on video bending plus voltage control

[pollo]

4chan' /diy/ is a nasty place, so it has just recently come to my mind that I should join a proper electronics community. Hello to everyone, and greetings from Chile!

I am in the (painstaking) process of building a modular synth, and I thought that it would be nice to have the whole audiovisual business giong on. I am not a great fan of the bending scene, but Karl Klomp's OMP-01 circuit has definitely caused me some fascination.

http://karlklomp.nl/pro/vbend.html

So I guessed trying to figure out the original schematic as well as adding a bit of opto-isolator voltage control, for LFOs, Env Gens and such, would be a nice idea. I also thought, since this uses 5v this could be a good reason to recycle some old cellphone wall warts. The video outs would be managed through a 3 way switch: outX, outY, and outX+Y.

It has been a pain. The only available AD8072 around here are in SOIC form, and RS Components charge a hefty sum for each. Soldering the first one was a test to my nerves, and the whole thing seems to have failed in my breadboard.  Maybe I have burnt the IC... Anyway, here is a circuit diagram i have created for my studies:

http://postimage.org/image/vnuk8v643/
(feel free to copy, alter, etc. just don't forget about the original authors)

Any kind of help would be greatly appreciated,
nico, aka pollo.

[expanoncolin]

Welcome Nico.  I found that this tutorial for soldering SOICs was incredibly helpful. http://www.sparkfun.com/tutorials/96 The technique of using desoldering braid appears to work very well.  Interested to see what circuit you come up with.

-Colin

[pollo]

hello colin, and thank you for your answer. i'll be sure to try this procedure next time

i have been revisiting the schematic and maybe the soldering wasn't the only problem. i had some shorted stuff and, well, klomp's original diagram is rather.... effin' unforgiving, to say. I am still dazzled at the function of VR1 and its associated looped capacitor; could it be some kind of passive filter or attenuator? should i add an electrolytic to ground in the fashion of C1?.

anyway, ere is an updated schematic:

http://postimage.org/image/i6gguj7vn/

greets and regards,
pollo.

edit: disregard the PSU section, i think i am going to have to use a WAY larger voltage multiplier to recycle the cellphone wallwart. also, the switch should be one of those elusive on-on-on types, like the 7211, so maybe a three pole should work better and be easier to find, or perhaps some sort of mixer. options vary

[expanoncolin]

I believe VR1 and VR2 are acting as parallel resistances on the photocells to control how much they affect the video signal.  I'm not sure of the use of those caps but it seems like they are there for filtering as you say.

[pollo]

that's it. This should do the trick.

or some trick, at least, besides magic blue smoke. seems klomp's intention was to play around variations on positive/negative feedback... i guess. i'm still in my electronics-design-childhood. i only hope the Vcc multiplier works OK; i've never worked with one of those before. and sorry about the mess, expressSCH was behaving in a quite picky fashion today.

http://postimage.org/image/h9psuoktt/

i`ll inform you of my progress as soon as those ic's arrive (and i had breadborded the stuff, and i pass my finals, of couse)

[jjplano]

hola pollo

soy Javier (jjplano), de Argentina

yo también llegué a los diseños de Klomp, buscando formas de procesar video analógico en vivo

te hago una consulta, el circuito que estás tratando de copiar, es este?

http://www.karlklomp.nl/pro/omp/omp-circuit1.jpg

supongo que no, ya que es mucho mas complejo lo que veo en tus esquemas que lo que aparece ahi, aunque se muy poco de electrónica honestamente

estas usando los AD8072? yo hice como dice Klomp en su página, los solicité como muestra a Analog Devices, y me llegaron 3 totalmente gratis en menos de una semana

ojalá logres hacer funcionar el circuito, yo iba a empezar esta semana a probar un poco

tambien le tengo ganas al Rupter, aunque ese parece mas complejo

[pollo]

(javier, espero no te moleste que responda en inglés, para no llevarle la contra a la lingua franca del foro)

hola javier!

yes, as i have quoted, that is the very circuit i am trying to copy, with the single addition of an optoisolator-based control voltage. if you want to discard the cv part, ignore R4 and R12 and everything above them. it is my thought that the sole complexity of understanding klomp's designs is his... kludgyness. I have not attempted to do the rupter for this very reason (and the expensiveness/smallness of those damned SMD ICs from my local dealer!!!) fair enough though, you should see my mad soldering skills, and by mad i mean schizoid mad.

i've ditched the whole power stage, though, giving up on the idea of recycling that 'effin motorola wallwart i had lying around. guess i'll just get a proper dc wallwart and regulate it afterwards. actually... i've put the whole thing on hold since as of now i've been trying to concentrate on my modular (audio) synth (my "phase 1" involves about seven modules, and "phase 2" is a baby10 sequencer, fonik's version), afterwards i'll start to work more seriously on my whole audiovisual "show", which is basically the CV OMP-1 and some video clips connected to some other stuff. 

also, i hate you, you pesky argentinian. AD does not give freebies to chile, for some reason; i guess too many engineering undergrads abused the system. still, LM393's, having such a high frequency response and being dual as well might prove to do interesting tricks.

[jjplano]

sorry, I didn't see this till today, this forum doesn't notify about your reply (odd)

I'm trying to analyze your schematics again, but there are many things I don't really understand

why do you replace the pots (VR) with 2k ones? I think I have never seen 2k pots

in his awful schematics, Klomp does not "know" the value of that capacitor on the right, but you put 1uf. why?

he tends to use all bipolar capacitors on his projects, but you put an unipolar on C1. it's a value thing? or are you just guessing?

sorry for all the questions, but I want to be somehow sure about this things, as my knowledge is really limited, and I want to make this really bad

thanks!!

[jjplano]

more!

on Klomp's schematic the pin 5 of the 8072 has an incoming of the first 1k pot and that's it

but on yours there is also a connection to the second 1k pot (on yours 2k)

in that second pot he drew an R with no value, but on yours that is gone

what is the funtion of the 3 position switch? I mean, besides of an ON-OFF, what happens in the second ON state?

sorry again for all the questions!

thanks

[jjplano]

pollo!

please don't leave me hangin!