Best way to add a mono subwoofer output with only RCA stereo out available?

[Brian Hall]

As an example, the Eversolo DMP-A6 does not provide a sub out and neither do the Fosi V3 mono amps.

What is the best way to extract a mono sub out for input to a subwoofer with only a single mono RCA input?

What I would really like is a component that takes line level stereo RCA inputs, provides RCA stereo outputs and one mono sub out. It would be great if it provided a way to set a high pass level for the RCA outs and a low pass level for the sub out.

 

[sigbergaudio]

As an example, the Eversolo DMP-A6 does not provide a sub out and neither do the Fosi V3 mono amps.

What is the best way to extract a mono sub out for input to a subwoofer with only a single mono RCA input?

What I would really like is a component that takes line level stereo RCA inputs, provides RCA stereo outputs and one mono sub out. It would be great if it provided a way to set a high pass level for the RCA outs and a low pass level for the sub out.

With DMP-A6 you could use XLR to your speakers (or power amplifier), and then use a Y-split to sum the RCA stereo output into a mono cable.

You still wouldn't get the high pass feature though. Then you need a more advanced preamp like for instance the MiniDSP SHD or perhaps the newer NAD preamps / streamers (NAD M12, NAD M66) depending on required functionality and acceptable price point.

 

[DVDdoug]

The best way is with an active crossover. Many crossovers have the ability to sum the bass from both channels. The MiniDSP can be used as a crossover and it's a popular solution.

Some subwoofers have a built-in pass-through crossover with high-pass RCA outputs.

use a Y-split to sum the RCA stereo output into a mono cable.

You should never "short" the left & right outputs together. It's OK to use these adapters as a splitter, sending the signal to the main amplifier and the sub amplifier. Usually the bass is mono (same in both channels) anyway, so you can choose the left or right channel.

 

[gsp1971]

NAD C389 and C399 integrated amps both take line level stereo RCA inputs and provide dual mono sub out.

They also provide pre-out in case you still want to feed the Fosi V3 mono amps.

 

[Brian Hall]

With DMP-A6 you could use XLR to your speakers (or power amplifier), and then use a Y-split to sum the RCA stereo output into a mono cable.

You still wouldn't get the high pass feature though. Then you need a more advanced preamp like for instance the MiniDSP SHD or perhaps the newer NAD preamps / streamers (NAD M12, NAD M66) depending on required functionality and acceptable price point.

I tried using the RCA outs with a Y cable and it didn't sound right for some reason. An advanced preamp is overkill for this. It just seems like there is a need for something better than a Y cable, but not too fancy since there are still too many components with no sub out. I was disappointed to see that Fosi's new ZD3 dac does not have a sub out, other wise it would have worked.

 

[NTK]

As an example, the Eversolo DMP-A6 does not provide a sub out and neither do the Fosi V3 mono amps.

What is the best way to extract a mono sub out for input to a subwoofer with only a single mono RCA input?

You can build a stereo-to-mono summing converter following Rane's circuits.

Why Not Wye?

Wye-connectors (or "Y"-connectors) should never connect two outputs together, but Rane tells you how to use them correctly.

www.ranecommercial.com

What I would really like is a component that takes line level stereo RCA inputs, provides RCA stereo outputs and one mono sub out. It would be great if it provided a way to set a high pass level for the RCA outs and a low pass level for the sub out.

Since almost all powered subwoofer will have a low pass filter for itself, what you need is a high pass filter for you mains. You can get a simple analog one from Hsu Research.

High Pass Filter

We will customize the Bass Optimizer box to become a 2nd order (12 dB/Oct) high pass filter for keeping bass from your main speakers. This prevents the main speakers from straining to do the subwoofer's job in situations where you cannot program your mains to "small" on a surround sound receiver...

hsuresearch.com

 

[Brian Hall]

NAD C389 and C399 integrated amps both take line level stereo RCA inputs and provide dual mono sub out.

They also provide pre-out in case you still want to feed the Fosi V3 mono amps.

View attachment 394786

Overkill for what is needed. The DMP-A6 works well as a preamp and I have the V3 monos. Every source like streamers/dacs should provide a sub out. Big failure on Eversolo's part.

 

[Kal Rubinson]

ried using the RCA outs with a Y cable and it didn't sound right for some reason.

