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

The clarification I am looking for is the “Parts Express” LOC, that is mentioned earlier in this thread. It states that it has a 30 watts max rating. If my amplifier is rated at 400 watts, what reliability concern is there due to the vast differences in ratings?

Of course max wattage rating matters, otherwise they won’t state that specs. For example, the Russound ADP-1.2 Speaker-level to Line-level Adapter is rated 250watts rms/ 500watts peak by using 1/2watt and 1watt resistors. If you apply power higher than the rated power to the LOC, its resistors will burn out!

https://images.crutchfieldonline.com/ImageHandler/trim/1736/1129/products/2008/543/x543ADP12-f.jpeg

BTW, be very careful using high level connection for subwoofer if your amplifier speaker negative output is not grounded (balanced, BTL or some class D amplifier), best to confirm with your amplifier manufacturer.
If your amplifier has floating speaker negative output, a Jensen Transformers speaker to line converter is one of the solution.

https://www.cs1.net/pic/jensen_transformers/SC-2NR_manual.pdf

@nsm1979

Hi Neil, the last time I checked, Rythmik did offer an amp option that contained a high level input. I would contact Rythmik with your questions.

Bring back an old thread from 2019 to get clarification.

I am researching the viability of adding a pair of Rythmik L12 subs to my system that is based on shortest signal path.  I run a DAC directly into mono amps that sit at the base of my speakers.  No preamp, no LFE or subwoofer connections in my system.  My speaker cables are only 12” in length.  I prefer high level input connections.

Miller Carbon suggested a solution to connecting a subwoofer to high level signal source when a high level signal source input is not available on the subwoofer.

The clarification I am looking for is the “Parts Express” LOC, that is mentioned earlier in this thread.  It states that it has a 30 watts max rating.  If my amplifier is rated at 400 watts, what reliability concern is there due to the vast differences in ratings?

Hopeful the Electrical Engineers and millercarbon will chime in and provide clarification on why the difference in ratings would not be a potential reliability issue.  These electrical concepts are above my pay grade.

Thanks in advance for sharing your wisdom.
 
Neil

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

@millercarbon I see what you mean. One thing is why would any possible distortion be present through the pre-outs but not through the speaker outs? I don’t think the power amp is doing anything to make the signal out of the pre-amp cleaner. I figure it’s just amplifying, which whether done through the RCA outs, or eventually through the power amp and speaker terminals, it’ll still be there. Unless the argument is based on the the Y-adapter itself causing the distortion, not the pre-out signal.

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.

Wanted to post a follow up. I've spoken to all 3 companies in the mix, Rythmic, Cambridge Audio, and Schiit, they all said to use the RCA line out with a Y splitter.

This is what you call CYA. Both methods are at best the same. Both methods run the risk of introducing a bit of distortion. Think about it. But the distortion of the LOC affects only the bit going to the sub, and is simply never going to be heard. (Done it, so experience here not opinion.) With the Y however then whatever distortion it makes goes right into the amp and comes right out the most high resolution high hearing sensitivity part of the system. Not taking sides just let's be clear. Its so true, already you are asking what is the best part to use. Whereas with the LOC it just doesn't even matter.

Where the CYA comes in is even though its definitely not the best way to go SQ-wise, it is definitely the lowest risk of customer screwup. Which people think businesses mostly try and make good stuff. When really the hardest part of all is making stuff their customers can't screw up.

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

Wanted to post a follow up. I've spoken to all 3 companies in the mix, Rythmic, Cambridge Audio, and Schiit, they all said to use the RCA line out with a Y splitter. They said the speaker post connection would at best sound the same, but have the side affect of potential distortion so there's no real point in using that connection unless the sub was made to use them.

I tried using the amps speaker post output anyway, the volume levels were not incredibly different, they were about 25% louder than the RCA line out. In the end I couldn't really notice any difference in sound quality between either one when volume matched. So I'm going to stick with the RCA line outs using a Y split for peace of mind.

Now I have one last question, I've been using BJC LC-1 cables to my power amp, but for now only had left over cheapo component video cables I was testing to the subwoofer. I would like to get RCA's that are Y split themselves to not have to use an added Y adapter. However BJC cannot make the LC-1 cables in Y configurations, only their MSA-1 cables which don't have the same gauge, shielding, etc..

So I'm not sure if it would be best now to use 2 higher quality LC-1 cables attached to the separate Y-adapter, or use 2 lesser quality MSA-1 cables already Y split and eliminate the use of the adapter.

