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
almarg's avatar
Ag insider logo xs@2x
almarg
9,670 posts
 
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
fundsgon
150 posts
 
Sheesh! Al, I have to ask u how the SMS-1 would interact with my classe Ca-m300 mono blocks? I used zip cord to connect the SMS to the speaker terminals on each amp. The SMS power supply is an external dc unit.

almarg's avatar
Ag insider logo xs@2x
almarg
9,670 posts
 
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

atmasphere's avatar
atmasphere
11,651 posts
 
Does the crossover have outputs for the mids and highs? If so, even if they are single-ended, this would be worth trying.

Some of the ARC amplifiers that have allegedly balanced differential inputs really don't do well with single-ended inputs (which indicates a radically  poor Common Mode Rejection Ratio spec). This is so profound with some of them that if operated single ended they have lower power and much higher distortion. But if your amp is not one of those types this would be worth trying.

(FWIW our amps behave the same whether the balanced or single-ended input is used.)
koestner
632 posts
 
I have had the same experience. I got a Musical Fidelity Tube buffer that has a 300K input impedance. I stuck it between the pre out and the sub in. Now the overall input impedance was raised quite a bit and it effectively removes the sub from the circuit.
More to discover