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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
georgehifi's avatar
georgehifi
10,312 posts
 
The xover as you say is 20kohm input, this combined with the se input 150kohm of the DS450 is a total loading of 17.6kohm.
The owners manual states of the LS17 regarding the minimum load for it.
"20K ohms minimum load and 2000pF maximum capacitance."

It would be nice if that LS17 was around 100ohms output impedance or less. The next best is to get the input impedance of the xover changed from 20k to say 100k, it’s just a small resistor and usually doable (1/2hr work) if the first active stage of the xover is fet input, if bi-polar there maybe offset problems.

The capacitance you can measure if you have a capacitance meter, but I dare say your interconnects will be under the 2000pf max, unless your running cheap high capacitance very long lengths.

Cheers George
erik_squires
16,008 posts
 
Easiest/cheapest solution is to get an impedance multiplier for the crossover.

Just making sure. You use 2 RCA cables to go from the ARC right? if you use a Y splitter to combine them before the crossover, that would be bad. :)

Best,

Erik
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?

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