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Low Level Hum

Postby andyd » 09 May 2013, 04:46

Hello, when I turn my Electro 3 on there is a hum coming from the speakers. And if I touch the metal casing it goes away. I've tried a few different things (EB tech Hum-x) (plugging into different socket) but am convinced it may need service. Any Ideas would be welcome thank you Andy
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Low Level Hum


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Re: Low Level Hum

Postby mjbrands » 09 May 2013, 14:51

You mention the hum comes from your speakers; if the unit itself isn't producing a humming sound, than that should exclude a vibration in the power supply (capacitors, transformer windings). Where do you touch the housing? Do you press on some paint (i.e. non-conductive material) or do you need to press (touch) something specific?

When you hear this hum, do you have your Nord connected via USB to a computer? If so, does the hum go away when you unplug the USB cable from the Nord? If you get this issue at home with USB connected (and you want to keep USB connected), could you try replacing the Electro with your Wave and see if it hums when connected up in the same way?

I assume your Electro has a two-prong mains plug (I haven't seen anything else on Nords). That means it has no ground connection and should not pick up ground hum from the mains. Since it has no ground, that Hum X unit also doesn't do a thing for it, since that conditions the ground pin (which the Nord isn't even connected to). That said, the Nord can definitely pick up ground hum when connected to other equipment. For example, connecting to the Nord via USB causes the Nord to be grounded via that USB connection. You can also pick up ground noise via your audio outputs, or example to powered speakers or an audio interface.

Do you also experience the hum on the headphone output? If so, can you disconnect the USB and audio outputs and see if that makes it go away?

If you also hear humming on your headphone, the hum is probably introduced into the audio signal in the Nord itself (I don't expect this to be the case). If you only hear it on the speakers, it might be caused when the signal enters the inputs of your speakers or audio interface.

If the USB connection is causing the issue, I see several potential solutions:
  • Get a USB isolator; this electrically disconnects both devices connected via USB
  • When using a laptop, have it run on battery while playing
  • Plug both the Nord and the computer into (practically) the same power outlet

Regarding USB isolators: most of these are full-speed USB devices. Confusingly full-speed USB is only 12 mbit/sec (roughly 1-1.2 MB/sec). High-speed USB is the regular 480 mbit/sec version of USB. If completely restoring a Stage 2 via high-speed USB takes 15 minutes, I don't want to know how long it would take when only using full-speed USB (probably many hours). Note USB isolators may need a separate power supply when connecting USB powered devices, but since your Nord has its own power supply, I don't think you'd need one of those.

This is the cheapest USB isolator I know of (doesn't have a nice case and doesn't come with a power supply): https://www.olimex.com/Products/Modules ... e/USB-ISO/
Here's a pretty standard one: http://keterex.com/kxusb150.php

These things are often used by people messing around with electronics (such as Arduino controllers) to protect the USB port in their computer from blowing up in case they make a mistake.

Converting the audio outputs of the Nord to a balanced signal will take care of the hum provided it isn't already part of the audio signal on the Nord (most likely it still is fine when the Nord outputs it on its audio outputs). To do this, you'd connect a DI box to the audio outputs and you then run that balanced signal (with different cables) to the powered speakers or the audio interface. A balanced signal is highly resilient to picking up outside noise and (more importantly in this case) it electrically decouples the Nord from the mixer/interface/speakers it is connected to. This should take care of the humming.

If you play at gigs, using a DI box is an especially good idea. Not only can the cables from your Nord to a mixer (or other front-of-house equipment) be much longer without pickup up noise, it also protects your Nord from the FOH equipment. If (for example) there would be a malfunction in the mixer your Nord is connected to, this might put dangerous voltages on the audio outputs of your Nord. A DI box would protect you against damage (not by lightning strikes, etc.). Without a DI box, you might blow some of the EMI 'fuses' on the Nord's outputs - these are intended to protect your Nord (and you) against such situations, but they will intentionally blow and you'll have to send your Nord in for repairs. Note that unless your powered speakers or audio interface have balanced inputs, a single DI box is not going to be of use.

Phew, that was a lot of text.

Start by disconnecting USB and/or plugging your computer/Nord/powered speakers into power outlets that are very close together (so like on the same power 'group' - no idea what the proper English term is). If that makes no difference I suggest finding someone who will lend you a DI box (I think you can get passive stereo ones starting at around $60) and some cables. If the DI box helps, you know buying one will solve your issue. If it doesn't help, then it is time to research other causes.
Last edited by mjbrands on 10 May 2013, 14:02, edited 2 times in total.
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Re: Low Level Hum

Postby bluesbaba » 09 May 2013, 22:51

Phew, that was a lot of text. he he
yeah ..but good info dude..Respect!
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