RCA out on 2channel amp

[meistah 10+ year member]

Hey all, haven't posted on an audio forum in years, I'm out of the loop! .... I searched around and couldn't find an answer to this, sorry if it's a common question.

I currently have a system with a 2 channel amp running to the deck for my front speakers. It has RCA outs on it. I'm adding a mono amp and sub, was trying to take the easy way out by just using the RCA outs on my first amp, but can't get it to work properly. It works, but it acts like a speaker (ignores the gain and LPF settings on the mono amp). I tried using the LPF on my deck but it just filters the lower frequencies for the sub as well.

I currently have it hooked up like the diagram I included, I know this isn't correct, but I can't seem to get it to work any other way. Is this just how RCA outs work? I've never used them before. If it's not possible no biggie, I'll just run another RCA to the deck, this was more out of curiosity than anything.

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[All_Logix 10+ year member]

I would say that it is probably that the rca's running from the HU are pushing out only higher frequencies, for example they are hooked into the front and rear speaker preouts and not the subwoofer, so, it could be only able to pass through say 300Hz-10kHz, which will make your subwoofer sound like junk. I would pull out the HU and see where the RCA's are connected

 

[meistah 10+ year member]

Possibly, this is more of a theoretical question, as I could pull the deck out and hook it up properly with a separate rca instead of having it daisy chained to my other amp. What strikes me as odd is how it ignores the gain settings. The mono amp currently has the gain turned all the way down and the sub filter quite low as well, in theory I should barely be able to hear it, yet it is loud and plays like a fullrange speaker.

 

[All_Logix 10+ year member]

Yeah, you could run a new pair and be perfect, that is strange that it is pumping with the gain real low, unless that amp is throwing out one hell of a voltage on the output...running new RCA from the HU is going to he the quickest way to solve your problem though I think