It is likely that shorting the two RCA outs are having some effect on the XLR outs as well. Some isolation is needed and can be implemented with a few resistors.

 

[Brian Hall]

It is likely that shorting the two RCA outs are having some effect on the XLR outs as well. Some isolation is needed and can be implemented with a few resistors.

I figured it might be something like that.

 

[sigbergaudio]

I tried using the RCA outs with a Y cable and it didn't sound right for some reason. An advanced preamp is overkill for this. It just seems like there is a need for something better than a Y cable, but not too fancy since there are still too many components with no sub out. I was disappointed to see that Fosi's new ZD3 dac does not have a sub out, other wise it would have worked.

MONACOR: Products

Stereo/mono converter 1 x stereo to 2 x mono Input impedance: 4.7 kΩ Connections: input 1 x RCA L/R, output 2 x RCA mono Dimensions: 65 x 22 x 37 mm

www.monacor.com

I've used this, worked like a charm, but a bit complicated wiring. You need two y-splits, so that you can continue the RCA L+R to your speakers, and another set of L+R into that box and then on to the sub(s).

 

[Brian Hall]

You can build a stereo-to-mono summing converter following Rane's circuits.

Why Not Wye?

Wye-connectors (or "Y"-connectors) should never connect two outputs together, but Rane tells you how to use them correctly.

www.ranecommercial.com

I tried a couple of boxes like that from Amazon. Neither one put out a signal at all.

Since almost all powered subwoofer will have a low pass filter for itself, what you need is a high pass filter for you mains. You can get a simple analog one from Hsu Research.

High Pass Filter

We will customize the Bass Optimizer box to become a 2nd order (12 dB/Oct) high pass filter for keeping bass from your main speakers. This prevents the main speakers from straining to do the subwoofer's job in situations where you cannot program your mains to "small" on a surround sound receiver...

hsuresearch.com

That would be nice if it had the rest of the functionality -- provided a sub out which is my main objective.

 

[Brian Hall]

MONACOR: Products

Stereo/mono converter 1 x stereo to 2 x mono Input impedance: 4.7 kΩ Connections: input 1 x RCA L/R, output 2 x RCA mono Dimensions: 65 x 22 x 37 mm

www.monacor.com

I tried two different boxes like that from Amazon. Neither worked and also don't pass the RCA stereo outs.

I'm looking for RCA stereo in -> magic box -> RCA stereo out and one mono sub out. It seems like there should be devices that perform that function, but I haven't been able to find them.

 

[sigbergaudio]

@Brian Hall A DSPeaker Antimode X2 will also provide you with sub out as well as room correction. That's not super expensive.

 

[sigbergaudio]

I tried two different boxes like that from Amazon. Neither worked and also don't pass the RCA stereo outs.

I'm looking for RCA stereo in -> magic box -> RCA stereo out and one mono sub out. It seems like there should be devices that perform that function, but I haven't been able to find them.

Well this one works.

 

[Brian Hall]

@Brian Hall A DSPeaker Antimode X2 will also provide you with sub out as well as room correction. That's not super expensive.

I'll check it out. At first glance it still seems like overkill for what I'm needing.

 

[sigbergaudio]

I'll check it out. At first glance it still seems like overkill for what I'm needing.

There are unfortunately not loads of products like the one you are looking for I am afraid. And also way too few products (preamps/streamers) with proper support for subwoofers.

 

[Brian Hall]

MONACOR: Products

Stereo/mono converter 1 x stereo to 2 x mono Input impedance: 4.7 kΩ Connections: input 1 x RCA L/R, output 2 x RCA mono Dimensions: 65 x 22 x 37 mm

www.monacor.com

I've used this, worked like a charm, but a bit complicated wiring. You need two y-splits, so that you can continue the RCA L+R to your speakers, and another set of L+R into that box and then on to the sub(s).

I have the Y cables from trying those boxes from Amazon. Why do these devices not also provide a pass through for RCA stereo? Seems like an obvious thing to provide.

 

[EDMoser]

Have a look at active crossovers for car audio.

 

[ehabheikal]

A lot of subs have crossover inside.

 

[mhardy6647]

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Splitting 1 to 2 is trivial and "Y-worthy".
Combining, not (quite) so trivial, but still straightforward in most cases.
I also see that Rane's tech note has already been mentioned.