Newbie Gain Staging ?

  • Thread starter Thread starter Guinness_Bottle
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Guinness_Bottle

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Hey folks...I have been bouncing around sites and really found this is my wheelhouse...because I'm a real n00b when it comes to fundamentals...

I got a pretty simple issue......

I have an ART PRO MPA II that I not only want to use as a mic pre, but as a line amp too to bounce my sounds and vsti's through.

I know my AI puts a line out signal of +16db....sooo.....I understand I need to pad the line out.

I was wondering if an inline pad @ -50 would suffice or using a passive DI like ART Zdirect which can attenuate -40db

The only problem I have with the inline pad is I would be going from TRS out ->> XLR Pad In -->> XLR Pad out to XLR in

than XLR out to TRS in (because I need to use the Line In not the Mic In to bypass the AI's mic pres, right?)

The above config seems a little wonky...even though a balanced signal all the way through isn't really an issue as it's a bedroom and a very, very short run.

Am I doing this right for what i want to do?

Any help is appreciated and thanks in advance!
 
Your audio interface will only put out +16dBu (you didn't specify dBu or dBV) from Full Scale digital (eg. say -0.1dB FS).

I'd probably not drive the interface that hard.

From the ART operation manual download, the preamp has a minimum 0dB gain, and you can turn down the output.

However, I could not see an input pad.

-50dB pad is extreme. I'd maybe try -12dB which would take the maximum +16dBu output down to +4dBu. Run the variable input impedance at its maximum.

For cabling, just get on to Blue Jeans cable and order a cable with TRS at one end, XLR at the other. Or use an XLR-XLR cable with an XLT-TRS adapter. Then you can use a standard XLR barrel pad.

There's a few ways you could do what you want. Hope this helps.

Paul
 
I know my AI puts a line out signal of +16db....sooo.....I understand I need to pad the line out.
Click to expand...
It doesn't "put out" a signal of +16dBu -- The circuit fails at +16dBu.

If your converters are calibrated to -16dBFS (they're probably really close if not right there) well, as mentioned, I wouldn't run that unit too hot.

For the most part, I think you're over-thinking things... Bring a mic up to somewhere in the 0dBVU area and be done with it (you'll probably "automatically" have levels peaking around -12 or -10dBFS digitally speaking). When you're using line-level inputs, the same rules apply -- It's the output voltage that's going to be your best friend or your worst enemy...
 
Massive Master said:
It doesn't "put out" a signal of +16dBu -- The circuit fails at +16dBu.
Click to expand...

John, without knowing the device or its specs, how do you arrive at that conclusion?

Surely the specified maximum output signal is exactly that?
 
OK, so let me see if I got this right....

In a nutshell, line in to a mic in on the pre is, essentially, just a mic level with the input gain on the pre cranked up??

So, just knock a little off with a pad and find the sweet spot on the variable impedance?

Again, thanks for the input guys
 
John, without knowing the device or its specs, how do you arrive at that conclusion?
Click to expand...
Point - I thought that number (given in the first post) was a bit low. The spec number is +27dBu which I don't believe for a second.
In a nutshell, line in to a mic in on the pre is, essentially, just a mic level with the input gain on the pre cranked up??
Click to expand...
This is confusing me too -- It's either a mic in or a line in. Mic level signals are very low and require and amplifier stage to get the signal to line level. Line inputs won't have that stage (or there may be a bypass for that stage via a MIC/LINE switch or something).
 
Well, it's really just a mic pre.. there is no "line in" or a setting on this amp...

There are Mic (XLR) In and Hi-Z In...

So from my understanding...the only thing I needed to do was match the input levels close to what the amp wants to see....The variable impedance setting makes impedance matching irrelevant.

Of course, this would be a non-issue if not for the unconventional way I want to use the pre.
 
The Hi-Z inputs are line level (well, adjustable instrument/line level).
 
Massive Master said:
Point - I thought that number (given in the first post) was a bit low. The spec number is +27dBu which I don't believe for a second.
Click to expand...

@John: I'm still scratching my head here, John! I don't think that the OP has stated which audio interface he/she is using... :confused:


@Guinness_Bottle: the input spec at the XLR inputs for your ART preamp is +19dBu (balanced), as taken from the user manual. Those figures will assume that all gain controls are at minimum, and the output control set at its central position (no gain or attenuation).

My advice: You can see how things go without a pad between audio interface and the ART. If necessary, lower the signal level coming from the audio interface from software. Alternatively, use a fairly conservative pad, say -15dB or so, between audio interface and pre-amp.

I suggest that the variable impedance on the ART be set at maximum, as the audio interface may not like driving lower loads.

If you are taking audio back from the ART into the audio interface, you can use the ART's output level control to get appropriate levels for the inputs on your audio interface.

Hope that helps?

Paul
 
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