Hello everyone!

I have an HP laptop + a Presonus Firebox. NO Performance problem! I always use it with headphones since it is my home daw. After several months of having it I discovered a very strange noise problem:

All the line outputs make a very strange noise. It is not hum. It is like 'computer interface' noise, like if I could head all activity happening in the laptop (disk activity, mouse, etc.).

Before going further, let me know that I tried to debug the problem so I tried every possible combination. This is the rarest thing:

Firebox connected to the laptop via FireWire cable. No inputs connected to Firebox, just the line output to the amp. The Firebox is TURNED OFF, without power supply connected. Still, the noise is there!!! Also, the noise totally disappears when I run the laptop with battery. It means:

1) Almost sure it is not a defective Firebox (happens in every output and with the unit off)
2) It is not the audio cable (tried different ones)
3) It is not firewire cable or chipset (I have the onboad Ricoh chipset and an Expersscard TI chipset. The same with both with different FW cables).

anyone experiencing something similar? Could it be the laptop power supply? would a bad laptop power supply 'pass' the noise to every port of the computer? If so, is there any laptop ac filter? I tried connecting to different sockets, even putting the amp to one socket and the pc to other. Still no luck.

i would appreciate any help. I searched the web, and some people had the same problem. Still no concrete answer. Have in mind that it is not a regular audio noise (hiss, 60hz hum, etc.)

Thank you very much,

Have a nice weekend!

Danny Bullo

me again...
after reading a lot about if (I was desperate) this is the conclusion I have:

1) Buy a 3 prong to 2 prong adapter and use it between the laptop power supply an the wall socket.

2) Buy this hum isolator:

http://www.amazon.com/exec/obidos/ASIN/B0002E4YI8/ref=nosim/coffeeresearch99212-20

Some people say it is NOT SAFE to rand a 3 to 2 prong adapter. Is that true? It would be for the laptop, not for the power amp. Should I buy that eliminator (around $60)

Thank you

Danny Bullo

Danny,

Using a 2-prong adapter defeats the safety ground, so it's not safe.

You said that you "always use it with headphones", but later you mention a power amp. Where do you plug your headphones in: Firebox or amp? You need to tell us about this amp. Brand, model, etc. Does it have balanced inputs? Anything else plugged into the amp?

Based on your description of the noise, it is digital noise from your laptop coupling into your amp. If your amp has balanced inputs, you may be able to control the noise by disconnecting the shield on the laptop side of the cables to the amp. I can point you to a wiring diagram if you need it.

I wouldn't buy the hum eliminator: you have a digital noise problem, not a 60Hz hum problem.

Murray

Thank you very much for you answer, MurMan!

When I got no noise from the headphones was from the headphones jack on the audio interface.
Then amp is a regular guitar amp. I use a regular 1/4 inch cable from the Firebox to the Amp.

Based on your description of the noise, it is digital noise from your laptop coupling into your amp. If your amp has balanced inputs, you may be able to control the noise by disconnecting the shield on the laptop side of the cables to the amp. I can point you to a wiring diagram if you need it.

do you mean instead of using a 3 to 2 prongs cable, alter the firewire cable running from the computer to the audio interface?

As I said, the noise occurs even with the audio interface turned off, when the firewire cable is plugged.


I will try a 3 to 2 prongs adapter. It if solves the problem, I now what it is and I can go ahead and buy
Ebtech Hum X Voltage Hum Filter

which is similar to 3 to 2 prongs, but safety.


can yo pass me that diagram?

thank you!

Danny Bullo

UPDATE:

I put eh 3 to 2 pongs adapter in the laptop power supply and the noise disappeared completely. Thank you all.


now the thing is...is it worth that device for 80 bucks?

I'm from Argentina and currently living in New York. I know a lot of apartments that are ungrounded (2 prongs). I dont know from anybody who suffered any electrical shock for using a laptop. Of course....high consuming devices such as freezer can be very dangerous......but can a laptop be really dangerous?

