I've been using the Vortex 6 on the mid/high bandpass on my KF730's for about 1.5 years and have been very pleased with their sound and power for up to 4 boxes per channel in stereo mode. This is a great sounding amp. Thus I didn't bother to test it because I'm not interested in another amp for this application - I just wanted to replace the I-Tech's I use on the lows and subs.
But. Since Dan got me a gig that had something to do with fish and little kids AND I got paid...
Vortex 6Lights flickered a little with continuous 1kHz 50ms on / 50ms off signal at limiting in both stereo and parallel mode. For something new to do I plugged the amp into a Furman 20 amp PM-PRO Series II surge protector and it tripped within 3 seconds of its meter indicating 20 amps during the continuous test while I was still about a dB shy of full output. Bypassing this unit and plugging the amp directly into the 120v, 20 amp breaker stopped the tripping. Furman needs to use a longer time delay on its breaker for concert work. My Motion Labs RacPac 20 amp breaker never tripped in this testing either.
Parallel mode on this amp is not as simple as it is on the QSC and many others. Not only are the inputs wyed together internally, but the two channel outputs are as well. Thus when the Vortex 6 is run in parallel mode both channels are working together and the thing can drive loads at half the impedance of what each channel is capable of on its own in stereo mode. I ran all the tests in both modes and got the exact same results with the amp in stereo driving two 4 ohm resistive loads or parallel driving one 2 ohm resistive load.
The three LED's per channel on this amp from left to right are Power, Signal, and Clip. The first two are obvious, but the "Clip" LED is a 3 color deal that goes from green to yellow to red. Thus it never really indicates clipping until it's red, which for me took some getting used to. The limiter works very nicely and pulls the sine wave down quickly without visible distortion of the waveform. The moment the "Clip" LED turns yellow, limiting begins. If you increase the input signal quickly you can get the LED to very briefly turn red and then it jumps right back to yellow as the output signal is reduced - very nice. A final note is that in parallel mode the "Clip" LED on channel "A" alone indicates limiting and clipping, channel "B" only lights up green when driven hard. I have noticed that this amp is sensitive to overvoltage such as can occur when operating with gennys. The thing goes into protect mode around 128v or so if I remember and mutes its output. When the voltage is reduced, there is a nice ramp-up in volume as it comes back online, but I really think 120v audio gear should work up to 130v without issue.
The amp is quite efficient in transferring its heat as running this thing hard into limiting for a while and then muting the input signal resulted in the fan spinning down and turning off pretty quickly. Even at full speed the fan is not all that loud.
The sine waves looked very good at all frequencies.
Continuous loop of 1kHz sine 50ms on / 50ms off produced 74v RMS at the onset of limiting. Single 50ms sine bursts yielded the following with both channels driven to the onset of limiting.
Edit: Grammar and minor rounding error on Vortex 6 at 20kHz - changed from 34dBW to 35dBW.