Or is there another cable company that can make better quality custom Y cables for the same price as BJC?

@almarg I understand I meant terminate as just the end of the cable. You're right I miss-spoke saying pre-amp, I meant power amp. Thanks for the explanation!

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

I completely agree, that's the main reason I didn't want to go with any kind of adapter/splitter and just figure out some way to get a direct connection. It bugs me to spend money on better speaker cables and then terminate them with a Y-splitter.

Just for discussion using the resistors, is it possible to get unwanted feedback back into the pre-amp that can cause some other kind of distortion?

A Y-splitter coming out of the pre-amp to connect the amp and the sub will probably work just fine. Doing it that way the pre-amp will see the input impedance of the sub and amp. Where now it sees only the amp. Should not matter but not knowing any of those its impossible to know in advance. The bigger concern I would have, and still not much but it is bigger, is this puts a splitter in the signal path to the amp. More to the point, it puts an additional connection in the signal path. No matter how high quality a splitter you get, or how great the connection, there simply is no getting around the fact you're degrading the signal. Whereas using the power amp speaker path leaves your signal path pristine, untouched.

Frankly this is probably more a theoretical than practical concern. In all reality you will probably never hear the difference. But it will be there. That for me is enough to not even want to try, and is why I suggested the LOC instead.

@millercarbon Thanks that's a lot of good info, I'll read up on it more closely, seems like real easy job. I ended up buying the Y-splitter to see how that works out in the mean time. I could already use some cheap stock rca's I have laying around to try out the resistors.

Here is the actual LOC circuit along with a very succinct explanation
http://www.epanorama.net/circuits/speaker_to_line.html

Study it. This is exactly what I did. It was worth it to me to install this circuit- really nothing more than 2 resistors and one short length of wire per channel- inside my amp. It is however a very simple circuit. Keep in mind it does not matter at all where this circuit is located. When you buy a sub with speaker level inputs the exact same circuit will be used only inside the sub. 

Also like the above link explains these are 1/4 watt resistors. They can be so small because hardly any power goes through them. Regardless of volume. Regardless of your amps power. Regardless of how much you turn it up. The difference between one LOC made for high power and one for lower power is not the resistor wattage. Its the resistor value. The 10k resistor isn't used to pass power. Its used to attenuate. A bigger amp would use a 20k or greater resistor, but it would be the same 1/4 watt value.

What this means, being so small, no heat output, you can put it anywhere. You could practically wire it into an interconnect if you wanted.

Also the parts are like $2. Total. Quality just does not matter. It might if you were using it to listen to the full range signal. In this case though, low bass only, waste of money.

How you do this depends on a lot of things I just can't know. What you like the looks of, for example. What interconnects you're using. What you may or may not be comfortable soldering or modding. You could for example very easily remove the RCA from the end of one interconnect, solder the resistors, and attach the wires at the end to your amps speaker binding posts. Direct from the speaker outs to your RCA ins.

That one link above, just the one page, contains a wealth of information. You just have to figure out your best way of making use of it. I did, and mine works and looks just as good as any professionally built component. Yours can too. You just have to decide how you want to do it. Heluva lot less work than boxing and shipping. Lot more satisfying too.

Use a Paradigm X-20 crossover if you can find one used. Speaker level in - RCA out. Phase, frequency, and level control included.

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

@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.

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

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.

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”.

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.

I’ve done some more reading and found using an XLR to RCA cable is a bad idea. Mainly because to make the cable the XLR (-) lead is shorted to the ground lead on the RCA side, which could cause feedback issues and potential damage, so those options are out.
https://forum.audiogon.com/discussions/cd-player-xlr-output-buzzing

So my options are then what yogiboy and jtcf suggested to use an RCA Y-splitter, or my original though of using a speaker terminal to RCA cable.

@jtcf I just don’t see the reasoning in using a Y adapter if I could just use a straight cable from the source to the Sub. Is the adapter going to give me a better connection or signal in some way than a straight cable? I would still need to spend more because of the cost of the adapter and also an extra set of cables as well. And I figure it could potentially introduce more adapter related issues unnecessarily.

Just use a Y adapter from the Cambridge.The one yogi recommended is a nice high quality connecter,the same one I use.

You can go line level using a y adapter on the Cambridge outputs. I use this product from my preamp to run my sub line level!
 https://www.audioadvisor.com/prodinfo.asp?number=AQM22FHRD

Your option 3 using an XLR-RCA adaptor between the CXN and the L 12. 

The XLR input on the Aegir is for monaural balanced connection only.