Oakley Four Voice ASV

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oozitron
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Oakley Four Voice ASV

Post by oozitron » Sat Dec 29, 2018 1:05 pm

I have wanted an Obie 4VS for well over 35 years, and have come to the conclusion that the ASV is the way to get me there. I am sacrificing my TR-808 to fund this project, so I want to be sure that what I'm hoping to do will be possible. I have decent DIY experience building CGS, Oakley, JHaible & MFOS modules, as well as a MIDIBox Sequencer. So here's my initial plans and a few questions...

This will be a ~1m wide case designed to sit just above a MIDI controller keyboard. It will have four ASV units in a row. On the far left will be a Yarns (MIDI>CV/Gate), two FourMix modules and a "master VCF" attenuator.

The Yarns' 8 outputs will be wired (normalled) to the CV/GATE jacks on the ASVs. Plugging CV/GATE into an individual ASV (with a step sequencer for example) would disconnect it from the Yarns.

The two FourMix modules will each be wired (normalled) to the 4 ASV MAIN outputs. Having two mixers will allow a stereo mix, as well as a way to send varying amounts of each ASV to a "dry" channel and to a "wet" channel with effects. Plugging directly into an ASV's MAIN output jack would disconnect it from the FourMix modules for separate processing.

The "master VCF" would be a single attenuator & knob that would send 0~5v to all four VCF mod inputs. So for polyphonic playing, you could sweep the filter of all four ASVs at once with a single knob. I get giddy just thinking about this :goo: (of course you'd need to set each ASV's VCF controls to similar settings to make this work properly). I would need a constant voltage source to feed the attenuator; maybe from one of the FourMix modules?

EDIT: just realized that the VCF FM2 jack is not the place to wire in my "master" VCF attenuator. Hopefully I can kludge in a handwired connection on the Main PCB so as to not honk up the existing VCF FM2 setup.

I'm not really designing this to use with the modular, so to save some $ I'm not going to include all the patch points. I would forego the "Socket Board" and only have the KEY-CV IN, the GATE IN, the VCF IN and the MAIN OUT jacks. All would have normalled connections (as mentioned above), and would only occasionally see a plug.

I would assume that several of the ribbon cable connections would have to have links soldered in to make things work without the Socket Board. I should be able to figure out all that if there is a list of what each connection point is on the Main Board's ribbon pins. Is that available?

I would like to add a switch (next to the GATE IN jack) that turns on the "drone" for each ASV. I'm guessing that having the GATE IN jack normalled to the Yarns would make the "built in" drone function not work. Hopefully a couple pieces of wire and a switch would work (?)

Would love to hear thoughts on my ideas, especially if there's something idiotic :roll:

thanks,
Andrew
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Re: Oakley Four Voice ASV

Post by Synthbuilder » Sun Dec 30, 2018 5:48 am

oozitron wrote:... so I want to be sure that what I'm hoping to do will be possible.
Yes it's all possible and I don't think any of it will prove troublesome. I wouldn't sell your 808 though. I wish I still had mine.
I would need a constant voltage source to feed the attenuator; maybe from one of the FourMix modules?
There's a very good +5V and -5V reference on the Fourmix which would be suitable. Your master frequency control could then sweep from -5V to +5V.
Hopefully I can kludge in a handwired connection on the Main PCB so as to not honk up the existing VCF FM2 setup.
You'll need to to add a resistor to the pot/switch board as the VCF CV summing circuitry is on there. It's easily done though.
I would assume that several of the ribbon cable connections would have to have links soldered in to make things work without the Socket Board. I should be able to figure out all that if there is a list of what each connection point is on the Main Board's ribbon pins. Is that available?
I haven't done a list of the I/O connections but it's pretty straightforward once you see the schematic of the socket board. All you'll need to do is solder some little wire links in place of the 16-way headers on the main board to mimic the normalised connections on the input jack sockets.
I would like to add a switch (next to the GATE IN jack) that turns on the "drone" for each ASV. I'm guessing that having the GATE IN jack normalled to the Yarns would make the "built in" drone function not work. Hopefully a couple pieces of wire and a switch would work (?)
The drone mode won't work as soon as you add external CV/gate - which, by the way, is accessible via the Oakley Bus header on the main board. So you will need to add a switch to select between the gate output of Yarns and +15V (or the +5V reference).

