# Ground Loop (?) Hum



## neldom (Apr 29, 2009)

I've been trying to get a little bit more into the home recording game the last little while and have run into an issue.
I'm trying to double track my guitar by running one mic from the cab to my Fast Track C400 and run another direct line to the other input on the C400 for reamping, etc.
I first tried just splitting out of my Strymon Flint as it generates a stereo signal and I thought that would be easiest, unfortunately once plugged directly into the C400 I got a terrible hum, which I assumed was a ground loop.
So I started digging and saw the most common method is using a DI which allows me to use the Low-Z out of the DI right to the second input.
A DI also affords me a ground lift connection to avoid that nasty hum.
However, much to my chagrin (after purchasing the cheapest Leem DI available) I still had the noise on either ground lift or without (albeit a distinctly different hum between the two).

So my question is, is the culprit most likely the cheap DI I am using or should I start looking elsewhere for a solution?

I have really no experience with this sort of thing, so any direction would be appreciated.


----------



## ronmac (Sep 22, 2006)

Are you using a laptop, by any chance? If so, try running without the ac adaptor as a test.


----------



## neldom (Apr 29, 2009)

No, it's a desktop. 

That's a good call though for sure.


----------



## ronmac (Sep 22, 2006)

OK. Is the strymon running via adaptor or battery?


----------



## neldom (Apr 29, 2009)

The Strymon is via adapter (no battery option), though the Strymon was my "no extra purchase" option. 
I'd prefer to be using the DI, or other tried and true option which leads to no hum.


----------



## Noise Supply (May 31, 2013)

Is your DI passive or active? And does your guitar have active or passive pickups? Rule of thumb: passive pickups = active DI, active pickups (like those on a lot of acoustics with onboard EQ and stuff) = passive DI. Although if this was an impedance issue with the DI, it should sound a lot more gross than just a hum. So I'm doubting that's actually the issue.

You are plugging the balanced (XLR) output of the DI box into a balanced input on your recording interface, correct?

I'm a little fuzzy on the exact setup - can I bother you for a more detailed walk-through on the signal flow? I'm sure we can figure this out.


----------



## neldom (Apr 29, 2009)

The current setup is passive pickups to a passive DI, the DI sends the balanced out to the balanced input on the recording interface and the unbalanced out to the pedals/amp chain. 
I didn't realize about the passive/active combo you mention so perhaps that's the route I should pursue. 
Thanks to both of you guys for the input.


----------



## Noise Supply (May 31, 2013)

Passive to passive could work, but you run the risk of it sounding very off... Quiet, distorted, etc. A hum makes me think it's another problem, but to be honest, I haven't done passive to passive, so I'm speaking more on guidelines that I'm aware of, but haven't really broken myself, so I'm not sure exactly what it sounds like. 

You might at least want to rule it out by borrowing or renting an active DI. Or if your setup is small and portable, see if your local store will let you bring it in and demo some DIs.


----------

