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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 paralleled combination of gfa555se and ARC 450D (150kohm) could be too much for the LS17’s output.
Are you using the 555se’s unbalanced? because that is 100kohm where the balanced is only 10kohm.

Cheers George
auxinput
2,920 posts
 

I have read in another thread that the multiple outputs on ARC preamps are just additional outputs that are all wired directly to the single analog stage in the ARC.  In other words, this is no better than using a Y-splitter cable to feed both the X30 and the main amp.  In this situation, you could have a scenario where the combined impedance of the X30 and main amp is dropping the impedance average so low that the ARC can't drive them properly.  I don't know if this will affect the highs, but I suspect that it is possible (others on this forum will have to confirm this).

The only preamp I have found to actually have multiple output audio stages is the Classe CP-800.  You can actually use multiple outputs on that preamp at the same time without an impedance problem.

Alternative is to get something higher end like a Bryston 10B crossover.  Use the balanced outputs on the ARC to drive the Bryston crossover, and then use BOTH the low-pass and high-pass outputs on the Bryston to drive the sub/main amps.

georgehifi's avatar
georgehifi
10,312 posts
 
Use only the single ended (rca) outputs of the LS17 as they are (350ohm) 1/2 the output impedance (700ohms) of the balanced and use a "Y" splitter to rca feed to both the 555 rca input (100kohm) and 450's rca inputs (150kohm). All should be fine then.

Cheers George 
audiolover718 OP
132 posts
 
Looks like  this person ran into the same issue! LOL

https://forum.audiogon.com/discussions/arc-ref-3-main-output-impedance-question?highlight=paradigm%2...

audiolover718 OP
132 posts
 
Georgelofi, I am not directly connecting the 555 to the ARC, I'm using a paradigm crossover in line between it.  Apparently it has an input impedance of 20kohms. According to the thread I referenced, this is a not optimal, as well as using single ended and balanced simultaneously from the arcs output. 

thanks for the suggestion, but I don't have quality interconnects to go all single ended.   I might pursue having a buffer made as per the thread I referenced. Seems he was in a very similar situation, with the same crossover unit as I.  
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