connect a powered sub with a single rca input to a stereo amp with NO preout or subout?

Duke of Refern

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I have a yammy sub that was once part of a HTIB, and only has a single rca "input". I want to connect it to simple two channel amp with no pre outs or sub out, just speaker posts, cd and phono inputs and one "line out".

I have a Y rca running from the the dual line out rca's on the amp, to the single rca "input" on the sub, and it produces sound but it's all over the place. Is there a better way to connect these two things?
 

Duke of Refern

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No, go right ahead. I ended up buying a different amp, a used Denon, which is fantastic, and a dedicated sub out. In the end I was wasting my time with the old amp. Problems are over.
 
The subwoofer is passive? No power cord?
If it is passive then you will need a subwoofer amp to drive it. That will have a low pass filter so the sub only gets bass. Get one with speaker level inputs.
If it's active then the "line level" out you used is a record out which doesn't change with the volume control of the amp. So when you turn the main speakers up the sub continues to play at a lower level, Won't work unless you keep the volume about the same level all the time. And the sub still gets full range audio which it's not meant to play.
 

Duke of Refern

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Yes it's powered. I've reconnected it via a line level converter, which makes it much better, and solves the volume control issue, but I understand its forwarding a stereo signal to the sub, ie not summed.

If anyone has any idea how to overcome that, I'm all ears.
 

bogdescu

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Bump!
Same here. Yamaha YST-FSW150 active (powered) sub and Rotel amplifier, with no sub-out, just tape out and the like. I play music from a DAC if that's in any way important...
Any reply would be appreciated !
(Duke, I believe I am not hijacking the thread, seems we have the same problem, correct?)
 

Duke of Refern

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Duke of Refern

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Jul 17, 2017
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No, go right ahead. I ended up buying a different amp, a used Denon, which is fantastic, and a dedicated sub out. In the end I was wasting my time with the old amp. Problems are over.
 

bogdescu

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Oct 18, 2017
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Yep, it seems it's a no go situation. Talked with a knowledgeable technician today and got this answer:
1. first problem is: the tape-out analog rca exits on the amp deliver constant volume, irrespective of how the pot on the amp is set. Hence, the sub and the two regular speakers will have to be adjusted for volume separately (and constantly go out of tune, I may add).
2. second problem: the above is true even if we connect the sub to only the R or L channel, assuming (or hoping) that the low tones on a recording are distributed approximately fifty-fifty on the stereo channels. If we bridge the connector with a primitive solution (an Y cable for example), at worst we can fry internal components of the amp, at best we will turn the whole system into a mono (not stereo) system, because bridging on the tape-out will have this effect.
My solution: I will try the sub on one channel, just for fun. But there is no way it's staying there...
 

Duke of Refern

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Duke of Refern

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You're right of course. I searched gumtree here for six weeks everyday and finally found a denon avr 1603 for just $50, in terrific cond, just needed a cosmetic clean up and a dust internally. It sounds a treat. Bargains are out there....
 

bogdescu

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Not to prolong this discussion, but to note what my conclusion was after yesterday's fiddling. Plus – hey – it's fun writing about old amps when it's increasingly cold outside here in Poland:

I ended up by making an experiment and adding the sub to one channel only, on the tape-out output of the amp, resorting to setting the volume separately on the sub and the main amp, as well as pretending that listening to one channel only on the low frequencies is not a problem.

My first remarks:
- It's a perfect way to test the combination, I don't believe my sub+speakers combo would sound substantially different if there was a dedicated sub out on my amp.
- I have a rotel integrated driving a pair of vintage 1979 Tannoys. The only way the result is listenable is setting the sub to a _very_ low volume. I suspect this would be true almost in any setup. And even if there would be a way to feed a correctly combined left-right mix to the sub. It's simply very difficult to not dismantle musicality when adding a subwoofer.
- The Yamaha itself is... well... not a very good speaker. Boomy and soft, turns sound into vibration way to early and lacks any precision and dryness.

In essence, supplementing with a sub is a good idea if the music is just to create an environment while cooking or working around the house. As soon as I turn my full attention to the music it starts to be difficult to accept. Sure, bass is where there used to be nothing, but it's more of a placeholder, just doesn't have enough information in it.

OK, I have to stop, I sound like an audiophile :)
 

Duke of Refern

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