LXR output noise/interference

edited April 2014 in General
This morning I noticed a whining background noise coming from the LXR. I'm using a new mixer with powerful preamps, so that's perhaps why I haven't noticed it before. The noise is loudest on the first output. 

I recorded the amplified signal, once with the lxr playing a muted pattern, once playing an empty pattern.
As you can hear, there's definitely some kind of modulation from the sequencer going on. Even on the empty pattern there's a very audible click bleeding into the signal.

I've tried using different power outlets and power supplies but the noise remains. What is causing this? Could it be the trigger board?



  • edited April 2014
    I experimented some more and found that the click you hear on the empty pattern changes accordingly when I change the resolution of clock outs 1 & 2.

    I don't mind a little hiss here or there, but this sounds like a damn fax machine! :)
  • Sorry to bump this, but has anyone else experienced this type of interference? It's quite annoying and makes it impossible to do any recording...
  • Julian is on holiday (see first thread)
  •  have you the usb connected when hearing the noises ?
  • Nope, I've never connected anything to the usb port. I'm an old-skool midi dude B-)
  • Hahahaha i guess i should do the same
  • Did you trace back the output contacts and check for shorts? 
    In this thread: http://forum.sonic-potions.com/discussion/392/few-hardware-glitch-my-bad (middle of the page) are graphics showing the connection to the tip contacts of output 1 and 2. 
  • I do have a midi clock signal coming in through the midi in socket.

    I don't think anything's shorted on the main board at least. It sounded flawless until I installed the trigger IO and started using this new 8-track recorder/mixer. The trigger board does seem to work as it should though, I can trigger stuff and the clock outs work as well.

    Perhaps tomorrow I'll try to disconnect the trigger IO from the main board to ascertain if the problem is directly related to that. 

    As an aside: are the outputs on the LXR balanced?

    Thanks for helping out fellas.
  • I actually had something that sounded very similar - I had just got my Focusrite 18i6 and wired everything up (OP-1, micromodular via midisport 2x2, LXR via midisport 2x2.

    I would get weird 'ticks' and digital noise from the LXR whenever midi activity occurred on the midisport, even activity just on the micromodular

    I fiddled around for a while trying to isolate what was causing it - then it went away! As far as I can tell I had it wired up as I originally had it, but no noise at all... I actually suspect a cable/connection/earth shield problem.
  • Same thing happened to me. It was a ground loop, which I "solved" by moving the plug for the mixer into a different power strip. I was really freaked out until I was able to resolve that.
  • I have this type of thing happen all the time. Its one heck of a quirky unit I can tell you that. But sometimes I just power it on and off and it removes the weird noses I was hearing. Also noticed crackling sounds a lot when tweaking mixer section params.
  • @Revok - No, they are unbalanced mono jacks. 
  • From what I understand, balanced cables are well protected from ground loops, though I've never been able to tell if you can just plug them directly into unbalanced jacks (both input and output).
  • edited April 2014
    It is not the cable that protects against interference, it is the technology itself. A balanced connection features two wires carrying the audio signal. One wire is in phase with the original polarity, the other one is reversed in polarity. A balanced input uses a differential amplifier to recombine the signal. By doing this interferences can be filtered out. 

    Sorry for the german description in the image, I had no other one. 
    Sender = transmitter // Störung = interference // Empfänger = receiver

    You can use a balanced cable to connect a unbalanced output to a unbalanced input, but you won't benefit from doing so.

    Back to topic now... :)
  • I've tried using different outlets already, might try to use different cables next. 
    Perhaps I should get some DI boxes.

    It really sounds like you can hear everything going on inside the LXR, even the processor. It creeps me out.

  • I don't think it is caused by the cables. 
  • edited May 2014
    There is definitely a noise, but only under certain circumstances for me.  I'm using an MOTU Ultralite.

    The setup I'm describing below is out of bounds for what people would be likely to use or encounter (max everything), but I'm detailing it for the sake of completeness.

    - output 1(L) from LXR->interface input 1
    - only 7.5V PSU plugged in; no MIDI or USB connection
    - monitor controller and speakers up to max
    - interface input preamp up to max
    - start from initial menu after boot
    - no sequence playing
    - turn the encoder, noise is noticeable (you hear a high-pitched click for each increment)
      - press of encoder generates the same noise, but super brief
    - ditto for turning any of the 4 pots (each time a new value is interpreted?)
    - press any of 16x sequence buttons, same noise is noticeable (1x blip)
    - no noise noted when pressing playback, menu or voice buttons

    If I use any other output, nothing is noticeable by ear.

    Ditto, if I run the sequencer with an empty pattern, nothing is noticeable.
  • edited May 2014
    hmmm I never noticed any noise that was not aused by my crappy m-audio soundcard.
    when I hooked the unit up to a propper interface it was dead silence (and the m-audio was continuing to make noise even with nothing connected ;) )

    I only experience noise when I connect the USB cable due to a ground loop, which can be solved with a cheap USB isolator box.

