Mangrove trimming procedure struggle

I’ve been having some tracking issues with one of my Mangroves recently, so I’ve delved into the trimming procedure outlined in the manual. I’ve never calibrated an oscillator before, and, while I’m pretty confident I’m following the instructions properly, I think I’ve somehow made it worse, or at least not made it any better. The oscillator shifts upwards about a quarter tone when I plug 0V in, and is a semitone out when I give it 2V. Tuning it to 80Hz at 0V and then putting the 2V in gives me around 330Hz and I can’t seem to get closer than that. I’m using a Maths and a Blinds for my voltages.

Anyone done this before and/or got any tips?

Edit: I’ve been able to get it down to 320Hz with 2V and the tracking sounds much better. Still quite a noticeable shift in pitch between having nothing plugged into v/8PITCH and putting 0V in there, but I’ll survive. Post can be deleted.

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longish necrobump! apologies, but this might be helpful to others in the future?

having some troubles nailing this procedure and wanted to bounce some thoughts off the community.


  • first hurdle was getting past my assumptions and realized that the CCW and CW directions in the guide are relative to looking at the unit front-on, rather than from the back. that helped a lot. tune flatter if the 0V-2V jump is flat, tune sharper if the 0V-2V jump is sharp; makes sense.
  • using O’Tool+ for pitch and voltage reference.
  • using TT for voltage source in my calibration.
  • when TT CV out is set to V 2, accuracy isn’t exact. I get 0V = 0.003 and 2V = 2.03V according to O’Tool. This is true of all the CV outs (none are pure 0.000V). Not a performative issue at all, but I think it’s messing me up with calibration.
  • I am able to get 80hz -> 320hz tracking by trimming with these approximate voltages out of TT, but only a session or two later and/or when switching CV sources (to Ansible or another TT out), things are wonky again.
  • I can get a pure 2.000V out of TT with CV 1 VV 197, but pure 0.000V is not possible. but 0.003V seems wicked close.


  • how have others trimmed their Mangroves for 5 octave tracking? what tools helped? do you notice it going out of calibration after a short time?
  • following the guide, should I try patching a dummy cable in for my 0V and then patch TT (with VV 197) in for my 2V?
  • also seeing this noticeable pitch shift. is this due to using slightly offset voltage in calibration?

any help would be appreciated – starting to spend more time trimming than I am playing :confused:


To be honest I struggle to get more than 2 octaves out of either of my Mangroves. I’ve spent more time than I’d care to admit on this, and have come close to pulling my hair out a number of times, but I just can’t seem to figure it out. Going by the instructions in the manual, it should be perfect. As I said in the OP, I’ve been using a Blinds and a Maths, as I only got my TT a couple of months ago, and I spent a long time making sure I got to around x.00x for each voltage, but it doesn’t seem to have improved.

Glad I’m not the only one! Love my 'groves to bits, but I’d love to get this sorted!

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Bumping this old thread…

I am having some issues with the tuning accuracy of my Mangroves. I tried using the trim procedure using a Beast’s Chalkboard module, using the 0 and 2 volt settings. After repeating the steps, I find that things are completely off and the trim can’t be adjusted any more. Each time I would repeat the steps, the gap got worse.

Has anyone run into this before? If I tune to 80 hz with 0 volts on the Beast’s Chalkboard, then add 2 volts, I am getting 309 hz with no ability to get it up to 320.

I find it if I loosen the trim and then start over, I can get back to 320. But after tuning to 320 and switching back 0, I’m not back to 80 and it’s inaccurate. Not looking to get perfection, but my chords are out of tune when trying to use 2 mangroves together.

Just FYI it’s a known issue that “nothing plugged in” doesn’t equal “zero volts in” on the Mangrove. So be sure to use a true 0v source rather than unplugging!

A good way to get close (before trying to dial it in exactly), is just using your ears. If you have a sequencer setup a simple sequence that alternates octaves quickly (preferably 2 octaves apart), and turn the trimpot by ear. That’s how I calibrated the first 100 back when I started.

Furthermore, using this sequencer technique, you can view the Formant output in a spectrum analyzer (eg: Spectrum in Ableton). Set the following for the closest to a sinewave: Formant@10:00, Barrel@12:00, Air@2:00. Now as the octaves switch back and forth, you should be able to tune the harmonics such that they line up. That was our approach in the workshop until recently.


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?