Nord's classical Virtual Analog Synth Nord LEAD 1/2/2x/3/4/A1 and Nord Rack versions

LFO 2 Amount knob affecting 2nd oscillator in a strange way

Postby synthguy » 20 Jul 2020, 21:12

Hi all,

I posted a couple of days ago about my Nord Rack 2 acting up. I've been reading a lot and have managed to figure out solutions to most of my problems, but one still remains.

When I turn the Amount knob of the second LFO, the pitch of the OSC2 goes crazy (OSC1 is fine). It doesn't matter whether it's set to ARP mode, or what the LFO is assigned to, turning the amount knob makes OSC2 go crazy. It only seems to be normal right in the middle, which doesn't even make sense as it's not a bipolar knob.

Here's a video so you can see for yourself: https://streamable.com/vdr54g

As you can see in the video, changing the rate doesn't do anything and the only way to make it stop is to put the knob back in the middle. The LFO2 is currently assigned to filter cutoff so definitely shouldn't be affecting the pitch of OSC2 in any way.

A similar thing happens when I change the Semitones knob - instead of just increasing the pitch of OSC2 like it should, it has a very similar effect on the sound as turning the LFO2 AMT knob does. The strange thing is, when I'm turning the semitones knob then it will sometimes randomly stop fluctuating and just stay at the same pitch, and sometimes this actually causes the LFO2 AMT knob to work as expected too. But then OSC2 is completely out of tune with OSC1, and the second I turn the semitones knob even the slightest bit then the crazy pitch oscillating effect comes back.

Any ideas what this could be? Presumably I need to take it to be repaired? Thanks in advance.
Last edited by synthguy on 20 Jul 2020, 21:13, edited 1 time in total.
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LFO 2 Amount knob affecting 2nd oscillator in a strange way


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Re: LFO 2 Amount knob affecting 2nd oscillator in a strange

Postby 23skidoo » 21 Jul 2020, 03:46

Hm, this seems like there's a bad solder joint or bridge on one of the pots and/or switches on your board - possibly screwing up the ground or VCC supply to the pots, and/or crossing one pot's value onto another pot's return wire. Has this unit had significant repairs done to it in its history - pots or switches replaced?

Since you see this between those two switches, I would suspect the problem lies somewhere in relationship to them and the OSC2 pitch. Put it on a MIDI monitor and see if you see multiple CCs changing when you move just one of these - if the synth engine is seeing the wrong (or multiple) control changing when you move one, that's a dead giveaway that you've got a hardware issue.
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Re: LFO 2 Amount knob affecting 2nd oscillator in a strange

Postby synthguy » 06 Jan 2021, 11:18

Hi, thanks so much for the response! I posted this question on a few forums and completely forgot to come back and check here if anyone had responded.

I'm trying to test what you suggested but not sure exactly what I need to do. I downloaded Pocket Midi which is a Midi Monitor for windows and then connected the MIDI OUT of my Nord Lead into the MIDI IN of my midi interface, then chose that channel to be monitored in Pocket Midi. But turning the knobs on my Nord shows nothing at all in the MIDI monitor.

Is that what you meant but I've just got it set up incorrectly somehow? Sorry for my lack of knowledge on the subject!
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Re: LFO 2 Amount knob affecting 2nd oscillator in a strange

Postby 23skidoo » 06 Jan 2021, 17:24

Well I can't help you debug your MIDI setup - you need to figure out how to correctly get MIDI to and from your synth on your own. There may be a system setting/option on the synth (I don't use a 2/2x) to enable MIDI CC transmit for the knobs, which you may need to turn on, also. But once the knobs send MIDI CCs that you can see, you'd want to check the data coming from one of your problem knobs and see if the synth things there are multiple controls changing (normally a knob will send only one CC at different values, e.g. CC74 will have a range of values depending on where the filter knob is, for example). If you don't understand MIDI or CCs or how they work, I would recommend either you learn how MIDI works on a fundamental level and try using it (and viewing it) on a working synth before trying to troubleshoot for the first time. I was suggesting this as a quick diagnosis tool for an experienced user. In your case, though, finding a competent synth repair shop may be well worth your while.
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Re: LFO 2 Amount knob affecting 2nd oscillator in a strange

Postby synthguy » 07 Jan 2021, 15:43

Okay, will give that a go! Thanks so much, this was really helpful :)
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Re: LFO 2 Amount knob affecting 2nd oscillator in a strange

Postby synthguy » 11 Jan 2021, 21:25

Okay, so I've got the synth to send MIDI out which I'm reading using the Pocket MIDI program.

