ART Digital MPA default vocals setup?

S

skycanyon

New member
I'm using the first-version ART Digital MPA as a preamp to record vocals. (The mic is an Audio-Technica 4040.) When I followed instructions to set controls at a default level, I couldn't get the predicted response. The manual says:

"Start by turning down the Input Gain knob and centering the Analog Output knob. Use the analog meter to view the operating level by depressing the switch under the center of the analog meter. The meter will now indicate how much tube headroom there is. [None of the switches under the meter do anything like this.] Set the +20dB switch to the out position. Increase the Input Level knob until the meter reads above –10dB. If you have turned the input knob fully clockwise and the indicated level is still below –10dB on the meter, center the input knob and depress the Gain switch. Increase the Input Gain until there is sufficient level. This procedure optimizes the gain elements to provide the widest dynamic range possible."

For one thing, no knob cranking I tried would budge the meter needle. Not even cranking up all gain and output knobs. And pressing the +20dB button.

I finally set gain and outputs at 3/4 and then created a conversation-volume signal near the mic. That moved the preamp indicators to the expected levels. In a subsequent test, Reaper recorded this input as expected.

Before I go charging ahead with my workaround, is there something I should know about this deviation from the manual?
 
Did the second channel give you the same result? Did you turn the phantom power on?

You shouldn't have to turn the gain up that much with that mic.

Did you have the meter set to read the output or the tube? Do you have the pad engaged on the 4040?

Maybe the tubes need replacing. Maybe the meter is out of calibration.
 
I haven't tried the second channel because it never dawned on me that one of channels in my rarely-used preamp might be broken. I'll try that next. Yes, phantom power has to be on or I get nada. Meter reading the output. No pad. I suppose the channel test might be a clue as to tube condition?
 
Test on channel 2 same results. Being a newbie, not sure how to test the tubes. Or calibrate the meter, which seems secondary but necessary.

Per your comment about the abnormal gain setting, here's more detail about which knob is where. Input Gain at 3/4 of rotation, Digital Output maxed, Analog Output at 1/2 of rotation, Input Impedance straight up (600).
 
What are the meter readings in Reaper? That's really what counts. Digital output shouldn't have to be maxed out either. Set your levels to peak in Reaper at about -18dBFS to -12dbFS no need to be louder than that on any individual track.

I would say you need to replace the tubes. Maybe the previous owner left it on all the time. Could also be the power supply for the tubes is bad.

Pay the $5 for matching, it's worth it if you ever want to record in stereo. Avoid Groove Tubes they are shit.

The JAN tubes are great for audio. I have JAN 12AX7's over 30 years old that I am still using.

www.thetubestore.com - JAN-GE 12AX7WA Audio Tubes

I put these in my Rivera Quiana55 amp, a matched set of three. They are quiet and sound great.

www.thetubestore.com - Tung-Sol 12AX7 Audio Tubes
 
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I think what they left out of that instruction is you should be speaking or singing into the mic while setting those levels. If your room is quiet the meter isn't going to budge until you start getting into really high gain values. You're not recording silence!

Also what is left out of the manual is that a reading of "0" dBVU is outputting +4dBu at the analog output.

According to the manual the "tube" setting is just telling you how much headroom you have depending on the setting of the plate voltage. If you want the cleanest amount of tube headroom use the "high" voltage setting. If you want a little bit of tube grind use the "normal" plate voltage setting.

Keep in mind that "0" dBVU (analog) is roughly the same as -18dBFS to -20dBFS (digital) under common protocols used in the US and Europe.

IHNFI how you would calibrate the meters to properly display tube output on that device. You would need a copy of the repair manual.

http://en.wikipedia.org/wiki/DBFS

http://www.sengpielaudio.com/calculator-db-volt.htm
 
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Thanks so much for all the relevant details. I'll check to see what's arriving in Reaper and then return here.

I'm the original owner on all this gear. It took me years to put together my equipment and find a place to set up. Now that the pieces are in place, most of them have been sitting around generally unused.
 
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