Grounding Issue with Laptop AC adapter

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Rufio90210

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Hi,

I have a macbook pro laptop and my audio interface is the Apogee Duet 2. Whenever I plug my guitars into the apogee interface 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

Luke
 
Is the Duet running on USB power or are you using a power adapter plugged into the wall?
 
Rufio90210 said:
Hi,

I have a macbook pro laptop and my audio interface is the Apogee Duet 2. Whenever I plug my guitars into the apogee interface 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

Luke
Click to expand...

Are you using an instrument signal level setting on the apogee? Make sure you're doing that.

Is anything else plugged into that outlet? Unplug it if so.

I just went through ground problems. Look for 2 prong cables in the chain and remove them along with any unbalanced cables. Try to have a 3 prong power strip with every balanced cable plugged into it.
 
4tracker said:
Are you using an instrument signal level setting on the apogee? Make sure you're doing that.

Is anything else plugged into that outlet? Unplug it if so.

I just went through ground problems. Look for 2 prong cables in the chain and remove them along with any unbalanced cables. Try to have a 3 prong power strip with every balanced cable plugged into it.
Click to expand...


Here is my set up

Instrument --> DI BOX -- > Apogee Duet 2 --> MACBOOK via USB

I have tried both Mic and Instrument setting on Apogee, there is nothing else plugged into the outlet.

I am in the UK so have a 3 prong plug.
 
Get an iso/hum box.

Get a longer lasting battery...or play faster. ;)

Get a PC. (Couldn't help myself...just kidding :) )
 
miroslav said:
Get an iso/hum box.

Get a longer lasting battery...or play faster. ;)

Get a PC. (Couldn't help myself...just kidding :) )
Click to expand...

I bought the Behringer HD400 ac hum destroyer which arrived today and does not work. Im hoping its just a faulty unit and perhaps a replacement will work.
 
Get an outlet tester to make sure the outlets are wired right. They are like 7 bucks. Clearly there is a problem with the grounding so you need to eliminate things. Try to eliminate the outlet. If it's a cheap guitar they have shielding issues sometimes so maybe it's that. A lot of guitars hum. Does any other equipment hum when plugged in? Try a mic, etc.
 
It's probably not a ground problem. The fact that it's quieter on battery indicates that it's just a noisy power supply that is either poorly filtered, slightly underspec'ed, or nearly dead. You could try to run a wire from the metal chassis of the interface to a good earth ground point like the cover screw on a well-grounded wall outlet, but I'd almost be surprised if that helped much. What it really needs is a filter between the wallwart and the computer. The actual electronics part of that filter is simple - a resistor and a cap - but since apple uses proprietary connectors it would require hacking your one (?) working power supply. Theoretically, you could hack the filter into the USB connection (I personally have a bunch of spare USB cables), but we'd have to look into that a bit.

In the meantime, ditch the DI. It's not doing you any favors by stepping down the level from your already probably slightly weak guitar signal even further into whatever noise floor your interface is adding. Plug straight into the Instrument input on your interface. That's what it's there for. It's not going to eliminate the noise, but it might be just enough to make it usable.

Course, I'd want to make sure that all this noise is actually on the record side first, rather than just the monitoring. Have you tried recording with the thing plugged in and then playing back from battery and/or vice versa?
 
Rufio90210 said:
I bought the Behringer HD400 ac hum destroyer which arrived today and does not work. Im hoping its just a faulty unit and perhaps a replacement will work.
Click to expand...

Where did you put that in the signal chain?

You may solve the problem by using a USB ground isolator.

I hate computers and this stuff, the old computers never had ground issues, the new stuff has to comply to all the world wide grounding regulations and this causes audio ground problems.
I found this little blog article that may give you an insight. LINK

Alan.
 
I agree with Ash', can't be an earth loop problem since the only thing earthed is the MacBook PSU? (unless Luke has completely forgotten to tell us about some active monitors! In which case there are other solutions)

One thing bugs me "overload is compromised on battery power"??? The supply rails inside a laptop are regulated and converted all ways up to Christmas, battery/mains, should not matter.

Luke, are you sure the PSU is not coupling into the guitar pups? Wall rat/line lumps are bloody awful for radiating ***t!

Allan: We have had earth hum loops as long as we have had mains powered audio. Pan decks, Ferrographs and guitar amps just for starters. Modern safety regs begat nowt!

Dave.
 
ecc83 said:
Allan: We have had earth hum loops as long as we have had mains powered audio. Pan decks, Ferrographs and guitar amps just for starters. Modern safety regs begat nowt!

Dave.
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Tell me something I don't know as I have been sorting this stuff for years, however when it comes to digital ground loops they are harder to overcome than lifting an audio ground wire from an xlr. I am not saying that things should be made dangerous for the sake of audio, I am saying that if they made this stuff with quality in mind there would not be ground problems with power supply units. You can buy aftermarket power supplies with proper ground design that do not cause noise, but of course they cost more because they are built properly.

Yes, of course if the apogee is plugged into the computer and nothing else is plugged in there is no ground issue, but once you plug in monitors (powered or with an amp and passive) an external device like a keyboard or drum machine, guitar amp simulator, etc then you start to get problems. I even have audio isolators on my studio desktop computer and even though the computer seemed to have no ground loop problems, the noise floor still reduced greatly.

Alan.
 
"Tell me something I don't know as I have been sorting this stuff for years,"

No offence or slight intended Alan, just don't want folks to get the impression that earth loops are a new phenomenon!

"We" did not have "digital" loops* back in the day of course because we didn't have digital kit! The Home Recording market has grown up largely providing people with gear in isolation, if they have a mic, AI, desktop and even active m0nitors if all is fed from a single, double outlet they are unlikely to get a hum loop The trouble starts when peeps add extra earth gear, maybe powered from an outlet across the room**

Then "professionals" usually exchange signals via balanced systems and although these are not immune to ground loop issues (not their primary purpose) they often help a great deal. Transformers too were very prevalent on the outputs at least of desks but in this pristine, digital world it would be a shame to degrade signals if we don't HAVE to!

The classic Earth/G loop scenario for the tyro is a laptop PSU which carries thru the mains earth and earthed, active monitors. I can never understand why PSU wall rats are made this way? In the very unlikely event of a laptop chassis going live (never read or heard of such a thing) it is doubtful if the low voltage charger cable could carry the fault current anyway and blow a trip!

*There is/was a particularly nasty loop fault that could occur with Firewire systems and the fix was very obscure and known only to the MOBO vendor it seemed. So yes Al', Digital *t'appen!

**I am as guilty as anyone here but we rarely see the advice given to group ALL audio gear onto one socket diss' board and run that from one outlet? So called "star" supply.

Dave.
 
ecc83 said:
The classic Earth/G loop scenario for the tyro is a laptop PSU which carries thru the mains earth and earthed, active monitors. I can never understand why PSU wall rats are made this way? In the very unlikely event of a laptop chassis going live (never read or heard of such a thing) it is doubtful if the low voltage charger cable could carry the fault current anyway and blow a trip!
Dave.
Click to expand...

This is my main point, if we need earth on lap top power supplies, we need them on phone chargers and every other charger, but we don't? LOL

No offence taken by the way.

Alan.
 
witzendoz said:
This is my main point, if we need earth on lap top power supplies, we need them on phone chargers and every other charger, but we don't? LOL

No offence taken by the way.

Alan.
Click to expand...

Heh! At a factory where I was a sort of "toolmaker" they had a guy come round doing PAT testing (I am qualified and could have done it but they would not have paid!). He was putting PAT passed stickers on wall rats with PLASTIC earth pins! Nice lil earner if you can get it!

And, since the pulse transformer must be proofed to isolate well above peak mains volts I cannot see any point in it carrying thru an earth? Screen it inside and earth that for sure. One problem is that with totally "floating" gear you can get a capacitively coupled "tingle" and even some static build up but a one or two meg' bleed R soon fixes that.

Dave.
 
I can't see how it is the laptop, as Dave stated, the AC is converted to DC and usually runs through the battery, so technically one is always running on battery. I think there are a few laptops that will run without a battery, but usually the battery completes the circuit.

I would suspect the problem is somewhere else and the laptop being plugged in has something to do with interference with another piece of equipment that isn't shielded well or the converter is too close. Also, make sure you don't have your mobile too close or WiFi is causing it or ...
 
DM60 said:
I can't see how it is the laptop, as Dave stated, the AC is converted to DC and usually runs through the battery, so technically one is always running on battery. I think there are a few laptops that will run without a battery, but usually the battery completes the circuit.

I would suspect the problem is somewhere else and the laptop being plugged in has something to do with interference with another piece of equipment that isn't shielded well or the converter is too close. Also, make sure you don't have your mobile too close or WiFi is causing it or ...
Click to expand...

Not true, I have an old laptop use as a media player LOL, and it has a completly stuffed battery, computer goes of instantly if mains turned off, so it's not running on battery at all.

The problem with the earthing is I believe that the earth pin on the mains is connected to the neg of the low volts side (correct me if I am wrong), creating a ground which is whats causing the ground loop problems. If the supply was a proper floating supply there would be no ground loop and no chance of a mains shock, but these cost more money, you can of course buy one. Old lap tops had this kind of supply that is why there is no mains earth pin on these old supplies, but costs rule with computer buyers.

Alan
 
witzendoz said:
Not true, I have an old laptop use as a media player LOL, and it has a completly stuffed battery, computer goes of instantly if mains turned off, so it's not running on battery at all.

The problem with the earthing is I believe that the earth pin on the mains is connected to the neg of the low volts side (correct me if I am wrong), creating a ground which is whats causing the ground loop problems. If the supply was a proper floating supply there would be no ground loop and no chance of a mains shock, but these cost more money, you can of course buy one. Old lap tops had this kind of supply that is why there is no mains earth pin on these old supplies, but costs rule with computer buyers.

Alan
Click to expand...

It works when you pull the battery out and it is plugged in? Battery doesn't have to be charged (or hold a charge), just in place was what I meant. Many won't work without a battery, charged or not.
 
DM60 said:
It works when you pull the battery out and it is plugged in? Battery doesn't have to be charged (or hold a charge), just in place was what I meant. Many won't work without a battery, charged or not.
Click to expand...

Ok no worries, now I get what you mean.
Alan.
 
witzendoz said:
Ok no worries, now I get what you mean.
Alan.
Click to expand...

This HP i3 is now running just on the PSU (mind you, it started in safe mode and took fekkin ages to boot back to the forum and THEN I was not logged in!)

I don't see the problem with the power supplies. They use a bridge rectifier and a 400V cap' about 220mfd iirc., then a power FET as a switching device. The output is transformed down by a ferrite cored HF transformer and that MUST be 1000V or more capable whether the output neg supply is earthed or not! I very much doubt if a different, higher grade traff is used for the "floating" supplies?

Like much to do with good audio and computers, the computer people DGAF about us!

I know how "I" fix laptop earth loops (personal use only) but it would be irresponsible of me to post it on a public forum.

Dave.
 
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