ART Pro Channel II + Crown XLS1500: Problems
 

I picked up an ART Pro Channel II off of eBay. I have it running into channel 1 of a Crown XLS 1500 via balanced XLR. However, I'm having some issues.

1. Out of the box, with normal settings, there is a bad background buzz. I played with lots of settings, bypassing the compressor, bypassing the EQ, but the buzzing persisted. Then I tried setting the "tube voltage" button to "high", and suddenly 95% of the buzzing went away. I tried swapping the tubes with a different pair of 12AX7s I had lying around, but it didn't change the problem at all. The only usable setting seems to be with the "tube voltage" set to high. The normal setting is basically unusable. I'm stumped as to what could be wrong. Maybe a tube bias problem?

2. The output level seems to be too weak to drive the Crown. If I set the preamp to just below clipping, and then set the compressor stage to just below clipping, and then crank the master output level to its highest setting, I am still unable to get the "-10db" light on my Crown XLS 1500 to light up. (My Carvin BX500 is much louder even at half-volume than this combo at full blast...)


If anyone is using this setup, I'd appreciate some tips. Thanks!

On the back of the ART is a +4 / -10 button--have you tried both settings?

Yes... However, if I switch to -10DbV mode, I can't even get the -20db signal light to flicker on the Crown! Clearly +4dbU is the correct output setting with a balanced XLR...

Hmm, well I played some more with it, and the buzz is definitely worse with some basses than others, and it gets somewhat better if I move farther away from the unit. The sad part is, I don't have any noise issues with the GK 700RB-II or the Carvin BX500, so I'm not sure what is so different about this preamp.

Worse, after power cycling the unit, I was unable to repro the behavior where the buzz went away with the high tube voltage button. No clue what's going on there. It's almost like something inside the unit is producing interference which is getting picked up by the instrument, and then amplified.

Furthermore, in order to drive the input stage on the Crown XLS 1500, I have to crank the output stages on the ART to the point where the signal is really, really noisy. Lots of hiss.

I can improve it somewhat by driving the preamp stage harder and using the compressor stage to limit clipping. However, it's still really, really noisy, and the output signal is still not powerful enough to make the Crown level meter hit -10 dB.

If not doing so already, use the 1/4" output to feed the power amp, not the XLR.

Riis

Really? I would not have thought to try this. The 1/4" out is an unbalanced signal which, in most equipment, just doesn't produce the same output voltage as the balanced out. Plus, the Crown XLS 1500 doesn't have a 1/4" input, so I would need to use a 1/4" unbalanced TS to XLR cable. I guess I'll give it a try, but I don't see how this would help...

The crown has 1/4" input. It's in the rear next to the others. I'm currently driving mine via 1/4" input.

Hmm. My art is not noisy at all. I would return it for a new one...

To the OP: The graphic reads "Link / Out". The ART's XLR output is for running a signal to a mixer. An unbalanced 1/4" > 1/4" will be fine for the ART > power amp connection. Can't explain why it works but it does 9 times out of 10.

Riis

I don't know about the Pro Channel II, as I have the Pro Channel. In the Pro Channel only the first tube (preamp section) is a 12ax7. The rest are 12at7. I don't think that is the problem, though.

You should have plenty of gain available to drive the XLS (meaning there is something not right in your case) and there shouldn't be a buzz. Try using a CD player as input for example to see if the buzzing is still there. Are you using both preamp and power amp on the same mains circuit?

+1 to I would return it and get a new one.

You can use both XLR and 1/4" with the XLS. The 1/4" is an input on the XLS. The XLR on the Art has more max output. I always use the XLR on the Art to go to the power amp.

Yah... I recall the 2nd tube is a 12AT7... and I always run it at high voltage - check your +20 dB gain button next to the phone jack input setting so as to match your bass/technique - as well as the +4 button on the back - get all that sorted and you should have plenty of output for the Crown and less noise.

If so inclined - unplug the unit and open the box and loosen, then crank down on the grounding screw next to the V1 tube.

If that ground is loose the unit will buzz.

I soldered a lead from the board to the chassis ground lug - but a simple re-crank on the screw may suffice.

IIRC the 1/4" output is a balanced TRS. it's been a while since I used this unit but that's how I remember it.

Grounding, broken trace or component problem towards the front end (inpit end) of your preamp bleeding off or otherwise damping down your signal from the bass?

I'm guessing there as you say moving away from the unit changes the buzz. That can indicate something to do with grounding, sheilding, or RF interference, etc. It seems as if the pre is getting a weak, noisy signal that it can't boost enough to drive the poweramp. Could also be power supply maybe?....more guessing there on my part.

I would try it through my PA, or mixer + headphonesand try all the different routing and gain switch options. If it seems nothing works right in any configuration, it could point more towards the input of the unit. or possibly weak power in the entire unit (power supply).

I ass-u-me a used unit bought off ebay.

The 1/4" output on the Pro Channel II is labeled "unbalanced", so I assume it is. However, obviously, depending on the output drive capability of the unit, unbalanced outputs can still push seriously high voltages. However, I doubt it would be *more* voltage than it pushes out of the balanced line next to it.

I had no idea that the "Link/Out" 1/4 jack on the Crown XLS is actually an *input*. That's pretty poor labeling! :)

I'll give that a try.

With respect to the unit, it's a used EBay purchase. So no "sending it back for a replacement" I'm afraid. :(

Incidentally, I also have the "regular" ART Pro Channel which works great as a microphone preamp, but I've never tried using it as an instrument preamp because it lacks the high-impedance input which bypasses the microphone gain stage. That was something they added on the model II, so I decided to give it a try as a bass preamp.

When I get home, I'll do an A-B comparison between the two and see if I get significantly different output levels and noise differential.

I was going to mention using the 1/4" output to the Crown, if only because it frees up the XLR out for a sweet FOH or recording signal. A short high quality 1/4" unbalanced cable to the Crown isn't going to be detrimental to your signal integrity in the least, and it makes sense based on the Pro Channel's intended application that the XLR output is at a low level that won't overdrive a mixing board's input.
Since you say it was used I'm assuming the previous owner didn't include the owner's manual, so I recommend finding it online as this will likely answer many questions.

With the buzzing it sounds to me like there's something wrong with your ART.
That unit is on my short list for tube preamp upgrade, so I selfishly hope they aren't all like that. Sorry you're having troubles.
To me, on paper this sounds like a dream rig.
Good luck!

As I mentioned before the XLR max output on the Art is more than with 1/4".

I don't know where you got that info from. It sure does. It's in the back beside the mic input. I have been using the old version for about two years now and it works great with bass.

i am super cereal - check the the ground screw.