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DAC to CV

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Author	Topic: DAC to CV
Olle Romo Member	posted 25 November 2006 14:24 Maybe not the right forum, but does anyone know how to turn the audio out from the DAC to CV suitable for controlling a modular? Anyone heard of a device that'll do it? Best, Olle IP: Logged
SSC Administrator	posted 25 November 2006 15:26 The Capy outputs filter out DC, so you have to output an audio signal that is modulated by the control signal that you want. Take the signal that you want to use as the CV and use a Kyma VCA to multiply it by a PulseTrain with a period of 2 samples. (In a way this is like a sampled version of the CV: a square wave whose amplitude is the value of the CV). Take the resulting line-level output and feed it into an envelope follower on your analog synth. The envelope follower should function as a low pass filter on the "digital" control voltage. Or you could feed the audio into a LPF on your analog synth and set the cutoff to the highest frequency change in your control voltage (e.g. 10 hz). IP: Logged
Olle Romo Member	posted 25 November 2006 18:22 Very cool!! Thanx About the DC filter - is it digital or analog? What is the cutoff? ATB, Olle IP: Logged
armand Member	posted 25 November 2006 19:39 A bit of an side-track. Would it be possible to integrate the upcoming 'Continuum Voltage Converter (CVC)' from Lippold Haken with the Capybara 320? http://www.hakenaudio.com/Continuum/html/accessories/CVC.html If so? here's another wish; an equivalent of this device with control voltage inputs... IP: Logged
SSC Administrator	posted 26 November 2006 09:54 Olle, the output converter has an analog HPF (the converter chip itself might also have an HPF, I have to double check that). The input converters have no analog HPF; the converter chip itself filters out DC. The cutoffs are < 10 hz (have to check for the exact cutoff). Armand, to get input CVs, you could use the reverse of the process described above: on your analog synth, use the CV to amplitude modulate a very high frequency square wave. Send the squarewave to Kyma, where you could use an AmplitudeFollower to re-extract a control signal. IP: Logged
pete Member	posted 26 November 2006 11:53 I think it may be better to have the pulse train with a period of 10 samples as the analogue output filters are supposed to filter out half sample rate upwards. If the pulse train fed a scale and offset to make the square wave go to full plus and minus one before it feeds the VCA, then you could make use of the balanced output and feed the hot and cold into the anodes of two separate diodes which are joined together at the cathode. This may have two problems in that the output is isolating transformer emulating which means that if you load only one leg, that leg will go to 0 volts and the other will get the full joint voltage. If the output was resistor loaded before the diodes , this should keep the output centered around zero. The second problem is that the diodes voltage drop will make an offset in the output signal. This could be compensated for with an opposing offset built into the Kyma sound. For greater accuracy you could build a precision rectifier with two op-amps two diodes and four resistors. This would need a small supply but it could help if the CV range needed to be greater than the output gives. Also adding a series resistor and parallel capacitor to the final output of either circuit should get rid of the gaps in the signal. Hope it helps. Pete IP: Logged
Olle Romo Member	posted 26 November 2006 14:25 Thanx Pete. This is so far above this drummers head I barely know its there but I sense it's something good. So if I took your post to a decent tech, would he be able to make something of it? Or do you know of any available schematics on the net, or something...? A box that both filters and does the stuff you describe would be very handy. Best, Olle IP: Logged
pete Member	posted 26 November 2006 16:52 The schematic is in my head but it's not that complicated. I could make it, and then I could try it out. The problem with designing things and describing them with out making a prototype is that there is always a possibility of some point that I've forgotten to mention. I would need info on the requirements of your CV i.e.range, plug type and connections. You could try a local tech. I don't think I've worked out something that is all that difficult to understand. Pete IP: Logged
Olle Romo Member	posted 27 November 2006 01:19 Pete, It's for a Modcan. Banana jacks. 0-5V. Impedance 50-100K. It would be good if it had a LPF with a bypass switch too. Any thoughts you may have about this will be greatly appreciated . Sorry if this is getting too OT. ATB, Olle olleromo@pacbell.net IP: Logged

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