Don't think my preamp likes feeding signal to two seperate places.

Erik, note in the initial post that he is connecting the LS17 to the DS450 power amp directly, via XLR.

Treble gets a little less extended.

If the cable length from the LS17 to the crossover is particularly long, and/or if the cable has high capacitance per unit length, that could be a contributing factor in addition to the impedance issue that has been cited. The capacitance of the cable to the sub crossover will affect the signal received by the DS450 essentially the same as if the only cable present on each channel was the one connecting the LS17 to the DS450, and if the capacitance of that cable equaled the total of the capacitances of the two cables you are using. In either case, given that all of the preamp’s output connectors are driven by a single output stage, a low pass filter would be formed by the interaction of the preamp’s output impedance with the total of the cable capacitances that are present. If either cable is particularly long and/or has high capacitance per unit length the high frequency rolloff and/or phase shifts introduced by that filter could occur at frequencies that are low enough to be audible .

Would the preamps up the range not have this phenomenon?

While I don’t have specific knowledge of all of the recent high end models, just about every one of the many spec sheets I have seen for ARC line stages and preamps at www.arcdb.ws indicates a recommended minimum load of 20K. And just about every one of the many schematics I have seen shows the output connectors that are provided for each channel all being driven from a single output stage, with the RCA connector connected directly to XLR pin 2, and with the two XLR connectors (if provided) connected directly together.

Regards,
-- Al

P.S. to my previous post: Now that I think of it, even if the SMS-1 wouldn’t create the problematic circuit path I described above, a similar path might be created via the SMS-1’s connections to the Adcom amp, and then via the Adcom amp’s safety ground connection (assuming it has a three prong power plug). Sheesh indeed :-)

what if I used balanced to SE converters and used the other currently unused balanced output on the preamp.

That should work ok provided that the chosen converter has a relatively high input impedance, so that the parallel combination of that impedance and the input impedance of the DS450 is not too low for the preamp to handle comfortably. (Keep in mind that the preamp’s two XLR output connectors for each channel are undoubtedly wired directly together, and driven by the same output stage).

It’s never been clear to me if ARC’s 20K minimum load recommendation applies to the balanced outputs or the unbalanced outputs or both. But to be safe in this case I think it would be preferable to look for a converter having an input impedance of 47K or more.

Good luck. Regards,
-- Al

Regarding the SMS-1, the one concern I would have about connecting it to the DS450 outputs relates to the fact that the DS450 is a differentially balanced amp. So presumably its negative output terminals as well as its positive output terminals have full amplitude signals on them. The concern would be that depending on the internal grounding configuration of the SMS-1 and the design of the external 12VDC power supply it apparently uses, that a low impedance path might be created from the amp’s negative output terminals to the circuit ground of the SMS-1, then through some unknown but possibly low impedance to the AC safety ground of the SMS-1’s power supply, then via the AC wiring to the amp’s AC safety ground, then probably through a low value resistor within the amp to it’s circuit ground. In effect possibly putting a near short circuit on the amp’s negative output terminals, and applying a much higher voltage across that resistor than it was designed to handle.

If the SMS-1’s power supply had a two-prong AC plug (i.e., a plug that doesn’t have a safety ground connection) I would be confident that wouldn’t be an issue, but photos I found online appear to indicate that it has a three-prong power plug, which leaves me uncertain.

So if you decide to go that way it I’d suggest asking Velodyne what the impedance is between the SMS-1’s negative speaker-level input terminals and the AC safety ground pin of its power supply. If it is high, or if those points are electrically isolated from each other, there won’t be a problem.

Regards,
-- Al

Fundsgon, I see no indication in the manual or the datasheet for your amp that it has balanced (or bridged) outputs. So as would be the case with most amps I don’t see any problem using the SMS-1 with it.

And I would expect that even in some and perhaps most cases involving amps having balanced or bridged outputs there would not be a problem; as I mentioned earlier it would depend on the internal grounding configuration of the SMS-1 and the other components that are involved. But in the absence of specific information to the contrary I would not rule out the possibility of a problem arising if it is connected at speaker-level to amps having balanced or bridged outputs.

Regards,
-- Al