Originally Posted by matt_garman
I had some concerns about the Emotiva XDA-1...
First off, I got the Emotiva XDA-1 and have absolutely no problems with the amount of power coming out of either the XLR or RCA outputs (for connecting to my QSC RMX2450 power amp).
I didn't take any measurements, but I believe the Emotiva actually puts out more power, or at least is a better impedance match to the QSC. Here are my observations:
- When I first got the QSC (and started using the HK3490 as a preamp), I expected an enormous difference in available volume (nearly 4x the wattage). However, whereas we used to run the HK with the integrated power amp around "-30", we maybe averaged around "-35" with the QSC. And that was with the gain on the QSC turned all the way up.
- The front of the RMX2450 has green "signal" LEDs for each channel. When using the HK3490 as a pre-amp, the LEDs barely lit up, and when they did, they were quite dim.
- Having replaced the 3490 with the XDA-1, I find that the signal LEDs light up almost constantly, and are significantly brighter.
- With the XDA-1, I've also turned the gain down on the QSC, to less than half. Even at this point, I have way more volume than I could ever want.
I sent an email to Harman/Kardon technical support, asking what the output voltage and impedance was on the HK3490's preamp outputs. Their reply:
The max output voltage is 9V RMS. The output impedance calculates out to approximately 16k. This is pretty high for use as a stand alone pre-am. Almost makes me wonder why we bothered with the removable jumpers. The 16k source impedance would cause a signal attenuation when working into a lower impedance load. If the input impedance of the amp were equal to the pre-out (16k), it would equal 6dB of attenuation. For lower amp input impedances, it would attenuate further and for higher amp input impedances, it would attenuate less. Most power amps have an input impedance of around 100k which shouldn't cause any problems, but it could start causing problems for those which have lower input impedance.
The specifications for the RMX2450 say that the input impedance is "10k ohms unbalanced / 20k ohms balanced".
My understanding is that XLR inputs are usually balanced, and RCA is unbalanced. When using the HK3490 as a preamp, I was using RCA-to-XLR cables, so I'm not sure if that's considered balanced or not.
I'm not sure what the output impedance of the XDA-1 is (although I asked the question on their forums
Anyway, I have to admit to this being just above my head. But the impression I get from HK's response is that the 3490 wasn't really designed to be used as a standalone preamp.
Also, as a side note: for being a huge conglomerate, Harman/Kardon has nice, personal technical support. I bought my HK3490 off of ebay, which I assume means I have no warranty. Still, I was able to go to their website, send them a question, and get an actual, useful response within 24 hours. I've asked HK other questions about the 3490 before, and received similarly quick, helpful replies.