Guitar Amp to Computer Hum

[philby1]

Hi
I'm getting a hum when I plug my guitar amp/mixer into my computer. I know to only expect a fairly average result, but for what I want, it more than does the job. Everything worked great. Then months passed while we had house renovations done including electrical work. When I went to plug in again, there was a hum. I dont' know if the electrical work is to blame. (I'm in Australia on 240vAC).

This hum occurs through the amp and computer speakers and is present even when the amp volume is turned to '0'. I've tried plugging into the same power outlet for all equipment as well as plugging into separate outlets. I've tried different cables. I've disconnected the power to the mixer, leaving it as a passive connection between amp and computer. Nothing helps.

I've drawn up a pdf diagram showing how things are set up. If anyone can help, I'd really appreciate it. Diagram: http://www.worldofprinting.com/recording.pdf.

Thanks,
Mark.

[steve]

Do you get a hum from the amp (more than is normal) with nothing plugged into it other than the power cord?

[philby1]

Hi
No more than I always have - just a very distant hum which only marginally increases when the volume knob is turned up. At about the 9 o'clock position where I normally play, that hum is barely perceptible.

Thanks,
Mark.

[kozikowski]

There is another poster on the forum with a similar problem. I don't mean he has hum, I mean he fixed his computer system and it doesn't work any more -- but his "new" broken computer is normal. The way he had it wasn't.

What you have now is what I would expect. What you had before is unusual. If the electric people ran grounds and repaired the cables in the walls, it's possible, now that you have everything tight, that the Mic-In of the computer is no longer able to ignore the mismatch.

The computer's Mic-In is mono and insanely sensitive. I'm not shocked that you're running audio cables between equipment and getting hum. That's normal. You're supposed to connect a free-standing microphone there, not something else plugged into the wall.

This is where we usually send people off to buy a UCA202 USB sound device. It's digital, it accepts high-level sound signals, and it's stereo.

http://kozco.com/tech/audacity/pix/UCA202.jpg

Koz

[philby1]

This sounds good and located them on eBay. Very affordable. Just one question based upon ignorance: Why do I get a hum even when the volume is turned down? I would have thought turning the volume knob to '0' would cut all power to the speakers. Thanks,
Mark.

[kozikowski]

The hum isn't coming through the sound services. It coming in through the cable shields, ground connections, and power cables.

Do you have one or more pieces of sound equipment that you can plug in "backwards?" That's a classic place where a power plug can cause problems. I have a tuner with a non-polarized plug -- goes in any direction, but it only works well one way. The other direction -- wait for it -- hums.

Koz

[philby1]

No, none of my equipment can be plugged in incorrectly. I've now ordered the Behringer interface, so I'll see how that goes. It gets very good reviews on the net, as I'm sure you're aware.

[kozikowski]

It is possible that something in your wall plates is messed up. In the US, we can buy a simple plug-in thing with three lights on it. In a proper wall plate, only two of the lights are supposed to come on. I've owned two houses and they both had at least one wall plate wired wrong when I moved in.

http://www.amazon.com/50542-Receptacle- ... B002LZTKIA

Koz

[Trebor]

http://forum.audacityteam.org/viewtopic ... 52#p131252

[philby1]

I have a further question regarding the Behringer U-CONTROL UCA202. (I'm still waiting for it to arrive so can't test it out and can't find any info on the net).

As discussed above, I have humming when RECORDING. But a second problem I have is at small get-togethers. I plug my laptop into my guitar amp with a mixer in between and use that setup for playing music, operating mics, etc. When the laptop is on battery power, that's great. When plug the laptop into mains power, humming starts (volume of hum depends on how high volume knob is).

Can I somehow fit the U-Control in the line (I guess in between the laptop and mixer)? Or does it simply not work that way - being strickly for recording?

Thanks,
Mark.