1222 Performance VCO Tuning Stability Issues

KOSMO MODULES
1

Hi Everyone,

I’ve recently built 4 of the 1222 modules, but unfortunately I’m finding them very difficult to use due to the tuning drifting constantly.

Here are the various issues I’ve got with them:

  1. After playing them for just a few seconds, the tuning is often out by a semitone or more. I would play the same sequence of notes and you can hear it shift rapidly.

  2. The general tuning seem to drift over time as well, over the course of one hour, it would gradually go up in pitch, maybe a semi tone every 5min or so up to 4 semi-tones.

  3. I’m not sure how accurate the in-built tuner is but it can not stay stable, the leds would go from red to green to red multiple times per second. Which I’m guessing would have something to do with the overall tuning being unstable

  4. I find that I have to re-calibrate the center note every time i use them.

I’ve changed R42 for 1k, and the problem seem to occur regardless of the waveform. All of them have the same problem too

I’m wondering if anyone has had similar issues and if they have managed to fix them?

Thanks!
Kevin

2

Sounds like you definitely have an issue, the built in tuner will settle into a stable position. And I’ve found mine to be quite stable tuning wise

Is your power supply adequate to run everything? If you unplug two of the osc does it still misbehave

Also, there are a number of threads on this module I’d look through

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3

Well, that did it, thanks!

So it looks like having all 4 of them plugged in to my power supply at the same time is causing the issue.

I unplugged them one by one and the tuning of the oscillators that were left changed every time. When I got to only one left it stayed stable.

I’m using a frequency central microbus, and all 8 slots are taken so it may be drawing too much power?

Very interesting, looks like I’m gonna need to find a better solution to power up these modules.

Thanks!

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4

Anyone ever measured the 1222 current draw?

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5

What is your wall wart rating? I use a 1.5amp powering one bus and a 2amp powering two more.

Not sure exactly which is connected to what but pretty sure I have my 1222’s on one bus with other stuff no problems

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6

I’ll give it go, I’m kind of curious now too

7

So my wall wart is outputing 1000mA, I believe it’s the one that frequency central linked to in their build guide, I didn’t really think twice and went along with it.

Do you think trying a 2amp one would be worth a shot in my setup?

8

I’ve seen a thread about this Power Consumption Specs of all Modules? - #3 by Dud but it looks like the project didn’t come to fruition yet.

How would you go about measuring it for the 1222?

9

So I think I’m doing this right, made a little breadboard to break 12v and -12v, with my meter in between whichever I want to measure.

For the 1222 with nothing plugged in I’m getting 83mA on +12v and 19mA on -12v

image
image3024×4032 3.22 MB

In which case, a 1A supply should theoretically power like 10 1222s

I’ll make something up with a switch so I can measure quicker and check the stats on the other modules

10

Just a footnote to point out that a safer and less fiddly approach is to add two 10 ohm resistors to the supply rails, and measure the voltage drop.

Or if the board already has 10 ohm resistors on the way in, measure the voltage drop there.

(resistors are a lot cheaper than the fuses in your multimeter)

I think @analogoutput has a utility PCB that does that, but cannot find the link right now.

EDIT: It’s linked from the post @KevinG linked to above: Power Consumption Specs of all Modules? - #3 by Dud

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11

I can see the danger in forgetting to switch the lead back, my meter yells at me if I’m in the wrong mode though and is supposed to be good for 10A. Measuring the voltages does sound a lot less fiddly tho

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Your meter handles 19 mA and 10 A via the same input? What meter is that?

13

Fluke 115–maybe I’m confused? Lol

14

No, you’re right, it seems it has one current input (and fuse) for all current ranges, with mA resolution.

(that fuse costs more than my standard multimeter, though :grinning: (which on the other hand can measure down to 0.1 uA, or so it says, at least)).

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15

It’s a nice meter, I wasn’t going to go name brand but I thought about how my dad still has his fluke from the 80’s (which probably cost a fortune in the day, or maybe a transmission rebuild in his case) Hopefully I won’t have to buy another haha.

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16

I had this same problem when running a 1000mA Wall Wart - same combo with the frequency central microbus power supply.

Upped it to a 2000mA supply and all was fine.

I’ve not considered the total current draw of a ‘row’ of Kosmo units, but went on the premise that the same PSU with similar configuration on Sam’s cabinet-build instructions mean I’ll be in the right ball park.

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17

So far with my 1000mA Wall Wart I’ve managed to make the following work at the same time:

  • x2 Performance VCO
  • x1 Quad VCA
  • x1 Midi-CV module
  • x2 ADSR

Anything extra in that mix and the oscillators start to drift. I’ve ordered a more powerful wall wart, I’ll report back once it’s arrived.

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