Originally Posted by FireDragon
My Sound Blaster ZxR will arriving Monday. I will be feeding the analog line outs into the Emotiva UPA-700 amplifier. As I understand it, the ZxR line outs have 2V RMS for maximum range. The UPA-700 has 870 mV RMS for maximum volume. I don't want to either overdrive the amplifier or blow my ears out by accidently using maximum volume.
Can I use the Speaker Level settings to change the maximum line out voltage? Setting each of the speakers (except the subwoofer which is separate) to -7.3db should do the trick.
If that is correct, then 100% volume would match 100% speaker volume. This would be, of course, independent of minor tweaks for room adjustment or of equalization.
Am on the right page here or do I need to add a preamp into the picture?
Originally Posted by Paul17041993
I would imagine that should do the trick, if you wanted you could try putting some resisters in the connections to dampen the output, though I'm not incredibly sure what impedance you would need and what effect it may have on the frequency response, you would want some high quality ones...
in my case I just have my computer volume set to 50% and adjust volume via my amp, I know why you need yours the other way round but the concept is pretty much the same, I wouldn't expect you would need the full 0-100% range so I don't think you could ever have it set too high for a long enough amount of time to damage the pre-amps in your UPA-700, just set the amp to a high enough value that you can get a good range in your pc volume while not too high that you pick up interference or loose the ability to go really quiet, and there's usually a point in any sound card that they loose quality after a certain volume (hitting the DAC's clip if you will).
Thanks. I thought that was the case, but I have never needed to do that. I know that I will lose a little over a bit, but as long I am using 24 bits on the sound card that won't really matter. I suspect that I will lose several more bits (possibly 5 or 6) just keeping the sound at tolerable levels.
I prefer to do that over spending another 300 or 400 on a preamp. Just an external volume control is amazingly expensive. Shame the UPA-700 doesn't have one.
I have considered inserting resistors, either directly inline or as a voltage divider. I might still do that, but then I have to build a box with its own connections and work out the electrical details. Not my strong suite, but I might do it eventually anyway. I suspect that there isn't enough capacitance to affect the frequency response significantly (from what I have seen on other posts). I know the input impedance for the UPA-700 is 47k, but I don't know the output impedance of the ZxR. I could either put a resistance directly inline which would then act like a voltage divider (the output impedance and the input impedance already acts like a voltage divider so that just makes one side larger). If I did that it would around 110K. Or I could use two in a ratio of approximately 113 :: 87 to ground that would act like a voltage divider and feed from the center point. In that case I think that they would a lot smaller, but I am not really sure. I would have to study the circuits other people have done. I would use high quality resistors, probably thin film. Since this would a fixed attenuation, I wouldn't need to worry about the noise that a pot would potentially introduce nor would I need any of the more sophisticated digital attenuation circuits (beyond my ability to design in any case).
I have another question that has occurred to me. Creative Labs sort of short changed us and used the pcm1794 for the front speakers but the pcm1798 for the satellite speakers. The pcm1798 is not as good, but has the exact same pin out and from what I can tell is used identically. I am wondering if swapping the pcm1798s for pcm1794s could be a straight drop in with no other consequences (assuming I can do the soldering). The only thing I couldn't figure out is how the 1794s determine the output voltage level which can be 2V, 4V or 9V where the 1798 is 2V only.