ARP Odyssey MKII/III VCO - Eurorack Format

isak · Posted: Fri May 03, 2013 9:47 am Post subject:

Guys I think that Andy or frequencycenteral speak of this matter in the big ody thread.
Damn...can't find it Mad

steffensen · Joined: Jul 11, 2012 Posts: 103 Location: Sweden

noiselector · Joined: Mar 30, 2013 Posts: 21 Location: France

The common ground in the case or panel wouldn't be a problem if you get separate ground traces for each oscillator avoiding the ground loop between them,(only common point in the power conector).

steffensen · Joined: Jul 11, 2012 Posts: 103 Location: Sweden

noiselector · Joined: Mar 30, 2013 Posts: 21 Location: France

You don´t need to insulate the board from panel.
You need create a GND trace from power connector through oscillator 1 to chasis and other from power conector through oscillator 2 to chasis.
Original Arp VCOs are built in different boards so this issue doesn't occurs.

steffensen · Joined: Jul 11, 2012 Posts: 103 Location: Sweden

noiselector · Joined: Mar 30, 2013 Posts: 21 Location: France

I see...

Sync in jack socket seems to be the problem.
did you try to dismount them from panel?
(offtopic: what software was used for creating the VCO layouts? I like the components view more than eagle.)

steffensen · Joined: Jul 11, 2012 Posts: 103 Location: Sweden

noiselector · Joined: Mar 30, 2013 Posts: 21 Location: France

yeah, check the GNDs in that points (i think you are using a switch for on/off sync as in the dual version but using separate boards for each vco, correct?)

steffensen · Joined: Jul 11, 2012 Posts: 103 Location: Sweden

isak · Posted: Sat May 04, 2013 1:40 am Post subject:

If the sync GND jack is the problem then I have a simple isolating solution.
Do you know the Teflon paper roll?
It's thin, white and comes in a small round package.
You can just roll some on the jack and then put it in the panel.
Tell me if it helped Smile

noiselector · Joined: Mar 30, 2013 Posts: 21 Location: France

He uses a switch for the hardwired sync instead jack sockets , some type of ground loop through this switch when sync is off could be causing the issue.

isak · Posted: Sat May 04, 2013 4:47 am Post subject:

Let me get this straight...
Sync on/off is turned on with a toggle switch, right?
The problem happanes is when the synch is off cause the toggle switch body is grounded with other pots/jacks on the front panel, right?
Assuming that what I understand is correct ...put teflon paper on the toggle it self.
Or I'm totally out of direction and I really don't know what your talking about Rolling Eyes

steffensen · Joined: Jul 11, 2012 Posts: 103 Location: Sweden

furio · Posted: Sat May 04, 2013 10:11 am Post subject:

interesting! ...otherwise, simply a sync single wire (ungrounded) custom patch cable.

isak · Posted: Sat May 04, 2013 2:34 pm Post subject:

noiselector · Joined: Mar 30, 2013 Posts: 21 Location: France

waiting for success ....
A picture of my boards.
I want to use some of them as LFVCO changing the cv1 input jumper for a toggle switch to 270K resistor. I see Furio's panels don´t include this socket but I think it is interesting too in this single version. Do you think there is enough space for add a socket for a miniature toggle switch in your panel?.

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steffensen · Joined: Jul 11, 2012 Posts: 103 Location: Sweden

Had a minute free, so i detached the sync-switch and tried. Same issue happens.
However, as i dont have the real Odyssey here, i compared my results to the Oddity VSTi, and its behaving pretty similar.
Tho, the VCO's do phase each other out a lot more when tuned together/close than the Oddity does.
As they are analog, they should have different cycles, but they seem to share the same cycle each time i turn it on.

I used some crappy trannies when i did my VCO's tho, so ill see how it behaves when replaced by quality ones i have here waiting..

steffensen · Joined: Jul 11, 2012 Posts: 103 Location: Sweden

Had some time over, so i went ahead and replaced all my 3904/3906's. Used some fishy ones, and the new ones are quality trusted ones from Mouser. Also made a Ground-chain between the pots on each section while i had it opened.

The Ground-chain didnt do much difference i think, but the new trannies made a lot of difference! Improved sound, MUCH lower pitch, and a lot less locking. They still lock together a bit, but the original does this too i hear.

I have also been informed on the reason behind this, and the fix is to put a 100nF cap after the 10uF caps.
The 100nF might be filtering too much, or too little, so one can decide for one self here.
Ill see if i do this at some point, it would need some hacking on this layout.

furio · Posted: Fri May 10, 2013 9:34 am Post subject:

Hi everyone,
I have just finished to scketch the PCB of the Ring Modulator (version for 'Erthenvar' jacks).
If someone would like to help me check it, here is the preview ... The 150K Input2 is to be soldered on the side of the tracks .... The 5K6 and 100n capacitor can be soldered inbetween the socket in the middle/under of the CD4011. The euro power connector must be angled.

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modulardoom · Joined: Mar 13, 2013 Posts: 5 Location: portugal

I have built this VCO and works fine but I hear some change in the PW when I turn the PWM potentiometer but nothing is connected in the PWM jack. This is ok? I think the PW shouldn't change turning the PWM pot with nothing in the input.
Question

furio · Posted: Thu Jun 06, 2013 12:48 am Post subject:

elmegil · Posted: Thu Jun 06, 2013 5:08 am Post subject:

If it's a bother, use a switching jack and connect the switching lug to ground?

furio · Posted: Sun Aug 25, 2013 10:02 am Post subject: