Moving VCOs from Oakley to synthesizers.com CV standard

[eljay]

Hi Tony, I'm in the process of moving my Oakley VCOs and ASVs over to the more widely used standard used by synthesizers.com, Eurorack and others, namely 2V equates to middle C. This then makes it compatible with my Yarns clones and my Eororack modules.

From reading through previous threads I have established that I can modify my Version 4 midiDacs to the same standard with the addition of a 180k resistor link between the init trimmer pin 1 and U1 pin 6 and re-calibration. I assume I'll join the pins on the underside of the board.

The resistor changes for my SVCOs V2 is all documented (Change R12 from 120K to 180K) as is the change for the ASVs (Change R40, R47 from 150k to 220K) and the VCO Issue 7 (Change R9 from 180k to 220k). I've already moded and re-calibrated my two ASVs and they are now set-up to work with my Yarns clone.

I also have two VCO Issue 6 modules. Am I correct in thinking that for these R28 should be changed from 180k to 220k?

Are any changes required for the VCO controller modules?

[Synthbuilder]

I also have two VCO Issue 6 modules. Am I correct in thinking that for these R28 should be changed from 180k to 220k?

Yes.

Are any changes required for the VCO controller modules?

No.

[Synthbuilder]

From reading through previous threads I have established that I can modify my Version 4 midiDacs to the same standard with the addition of a 180k resistor link between the init trimmer pin 1 and U1 pin 6 and re-calibration.

Just noticed this. It's an 18K resistor you need, not 180K.

[eljay]

Well spotted Tony, my typo, thanks for correcting this.

[eljay]

Just for completeness for anyone reading this thread with a view to doing something similar, I forgot to mention in the list of resistor changes that the SVCO-B Octave board requires R18 to be changed from 270k to 100K, This change is to allow the LFO mode to be calibrated correctly.

[eljay]

The modification process is completed and was very straightforward except for a minor distraction caused by some faulty resistors causing envelope problems in one of my ASVs, covered in a separate thread, nothing to do with modifying the volt/octave range.

I have modified two V4 midiDacs, two V6 VcOs, two V7 VCOs, two S-VCOBs, one SVCO-A, two ASVS. All recalibrated and tested, only minor adjustments were required. This will ensure better compatibility with my MFOS sequencer and quantizer, my Yarns modules and my keystep pro and eurorack modules. Can't think why I waited so long to make the changes as they were a lot easier than I had anticipated.

[umma gumma]

Good tips, thanks for posting!

[euphonic]

Thanks for sharing this, Eljay. I didn't know that Oakley VCOs differed in this respect. Does the modification affect the frequency range of the VCO? Or does it shift the range? And if it does, do you know (or can you measure) how much?

[Synthbuilder]

I didn't know that Oakley VCOs differed in this respect.

They don't now, but they did. The original Oakley VCO existed before Eurorack was a common thing so there were no standard to which 1V/octave was measured. So I used my own standard of only positive voltage key CV. This fitted in well with vintage analogue synths and many of the midi-CV convertors around at that time.

For the last few years I have been recommending the VCOs in all my projects, and the midiDAC, to be built to the newer standard and the Builder's Guides reflect this by giving two options.

Euphonic, your pre-built system corresponds to the newer standard.

Does the modification affect the frequency range of the VCO? Or does it shift the range?

It's simply an offset in pitch. So essentially it has the same affect as a change in octave setting. It doesn't affect the scaling nor the actual range of oscillation.

Tony

[euphonic]

Thanks, Tony, for the explanation. I understand that using only positive voltage key CV makes a huge difference!

And it is really reassuring that I do not have to implement this mod.

[Pav]

Hi Tony bumping this .. I believe the buildguide for svcov2 a and b say change R12 from 120 to 180k, which means the statement in eljays first post:

>>The resistor changes for my SVCOs V2 is all documented
True
(Change R12 from 180k to 220K)
False.

Was a typo on his part he and I think.

[Synthbuilder]

Was a typo on his part he and I think.

I've taken the liberty to edit his original post and corrected it.