How to connect Wiim SUB-pro to Preamp with RCA Output

[Anatollica]

Hi all,


I’m considering buying a Wiim SUB, but I’m not sure how best to connect it to my system.

My setup:

• Preamp: Vincent SA-31 (two sets of stereo RCA outputs: Output 1 L/R and Output 2 L/R)
• Power amp: Only has speaker outputs, no line-level or sub out
• Speakers: Passive, connected to the power amp
• Subwoofer: Wiim SUB, which has only a single RCA line-in (mono)

My idea was to use one of the preamp’s RCA outputs for the power amp and the other for the subwoofer. Since the sub has only a mono RCA input, I thought about using a Y-type RCA cable to combine L/R into one input.

However, someone at a local Hi-Fi shop warned me that connecting L/R this way might cause problems — possibly making the stereo outputs collapse into mono, which I definitely don’t want.

So my questions are:

1. Can I safely connect the Wiim SUB to the Vincent SA-31 using its second set of RCA outputs?
2. Do I need a special adapter or summing cable for stereo-to-mono, or is a simple Y-cable enough?
3. Alternatively, should I use some DSP between my preamp and amp to manage sub integration?

Any advice on the correct and safe way to connect this sub would be very helpful.


Thanks!

 

[harkpabst]

Hi @Anatollica!

You must not directly connect the L + R stereo outputs using a Y style cable or adapter. These are splitters, meant to split one single (low output impedance) output into two, which can be connected to two (high input impedance) inputs. Even if the cables fit mechanically, they must not be used to join the left and right output together.

Here's a little more info on why this is to be avoided and potentially dangerous:

The Stereo-to-Mono Summing Cable That No One Makes | Late Reflections – the Silent Sky Studios Blog

silentsky.net

You either need an active summation device or at least a cable that decouples the outputs from each other sufficiently using resistors. Unfortunately (and as pointed out in the aforementioned link), such cables are not to be found commercially (to the best of my knowledge). You might be able to pick up a readily made passive summation box but I have no recommendations. To learn a bit on how you could build something yourself have a look at this discussion (in particular the PDF attached to post #8):

Ways to sum stereo to mono before the power amplifier?

Hi all, I've been building a few test boomboxes with class D chip amps and for my next one I'm looking at a single woofer/tweeter config, so a mono amp is required for maximum power benefit. There are plenty of mono boards (3116/3118 etc) available, but I want to know how to best sum a stereo...

www.diyaudio.com

 

[Burnside]

So would you suggest something like this?

https://cpc.farnell.com/unbranded/smc-1/audio-converter-stereo-mono/dp/AV19945

 

[Anatollica]

Hi @Anatollica!

You must not directly connect the L + R stereo outputs using a Y style cable or adapter. These are splitters, meant to split one single (low output impedance) output into two, which can be connected to two (high input impedance) inputs. Even if the cables fit mechanically, they must not be used to join the left and right output together.

Here's a little more info on why this is to be avoided and potentially dangerous:

The Stereo-to-Mono Summing Cable That No One Makes | Late Reflections – the Silent Sky Studios Blog

silentsky.net

You either need an active summation device or at least a cable that decouples the outputs from each other sufficiently using resistors. Unfortunately (and as pointed out in the aforementioned link), such cables are not to be found commercially (to the best of my knowledge). You might be able to pick up a readily made passive summation box but I have no recommendations. To learn a bit on how you could build something yourself have a look at this discussion (in particular the PDF attached to post #8):

Ways to sum stereo to mono before the power amplifier?

Hi all, I've been building a few test boomboxes with class D chip amps and for my next one I'm looking at a single woofer/tweeter config, so a mono amp is required for maximum power benefit. There are plenty of mono boards (3116/3118 etc) available, but I want to know how to best sum a stereo...

www.diyaudio.com

Thank you! Do you think this might help:

Amazon.com: SPRODIO Single Stereo to Mono Converter, RCA L/R Audio Adapter Stereo to Mono summing Cable Adapter SC21 : Electronics

Buy SPRODIO Single Stereo to Mono Converter, RCA L/R Audio Adapter Stereo to Mono summing Cable Adapter SC21: Connectors & Adapters - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

I am not technical guy, so I will not be able to do it bu myself. ))

Maybe there could be some additional Digital Sound Processor between preamp and amp that will split signal to amp and sub?

 

[harkpabst]

https://cpc.farnell.com/unbranded/smc-1/audio-converter-stereo-mono/dp/AV19945

Amazon.com: SPRODIO Single Stereo to Mono Converter, RCA L/R Audio Adapter Stereo to Mono summing Cable Adapter SC21 : Electronics

Buy SPRODIO Single Stereo to Mono Converter, RCA L/R Audio Adapter Stereo to Mono summing Cable Adapter SC21: Connectors & Adapters - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

Yes, both these devices will do the trick. Get the one, which is less expensive for you to obtain.

Both boxes are passive (no power supply needed), so all they really do is to implement the resistors mentioned in the descriptions above. Unless the output resistance of the pre-amp was unusually high (they don't provide this information for the SA-31) the exact values of the resistors used are not critical at all, so any box should work.

Maybe there could be some additional Digital Sound Processor between preamp and amp that will split signal to amp and sub?

You mean like you would buy an additional processor? The miniDSP 2x4 HD can certainly do that. The question is if you need it/want it anyway.

The WiiM Sub Pro already provides you with the DSP for its own needs (including RoomFit room correction) and the cheap mono converters do work. If you plan to apply Dirac room correction to your entire system you can certainly go with the 2x4 HD. You just have to spend the money for the processor, a UMIK-1, and the Dirac license.

 

[Burnside]

Yes, both these devices will do the trick. Get the one, which is less expensive for you to obtain.

Much appreciated - I wouldn't want to fry my Sub Pro or Linn amp!

 

[Anatollica]

Yes, both these devices will do the trick. Get the one, which is less expensive for you to obtain.

Both boxes are passive (no power supply needed), so all they really do is to implement the resistors mentioned in the descriptions above. Unless the output resistance of the pre-amp was unusually high (they don't provide this information for the SA-31) the exact values of the resistors used are not critical at all, so any box should work.



You mean like you would buy an additional processor? The miniDSP 2x4 HD can certainly do that. The question is if you need it/want it anyway.

The WiiM Sub Pro already provides you with the DSP for its own needs (including RoomFit room correction) and the cheap mono converters do work. If you plan to apply Dirac room correction to your entire system you can certainly go with the 2x4 HD. You just have to spend the money for the processor, a UMIK-1, and the Dirac license.

Thank you very much for your kind support!