;)

Danny Bullo

When I got no noise from the headphones was from the headphones jack on the audio interface.
Then amp is a regular guitar amp. I use a regular 1/4 inch cable from the Firebox to the Amp.

Regular guitar amps have unbalanced inputs (TS 1/4 inch connectors). The special cable and wiring diagram that I mentioned won't help you because it requires an amp with balanced inputs (TRS 1/4 inch or XLR connectors).

do you mean instead of using a 3 to 2 prongs cable, alter the firewire cable running from the computer to the audio interface?

No, the fireware cable should not be altered in any way. I was talking about altering the audio cable from the audio interface to the amp. Now that we know it's an unbalanced amp, you can forget about this suggestion.

I'm from Argentina and currently living in New York. I know a lot of apartments that are ungrounded (2 prongs). I dont know from anybody who suffered any electrical shock for using a laptop.

Dead men don't talk. Dark humor, but you get my point?

Of course....high consuming devices such as freezer can be very dangerous......but can a laptop be really dangerous?

This is a common misconception. The danger of electrical shock from a device is not related its power consumption. You can be electrocuted by touching a 3 watt night light with a broken bulb. Laptops with external power supplies may be safe (depending on the design of the power supply) to use with a two-prong adapter, but there is absolutely no way that I or anyone else on a forum should advise you to defeat any safety device.

I put eh 3 to 2 pongs adapter in the laptop power supply and the noise disappeared completely. Thank you all.

now the thing is...is it worth that device for 80 bucks?

I looked at the Amazon listing and see that there are two Ebtech devices. One of them is for ac power and the other is for audio lines (1/4 inch phone jacks.) My guess is that the ac power version will not help your problem because it isolates the hot and neutral wires with a transformer but I'm assuming that it doesn't isolate the safety ground. Based on what you've described, the safety ground is part of the noise signal path, so this device isn't the answer. The audio version probably will eliminate the noise because it will isolate the laptop ground from the amp ground, but it is an audio transformer that will color the sound. However, guitar amps are not studio reference monitors, so the effect of the transformer probably can't be heard.

Grounding problems are really hard to diagnose on a forum. (That's why you don't see a lot of other people jumping in here ...) Good luck.

Thanks a lot MurMan!

Good vibe, dude!


I guess I'm moving soon, so maybe it is that apartment, that has a terrible grounding, hehehe.


Thanks again!

Danny Bullo

Hello! I own a presonus firebox and I'm having the exactly same problem. I've been using a home stereo system to "monitor" (I mean, it's a home stereo system!) my recordings, and the noise was there, but not very annoying, so I just left it alone.
 
Now I've bought a pair of presonus Eris 5's and now I realized how crazy loud this is! It's unbearable.
 
I am using a desktop computer connected to the firebox through a 6-6pin firewire cable. The firebox is connected to the monitors using TS cables (unbalanced). They're all connected to a 1KVA voltage stabilizer, which is connected directly to the AC outlet (which is 220V, btw)
 
Could the TS cables be the source of the problem? I wonder if I should get rid of the noise it by using balanced TRS cables, since both the interface and monitors have balanced TRS jacks.

Absolutely yes!  A very quick look into this issue and you will find thread after thread where the problem was solved once proper balanced cables where put in place. TS patch cables are for your guitar, studio gear should all be connected with balanced cables. Don't buy gear that does not have balanced connections. 
 
And with the OP above, you'll notice he originally said: 
2) It is not the audio cable (tried different ones)
 
But he does not say those other cables were balanced so his conclusion was most likely wrong.
I like the other thread where the noise was coming from a frigggn wireless router sitting under the desk! Duh! How many times does the word Wireless have to be repeated before people get it.  

Thanks, Cactus Music! I put the TRS cables and they work awesome! Noise is not 100% gone, but it's like 99%.
 
 
Althought now I have another issue. I have a Behringer XENYX1202 mixer, which both main out and ctrl room out are unbalanced TS. I wanted to hook it up in to the monitors (Eris 5s), which are TRS.
 
 
Should I not do this and instead leave the the monitors connected to the firebox's output (TRS) ?