Tonight I noticed I have this annoying "hum" from my Empeg when connected to my home audio setup. I eventually diagnosed it as some sort of induction from my computer, which gets carried by the USB and/or serial cables. When either of these is connected, I get a hum. In the course of diagnosing this I realized I get a similar hum from my sound card's output. What the hell can I do to further diagnose this hum, and get rid of it? It's a low frequency buzzing humming sound you might get from an electric guitar with a bad patch cable. It's definitely related to my PC in some way but I have no idea how to get rid of it. I'd love to hear if anyone else has had such a problem.

---
MkII 080000554

Excuse me if this is too obvious, but have you checked the volume levels of the sound card inputs you are not using? I had a machine with the Microphone input set to max... Had the same effect.

Brian H. Johnson
MK2 36GB Blue
"Born to Lose..."

Good call, Bootster.

Yeah, Tony, when you play the Empeg through your home computer, is its volume turned all the way up to 0db? You should be able to play it that loud and bring the volume down on your sound card.

Also, other things to check involve grounding, inductive noise, and power supply isolation.

First: Are all your computer peripherals plugged into grounded outlets?

Second: Have you tried plugging the Empeg's power supply into a different outlet?

Third: Have you made sure that your audio and USB cabling isn't wrapped up next to the video cable running to the CRT? Or wrapped up with the power wires? Inductive noise could be a factor.

Fourth: Is the Empeg plugged into the wrong input on the sound card? It should be going to the sound card's LINE INPUT, not its microphone input.

Let us know if you get anywhere with this.

___________
Tony Fabris

Yes I thought of that one. Not the case. I remind you that it only happens when the USB and/or serial cables are connected to my Empeg. I have all my SBLive playback mixers set to Mute except WAV out, and all recording mixers set to mute as well. (further info forthcoming in reply to tfabris' post)

---
MkII 080000554

Some of these are valid possibilities I guess. Yes, my Empeg is at 0db. But I'm not actually going from my Empeg into my sound card. Here's my setup for some clarification:

Kenwood stereo receiver (most gain comes from here)
    + BST 4 channel mixer (a tiny bit of gain and equalization)
        ch1 Empeg (0db, no gain)
        ch2 SBLive sound card
        ch3 CD changer
        ch4 VCR

So, the 4 sound sources go into the mixer, are equalized and given a tiny bit of gain, and then go into the receiver. My CD changer and VCR inputs have no hum at all, even when I turn their gain up very high. This rules out any issues with the mixer or amplifier creating the noise. All cables have been switched and checked, and I've tried using the same devices on different mixer inputs. So the hum happens with the sound card, or with the Empeg when the USB/serial cables are connected. All computer stuff is into grounded (3 prong) outlets. Also, the Empeg is on the same power supply as the amplifier, but a different one from the computer. (Well, different surge protector, from the same outlet actually, but I can't really reach any other outlets.) USB and serial cables aren't wrapped up in any other wires.

I think the above info rules out all except #2. I can't really get the Empeg to another outlet without a long extension, but I really don't think power supplies are the most likely candidate, are they? I think the fact that the hum happens *only* wheh the USB or serial cables are connected means something is coming from my PC, right?



---
MkII 080000554

I really don't think power supplies are the most likely candidate, are they? I think the fact that the hum happens *only* wheh the USB or serial cables are connected means something is coming from my PC, right?

Actually, the fact that the hum happens with the data cables connected practically guarantees that you're looking at a ground loop problem- and the way the various components are powered/grounded is likely to be most of the issue.

Check out the FAQ thread titled "Common installation problems". Although this is for cars, one of the sections is about ground loops and links some documents on the subject. Perhaps it would help you to look at this information.

It's interesting- you're the second person on this BBS to complain about noise problems when sending the Empeg through a mixer. The first happened to be Doug316, the original owner of my Mark1. I wonder what it is about mixers that brings out the worst in computer equipment?

I should ask my audio-producer friend about this. His job is to work with computer-based audio mixing products and he's got a serious garage studio with multiple mixers.

___________
Tony Fabris

Grounding sounds like the culprit here. Here are a few things you should check:
- See if the PC and the stereo/mixer setup on on the same grounded circuit (Same power bar or same wall circuit)
- Check to see of the mixer is a grounded device? Does it have a three prong plug (North America, not sure of UK/Euro plugs) If not, perhaps ground it's chassis to the amplifier, simple 20 gauge single strand should suffice.
- Grab a buddies voltmeter and check to make sure your PC chassis is a proper ground, and make sure the systemboard in the PC is properly grounded to the chassis as well.

If all that doesnt solve the problem, then perhaps running the simple 20 gauge wire from the chassis of the Empeg unit to the chassis of the mixer/amplifier setup should do the trick.

Have fun! Or just simply disconnect the serial & USB cables when playing at home.

Hmmm I'll play around with grounding things or moving things to different circuits tonight. I didn't know grounding could cause so much of a problem.

---
MkII 080000554