Output for Pro Audio | Isn't 2V good enough?

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johnnyjo

Member
Joined 2014
I've had several discussions with people who state that miniDSP products have consumer grade I/O and would probably not suit pro audio use.

I want to create a digital crossover and use FIR filtering to tune my sound system. The miniSharc and the miniDAC seem like the perfect combo.
This setup has a few limitations when considering pro audio:
  • unbalanced output
  • no compressor (most pro audio systems have this)
  • 2Vrms output signal

Lets touch on the output signal first. I always thought that line level output meant 1V. Pro Audio balanced output is 1.23V. Why wouldn't the 2V output of the miniDAC be good enough?

Do I have this wrong?
 
Sangram

Sangram

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Joined 2002
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'Line level' is -10dBV, which is about 316mV RMS.

'Pro' level is +4dBU, which works out to 1.3V RMS.

Note the 'RMS' is extremely important. Most DACs run off 5V supplies or close enough, and thus cannot deliver 2V RMS. That is probably the P-P rating, which is 0dBV (0.775 mV RMS).
 
M

MitchMev

Member
Joined 2015
johnnyjo said:
@torgeirs
Thats why I ask about converting the unbalanced outputs of the DAC to balanced. I'm trying to get the whole system balanced. Maybe there is a circuit I can implement.
Click to expand...
You want to implement a circuit like this:

converter.gif


I've done some research in this myself, although I've never built an unbalanced-to-balanced line converter. Let me see if I can find those resources again.

A simpler way to implement would be to slap an audio transformer in there with a center-tapped secondary. Good audio transformers are quite pricey though.

Edit: http://sound.whsites.net/project51.htm

They even make ICs: http://www.ti.com/lit/ds/symlink/drv135.pdf
http://www.thatcorp.com/1600-series_Balanced_Line_Driver_ICs.shtml

Here is probably way more information than you'll need:
http://sound.whsites.net/articles/balanced-interfaces.pdf
http://www.douglas-self.com/ampins/balanced/balanced.htm

The basic idea is that you're splitting the signal and passing one path through a non-inverting gain stage and the other through an inverting gain stage. It is important that both stages have exactly the same gain (usually pretty low) and impedance characteristics (within practical limits of course).
 
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cbdb

Member
Joined 2008
Pro level is +4dbu nominal, not max level. The max level is that +4dbu (or 0VU ) plus headroom. Look at a tape machine VU meter, it goes to +3VU ( +7dbu). And you can go over that and still be ok. This is not the same as a digital 0db full scale. So real pro equipment is made with lots of headroom which means a max output level of at least 20dbu. This Neve input strip has a max output of +26dbu ! 44volts p-p.

http://ams-neve.com/1081-2/
 
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J

johnnyjo

Member
Joined 2014
So what have we got?
We've got a miniDSP board that:
  • outputs unbalanced
  • has low output levels or non-pro output levels

Are we in agreement that the output level is somewhat of an issue?
And if so, would it be worth it to look into either a transformer or circuit that can help fix this issue?
 
D

DPH

Member
Joined 2008
More likely the circuit. A daughter-board that provides appropriate single-ended to balanced conversion and amplification (if needed, check your amplifier's input sensitivity) is probably better than a transformer when galvanic isolation isn't the priority.
 
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