Troubleshooting a Subwoofer / Preamp issue...

[pangechace]

Was hoping you audio experts can help me understand why my setup is not functioning correctly with my subwoofer. I'll try to describe everything as simply but detailed as possible.

-Turntable hooked up to stereo receiver. Turntable & receiver have no preamps built in, so turntable is routed through an external preamp (ART USB Phono Plus)
-Speaker wires run OUT from the stereo into the SUBWOOFER, OUT from sub into Left/Right speakers (there is no direct SUB OUT line on receiver).

-When playing records, subwoofer gets NO bass (or ALMOST no bass). If I turn receiver volume up louder, sub just gets awful LOW RUMBLE throughout song. Even with the "LOW CUT" filter enabled on preamp, it has no effect on this rumble.
-Strangely, when I adjust the Balance from Center to full LEFT or RIGHT, the sub kicks in and sounds normal. But nothing at Center.

-Subwoofer sounds normal/great on OTHER receiver inputs (like playing from iPod) so it seems like a turntable/preamp issue.

Any ideas what I'm doing wrong?? Thank you for your help!

[circuit bored records]

I would need model numbers of receiver, speakers and subwoofer in order to make an educated guess what the problem is. I would guess off the bat your stereo receiver wasn't made to power a passive subwoofer in addition to a pair of speakers, but can't really offer much more than that without knowing more.

[pangechace]

I would guess off the bat your stereo receiver wasn't made to power a passive subwoofer in addition to a pair of speakers, but can't really offer much more than that without knowing more.

 

But the other inputs, such as line-in playing iPod, sound great and the speakers and subwoofer are powered easily/correctly - just not the turntable input.

 

Here are the models:

 

RECEIVER = NAD 325BEE

SUB = Polk PSW10

SPEAKERS = Paradigm Bookshelf Speakers (model unknown, maybe SE1)

TURNTABLE = Harman Kardon T60

PREAMP = ART USB Phono Plus

[slinch]

If the US Nad model is the same (like this: http://www.avland.co.uk/nad/c325bee/rearlrg.jpg), You can add a RCA splitter betwen PRE OUT and MAIN IN and run cables to your sub from there. In my opinion a better option than using the speaker in/out on your sub.

[circuit bored records]

What slinch said. Does he need the main in though? He should be able to run RCA cables from the pre out to the RCA ins on the sub if I'm not mistaken

[pangechace]

So wire direct from receiver to speakers, and one of these from PRE OUT to my sub's LINE IN?

 

And you suspect that might help? Like I said, the sub only has problems with my turntable/preamp input..

[pangechace]

What slinch said. Does he need the main in though? He should be able to run RCA cables from the pre out to the RCA ins on the sub if I'm not mistaken

 

UPDATE: I just connected with that method. Same as before.

 

iPod sounds great, with sub getting proper bass.

Turntable gets nothing but a faint low rumble (which becomes loud rumble when I boost the receiver volume).

Bass only reaches sub when I fade the balance to LEFT or RIGHT.

[kannibal]

Have you tried changing the phase?

 

I'm wondering if somewhere there is an issue where the two signals are countering each other...maybe the pre has an issue or the pre and amp or the pre and sub arent getting along with the low frequencies when both come into the sub...

[pangechace]

Yes I've flicked the Phase switch back and forth on the Sub, if that's what you're referring to.... it doesn't have an effect on the turntable input..

[5kater]

I'm having the exact same problem. I thought my sub might have been shot but then checked it on my other inputs and it was fine. My new record player - a U-Turn Orbit doesn't get any bass from the sub. My old turntable (Fisher MT-6420) didn't have this problem at all. It put out the bass just fine. The amp has a separate bass output.