The confusing thing is, it seems to be sending MIDI constantly. Like even when I don't turn any knobs, there is a constant stream of information coming from it.

It basically fluctuates between two values, B2 25 ** and B2 4E **, where ** is just two random numbers or letters. So the stream looks something like this:

B2 25 5A
B2 4E 41
B2 25 4E
B2 4E 3C
B2 25 43
B2 4E 41
B2 25 60
B2 4E 3C
B2 25 4A
B2 4E 3B
B2 25 44
B2 4E 39
B2 25 43
B2 4E 3B
B2 4E 3C
B2 25 3D
B2 4E 40
B2 25 45
B2 4E 3C
B2 25 42

Now, when I turn a different knob, then there will be another signal in there amongst the stream of 25 and 4Es. E.g, if I turn the frequency cutoff then there will briefly be some 4As in there. I'm not really sure how to read into this, as I don't know what a "healthy" MIDI in would look like.

If you have any ideas on whether this shows what the problem could be then please let me know! And thanks again for your help in troubleshooting here.
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Re: LFO 2 Amount knob affecting 2nd oscillator in a strange

Postby 23skidoo » 11 Jan 2021, 21:49

So your unit is sending a stream of CC on channel 3, CC 37 (0x25 = 37, Amp EG sustain) and CC 78 (0x4E = 78, OSC2 semitones). With those values I'd expect to hear OSC2's pitch and the volume of the synth modulating in realtime as you hold a note, is that what you hear, even without touching any controls? Do you have an LFO modifying these values? Make sure you're not sending any MIDI to the unit from an external source either.

4A is is CC74, filter cutoff, yes, so you would expect to see that one being sent as you turn that knob. Take some time to learn the MIDI format and to understand hexadecimal and decimal notations, it's very simple and will help you with troubleshooting. CC values are on page 91 of your manual.
Last edited by 23skidoo on 11 Jan 2021, 21:50, edited 1 time in total.
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Re: LFO 2 Amount knob affecting 2nd oscillator in a strange

Postby synthguy » 12 Jan 2021, 11:08

Aha, now we're getting somewhere!

If I have both the OSC2 semitone knob and the LFO2 AMT knob at exactly 12 o'clock, which is the position they need to be in to stop the sound going weird, then all of a sudden there is no stream of 4Es anymore.

I tried fiddling with the amp sustain knob and I think that must be broken too, it's just not as obvious when playing that that value is also fluctuating all over the place. If I turn the sustain knob all the way to the very right then it seems to stop the stream of 25s.

So now, I successfully have no MIDI signal coming out from the synth. However, if I move either the LFO2 amount knob or the OSC2 semitones knob away from the 12 o clock position then the constant stream of 4Es comes back, which you can also hear in the sound by the second oscillator fluctuating all over.

So, I think we've successfully diagnosed the issue.. but how would one go about fixing this?

Once again, many many thanks for all of your help!
Last edited by synthguy on 12 Jan 2021, 11:09, edited 2 times in total.
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Re: LFO 2 Amount knob affecting 2nd oscillator in a strange

Postby 23skidoo » 12 Jan 2021, 16:28

I honestly have no idea what kind of pots are on that hardware so I can't suggest a proper method for cleaning them or -- if they are sealed, cleaning isn't possible at all -- replacing them (are they surface mount? through-hole?) so I would at this point suggest that now that you've actually tracked it down to dirty/damaged/etc. pots you get thee to a reputable synth repair store and ask them if the pots are worth cleaning or just replacing. Pots are cheap, and a through-hole solder replacement job should be dead simple if that's all it takes, but that's beyond my ability to recommend at a distance and I'm not a synth repair pro.
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