›

Ground loop hum when many LEDs on

jazzmonsterjazzmonster
edited November 2014 in Troubleshooting
Hi, I bought a second hand LXR, already assembled. I'm not sure who built it but the general soldering job quality seems ok, except for the display which I had to resolder.

There seems to be a small but annoying issue with my unit. When I press the SHIFT button, an audible hum appears in the audio output signal. Also when many LEDs are lit up in the 'chaselight' section (16 LEDS at the bottom), the same hum appears. The more LEDs on, the louder the hum.

Has anyone come across anything like that before? I'm trying to identify the problem but I'm not quite sure where to begin.

The hum sounds like a ground loop. I can attach an audio sample if need be.

Thanks

Comments

  • gzifcakgzifcak
    i've seen that happen on other machines (909, 707) but i haven't noticed it on the LXR. maybe i haven't turned it up loud enough.
  • julianjulian
    what power supply are you using?
    So far I have never heard of a LED related hum. LEDs are not even multiplexed oder PWM'ed
    So I would guess it's a power related problem.
  • jazzmonsterjazzmonster
    Hi Julian, I am using a cheap power brick that came with the drum machine when I bought it second hand and I never checked whether it was up to specs. I noticed that in the wiki the specified power requirement is at least 600mA whereas the power supply I have is only 200mA! I'll replace it and see whether the issue is still there.

    Thanks a lot!

  • julianjulian
    sounds like you found the problem.
    a single LED will pull about 20mA when it is lit.
    so with about 10 LEDs you will already reach the limit of the power supply you are currently using.
  • docpdocp
    yeah, proper power supply is pretty important.
    with my first power supply the atmega crashed when too many LED were lit.
    a better power supply solved the problem :)
Sign In or Register to comment.