RCA converter to non RCA head unit

[GUte]

G'day fella's.
Got a Sony head unit that does not have RCA outs.
I have a RCA converter that you connect to speaker wires from the head unit.
It has provision for two channels. I only want to use one for a sub so I pinched the left front for this and bridged the left and front speakers to get my left back (I understand that I will not have stereo at the front).
The converter has pos. and neg for both channels each and one sep. neg/earth.
Wiring this up has got me confused. Any ideas?

Also I have an old 2 channel amp that has low and high inputs. It does not have a switch for sub or full.
Would this amp be fine to run a sub?
Thanks for any input.

Al.

[xl7fan]

G'day Al, if your amp has high level inputs I would ditch the converter & just run the speaker outputs from your headunit to the high level inputs on your amp. The amp should be fine for running a sub. ? If the amp has no inbuilt crossover you can buy an extenal crossover that is wired inline on the positive output terminal of the amp to the sub (it looks similar to a roll of solder) that will cancel out the high frequencies. Can you see whether the output terminals on the amp allow for bridge mode wiring as this will double the output power of the amp supplied to the sub.

Hope some of this makes sense.

Matt.

[Dooley]

I'm confused as to how you you're bridging things...?

So you nicked the left front for the sub, and then connected the left front speaker in parallel to the right ?

Downsides to that are not only it's mono, you've just put two speakers in parallel. So halved their impedance, most car speakers are 4 ohm, so now your head unit has a 2 ohm load.

If it can handle that, everythings fine, but headunits can only put out about 20W RMS. Be careful and listen for clipping.

As for the converter wiring, the speaker wires don't really have a polarity as such, it's there for the phase. So I'd assume the "neg/earth" is a ground connection, either to chassis or the head unit. IIRC, some people have had amps using RCAs as their ground when their ground strap isn't hooked up right or disconnected, so the RCAs must have a ground through the head unit. Well that's the most obvious thing to me.

Pretty much everything else what xl7fan said.

[GUte]

Thanks guys, Didn't consider the Ohms difference. Any other way of getting back 4 ohms?

Yeah Matt, gotcha on the crossover. I'll see if Tandy or Jaycar have one to suit this frequency. The amp is not bridgable. Am I able to bridge externally without any effect to the amp?

Thanks.
Al.