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

rhern213, sorry for the bad advice above. I've actually done this. The simplest solution is a Line Out Converter or LOC 
https://www.parts-express.com/stinger-sgn111-30-watt-fixed-line-out-converter--268-482

This is simply a couple of resistors between the wire inputs and RCA outputs. One resistor drops the amplifiers output voltage down to line level, the other provides the impedance load to whatever the output component needs- the sub in your case.

My integrated amp didn't have a pre-out and so when my new sub amp had like yours only line-level inputs I researched this to death before modding my amp. In my case I am comfortable modding and installed the parts inside my amp. It does look better that way. Electrically however it is identical to the above LOC, which I'm sure you will find a whole lot easier to use.

Why not send it back for a replacement with Rythmik subs that comes with high level speaker input. I see no reason to apply ‘band-aid’ solutions being suggested by Rythmik fanboys.

Or you can excercise Option 4. 

IMO, using high level input connectors offers the best possible integration with your mains speakers.

“The high-level input is designed to accept the stereo (two-channel) signals from the speaker terminals of your receiver, integrated amplifier, and basic amplifiers. This has the advantage of ensuring that your subwoofer receives exactly the same signal as the main speakers, which means that the character of the bass from the main system is carried forward into the Sub-Bass System”.

IMO, using high level input connectors offers the best possible integration with your mains speakers.

Okay so here's the thing. If you look at the schematic for subs with high level input connectors, the circuit is exactly the same as the LOC described above. Exact. Same.Thing.

The only difference is the circuit is inside the sub, as opposed to being in the LOC. But wherever it is located, it is the exact same thing.

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

@lalitk It’s just a PITA to return plus having to pay for return shipping for a 50lb package. And Rhythmic doesn’t have another similarly priced option. If I end up returning it I’ll get an SVS SB1000 which was my 2nd choice. It’s really annoying because even though on Rhythmic’s website it doesn’t explicitly say the L12 has high level speaker inputs, they have reference pictures on the L12 page that shows a back with the speaker inputs, which I see now is not actually an L12 at all. So while I’m sure it’s not done on purpose it is unintentionally deceiving of what you’re actually getting. If I had double checked before putting in my order I wouldn’t have bought it, but now since I waited 2 months for it and I do think it has the best specs and features I would like to try and get it to work as it should.

@millercarbon I see, the one thing is I just personally hate using any kind of adapters, converters, etc.. on my equipment. Even though it’s cheap and should work with no issues it’ll always be nagging at me that it’s not connected in an optimal fashion. If it were just a temp solution to get the job done I would do it, but I just feel if I’m paying $500+ I want it to work as intended with no additional trickery.

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?

At least they have a 45 day return policy if I can't find a solution I'm happy with.