I wanted to try a passive rotary mixer. I ended up finding something small that does the trick from Rolls, and I already had another piece of gear (sum box from Phonopreamps.com) that proved useful. The Rolls is too small and awkward to gig, but it's allowed me to test the concept.
I found the potentiometer-based method from line-outs for mixing was pretty good, though when attenuated I found the highs rolled off ever so slightly and made the bass a bit mushier than the source. In that arrangement, I also used the headphone outputs on the players to a resistor-based sum box where I could select one or more units to pre-listen.
Sound quality improved slightly, from what I could hear and certainly that's not empirical, when I swapped these two. I awkwardly controlled channel volumes with the headphone pots on the back of the units, summed with the resistor-based sum box, and monitored by headphones using the Rolls unit fed the players' line outs. I also tried swapping out the Rolls for just a normal powered DJ mixer with tone controls.
Even though I was inputting all these into a DSP set for consumer nominal signal and running pro nominal from the players, the headphone jacks seemed to pump out not just a hotter signal, but one more tolerant of the extra passive resistance further down the chain. That surprised me.
Anyway, it was educational, but I've hooked in a digital mixer for now and am going SPDIF from the capable players, then digitally to the DSP. More flexible and fewer cables. The digital mixing does present a certain tone, but the mixer uses single-purpose TI chips, so I wouldn't be surprised if what I'm hearing in "tone" is actually a lack of analog scrim over the signal in combination with the reflections off of the walls in this untreated room rather than any signature from processing. I don't hear this tone with headphones. I think with most analog mixing and/or additional DA/AD conversion stages, the midrange, which is most easy to hear first reflection distortion in the room, loses just enough fidelity to make that distortion harder to differentiate. Curiously, the lower treble "slap" from the walls is obvious regardless of the mixing method.
I will say, though, that in the past with a pure analog sound system, regardless of the source, the best powered analog DJ mixers with active mixing buses have tended to provide something special and transparent that additional AD/DA conversion steps seemed to rob it of. I'm running big horn subs, though, so I need the DSP to get proper delays.
Last edited by Reticuli : 10-15-2015 at 03:34 PM.