Marbles CV output range issue

Hi, very new to eurorack so potentially an understanding issue but:

It appears the CV out of my Marbles X generator is somehow not the full range I would expect.

If I use my keystep CV out I have no problem tuning my oscillator to e.g. middle C. However, if then patch it to the X2 out of marbles no matter what I do I have bias towards very low notes.

If I set the range +2V for X generator, and turn bias fully CW, spread full CCW, and steps fully CW I can’t get it to produce anything over an A2 on my oscillator even I put the tuning all the way up to it’s max.

I can achieve slightly higher notes when I set range to +5 or ±5 but obviously this a solution.

I thought perhaps it was some issue with my oscillator at first. I expected you tune your oscillator to the desired note and then the 1V/Oct to moves it from here. With 1V/Oct unpatched however I have just a low rumble with some limited response to tuning. As mentioned previously though it works as expect with Keystep patched. I patch it, nothing changes, then I hit a key and the oscillator moves to that pitch (+/- getting it in tune of course)

Unfortunately I don’t have a scope to help me figure this out on my own.

If there some way to calibrate an offset on Marbles or something?

I’m not in front of my modular right now but if I remember correctly, you have to go down a couple of octaves on the KeyStep to make it output 0V. I think its middle C, without using octave up or down, corresponds to something like 2V.

If you tune your oscillator to 2V and set Marbles’ range to +2V, it will only be able to reach notes below the note you tuned to. If I understand your problem currently, you should try tuning it a couple of octaves higher (or in other words, turn the KeyStep two octaves down when using it as a reference).

Thanks for your response. It doesn’t totally clarify it for me though.

If I have Marbles to +2V, even if I tune my oscillator to the highest pitch possible with the controls I can’t reach a middle C.

When using my keystep I can get the oscillator to go to extreme levels of pitch (either by just playing very low or high notes, or my manually adjusting the tuning of the oscillator). But for some reason when I plug marbles into the 1V/Oct I have a very limited range on my oscillator, most of which is so low it’s barely audible

I’m sorry, you’re right, I missed this part:

Of course, 0-2V will always be a very limited range of just two octaves – in comparison, the KeyStep goes up to 10V, I think. And its middle C, with no octaves up or down, corresponds to 4V (not 2 like I wrote before – I just tested it).

So at Marbles’ 0-2V setting you may not be able to push your oscillator as high as you want without adding a fixed voltage offset to Marbles’ output using something like a precision adder. Standards on what voltage middle C corresponds to differ, and apparently your oscillator expects a higher one.

This is the response I was afraid of :smiley:

Was hoping I could set an offset within Marbles.

TBH though I’m beginning to suspect there might be an issue with the CV of marbles.

I’m using the Pico System III. That has a CV source (the sequencer module) with range ± 5 Volts (specs here EricaSynths - Pico System III) and if it set to ~1 or 2 V I have loads of range on the tuning of the oscillator.

Might just need to pick up a multimeter to check

What is the color of the output LEDs?

OFF when BIAS is fully CCW, and faint green when BIAS is fully CW? Then there is no problem with the output, because the circuit driving the output LEDs is fully analog. If the voltage is in the right range, you’ll get these colors.

hmmm, yep those colour match up.

If I try get +5V from Marbles and compare to +5V from my other source it is noticeably lower in pitch though. Using a tuner I find almost half an octave between them. So ~0.5 V I guess.

If you try to get 0V, do you see the output LEDs lighting up in red?

Silly question (sorry) - is it a genuine MI Marbles ?

Ya it’s the real deal :slight_smile:

1 Like

No for 0V it’s off.

I tried another experiment. I used a CV mixer to combine the 5V on my pico sequencer with the 5V of my Marbles out. I measure the pitch with both mixes to max, and then only Pico, then only Marbles. Ideally I would see 5 octaves drop in both but of course I have no idea if there is any kind of normalisation going on in the mixer. But at least the drop should be the same.

But I got a 3.34 octave drop when removing 5V pico source, and only a 2 octave drop when removing the 5V Marbles source (yes I double checked I wasn’t on the 2V setting :smile:). I repeated for a different oscillator tune and got 4 octave pico drop, and 1.75 octave marbles drop. So it’s not the most robust method clearly. What is consistent though, and consistent with my ears also, is that the Marbles range seems lower than expected.

What is this oscillator?

I’m using the pico system iii. EricaSynths - Pico System III
It’s all I have I’m afraid so can check against others. It has 2 VCOs though and seems to be the same for both

Anyway, using the cv mixer with another voltage source gives me the control of the range I need. And I’m having a lot of fun :smiley:.

This does cost me two modules in my very limited setup so if anyone thinks of anything to try let me know. I’ll update if I find a solution or get to try it with a different oscillator.