if you had my system and $2,000 budgeted for an upgrade, where would you spend it?

Looks like a great system!

While I have no specific suggestions regarding a $2K upgrade, I would recommend that you contact Wisdom Audio and ask them what the apparently unspecified input impedance of the SCS sub is.  Powered subs commonly have relatively low input impedances, and like many ARC preamps your LS-25 (which I assume is what you are driving the sub with) has a recommended minimum load impedance of 20K.

Also, as can be seen in the schematic for the LS-25 at arcdb.ws, its two XLR outputs are wired directly together, and its two RCA outputs are wired directly together and also to pin 2 of the XLR connectors.  Therefore if the input impedance of the sub is particularly low it could be having adverse sonic effects on the signals received by the main speakers as well as by the sub.

Regards,
-- Al
 

I called Wisdom and the impedance is 25k.  Do I have any reason for concern there?

Good!  I've seen many other powered subs having line-level input impedances as low as 5K or 10K.

Also, fortunately, the input impedance of your power amp is quite high, assuming it is similar to that of the earlier pre-MkII version, which had an input impedance of 100K unbalanced and 200K balanced (presumably corresponding to 100K for each of the two signals in the balanced signal pair).

The parallel combination of 25K and 100K is an impedance of (25 x 100)/(25+100) = 20K, exactly corresponding to the recommended minimum load for the LS-25.  So not a problem!

If you are running a balanced cable to the power amp and an unbalanced cable to the sub, however, I'll add that there may be a very slight degradation in the ability of the power amp to reject "common mode" noise, due to the slight impedance imbalance that would result between the two legs of the balanced signal pair.  My suspicion, though, is that is unlikely to be an audibly significant effect in your setup.  But FWIW I'll mention that if you were to run (or already are running) XLR cables to the sub as well as to the power amp, that possibility would most likely be eliminated since both legs of the balanced signal pair would then presumably be loaded equally.  Although of course the relative quality of the sub's XLR and RCA input circuits, as well as any cable-related differences, are additional variables that enter into the mix.

In any event, enjoy!  Regards,
-- Al  
 

Marktomaras 02-04-2016 10:40pm
Would it make sense / make a difference to change only one to start with, or would I need to change all (save for the sub)?

What would be the order of importance in these connections to effect the most change?

amp - preamp
preamp - phono pre
preamp - dac
preamp - subwoofer

Lowrider57 02-05-2016 2:12am
... there are no rules on where to start; ARC preamp to ARC amp may result in the most dramatic change in sonics. Start with one cable change to see you like the sonic signature.

+1 to Lowrider’s comment.

Also, I wouldn’t discount the importance of the sub cable. For example, its capacitance will affect the signals received by the main power amp just as much as the capacitance of the cable connecting the preamp to the power amp, since both capacitances load the output of the preamp. Also, capacitance is proportional to length, and it appears that the sub cable is the longest of the interconnect cables in your setup. Finally, cable characteristics can affect ground loop issues, which can manifest themselves in ways that are more subtle than the low frequency hum they are most commonly associated with (see no. 3 below). And the possibility of a ground loop issue involving the sub, preamp, and power amp that are interconnected would seem conceivable.

Regarding order of importance, consistent with Lowrider’s comment I don’t think there is much predictability. But FWIW the following factors will work in the direction of increasing the criticality of an interconnect:

1)Higher output impedance of the component driving the cable. In this case that would probably point to the outputs of the preamp.

2)Longer cable length. Nearly all interconnect cable effects are proportional to length.

3)Susceptibility of the particular components to ground loop issues, which is generally not predictable. I’ll mention, though, that in a recent thread here there was an example of a significant sonic issue that turned out to be caused by a ground loop between a CD player and a preamp. The symptoms in that case did NOT involve hum or audible noise.

4)Use of unbalanced rather than balanced cables. Not applicable in this case.

It is common among audiophiles to consider upstream cables, starting with those connecting the outputs of the source, to be more critical than downstream cables. As you can see from the foregoing, I am not a believer in that philosophy.

Good luck. Regards,
-- Al

I am getting the feeling that the 300b IC cables are the weakest link, and that stepping those up properly to a better cable, with auditioning different options is a way to go.

To be sure that what I had to say about cables in my previous post is not misinterpreted, I'll add that I was in no way implying a perception that cables are the weakest link in your system.  Frankly, I don't know what the weakest link is.  As I said in my initial post in the thread, "While I have no specific suggestions regarding a $2K upgrade...."

Good luck.  Regards,
-- Al