    I do some more noise checks but first have to do some re-arrangement of my whole setup which is a mess at the moment :-p

    but it somehow sounds like a gnd loop to me. I even had this once with my laptop where I could hear mouse movements on the speakers.

    is everything connected to the same outlet?
  • edited May 2014
    The noise appears to occur only when I have my Memory Boy connected to the 2nd aux io out of my mixer/tape recorder. Probably some circuitry in the mixer circuit isn't well isolated. Further testing will be needed to confirm this.

    The LXR sounds even better on tape, by the way :)

  • I have noticed that a version of the recording I did for the compilation that was recorded with the USB input active has bleed on every track -- you hear some aspect of _other_ voices on each voice.

    This dovetails with the distortion and feedback I'd noticed before, which was at least partly related to ground loop but which would be much more pronounced when plugging in the USB input.

    The unpredictability of sound with (my) LXR gives me the sad sometimes.
  • edited May 2014
    I did a little testing.
    With only the audio IOs connected to my mixer the LXR is dead silent. even with massive gain.

    MIDI connection to the modular wich is connected to the mixer as well = silence

    but if I add a connection from the trigger IO to the modular I get digital ground loop noise in the background.:-/

    I have to play a little bit with my routing to see if I can make it go away.

    As for noise introduced by USB.
    I have the same problem with my Laptop and USB soundcards as well -> ground loop.
    Only thing that helps there is taping off the PSU plug GND connectors or using a cheap USB isolator box.
  • Any suggestions for a USB isolator? The ones I have found aren't what I would consider "cheap" (30+ EUR).

    Maybe I'll find a circuit diagram and can build my own though ;)

    Either way, is this not something that could be isolated on the LXR PCB itself (in a future revision) ?

  • edited May 2014
    Just one little hint, as i knew people which experienced problems in similar configurations, it may help to check the issue with an active USB hub in between...as a properly engineered active hub should be grounded as needed.
  • edited May 2014
    here are information on how to build one

    This seems to be the same, ready made, 24,94€ (just a quick google search. did not test tjis, but It looks like it uses the same chip as the DIY version)

    but there are others.

    Afaik you can also use them in front of a HUB

    I may include something like this in a future PCB revision. but I have to test it first.

  • I did some testing.
    in most configurations I habe zero noise.
    In certain conditions, especially with different PSUs and a lot of interconnections to different gear I get the described noise (ground loop). A simple NF filter got completely rid of it (similar to a DI box but much cheaper)

    So if you experience some annoying noise in your setup this may be a solution.
    Reichelt order no 'KFZ NF-FILTER' - 4.65€

  • edited July 2014
    Interesting topic. That KFZ NF-FILTER is a very good start for few money.

    My 2 cents:
    Ground loop hum:
    Use only one wall-outlet for the whole setup.

    If in any case 2 different AC circuits (in case more AMPERE needed) or just simple outlets (on the same AC circuit) are used, anything going between those two has to be separated by DI boxes.

    Try to rotate the main plug 180º (phase inversion) if there is still ground hum noise.

    Digital interference(s):
    An active MIDI cable (midi data is transferred) going more than 15-20cm in parallel to non-balanced audio cables gives you almost every time digital "noise" on your audio signal.

    "How much" / how severe, it only depends on the MIDI cable you´re using and what data type/amount you send over MIDI: you can hear it all the time, its not a myth ("some people" claim it a myth).

    Several MIDI-cables can all stay in parallel, just not to any unbalanced audio cables, try to cross audio- with midi-cables always in 90º.

    The digital interferences the LXR "itself creates" has reasons which Julian pointed out above, like: different PSU, interconnections to other gear... it is not particular to the LXR, many other devices would create "digital noise in audio range" in a given setup just as the LXR does.

    Anyone located near, or in Germany: try out that KFZ-Filter from Reichelt for a start :-)
  • but if I add a connection from the trigger IO to the modular I get digital ground loop noise in the background.:-/

    I have to play a little bit with my routing to see if I can make it go away.
    Hey julian, did you find any handy solutions on this? The lxr is so useful for my modular needs, but this noise keeps me from using the trigs. Thanks
  • Was a solution ever found for this issue? I can notice this high pitched noise when my trigger outs are connected to my modular. I've tried a number of different power routing changes but nothing helps.
  • I've also noticed the high pitched noise with my LXR, I've also got the trigger board installed.

    I'll disconnect the trigger board an report back.
  • edited February 2015
    I've disconnected the trigger board and the RF noise remains.

    While the above suggestion of using an RF filter may treat the symptom there must be a deeper underlying design/component problem that's causing it.
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