Banana Plugs to subwoofer (RCA) conversion

Banana Plugs to subwoofer (RCA) conversion

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Autopilot

Original Poster:

1,059 posts

134 months

Friday 3rd January
quotequote all
Well I’ve finally had some time at home to do a few jobs! The speakers all seem to work ok when plugged in to the speaker connects, so I made a few leads to convert an RCA at one end to a set of banana plugs at the other.

I wasn’t 100% sure what I was doing so found a video on YouTube which showed the cable being opened up, the core being used at the positive and the outer wire used as the negative. There is a possibility I didn’t get the cables right, but I’m pretty certain I did.

So what was the end result? Well, the sub works and I have two locations I can patch it to.

The downside is that is is absolutely unusable! As some of you predicted, the hum coming through the sub is pretty noticeable. It’s not even a background noise, you can hear it outside the room and is no good! I currently have a very long RCA cable running from under the stairs to the sub in the living room and it’s fine, so is very cut and dry as to what the problem is.

I’ll see the sparky soon and give him the good news that he has some work to do 😀

Apart from this, I’m really pleased I’ve gone to the effort of building the cables in. It looks really neat. I need to finish the install off under the stairs but that won’t take long to do as I just need to find something to put gadgets on and position the IR sensors so remotes still work ok.

Would I do this again? Erm, yes I would! It really is utter ball ache and has taken a long time, but it’s very satisfying to see 30cm of speaker cable between a wall plate and a speaker.

gizlaroc

13,560 posts

174 months

Friday 3rd January
quotequote all
The issue might be just the fact you no longer have a 75ohm load?

So you have used a sheiled 75ohm coax, but put banana plugs on one end?


Might just be easier to buy a these....


https://www.audiovisualonline.co.uk/product/31249/...


Edit: Are you saying it is speaker wire between the banana sockets behind the walls?

That is your issue with the hum, they are acting like and aerial picking up all the interference.

Can you not just take the wall plates off, get a sub cable, and use the old speaker cable to pull it through? So you have a proper sheilded 75ohm cable there instead?





Edited by gizlaroc on Friday 3rd January 16:53

TonyRPH

10,129 posts

118 months

Friday 3rd January
quotequote all
gizlaroc said:
The issue might be just the fact you no longer have a 75ohm load?

<snip>
Unbalanced RCA connections don't operate at 75 ohms.

The cable itself usually has a 75 ohm impedance, but that's largely meaningless in any (unbalanced) audio application.

The output impedance of the preamp / av amp driving the sub would be anything between 30 ohms and 1000 ohms.

The input impedance of the sub will be around 10k (10000 ohms).

This is not like RF where the impedance needs to be maintained end to end.

The OP might get away with a single ended to balanced connector at the amp end, to a balanced to single ended converter at the sub end - however he would then need to run dual cables, and the likelihood of eradicating the hum will be reduced but not eradicated.




gizlaroc

13,560 posts

174 months

Friday 3rd January
quotequote all
TonyRPH said:
Unbalanced RCA connections don't operate at 75 ohms.

The cable itself usually has a 75 ohm impedance, but that's largely meaningless in any (unbalanced) audio application.
Yeah of course.

I was thinking of making BNC cables up for running HD RGB video back in the day.



I still think he may as well just pull some shielded cable through using what is behind the wall now.

Autopilot

Original Poster:

1,059 posts

134 months

Monday 6th January
quotequote all
gizlaroc said:
That is your issue with the hum, they are acting like and aerial picking up all the interference.

Can you not just take the wall plates off, get a sub cable, and use the old speaker cable to pull it through? So you have a proper sheilded 75ohm cable there instead?


Edited by gizlaroc on Friday 3rd January 16:53
This is exactly what I shall be doing! I thought I'd actually posted this but obviously not. The cable goes up the wall in to the ceiling above, through the ceiling (The floor in the room above is still up at the moment), then it comes down the wall in to the under stairs cupboard, so as it all runs in straight lines and is fairly accessible, it shouldn't be too difficult to use the speaker cable to pull through!