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WIGGLING 'LITE' IN GUEST MODE

New module alert: Classic VCA for 5U
MUFF WIGGLER Forum Index -> Oakley Sound Systems  
Author New module alert: Classic VCA for 5U
Synthbuilder


This is basically a revised version of the Euro/frac Classic VCA module for the 5U formats. This module is my take on the 4019 VCA sub-module in the ARP 2600.

We have one less pot but one extra socket on this version. The functionality is mostly the same though. The loss of the 'gain' pot is almost compensated for by normalising the CV1 pot to an internal reference voltage. When no jack is inserted in the CV1 input, the CV1 depth pot acts like the gain slider on the original 2600. The CV2 can then be used as the CV input which can be switched to either lin or exp modes.

The extra output socket, OUT B, gives you the difference signal between the sum of the two inputs and the final output of the VCA. This is a sort of anti-output; when the VCA output signal goes up in level this output goes lower. You can use it as a ring modulator (gain set to max) or in conjunction with OUT A as a voltage controlled pan.

More information will be on the project page when the boards are ready to ship - which should be next Tuesday.

http://www.oakleysound.com/5uvca.htm

Tony
catatemycaps
Excellent! So many sweet modules to choose from and more keep coming.
Thank you Tony for making these.
drip.feed
Hi Tony

I want to start DIY, I want to start augmenting my MU with MOTM and I need more VCAs! So this could be just the ticket. Any idea of prices..?
Synthbuilder
First off, let me apologise for the delay in getting these ready for sale. When I wrote the original post I forgot I was going to be on holiday the following week. eek!

But I'm back now and the new 5U VCA's webpage will be updated today. I'm not quite sure I'll get the Builder's Guide done today but I'm going to try.

drip.feed wrote:
Any idea of prices..?


For the bits I sell:

Classic VCA (5U version) issue 1 PCB .......... 20GBP
Sock6 issue 1 PCB ....................................... 6GBP
16mm pot bracket set of three .................... 0.75GBP

Tony
drip.feed
Thanks Tony.
kecked
Does this VCA react to 0-5v or 0-10v? Output +/-5v?
Synthbuilder
kecked wrote:
Does this VCA react to 0-5v or 0-10v? Output +/-5v?


5V will give a gain of 0dB, ie. unity, for both lin and exp CVs. But one could easily make this 10V by changing a couple of resistors.

Tony
The Big Ear
Hey Tony,

Would it be possible to use a switch to select between in1 and in2?
Or is it a super cool feature to have both inputs at the same time?

PS a block diagram of this module would be nice as I'm still working out how the ring mod would work ;-)

Thanks,
ToAd
Synthbuilder
The Big Ear wrote:
Would it be possible to use a switch to select between in1 and in2?

You mean switch one off and engage the other? Yes with a DPDT in series with the input sockets.

Or do you mean send one input to either the CV1 or CV2 on the board. If so, yes to this too. Use a SPDT from the input socket to the CV1 and CV2 inputs on the board.

But in doing either of these I think you'll lose some of the additional features the module has to offer.

The Big Ear wrote:
Or is it a super cool feature to have both inputs at the same time?

Yes. It's the only way you're going to get things like the pan and ring mod function to work. And in the standard way of using VCAs to control modulation you need both depth (CV2) and offset (gain) controls. The gain control would essentially set the quiescent level of modulation while the externally applied CV would make the level go up and down about that point.

I haven't done a block diagram yet. And, unfortunately, I'm not likely to in the near future since I'm up to my ears playing catch up after the Summer break with a load of repair work. But if you have a look at the User Manual there's a bit of extra information in there about how the thing works.

Tony
Stereotactixxx
I would love to hear a comparative ring mod demo of the different Oakley options:
the actual Ring Mod, the Classic VCA and the way I'm doing it now, a VCA+multimix.
How do you find the sound of the Classic VCA compared to the Ring Mod?
Synthbuilder
Stereotactixxx wrote:
How do you find the sound of the Classic VCA compared to the Ring Mod?


I've not tried them side by side. But the Ring Mod module will be 'better' at standard ring modulation since the carrier bleedthrough is lower.

However, both circuits use a similar core design. The VCA has one core and the ring mod has two. I would expect the basic sound of each to be similar when used as VCAs. But the Classic VCA generates ring mod by signal cancellation rather than true four quadrant multiplication like the ring mod module.

Tony
Drumdrumdrumdrum
Does the ringmod work in the same way as the CS-80 VCA/RM? (And the MOTM190)?
Synthbuilder
Drumdrumdrumdrum wrote:
Does the ringmod work in the same way as the CS-80 VCA/RM? (And the MOTM190)?


I know nothing about the MOTM190, but I think the CS80 uses a true four quadrant multiplier. This would mean it behaves in a similar way to my Ring Mod module rather than this the Discrete VCA.

Tony
Drumdrumdrumdrum
Thanks. I get it now. I think you had to repeat yourself. oops
Isaiah
Would this PCB operate properly on +/-12V?
The Euro version obviously does, but I wondered if there were any changes that would have to be made to use the 5U PCB on +/-12V.

The specifications seem well suited to partner with CGS/Serge PCBs in a 4U case, which is why I ask about PSU voltages.
Synthbuilder
Isaiah wrote:
Would this PCB operate properly on +/-12V?

I've not tried it but it should do with the following small changes:

R30 & R29 are now 220R instead of 1K.

Tony
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