Where to Tap Speaker Wires for an RCA Adapter

SSTJ

SSTJ

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Not TJ-specific, but you all are my only community for questions like this.

Let's say I have a factory head unit going to a four-channel amp that provides 75W RMS to four Polk speakers. The amp has no pre-amp output, and I'd like to provide a signal to my powered-enclosure: Rockford Fosgate PS-8. The PS-8 can accept high or low level input.

If I buy one of these or these, to tap into the rear speaker wires, should I tap into the wires before the four-channel amp (between the head unit and the four-channel amp) or after the four-channel amp (between the four-channel amp and the speakers)?

Seems like tapping before the amp would provide a weaker signal, but maybe a cleaner signal?
 
Ideally you'd split the output at the head unit and run low level to your sub. But honestly the high level approach is fine for car audio. I'd do whichever was easier to wire up.
 
WallyWest said:
Ideally you'd split the output at the head unit and run low level to your sub. But honestly the high level approach is fine for car audio. I'd do whichever was easier to wire up.
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Ok thanks. Just curious, but can you tell me more about what's 'ideal' with the low-level?

Also, the first link I provided claims to drop the signal to low-level input, capable of doing so even with up to 60W RMS of input. So I suppose it would end up being low-level either way?

Crutchfield told me to do it right behind the head unit, before the four-channel amp. Just thought I'd see what others thought, and why.
 
SSTJ said:
Ok thanks. Just curious, but can you tell me more about what's 'ideal' with the low-level?

Also, the first link I provided claims to drop the signal to low-level input, capable of doing so even with up to 60W RMS of input. So I suppose it would end up being low-level either way?
Click to expand...

Yes, what happens is the sub is taking the amplified signal, stepping it down to standard line level voltage, and feeding that into it's internal amp.

It's better if your head unit has a dedicated sub output that you run direct to it. That way you can manage your crossover and bass levels at the head unit. Using the high level signal you can't do that. The amp on your sub should have a crossover knob to set the low pass cutoff, and a volume knob to tune how much bass you have relative to the other speakers. You'll have to play around with both of those to get it sounding right.
 
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WallyWest said:
Yes, what happens is the sub is taking the amplified signal, stepping it down to standard line level voltage, and feeding that into it's internal amp.

It's better if your head unit has a dedicated sub output that you run direct to it. That way you can manage your crossover and bass levels at the head unit. Using the high level signal you can't do that. The amp on your sub should have a crossover knob to set the low pass cutoff, and a volume knob to tune how much bass you have relative to the other speakers. You'll have to play around with both of those to get it sounding right.
Click to expand...

Gotcha. So I take you to be saying there's no point tapping at the high-level location (after the 4-channel amp), because the subwoofer's amp needs a low-level input either way. Since the PS-8 does offer a 'high-level input' setting, I didn't know if there might be some advantage to using that. If so, then I'd tap the lines after the four-channel amp.

And yes, I used to have a head unit with a dedicated sub output, but I'm going back to factory.

Thanks again.
 
Your sub amp takes high level which is speaker level or low level which is RCA which you don't have. You want to put the output of the deck to both the four channel and the sub. If you take the output of the four channel and run to the sub then it gets the distortion of the four channel amp, you don't want that. You don't need to buy anything else, those line converters are only for amplifiers that don't have high or speaker level inputs.
 
pagrey said:
Your sub amp takes high level which is speaker level or low level which is RCA which you don't have. You want to put the output of the deck to both the four channel and the sub. If you take the output of the four channel and run to the sub then it gets the distortion of the four channel amp, you don't want that. You don't need to buy anything else, those line converters are only for amplifiers that don't have high or speaker level inputs.
Click to expand...

Gotcha, thanks. So Crutchfield told me it would still be a good idea to use the RCA converter because it would level out the input to a lower, steadier signal (see here). Do you think there's any advantage? Or should I just run speaker wire directly to the PS-8?
 
SSTJ said:
Gotcha, thanks. So Crutchfield told me it would still be a good idea to use the RCA converter because it would level out the input to a lower, steadier signal (see here). Do you think there's any advantage? Or should I just run speaker wire directly to the PS-8?
Click to expand...

Oh, didn't realize you were talking about using one of those. No, those things are junk, IMO. And totally not necessary in your case since the amp on your sub accepts high level input.
 
SSTJ said:
Gotcha, thanks. So Crutchfield told me it would still be a good idea to use the RCA converter because it would level out the input to a lower, steadier signal (see here). Do you think there's any advantage? Or should I just run speaker wire directly to the PS-8?
Click to expand...
They are pretty good as far as tech support, I don't know if I'd do it but I wouldn't suggest they are wrong. I'd probably try direct to the PS-8 and if I was unhappy pursue other options.
 
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