Sub wiring help, high level speaker terminal to RCA line level Sub inputs

One other thing that I was thinking about is the effect on the audio signal after being amplified multiple times over if using the Speaker level outputs. So the pre-amp is slightly amplifying the signal, which is then fed to a power amp that is again amplifying the signal even more, which then in this case would be sent to a 3rd amplifier which would be amplifying a signal that had to be lowered by resistors in between, before finally reaching the Subwoofer itself.

Just in a logical sense to me going though that cycle seems like it has the potential to introduce more distortion to the sound than going one straight shot to the power amp.

Both approaches are capable of providing excellent results in many systems, and both approaches have their potential pitfalls. Some of my previous posts in this thread have described pitfalls that can occur in each of those cases.

As I’ve mentioned earlier potential pitfalls of the preamp-to-sub approach include the fact that the signals that are reproduced by the main power amp and the main speakers can under some and probably many circumstances be adversely affected by the input impedance of the sub’s amp, or by the capacitance of the cables connecting the preamp to the sub, or by both, notwithstanding how counter-intuitive all of that may seem. Although it appears those issues probably won’t occur with your particular equipment.

If all potential pitfalls are avoided, or do not apply to a given system, driving a sub via the power amp outputs has the potential advantage of providing the closest sonic match between the signals that are provided to the sub and to the main speakers, as was mentioned early in the thread.

Regards,
-- Al

LC-1 cables plus a pair of Audioquest splitters would be a much safer bet IMO than MSA-1 cables in a y-configuration, and the greater the length of the cables the more true that would be.

While there have been various reports and/or claims here to the effect that "splitters degrade the sound," my belief is that in most of those cases the reported findings result not from the splitter itself, but from some combination of impedance incompatibilities that can arise when a splitter is used; ground loop effects that can sometimes occur when an output is used to drive two separate components; and increased loading of outputs by cable capacitance, that can result when an output is split and is used to drive two lengthy cables.

I couldn’t find an output impedance spec on your streamer, or a spec on the capacitance of the MSA-1 cable. However given its small diameter and its double-shielding I suspect that the capacitance of the MSA-1 is far higher than the very low capacitance (12.2 pf/foot) of LC-1. If the sum of the capacitances of the cables to the two destinations is high and the unknown output impedance of the streamer is also relatively high the result would be rolloff and/or undesirable phase shifts in the upper treble, that would affect the signals received by the main speakers.

Also, if the resistance of the small shields of the MSA-1 is higher than the corresponding resistance of the larger shields in the LC-1 that could increase the chances that a ground loop issue might arise, depending on the unknown internal grounding configurations of the three components.

Based in part on my own experience with the Audioquest splitter as well as on my technical understanding of the situation I would have no qualms whatsoever about using them. And if that approach were to prove to be unsatisfactory (which I very much doubt in this case) I would feel certain that the cause is something else, such as an impedance incompatibility which your initial results already suggest is most likely not present.

Regards,
-- Al

Not sure I understand your question in the post just above. Regarding the first paragraph, a y-splitter would not be used to terminate the speaker cables. Regarding the second paragraph, the resistors would not be connected to the preamp.

In any event, the resistors themselves would not cause any kind of feedback into the power amp to which they would be connected, aside from what is known as Johnson noise which would almost certainly be audibly inconsequential in this situation. And in the unlikely event that the sub itself sent some sort of feedback to the power amp, that might have audible consequences as a result of being injected into the amp’s feedback loop (assuming the amp has a feedback loop), the presence of the resistors would reduce any such effects, not increase them. And likewise with respect to any RFI/EMI that may be picked up by whatever wiring is between the resistors and the sub.

Regards,
-- Al

One question is if the input to the Sub is only technically used as a signal, not carrying any loads, wouldn’t I simply be able to use a straight cable from my speaker terminals with RCA’s plugs on the other end into the Sub? This would provide the same function as that converter without adding in extra resistors?

You would be putting much too high a voltage into the sub without the converter. At best the result would be having to use the sub’s volume control near the bottom of its range, where the control’s resolution would probably be very coarse, and where the two channels might be summed together in an unequal manner. Also, if for some reason the sub’s volume control was inadvertently turned up too high while the system is operating damage to the sub would be possible, as well as adverse effects on your ears and your blood pressure :-)

Regards,
-- Al

P.S. to my previous post: A **possible** issue I see in looking at the converter Miller suggested is that its description mentions that it provides "D.C. Isolation for noise reduction." That may mean that it puts a capacitor in series with its inputs or its outputs. Depending on the value of the capacitor (i.e., the number of microfarads) the result could be some degree of frequency-dependent rolloff in the bottom octave or two, depending also on the input impedance of the sub’s amp (which does not appear to be specified).

But given the very low price, there doesn’t appear to be any downside to giving it a try.

Regards,
-- Al

Millercarbon’s suggestion looks to me like an excellent one in this situation. The 30 watt specified power handling capability of the speaker-level to line-level converter he suggested seems reasonable in relation to the power capability of the OP’s amp (20 watts into 8 ohms; 40 watts into 4 ohms), considering that the amp is only likely to be run near max power when the music reaches very brief dynamic peaks. Also, problems can arise when driving a powered sub via the outputs of an amp that is balanced or bridged, depending on the internal grounding configuration of the sub and the amp and on whether one sub or two is being used. But in this case the OP’s amp is neither balanced or bridged, when it is used in stereo mode.

OP, glad you found the thread you linked to, which I remember well as I was instrumental in diagnosing the problem. As you may have seen in the thread, an XLR-to-RCA cable or adapter that is specially configured with XLR pin 3 unconnected can be a suitable solution in many such cases. But many designs which provide both XLR and RCA outputs provide the same signal to the non-inverted signal pin of the XLR connector that is provided to the RCA connector, in effect splitting that signal internally. Meaning that the results of using the XLR connector in conjunction with a suitably designed adapter, while using the RCA connector to drive the other component, would likely be little or no different than using the Audioquest splitters others have suggested. (I’ve used those splitters myself, btw, in a different application, with fine results given that the output impedance of the component providing the signal was low enough to properly drive the two input impedances and the capacitances of the two cables that were involved).

In any event, though, it appears that Miller’s suggestion is the preferable one in this case, for the reason Lalit stated. The only possible issue I can envision is the unlikely possibility of a ground loop-related hum.

Regards,
-- Al