Elektor Oscillographics

macumbista · Posted: Mon Sep 19, 2011 1:25 pm Post subject:

OK, digging in a little deeper... since my modular already has several oscillators, two analog multipliers and two DC mixers, the only thing missing from this block diagram are the phase shifters.

Can anyone EE-skilled enough look at the phase shifter schematics and tell me what components would have to be changed in PS 2,3 if I replaced the dual-gang 300K pot (hard to find) with either a 200K or 500K?

According to Waite:

Integrated circuits IC3 and IC4 are simple voltage followers that unload two RC networks while providing a low output impedance.

So how could I recalculate the RC network with a different variable resistor?

Source of both images is Mitchel Waite's Projects In Sight, Sound And Sensation, as linked to earlier in this thread.

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blue hell · Posted: Mon Sep 19, 2011 2:56 pm Post subject:

The RC product is interesting, so when you go from 300 to 200 K you'd want to scale up the caps with a factor 1.5; also the fixed resistors could be rescaled, with a factor of 2/3 then.

Likewise, when going to 500k rescale the fixed resistors too with 5/3 and the caps with 3/5.

macumbista · Posted: Mon Sep 19, 2011 3:08 pm Post subject:

muchos gracias!

200K 1.3K 0.0015uF/1.5nF
300K 2.0K 0.001uF/1.0nF
500K 3.3K 0.0006uF/0.6nF/600pF (or 560pF, which is what is more common)

now I'm thinking about vactrols Twisted Evil

bugbrand · Posted: Tue Sep 20, 2011 4:31 am Post subject:

Oh, I actually did a basic layout for those sections - though I haven't really tried it out too much.. I also had to use a different value pot, so just played with a variety of different caps (trial and error!). Also, I used AD633s for the ring-mod sections - very good chips and simple to implement (though they're a little bit pricey). I really should get the little circuit mounted into a panel and set a system up with the layout suggested, but with regular VCOs instead of the 8038 ones.

macumbista · Posted: Tue Sep 20, 2011 3:14 pm Post subject:

I've used AD633s before, they're quite simple. One thing Waite writes about that I don't get how to do with them is X/Y balancing:

If the circuit is operating properly, P1 should make the waveform vary from amplitude modulation to suppressed carrier modulation. Potentiometer P2 will vary the symmetry of the modulated signal.

This isn't the DC offset function you could use at pins 2 and 4 of the AD 633 is it? See Roman Sowa's ringmod schematic (although he uses the DC offset at pins 1 and 3 instead)....

EDIT: quick look at the MC1495 datasheet tells me yes, Waite's "balance control" is a simple offset control. Thanks internets...

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creekree · Posted: Wed Mar 14, 2012 3:38 pm Post subject:

ok I am pushing this topic back to the top to ask if anyone has the attached files saved to their harddisk?
They seem to be lost, and I´d like to try this Oscillographics thing, I have a small portable TV that would fit perfectly into my modular!

Thanks for helping!

Christian

PHOBoS · Posted: Thu Mar 15, 2012 12:52 am Post subject:

I think the files you're looking for are on page 2.
(portable TV you say ? Wink

)

creekree · Posted: Fri Mar 16, 2012 9:37 am Post subject:

ha, I dont know how I managed to not find the files....
your project is what ignited my interest in the first place!
how exactly did you manage to use the TV as a display?
from the little that I have read by now I gather that the Oscillographics circuit was designed to drive a 2 channel oscilloscope.
this is not what I want- I´d like to have a dedicated portable TV built into a module, for the sole purpose of looking good in my modular (yes, I am that shallow)

Christian (who has to admit that he did not spend very much time reading about the subject at hand)

PHOBoS · Posted: Fri Mar 16, 2012 12:42 pm Post subject:

creekree · Posted: Tue Mar 20, 2012 10:47 am Post subject:

phobos,

Thanks for the advice.
When I get back home I will give it a shot. Being short of a set of computer speakers that I can gut, I think I will just build a set of LM386 amps to drive the deflection coils.

PHOBoS · Posted: Tue Mar 20, 2012 1:05 pm Post subject: