2. amps-preamps
  3. 126901-10110

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

Just discovered that my system sounded noticeably better when I disconnected the interconnects that feed my subwoofer crossover unit.  Simply having them connected, micro detail diminishes. Treble gets a little less extended. Is this what is meant as an impedance mismatch? It's obviously affecting the fidelity arriving to the main stereo amp.  Now I'm stuck with having better bass or better micro detail and sounstaging. Is there  anything I can do? I'm bummed out. The main stereo amp is fed by balanced out from the pre. The subwoofer crossover unit is fed by rca out from the pre. It seems like the preamp doesn't like feeding two things at once. This is a really upsetting discovery. It's not a huge difference, but noticable to me.  Now the system sounds absolutely incredible, but now I don't have any sub bass. 


ARC  LS 17 preamp-----main out rca to paradigm x30 sub crossover------adcom GFA555se (as subwoofer Amp)
 
Main output XLR to ARC  DS450

is this a limitation to the ARC ls17 circuitry? Would the preamps up the range not have this phenomenon? I know it's not arcs hi end model, but I wouldn't expect this from a unit at this price range. I wouldn't think I would have to have this compromise. 

Any thoughts?

audiolover718
fundsgon
150 posts
 
Check into a Velodyne SMS-1 subwoofer management system, it has speaker level inputs so may not effect your preamp. I use one with my ARC LS27 with no ill effects. 
audiolover718 OP
132 posts
 
Erik, I use two rca's from m the AC to the crossover, and two balanced cables to main power amp.  No splitters used. The signal is split internally in the preamp to all the various outputs. 
audiolover718 OP
132 posts
 
Fundsgon,

with the SMS-1, I just st wedge another set of speaker cables  at  the amp terminals? You sure there are no ill effects from doing that?

erik_squires
15,965 posts
 
I see. Yep, an impedance doulber or quadrupler would do it for you. :)
almarg's avatar
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almarg
9,670 posts
 
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

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