Guitar Amp to Computer Hum

[kozikowski]

One of the two main reasons that broadcast and high end entertainment corporations are not wired with consumer cables is this exact problem. Consumer equipment has the shield and case of the equipment as part of the signal because it's cheap to do that and in most cases it doesn't matter. This means a portion of your show appears on the ground prong of your power plug.

Broadcast systems don't do that and you can connect very different audio systems sometimes on different floors of a building and never know the difference.

The equipment most likely to cause ground problems are the power and speaker amplifiers because of the high energy they use. Any imbalance in their power plugs or wall sockets appears in the sound. Sometimes you can use one of those ground lifters -- two to three prong adapters on the power amplifier to prove where the problem is coming from. Leaving it that way is dangerous and so fixing the hum after the fact may prove to be interesting.

Koz

[philby1]

Hi Steve

Thanks to your significant help, I've got a result. Not the result that I envisioned but one I'm very happy with.

I'm not using the amp for monitoring but the headphones which are connected to the UCA202. The clarity (and lack of hum) is stunning. Last night, I recorded a 5-track piece of blues (rhythm, bass and three lead guitars each taking their turn). The result is amazing - despite my playing abilities! If I want to monitor via the amp (in the case that others are playing along and need to hear as well), I ran a lead from the headphone jack to the amp & ran the amp just at low volume. There's a hum there to a degree but it's not recorded. I'm going to purhcase an el-cheapo hum killer off eBay and stick in the line. I'm spending so little that if it doesn't work, it doesn't matter.

Thanks again for your help,
Mark.

[steve]

Cool, glad it's working for you. Do let us know if the "hum killer" works.

[philby1]

Hi Steve

The hum killer arrived today. Works perfectly. 100% of hum is gone! Now, with that, the Behringer UCA202 U-Control and Behringer Xenyx1202FX, I'm able to both monitor via my amp and record to Audacity in crystal clear sound. Very happy with it.

The hum killer is an eBay special: http://www.ebay.com.au/itm/GROUND-LOOP- ... 5d25fb6fd1. The pack shows it's brand as IMC and, supposely, for use in a car. Max. Input: 15amp. Frequency Response: 20Hz-30KHz.

Thanks again for all your help,
Mark.

[Trebor]

The hum killer is an eBay special: http://www.ebay.com.au/itm/GROUND-LOOP- ... 5d25fb6fd1. The pack shows it's brand as IMC and, supposely, for use in a car. Max. Input: 15amp. Frequency Response: 20Hz-30KHz.

magic_black_box.jpg (21.49 KiB) Viewed 1890 times

What's in the magic black box ?, isolation transformer ?

[philby1]

Yes. It terms it an "Isolation X'fmr coupled circuit".

Mark.

[kozikowski]

I wondered. Transformers need to be pretty big to "vanish." That Radio Shack thing has a frequency response of 300 to 5000 - slightly wider than a telephone, which is probably where they got it from.

Yes I'm reading from the back of the device packaging.


This is the Real Thing:

http://cgi.ebay.com/2-X-JENSEN-JE-11P-1 ... 0560881064

Koz

[kozikowski]

You can get small transformers to go down to lower frequencies, but they start sounding gritty down there. There are also ways to do it without a transformer, but if the device says that's what's in there, then that's it.

Koz