Joined: 02 Mar 2005
|Posted: Fri Feb 29, 2008 4:06 pm Post subject: ART Pro Channel tube preamp humming the wrong tune
| I am having a noise problem with my preamp (an ART Pro Channel, which is their combo tube mic preamp/tube compressor/tube EQ), so much so that the preamp is unusable. I'm not sure if it's a ground loop problem or if some device that is plugged into the electrical system is causing interference. I recently had a pot replaced on the preamp and it was apparently tested and checked out okay, so I'm assuming the problem is not the unit itself.
A small test using a noise filter plugin did help identify the noise at 60Hz and multiples of 60Hz thereafter (but some buzzing was still present), which would be typical of a ground issue, but of course I do not want to rely on the filter plugin and need to remedy the problem. I can't work with the building's electrical wiring because I'm in a rental apartment, and for all I know a neighbor has a dimmer switch or something else installed nearby on the circuit causing noise. I didn't have this kind of noise when the apartment below me was vacant. I don't know if this makes much sense, but if you are having a problem caused by a ground loop, and you plug in the device using a plug adapter to remove the ground pin, shouldn't whatever noise caused by the ground go away? I tried this and used an adapter to plug in the ART Pro Channel without the ground pin on the AC cord and still got the same level of noise and hum.
What I'm hoping is if I insert one of those dual transformer hum eliminators (such as the ART Hum Eliminator you see here http://www.artproaudio.com/products.asp?type=90&cat=13&id=106 ) it will clean up the signal, but I don't know if this would be a waste of time to try in my case.
Part of the problem is I don't have the most compatible setup, but it has worked up until now. I have used the ART Pro Channel tube microphone preamp as a quasi-mixer channel strip that plugs into the line level input (1/4" unbalanced) of my M-Audio USB Duo interface/audio card, which contains a built-in M-Audio DMP2 mic preamp for each channel (and FYI using a mic straight into the M-Audio yields no noise at all compared to the ART preamp). Using the line level input is the only way to bypass the M-Audio's preamps. The ART Pro Channel preamp does have an XLR balanced output, but plugging this into the M-Audio USB Duo interface with the XLR balanced mic inputs going through the built-in preamps is like chaining two preamps together in series (not a good idea).
Does it sound feasable to get rid of the hum--to insert a dual transformer of the type listed above between the unbalanced output of the preamp to the unbalanced line level of the audio interface? I can switch the line level inputs on my M-Audio interface to either +4db or -10db, but the M-Audio manual has them labelled as "unbalanced." Is it wishful thinking to think you can plug an unbalanced signal into a "hum eliminator" and then back into an unbalanced input and get a significant noise reduction? Would something like an AC power conditioner be a better idea? I'd appreciate the advice of anyone who has fixed this type of thing.
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