. which is nice.
|low res schematic. download the proper PDF below:|
anyways, back to the plot.. this is an excellent audio modular synth circuit, its the VCA5B design from toms 1900 series modules. it works very well and in exactly the same way as with audio at video frequencies too. i have no technical specs to back this up, but it works for me….. its also where i borrowed the design for the attenuverting inputs in my synth- its the same circuit but every 47k resistor or pot has been exchanged with 100k because i happened to get a good surplus deal on hundreds of 100k pots. guess what part most of my designs will be featuring for the forseeable future…
the PDF is here
the various corrections from the old EFM forum are here
and both of the above are linked to from this excellent site, which i have mentioned before. go there and read. then go build stuff.
heres the schem in roughly edited form:
|The original copyright holder of this image is Tom Gamble. i edited it a bit and changed some stuff, but its still essentially his work.|
once again, all rights and respect to Tom Gamble (and Bob Moog!!) for this design, all i did was change a couple of values and get rid of the squarewave output. i tried it and it worked. hooray!
download the full gen on the audio version here
heres some schematics for the comparators. type 1 is used for sync processing. feed any h or v sync signal in, patch the outputs to the sync input jacks on some vcos, and twiddle the knobs and flick the switch till you get sync lock. easy. no pcb layout for these as i built them on stripboard.
both of the above circuits are run from plus and minus 12 volts. the 3k9 pull up resistor means the output swings rail to rail, so it can trigger either of the 2 vco designs (one syncs on a -12 volt spike, the other on a +12) with ease.
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.