Combine left & right for sub

[wicked1]

I realize this isn't the perfect topic to ask this question, but I suspect it will be a very short answer.

If I get a sub w/ a single RCA input, (made for an amp that already combines the channels) do I just need to send the left and right channels through a diode per channel to combine them? (or is something like a 1k resistor per channel good enough?)

To clarify, I'd like to take the signal from my source, before it goes into the amps, and split it between the sub and the tube amp. Then the sub being mono in, I need to have the left and right channels combined. (I haven't bought a sub yet, but Im borrowing a friends and it only has a single RCA input jack)
My "full range" drives aren't quite what I'd call full range, so the sub will be picking up the bottom end.

Thanks!

 

[flyinglemur]

http://www.maplin.co.uk/Module.aspx?ModuleNo=218491&criteria=phono splitter&doy=24m3

 

[wicked1]

I'd be confident using that to SPLIT a signal, but not combine. My fear is that some of the signal would feed back into the amp or something.
I'm not an EE, so I dont know!

 

[flyinglemur]

It would feed back in any eventuality as it is the same physical piece of cable. What you'd want is something that duplicates, then try to combine

 

[Robert McLean]

wicked1:
Dont use diodes. Use 2 resistors, about 10K should be OK.

 

[korneluk]

Jensen recommends a 15K resistor.

-- josé k.

 

[wicked1]

I guess we're not talking about much power at this stage... are standard 1/4 watt resistors enough? (ive got a tun of every value 1/4 watt resistor).