Yarns produces a lower CV output than the Oakley midiDAC for any given midi note. Thus the ASV will need to be built using the MU tuning options. It's just a couple of resistor changes and the details are given in the Builder's Guide.

Tony

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Post by oozitron » Sun Dec 30, 2018 10:07 am

Thanks for the help Tony!

While I do love the 808, I've been building more and more percussion modules (HexInverter and Trevor's 9090) which are awesome with the MIDIBox sequencer firing them. And my true love is obese analogue synths with lots of knobs; percussion is secondary. Maybe I'll get a 606 someday to fill the gap :-)

Working with a local friend on the 808, so hopefully I can get this going soon.

happy new year!
Andrew
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Post by oozitron » Sun Dec 30, 2018 2:50 pm

Not sure what you mean by the Yarns' lower CV output... is it basically transposed down by an octave or something like that?

There would certainly be times when I would have something other than the Yarns "playing" some of the voices... (the Fat Controller, the CV outputs of the MIDIBox sequencer, etc).

Maybe I could just transpose the output of my MIDI keyboard controller to make up for the Yarns' offset?

Andrew
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Post by Synthbuilder » Mon Dec 31, 2018 5:27 am

oozitron wrote:Not sure what you mean by the Yarns' lower CV output... is it basically transposed down by an octave or something like that?
Yes. I think it runs 2V, or maybe 3V, below what I would set my midiDAC to. Nothing wrong with Yarns, it's just different to the midiDAC. There is no standard in the 1V/octave system that says what CV produces what pitch so octaves can be different between convertors, keyboards and VCOs.

But for compatibility with Yarns and other MU modules then build your ASV as the MU/dotcom option in the Builder's Guide. It is just the value of two resistors though so it's easy to change if you want to change it.

Tony

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Post by oozitron » Sun Feb 24, 2019 11:29 am

I'm about 85% done with my first two ASV voices and a Yarns is on the way :sb:

As previously mentioned, I am only using a few of the jacks (CV, Gate and Main Out for now) so I am not using the Socket PCB. I have sorted out where to make connections on the Main Board on the 3 connector fields so that the normalized functions work.

So where should I ground these jacks I'm using? Are the unused 18 points in the 3 connector fields good for this?

thanks!
Drew
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Post by Synthbuilder » Mon Feb 25, 2019 4:06 am

oozitron wrote:So where should I ground these jacks I'm using? Are the unused 18 points in the 3 connector fields good for this?
You could connect them to any of the unused 'ground' connections on the headers.

You could use individual screened cables from the ASV main board to each socket to carry both the signal and ground connection. This would be preferable if the connection is over 300mm or so.

The 'ground' connection on those headers is a dedicated connection back to 0V on the power supply header. It doesn't connect to anything else on the board.

Tony

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Post by oozitron » Mon Mar 11, 2019 5:52 am

Assembly instructions for pot board & front panel:

1) carefully line up pot & switch shafts with holes in panel

2) push pot board firmly up against panel

3) add 28 washers & nuts to pots & tighten

4) solder the LED legs

5) realize that you didn't put the 5 chips into the sockets on the pot board

:doh:

Drew
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Post by oozitron » Tue Mar 12, 2019 9:35 pm

Wednesday is power-up day!

After years of DIY, I've gotten into the habit of applying power to a new project with NO CHIPS in the sockets. I use the meter on the various V+ and V- sockets to make sure the chips will be getting the proper voltages (without burning them up!).

This is ok to do on the ASV isn't it? I want to be especially careful to not fry those pricey 3310 and THAT chips...

Drew
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Post by Synthbuilder » Wed Mar 13, 2019 4:25 am

oozitron wrote:This is ok to do on the ASV isn't it?
Yes. It's what I do too.

Remember to check the two sets of +/-12V that feed the VCO boards and the -5V that supplies the AS3310s.

The ASV will also work without the VCO board in place - although obviously they'll be no VCOs. But everything else can be tested.

Tony

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