Mangrove trimming procedure struggle

I’m just gonna throw out here that my Beast’s Chalkboard wasn’t 100% accurate, but for all I know you’re measuring its output, so probably not helpful :stuck_out_tongue:

I usually do check my voltages via multimeter. :sweat_smile: I figured that the whole point of Beast’s Chalkboard was to have accurate transposition of octaves and should work.

Switched to my Korg SQ-1 and that seemed to work better. Also used the techniques from @Galapagoose and those helped quite a bit too.

Almost no hobbyist (and darn few module makers) owns a meter good enough to calibrate pitch CV to millivolt accuracy. You really need to spend $1k-ish on a new bench meter or (like I did) buy a really high quality vintage meter with calibration to get something good enough for the job.

The delay method @Galapagoose outlines above is what I use even though I own both that HP bench meter and an excellent universal counter. I don’t find a need to refine tuning further, but I start with one octave and work up to three or four while listening to beats.

You have to accept that your system might be .997V/octave when you’re done (unless your meter is good enough, you can’t verify the reference), and you have to pick your reference carefully–and make sure your other references can be calibrated too. Many quantizers in Eurorack aren’t even as good as an subpar guitar, tuning-wise, due to the widespread use of 12 bit DACs with high INL. Precision adders can be off also. Having designed and built a couple myself, I can tell you it’s harder that it looks to build a module that will reliably add or subtract 1.000V to CV signals under a range of supply voltages and output loads. You’ll also find that many pitch CV sources have some offset–this causes grief when you switch voltages in & out of precision adders and the like.

FWIW, my Mangrove exhibits the input offset behavior but tracks fine.

(Aside: I don’t know if I got a really special unit, but my Jones O’Tool+ agrees down to .001V with my HP3478A bench meter. This is shockingly good performance–better than my Fluke 87.)


If you have an Ornament & Crime module, its TR4 input in Reference app is an extremely precise and accurate frequency meter (up to a millivolt), I use it all the time :slight_smile: (while sending 0v in the V/8 input of Mangrove to include the input offset).

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Been looking around, but couldn’t find the answer I was looking for in regards to Mangroves tracking

I have calibrated my Mangrove properly, but there’s still a big pitch offset when I plug into pitch.

Example, I tune Mangrove to C without anything plugged in, the second I plug into v/8 the pitch gets offset and out of tune.

Has anyone been able to fix this?

This is a known design issue, I believe. A workaround is to plug in a dummy cable, or 0V, and then tune.

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for reference, Trent has addressed this behavior as a known (early days) limitation:

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trying to tune my mangrove for the first time and having trouble. using a keystep input with confirmed 0/2v range. mangrove is warmed up and with C0/0v running into it with the pitch knob at 80 and 80 on the scope my C2/2v is reading at 335. i can adjust this down to 320 but then my C0 is reading at 75.

how can i make the C0 = 80 and the C2 = 320 per the manual by using the same trim knob? im truly confused

With the trim pot you are basically adjusting the spread between the notes. It takes a bit of back and forth to get it right.
Increase the trim, dial back master frequency knob, adjust trim, adjust master frequency, … Takes a moment …


thanks this worked. i was thinking about it wrong + it’s so touchy!


With the new, detailed manual driving some Mangrove experimentation I noticed one of mine was out of tune and I followed some of the steps here. I wasn’t able to get the Mangrove calibrated using the 0v <-> 2v calibration procedure, finding myself chasing the 100 & 400hz until hitting either end of the trimming pot. I was however relatively quickly able to calibrate the module by ear using a combination of the octave jumping sequence and a midi sequence I was familiar with. To my ears at least it’s now in tune to four octaves or so.

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I think something that needs clarification on the new manual is that the trimpot moves both the top and bottom note, so tuning by ear is a good way to check that the frequency, whatever it is, is being multiplied by 4. Even if you start with 100 at the bottom, at the end you might have 80 and 320

I have quite a specific question about Ansible and I’m not sure if this is the best place for it.
I was thinking on using Kria to calibrate my Mangrove. The intention is to send alternate octaves to follow the trimming procedure.

Is there a way to set a cv output at exactly 0v?

I was expecting that this would give me alternating 0v and 2v:
-Setting a loop of 8 steps with triggers in 1 and 5.
-Setting note at the lowest in both 1 and 5.
-Setting octave at lowest in 1 and third from lowest in 5.
-Setting root in the scale page at the lowest.

But now I’m not sure things are like this at all.
I don’t have any accurate source for voltages other than Ansible.
Does it matter if I send exactly 0v-2v, 0v-3v, 0v-4v, which is what I was planning to do? Or could I simply send alternate octaves as in 1-3, 1-4, 1-5, etc. without worrying about specific voltages?

First vco calibration ever. :sweat_smile:

I’d say using earthsea on ansible might be easier – there’s a clear 0v point and you just need to do two guitar-octave-shapes from there to get to 2v. you can also record that jump to automate the process a bit :slight_smile:

if ansible is going to be your main source of v/8 to mangrove, you’re fine to generally calibrate using whatever “0v/2v” means to your ansible. if you measured it with a voltameter, “0v/2v” might actually register as “0.02v/1.99v”, but generally you’ll get desired results over time because you’ll have calibrated mangrove’s understanding of “0v/2v” to your ansible’s understanding of “0v/2v”.

does that help?


Great, this is super helpful. Only recently I started using meadowphysics but hadn’t tried earthsea yet. Guess it was about time.

This makes a lot of sense. I’m planning on using Teletype eventually, which might make this stuff easier, but sure will bring a whole lot of new questions.

Thanks Dan!

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I started trimming the three sisters and I had it calibrated but then the frequency just started to endlessly drift sharp. It doesn’t seem to be slowing down or stopping. I have the output from the Mutant Brain playing a steady C3 from Ableton and that is going into the Beasts Chalkboard. Anyone know why this would happen? Now I’m afraid to calibrate the Mangrove.

OK this is interesting… I tried a second three sisters and the same thing is happening. It happens whether i have something patched into the v/8 or not. This is making it a little difficult to tune/calibrate to say the least.

My three sisters is definitely my most temperamental oscillator tuning-wise. is it possible that it was still warming up?

I thought the same thing but I’ve had it all day. Both of them are rapidly shifting. Super weird.

My 3Sis goes up and up all the time… you mean this?