Robaux 3PT

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KittenVillage
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Re: Robaux 3PT

Post by KittenVillage » Mon Feb 22, 2021 11:17 pm

woelfl wrote:
Fri Jan 01, 2021 3:57 pm
The calibration process is IMHO a bit :picard:

I just measured the output voltages with DMM. With main pot (B) fully CCW you obviously get 0V on all outputs (P, R, Q). If you're tuning C1 to 0V that means you'll get C5 with 4V (because "V/Oct", right?) So, with B fully CW, use G/H/I to get 4V on their respective outputs, P/R/Q. When done and double-checked, "A" to exit calibration and that's it. Simpler and faster than what's in the manual.

But then I wonder what's the point of those 3 trims in the back? If calibration is done with the tall trimpots on the front and those trims in the back are supposed to be left fully CW (as per build instructions), then why can't they just be replaced with fixed resistors, which would lower the BOM cost BTW...? While at it, what's the point of rectifying DC? :rofl:

Otherwise, this caught my eye not long after it came out, I'm really glad I finally got one, I'd say this is one of the most creative module designs I've ever seen.

There's obviously some room for improvements, like e.g. extending the CV range to cover at least full 0-5V range, or even make it generate both positive and negative voltages... would require a few more bits in the analog domain, but the current BOM can be optimized anyway, and this would make it a lot better... If there's a new version with some improvements such as these, I'd get at least two more...
I'm a bit stumped as to getting it up to a full 5v. I keep thinking that the trimpots in the back shouldn't be fully CW, even though the manual says they should. I do not a bit more travel between 0 and 1v than 1-2v (etc) during calibration, which makes me think that something's off. It's a bit frustrating, especially as the build went really easy. Is there a hardware limitation that it can't get to a full 5v?


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aragorn23
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Re: Robaux 3PT

Post by aragorn23 » Tue Feb 23, 2021 12:16 am

KittenVillage wrote:
Mon Feb 22, 2021 11:17 pm
I'm a bit stumped as to getting it up to a full 5v. I keep thinking that the trimpots in the back shouldn't be fully CW, even though the manual says they should. I do not a bit more travel between 0 and 1v than 1-2v (etc) during calibration, which makes me think that something's off. It's a bit frustrating, especially as the build went really easy. Is there a hardware limitation that it can't get to a full 5v?
Mine only went to about 4.8v (which seems relatively common), so I calibrated it to have a 4 octave range instead of 5. 1-2v does sound a bit off though...

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woelfl
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Re: Robaux 3PT

Post by woelfl » Tue Feb 23, 2021 3:25 am

aragorn23 wrote:
Tue Feb 23, 2021 12:16 am
KittenVillage wrote:
Mon Feb 22, 2021 11:17 pm
I'm a bit stumped as to getting it up to a full 5v. I keep thinking that the trimpots in the back shouldn't be fully CW, even though the manual says they should. I do not a bit more travel between 0 and 1v than 1-2v (etc) during calibration, which makes me think that something's off. It's a bit frustrating, especially as the build went really easy. Is there a hardware limitation that it can't get to a full 5v?
Mine only went to about 4.8v (which seems relatively common), so I calibrated it to have a 4 octave range instead of 5. 1-2v does sound a bit off though...
Yeah, same here, doesn't go exactly up to 5V, and I'd say that's a HW limitation, as that voltage regulator outputs cca. 5V, by the time this gets thru and out of the MCU it will be a bit lower than 5V. And in V/Oct world, you'd need 5V precisely to get a note C... so the range is not full 5 octaves, but a bit less...

Still, calibrating to 4V, you get a full 4 octave range, e.g. C1-C5, which for the purposes of 3PT is enough... it's not an arpeggiator or something like that so it'd really need a wide octave range...

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