You must log in or register to post. Registration is free! [ Register ]

The Recording Project Forum Index -> Signal Processing

FAQ Search Photo Album!
 ART Pro Channel tube preamp humming the wrong tune
View previous topic :: View next topic 
Post new topic  Reply to topic
Author Message
PeterK505 Offline
Active Member


Joined: 02 Mar 2005
Posts: 97
Location: USA


PostPosted: Fri Feb 29, 2008 4:06 pm    Post subject: ART Pro Channel tube preamp humming the wrong tune Reply with quote

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.

_________________
.............................................................................................................................................

"Even the smallest person can change the course of the future."
Back to top
View user's profile
PeterK505 Offline
Active Member


Joined: 02 Mar 2005
Posts: 97
Location: USA


PostPosted: Sat Mar 08, 2008 5:00 am    Post subject: Reply with quote

No need for anyone to reply here. I've decided to upgrade my audio card/interface with a Delta 44, Delta 66, or Delta 1010, which all have balanced inputs (and outputs) and will allow me to insert the preamp first, though now I'll have to get a headphone amp or something like a used Omni Studio. I figure I can a) improve my noise floor, b) get better latency results over USB 2.0, and c) upgrade my D/A converters from whatever is in my M-Audio Duo to the better quality Delta series.

Now, all I need to find out after I hook it all up is that the thing still makes noise because instead of having the audio card outside my computer I'm using a PCI card. Or maybe I'll still have noise and hum because the ART Pro Channel mic preamp/compressor/EQ unit contains three tubes! Laughing

_________________
.............................................................................................................................................

"Even the smallest person can change the course of the future."
Back to top
View user's profile
PeterK505 Offline
Active Member


Joined: 02 Mar 2005
Posts: 97
Location: USA


PostPosted: Tue Mar 25, 2008 5:47 pm    Post subject: Reply with quote

Disconnected the M-Audio Duo to a configuration that uses the M-Audio Omni as a break-out box to an M-Audio Delta 44 PCI card. Connected the balanced output of the ART Pro Channel preamp to a line in at the Omni with a XLR-TRS cable. Now, I've got 100% balanced connections from the output of the preamp to the Omni. All signal levels configured for +4 dbu at the Delta Control Panel. What did it all do for the noise floor? NOTHING! Evil or Very Mad When recording, I'm still looking at a noise floor on the meters of about -54db, which is the same when I was using the Duo.

Again, using the preamps on the Omni produces no noise at all, same as with the Duo.

I can hear audible hum coming from the ART Pro Channel's electronics simply when I turn the unit on and stand by it. When setup to record, I hear noise even before I've plugged in a microphone. Trying the ground-lift switch gives me even more noise (as the manual for the preamp suggests might happen because "all ART recording gear does not have a direct connection between the audio circuit ground and the chassis ground"). One of the more bizarre things is when I alter the output for the compressor stage from fully cut to fully boosted, the noise goes from loud to softer then to loud again! If I bypass the compressor stage (eliminating the whole point of using the ART Pro Channel in the signal chain) the noise drops considerably.

If I send the preamp to ART repair for yet a third time, the techs are going to tell me I have a ground loop problem without even opening the device to see if something is not right. I've got 100% balanced connections. Noise floor with the ART Pro Channel is -54 db. Doesn't that sound wrong? Am I asking for too much from a $300 preamp with three tubes?

(For another measure of the ground floor noise I get because of any possible ground loop, I've got a pair of Alesis Prolinear DSP monitors that have a digital display for the output, and they indicate -94db when no program is sent through.)

Interestingly, it looks like a similar discussion about the ART Pro Channel and noise ended up here: http://www.sweetwater.com/forum/archive/index.php/t-293.html

_________________
.............................................................................................................................................

"Even the smallest person can change the course of the future."
Back to top
View user's profile
Display posts from previous:    View previous topic :: View next topic 
Quick Reply      
Use this form to post a quick reply without having to go through the normal reply process.    
     
Post new topic   Reply to topic    The Recording Project Forum Index -> Signal Processing All times are GMT - 7 Hours
Page 1 of 1
Jump to:  


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum