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VCO octave question
MUFF WIGGLER Forum Index -> Oakley Sound Systems  
Author VCO octave question
terjewinther
I have several Oakley VCOs (the "standard" fullblown type, in both versions 2, 3 and 4 if memory serves me right) and I have just build two of the new Slim-VCO versions. They all sounds and works great, no question about that!

But I am a bit puzzled about the octave placement of the new Slim-VCOs. From the Users Manual:

"As far as I am aware there is no standard amongst modular systems that defines what pitch corresponds to what CV input. However, I choose to make my VCOs produce middle C (C4) at their typical settings when the 1V/octave input is at 5.00V. Thus, I would expect the SVCO-B to be producing 261.6Hz when its KeyCV input is 5V, the frequency pot set to 12 o'clock and the octave in the 8” position."

While this seems to be right, why not choose to octave the Slim-VCOs similar to the "standard" VCO?

As it is now, if I calibrate the Slim-VCOs exactly as they are supposed to be, they are several octaves apart from my other Oakley VCOs when given the same keyboard CV. I was a bit puzzled about this, so I re-did a complete calibration of one of my older Oakley VCO, and came up with the same situation. I even compared the Oakley VCOs (both types) against VCOs from MOTM and synthesizers.com, and this is my conclusion:

At 1.00 volts, 2.00 volts, 3.00 volts and so on, all my (older) Oakley VCOs play in the exact same octaves as MOTM VCOs and VCOs from synthesizers.com, but my newer Oakley Slim-VCOs need to be set several octaves higher to sound in the same octave.

When I set all other VCOs (including Oakley VCOs) to 32´I need to set my new Oakley Slim-VCOs to 4´to sound in the same octave. Why?

I know I can offset the new Slim-VCOs using the "TUN" trimmer, but it does not have sufficient offset - in fact it is already at full. Any change in the trimmer only puts the VCO further down.

As it is now, the Slim-VCO needs several octave higher CV to sound in the same octave. I believe this is because 5 volt was choosen for the new Slim-VCO as "middle C", while most of my keyboards have middle C as 2 volts (starting with 0.00 volts on the lowest key).
Synthbuilder
When built in the standard way the SVCO-A and B should follow the standard Oakley 2U VCO. However, this does depend on how the 2U VCO is calibrated but I calibrate mine with the Coarse pot at it's minimum setting so that when it's just off its minimum setting the VCO will track the SVCO-B at 8'.

Very shortly after the SVCO-B was released we realised that to make it match the MU format this would have to be different. There is a resistor, R12, on the SVCO main board that allows the absolute pitch to be changed. If you want the SVCO to match a Dotcom VCO R12 must be 180K. There's also a change made to octave board for the SVCO-B, R18 must be 100K. This information was not present in the first editions of the Builder's Guide but was added in November last year.

Tony
terjewinther
Great! That explains everything.
I will do the changes and see what happens.
terjewinther
I changed the resistors and did a complete re-calibration. Now both my new Slim-VCOs are swinging perfectly with my other VCOs. And they sound great too! SlayerBadger!

I have also downloaded the new versions of the users and builders guide for reference.

Thanks a lot.



Synthbuilder wrote:
When built in the standard way the SVCO-A and B should follow the standard Oakley 2U VCO. However, this does depend on how the 2U VCO is calibrated but I calibrate mine with the Coarse pot at it's minimum setting so that when it's just off its minimum setting the VCO will track the SVCO-B at 8'.

Very shortly after the SVCO-B was released we realised that to make it match the MU format this would have to be different. There is a resistor, R12, on the SVCO main board that allows the absolute pitch to be changed. If you want the SVCO to match a Dotcom VCO R12 must be 180K. There's also a change made to octave board for the SVCO-B, R18 must be 100K. This information was not present in the first editions of the Builder's Guide but was added in November last year.

Tony
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