1222 Tuner VCO Module

KOSMO MODULES
324

Stefan,

They say nobody beats the Biz. Apparently in this case the Aiz beats the Biz.

-Fumu / Esopus

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325

I have a new gremlin that showed up a couple weeks ago. After a certain amount of time, all three oscillators in my top row start wobbling (almost like a fast LFO is connected to the pitch). Have any of you experienced this?

Details:

  • it happens to all three at once
  • it does not happen to the oscillator in the bottom case
  • they are wobbly even when I completely remove any cables from the bottom case
  • the most recent modules I added to the top case were the Midimuso and the rotary phone module
  • I tested the pitch with and without any cv inputs and it still wobbled which rules out the midi to cv module as a potential cause (as far as the cv goes)
  • neither the wall wart or power supplies seemed that warm

The next time it happens I will double check the temperature of the power supplies and wall warts. I will note how long it takes to happen. I also plan to remove modules one at a time once it happens to see if one of the other modules might be the cause.

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326

That does sound to me like it might be a power issue. With no CV plugged in, that seems the most likely source of a problem common to all three.

Have you measured the current draw of the phone module? Has anyone measured the current draw of the MidiMuso?

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327

It’s got to either be the power supply itself, or something causing ripples in the power supply output.

A dual trace scope on the supply lines should show this.

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328

Swap one at a time from the top cabinet into the lower cabinet. Will help you figure out if it’s a module or the cabinet/psu

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329

Okay. So. It’s somehow midimuso related.

More notes:

  • The wobble came back almost immediately when powering up this morning.
  • Once I removed the Midimuso, the oscillators became stable.

Will shift the conversation to that thread when I know more.

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330

Mine have been doing the same thing on and off. I just tried unplugging the MIDImuso, but it doesn’t seem like it makes a difference. What’s happening is that the reference voltage is unstable. Here’s a video:

EDIT: I now unplugged everything but the VCOs and they’re behaving the same way. One more than the other.

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331

Could it be related to this ?

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332

Hmm, not a bad guess. Let me check that out.

333

Well, will you look at that:

image
image960×1280 406 KB

I put in a 1K and it’s stable. I measured the resistance of the 220R I removed, but it still measures 220, so I don’t know if it could be burned out. In any case, fingers crossed that the reference voltage stays stable.

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334

Let me know please. If so, I’ll do the same thing next week.

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335

May be worth a sticky at the top if it fixed it, or it’s own short thread…

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336

Yeah, still solid several hours later.

337

Cool, @Hackseven , give it a try and if it solves the problem

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338

Did you replace the resistor on all oscillators? The Truly Scientific Test would be to just replace one and see if its behavior changes while the others don’t. But this does look promising. I do think @lookmumnocomputer should update the schematic/bom with a 1k resistor.

339

I did replace both, but the other module was mostly stable anyway. Would just go wobbly every now and then.

340

I’ll try that this afternoon.

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341

Alrighty. Science results:

  • I put the Midimuso back in (to get the wobble back)
  • When the oscillators started wobbling, I replaced the 220R with a 1K on only one of three.
  • All three still wobble (even the oscillator with the new 1K resistor.

I could try swapping it on the others in case the unstability bleeds to other modules somehow.

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342

I think we probably had different problems that just happened to manifest the same. It could be that the MIDImuso draws enough power to push your power supply past the limit. What happens if you unplug several other modules but not that one?

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343

Seems like it might be a power supply issue of some sort.

  • I left the midimuso in and removed other modules one at a time. Each LFO I removed decreased the wobble slightly.
  • I tried different wall warts. I even swapped for one that was only 1amp instead of two which lowered the pitch and increased wobble. This seems promising.

I use two FC Microbus power supplies per case connected in parallel I think. Each case has one 12V 2a AC AC wart. Perhaps I need to get a better wall wart or explor other power supplies? Ideas?

I suppose I could also separate the Microbus and have a wall wart per bus, but I was hoping to keep it to one power cord per case.

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