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Author Topic: How to measure actual preamp gain applied (CA-UGLY)?  (Read 2333 times)

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Offline Gutbucket

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How to measure actual preamp gain applied (CA-UGLY)?
« on: August 09, 2011, 03:13:20 PM »
Like many preamps, CA-UGLY has a two infinitely variable gain potentiometers, one for each channel.  On my CA-UGLYs, each pot adjusts gain from mute (fully counter clockwise) to full gain +20dB (fully clockwise).

I use the two CA-UGLY(s) most often with four identical mics, almost always use the same mics into the same channels, and have adjusted the gain pots on them to provide output levels as closely matched as possible.. which is to say just pretty close as measured on the input meters of my recorders. 

I'd like to accurately measure how much gain I am applying to each of these four channels.  What's the best way to do that?

Gear:
I have a Behringer cable tester with a signal generator in it; I can generate test signals on the computer and play them directly, from a recorder or CD; I can record a pass-through test signal to one of my recorders and transfer the files to the computer to compare RMS levels; and I have a digital Voltmeter that I can use to measure output voltage directly.

What do you all suggest?
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Offline Lil Kim Jong-Il

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Re: How to measure actual preamp gain applied (CA-UGLY)?
« Reply #1 on: August 09, 2011, 05:57:29 PM »
If I were doing this limited to the gear listed, I would use a sine wave generator on the PC to put a signal into the pre-amp and then use the DVM to measure AC voltage on the input and output of the preamp and calculate gain from those measurements. Input test signal should be within the range expected from the mic.
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Offline Gutbucket

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Re: How to measure actual preamp gain applied (CA-UGLY)?
« Reply #2 on: August 09, 2011, 06:23:07 PM »
Any idea if the plug-in-power voltage present on the mic inputs of the preamps will present any issues for a source I plug into it (presumably the soundcard output, cable tester output, etc)?

PIP is not switchable on these, its always on when the preamp is powered.

Oh yeah, forgot to mention that I also could use the more accurate meters on the V3, but the Voltmeter should do and is probably even more accurate.  What's the calc for figuring gain when comparing two AC millivolt readings of a test sine signal?
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Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<<

Offline Gutbucket

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Re: How to measure actual preamp gain applied (CA-UGLY)?
« Reply #3 on: August 09, 2011, 08:45:44 PM »
That's just what I needed, thanks.
musical volition > vibrations > voltages > numeric values > voltages > vibrations> virtual teleportation time-machine experience
Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<<

Offline Church-Audio

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Re: How to measure actual preamp gain applied (CA-UGLY)?
« Reply #4 on: August 11, 2011, 07:24:41 PM »
That's just what I needed, thanks.

Take a known source like a cd player and plug it into the input of the preamp at low volume record one track with the preamp one with out to see the difference. In gain should be exactly 22.5 db per channel into a 10k input at max gain.
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Offline Gutbucket

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Re: How to measure actual preamp gain applied (CA-UGLY)?
« Reply #5 on: August 11, 2011, 07:43:02 PM »
Excellent, I was hoping you'd chime in, too.  Thanks Chris.
musical volition > vibrations > voltages > numeric values > voltages > vibrations> virtual teleportation time-machine experience
Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<<

 

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