I own the Outlaw Audio 7700 amplifier which I used to power my 3-way active open baffle loudspeaker pair, but I was planning on building another 4-way active system. Of course, this necessitated buying an additional amplifier, hopefully with the same voltage gain. I ran across this thread, along with a couple of others from different forums, where the 7500/7700 voltage gain was in question. I noticed on the ATI site on their specification sheet for different amplifiers, the ATI AT2000, which closely resembled the Outlaw 7500/7700, that for RCA inputs the voltage gain was listed as 34 dB, whereas the Outlaw Audio manual stated a 28 dB gain for RCA. Also, the XLR input gains for the ATI AT2000 were stated as 28 dB, but the Outlaw Audio with XLR inputs were stated as 34 dB. I began to suspect one or the other was wrong, with the Outlaw Audio manual being highly suspect.

Then it occurred to me that I could simply measure the voltage input and output and calculate the voltage gain of the amplifier. Note that this is all a moot point since I have purchased a used 7500, so I can be assured of an identical voltage gain regardless of whether the stated gains are reversed or not. But I figured I would post this here for future reference, just to set the facts straight.

I used a 400 Hz sine wave output generated by TrueRTA to a USB sound card to test all 12 channels of both amps with no loudspeaker load. I measured the output from the sound card (the amp input) and each amplifier output with a Fluke 87-V, a true RMS multimeter with a wide bandwidth. If you have an inexpensive multimeter, you may use 60 Hz as the sine wave output since most meters are accurate at that frequency. The measured sound card output was 248.2 mV (.2482 V) with RCA outputs and between pins 2 & 3 on XLR outputs. I then averaged all 12 channel outputs, which turned out to be 12.59V with an RCA input and 6.485V with an XLR input. Notice right off the bat the roughly 6V difference in channel output between the two. It sort of lets you know what's going on here and what the calculations are going to reveal, and why the voltage gain is 6 dB lower for XLR. Remember, by its differential design, the input voltage will be double that of RCA.

Gain in dB = 20 * LOG10 ( Gain Factor )

RCA Gain in dB = 20 * LOG10 (12.59 / .2482) = 34.10 dB
XLR Gain in dB = 20 * LOG10 (6.485V / .2482) = 28.34 dB

So they have been reversed in the Outlaw Audio manual. But one thing that is still a mystery to me is that the Outlaw Audio 7900 and ATI AT6000 and AT4000 specifications state the voltage gain is identical for either XLR or RCA inputs at 28 dB. Hmmm...