Thursday, 10 March 2011

the good Video VCO

heres the other VCO circuit ive been using recently. its an EFM design once again, but this time there are some changes from the original; ive got rid of the square wave and changed a cap and a resistor.
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

be seeing you


Wednesday, 9 March 2011

Video VCA and mixer by Tom Gamble of EFM

Heres a damn fine module, that i had no part in designing. its an EFM module, designed by Tom Gamble back in 1999. i was lucky enough to buy a load of his PCBs back then and have enjoyed building them, making music with them and endlessly tweaking them ever since.

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.
be seeing you

Tuesday, 8 March 2011

VCO updated

ive added  a wiring diagram to the VCO post from several months ago... wow, i actually updated something...
be seeing you

Sync Processor

you should probably build at least 2 of these. they accept positive or negative going sync pulses in any polarity or voltage between -12 and 12 volts and can extract a clean positive or negative trigger for the VCO's. this means you can use pretty much any Sync Pulse generator or VCO circuit with this device. and as its basically just a comparator you can use it for other purposes within a patch too.

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.

be seeing you

3 by 3 Mixer Matrix

theres 3 of these in one module. the attenuverting input channels (theres three on each mixer board, and 3 boards, so 9 inputs in total) are wired so that all 3 inputs on mixer 2 and mixer 3 are normalled to mixer 1s inputs. so you can set up some pretty crazy RGB mixes and feedback loops with only a small number of inputs. each mixer also has a DC bias and an output gain control, (voltage gain of 1 to 10 times) and also a paralleled output for feedback loops. this isnt buffered, and probably should be...

UPDATE 20110310:
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...

be seeing you-

Joystick/Voltage Reference/Distribution Amplifier

er... does what it says in the post title..

be seeing you..

Input Processor

heres the Initial schem for an external camera input processor. as yet, i havent built it. it worked when i modelled it in Spice, so it should be a starter for ten...

ill edit this post as time goes on with updates etc..
be seeing you

oscilloscope experiment

I tried using the vidsynth to provide line and field timing ramps to one of my scopes with a Z axis input, using the mixer matrix as an interface (allowing vert/horizontal scaling, l/r and up down positioning, inversion of all parameters and modulation of same) and a wavetek oscilloscope as the output device. pics taken of the scope screen with my phone cam.... it actually worked! heres some pics..

damn, but i look good in green...

i have also obtained a scanner, and am busy digitising and correcting all my notes and schematics.
be seeing you-