Bad hum when I plug in a guitar cable

[Donkay1963]

I’ve had the 32sd since January and it worked fine. Tried to record last week, and I get a loud hum when a guitar cable is plugged in to any of the inputs on the back. The unit records the hum, so its not the headphones. Also when I touch the metal on the chassis the hum goes away. I have tried 4 different outlets in the house, all with the same result.

 

[Mark Richards]

"when I touch the metal on the chassis the hum goes away."

When you touch the metal you are disrupting a ground loop. A ground loop exists when the DP sees more than one path to ground. A ground loop sounds like a low frequency hum or buzz.

Your DP32SD is grounded through the three prong AC plug. There is also a route to ground through any equipment or instruments connected to the DP32SD. If the DP32SD's electronics find another (shorter) path to ground through something else connected to the DP32SD, a ground loop results.

Even though it presents when you plug in your guitar, the guitar may not be the actual source of the hum that you hear. Possible other sources of ground loops and hums:

• Ground loop caused by external or rack-mounted gear connected to your DP-32SD
• Ground loop caused by a computer's USB port connected to your DP32SD's USB port;
• Ground loop caused by a break in the guitar cable ground shield;
• Hums caused by radio frequency interference from florescent lights & computer screens.

Here's a nice primer you might want to read:
https://www.prosoundweb.com/topics/...ublesom_hum_buzz_created_by_electric_guitars/

 

[Arjan P]

Sounds like a ground loop indeed - which is not necessarily a fault. Try using the same power outlet for both recorder and guitar equipment - if any. If that doesn't work, a DI box (guitar in, mic level out) will certainly work. Radial makes some great sturdy ones.

 

[.Strat Brat]

I've got a serious hum on my DP24 as well, so these learned responses are appreciated. I use step down transformers to power my DP24, since the mains power voltage here is 220VAC, but I also have my monitoring speakers connected directly to the 220 volts AC, per their spec, meaning that I do indeed have two separate paths to ground here. That said, I also suspect my step-down transformers may be inducing some hum as well.

Following Arjan's advice, I'll see if I can't find a DI box, and start my trouble shooting with that inclusion. Much gratitude as always.