Mono sub with L & R as input from Synth

[average_male]

Hello Everybody,

I have a subwoofer that takes in a mono rca jack and I want to mod it to take in a left and right signal coming from my synth which is has a left and right output. Would it be just a matter of splicing the 2 pairs coming out from the synth to the mono jack?

The simple set up:

If the above is doable, this is actually what I wanted to achieve:

Basically wanted to run my synth signal to my sub and have it play the Left and Right lows while the spliced connections to the speakers plays the highs and mids.

Would this cause any issues or bad performance?

I didn't want a buy a mixer and have another item in my studio.

Thanks for reading and appreciate any input,
Moe

 

[Hasselhof]

you could do a Y split or rather a Y-sum as you suggest. But I would recommend buying a sub with L an R inputs

 

[GordonW]

Funny... this is the second time this week, this subject has come up in discussions I've been looking at. So, I decided to make a diagram, of an easy way to deal with this- create what's called a "summing node", out of an RCA cable (or RCA jacks in a small project box- it would work the same.

For an RCA cable- a simple "summing node" can be made easily. Just get a pair of 10K resistors, and a sacrificial RCA cable. Cut the cable in half. Strip the ends, so you have access to all the center conductors and all the shields in both channels, from both ends of the cable. Take all the grounds (shields) and connect them all together. Take the center conductors from what you will now define as the "input" (label it, so you don't forget which end is which), and connect each center conductor, to one end of a resistor. Take the remaining free ends of both resistors, tie them together, and tie them to the center conductors of BOTH channels, from the other end of the RCA cable (which will now be the output end). Solder or otherwise firmly secure all the connections you just made. Carefully insulate everything so it can't short together... voila, you have a stereo-to-mono summing cable. Plug the "input" end to the source feeding the amp, and the "outputs" to the amp... and you should be good to go.

Here's the circuit diagram of what I'm speaking of, in general terms:

For the specific case of the OP here, who needs two (stereo) inputs and one (mono) output:

I've also included some "blocking caps" (to prevent any trace DC offset from the amp in the synth, from screwing up the input to the sub) and an additional resistor to form a voltage divider (to drop the speaker level to appropriate voltage for RCA input on the sub). This additional resistor can be a different value (higher resistance == more gain to the sub, if needed, while lower resistance == lower gain); pick a value that works with the setup, to get the gain control on the sub to a "useful" level somewhere in the middle of its range.

Just hook the inputs to the outputs of the synth (along with the main speakers) then, just plug the single mono output into the subwoofer. Both channels will be equally combined into a mono signal, at the amp, without significantly affecting the stereo separation of the signal going to the main amp.

I used to do this all the time in my older car audio days; there's absolutely no reason it won't work fine, with most solid-state home audio gear as-is. For tube gear, go to about a 100K resistor (instead of 10K)... otherwise, it's the same principle, other than impedance.

Regards,
Gordon.