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

Showing 3 responses by georgehifi

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
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 
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
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