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I have a macbook pro laptop and my audio interface is the Apogee Duet 2. Whenever I plug my guitars into the Apogeeinterface I've got a hum going on. I can get rid of the hum if I take out my laptops power cable however I then have an issue of the laptop overloading frequently (not running at full capacity without power cable) and running out of battery without the power cable.

Any advice on how best set this up to keep my power cable in my laptop while recording guitars?

Many thanks



kmetal Mon, 08/03/2015 - 11:23

I think there ar a bunch of threads on this around here, a lot of people have this problem. The first thing I'd try is plugging the laptop into different outlet in a different room and see if the hum goes away. After that maybe try unplugging the fridge and air conditioners briefly and see if it goes away. Could maybe be bad grouping I the guitar or amp? Hums are a process of elimination.

Boswell Mon, 08/03/2015 - 15:38

The external power supplies that most makes of laptops (including Apple) are supplied with are switched-mode, i.e. do not have 50/60Hz mains transformers, so do not cause hum in the traditional sense. However, they also are mostly designed to run without a ground connected, and this is likely to be what is causing the problem. I would run a separate ground wire from a connection on the chassis of the Duet to a known good earth in your house. This may involve clamping a copper ring round a rising water pipe.

DonnyThompson Tue, 08/04/2015 - 02:37

In my basement, directly under the breaker panel, is a steel rod, 3 inches out from the foundation wall, and poking up out of the cement floor by about 6 inches, it's about 2 inches in diameter, with a copper clamp-ring attached.

When I moved in 24 years ago, I had the house professionally rewired for 200 amp service, and I asked the electrician if the rod was by chance a grounding stake. He told me that this was exactly what it was; I asked him how far he thought the rod went down, and he told me that he'd heard of some grounding rods going down as deep as 20 feet below the basement floor, mainly in older homes where water came from a well on the property, and the pipes that came in from the well outside weren't buried deep enough, which is exactly what my situation is.
My house was built in '41, so I guess it's possible that it goes pretty deep. I also asked him if he was going to use the rod with the new breaker panel, and he told me that he absolutely was, because it would be a better ground than anything else he could fabricate or attach to.

This was a long time ago, so I don't know if codes have changed since then. Maybe now they attach to a separate ground, outside the house, as part of the utility pole at the street.

That rod must provide a good, solid ground - because I can honestly say that I've never had any kind of grounding issue in my house. In fact, I've never had to deal with any kind of noise caused by "dirty" power. I don't get clicks or hums when the refrigerator motor runs, or with air conditioning, or the furnace... the only noise issues I've ever had was with equipment that turned out to be defective.

I'm thinking that the well shaft would make a great grounding stake, too...if for some reason I had to have a second ground. It's galvanized steel, and according to county records, it goes down almost 100 feet, because that's where the water is.

Davedog Fri, 08/14/2015 - 20:56

Don't get me started on grounding. There's a whole bunch of books on it. A BIG problem with this subject is the actual meaning of the word and how it relates to electrical systems. Ya see....There's "grounding" and "grounded" and "earthed" and all sorts of variations to this.

Local laws in different states have their own interpretations to the National Electrical Code ( ie: Bible) most of the time they are in agreement with the basics set forth in The Code...some are specific to a region for reasons such as the make up of the earth within that region and things like how much land is used for agriculture as opposed to a large cityscape type of environment. Yeah...these things matter.......

One thing that must NEVER happen is TWO PATHS TO GROUND........Think about that for a minute. What happens in a short circuit? Where does the electricity go? Cause it sure as hell isn't magically evaporated. A ground has an impedance. The point is to get as low an impedance to ground as possible so things like a 'short circuit' will travel along the easiest route to earth it can and not spend a lot of time blowing crap up along the way.

You can have a multitude of grounding devices within a system.....ground rod...ground bar...cold water pipe...Ufer ground...ground goes on.. But these are ALL grounded together to create a system that does the work needed to ground or 'earth' a system. But why so many Uncle Dave?

In the Pacific Northwest where I live, the earth and the dirt is particularly acidic so it is required to have a minimum of a cold water bond as well as two 8' ground rods within 6' of each other and tied back to the system ground bar at the main service. This is also where the NEUTRALS are bonded to the system. And these are tied to the grounds at this point. This is standard in a 240/120 volt system like you would find in any home or residential type of system. "So why wouldn't you read voltage to the ground because of the neutrals returning the voltages in the half cycle? " The ground is the end of the POTENTIAL and unless there is reason to have a flow of electrons back through the system grounds, there can be no flow. This is where MOST noise in a system comes from. Improperly grounded systems.

Then there's redundant grounding systems like you would find in hospitals ,server rooms,swimming pools etc...Anywhere where there has to be an absolute equipotential plane at all times. In these cases there is a separate grounding wire tying all the metallic parts throughout the system together as well as the grounding conductor for the equipment.

My suggestion for recording studio gear is to always have a separate dedicated circuit for all the gear. IF you require more than one circuit then all circuits contained in the studio must be on the same phase to eliminate the possibility of crosstalk between other circuits in the facility like motors and refrigeration equipment. A separate transformer will eliminate every noise problem you could ever encounter other than that caused by single-coil guitar pickups....which is whole nother thing......