Using a subwoofer from a SR system with old Technics stereo? - diyAudio
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Old 6th September 2005, 10:33 PM   #1
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Default Using a subwoofer from a SR system with old Technics stereo?

I have Technics SA-300, SA-303, and SA-203 receivers. I'm currently using the 203 with some mid-80s Pioneer 3-ways with 12 inch woofers. Some of my music is missing the lower ends, beyond what my equalizer and/or bass control can correct (or make sound right). I also have a Magnavox surround sound system that came with a powered subwoofer; the subwoofer takes a single RCA lead from the receiver unit. It has a volume dial and a two-position phase switch, that's it.
Would it be safe and/or feasible to use this sub with any of my Technics receivers? Since it's an amplified sub, I don't know if I can use it with my Technics' "remote" speaker posts without blowing it out, nor do I know if it has a built-in crossover, or if that stuff is done digitally in the receiver.
Another idea I had (if I couldn't hook it up directly to my stereo via some stripped RCA splitter cables) was to split the audio input before the Technics - I use my iPod through my equalizer's aux inputs when I don't want to use the radio, so would it work to split my iPod's signal straight out of its headphone jack, with one lead going to the subwoofer and the other to the stereo?
Answers to the above questions and ways to figure out if my sub has its own crossover or not (and anything I can do about such problems) would be appreciated. Also, I believe somebody here helped diagnose my SA-300's broken FM receiver as a specific integrated chip, which I found a modern equivalent for and replaced, fixing the FM completely, so a belated thanks for that.
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Old 6th September 2005, 10:56 PM   #2
Stocker is offline Stocker  United States
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You could save yourself some time waiting for responses by experimenting.

Feed the sub a low-level signal, such as that from a tape deck or even the ipod, turned down low. Do not cut any frequencies, just play it straight. If you hear "a lot" of high frequency coming through the sub, you may not have (and want to add) a crossover before the signal source to the sub.

A bit of searching, here or on google, should find you a speaker-to- preamp level conversion circuit with a very low parts count. It may work to split the Ipod output as you mentioned.
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Old 7th September 2005, 08:59 PM   #3
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I just tried a song with a strong bassline but with a lot of hi-hat stuff and vocals, too, and it sounded like it was being sung through a sock. Very muffled high up (I could only hear the voices faintly) but window-rattling down low.
I was able to turn my iPod all the way up to max with the sub's volume control at halfway and it wasn't even close to being dangerously loud. So, I'm fairly certain that for some reason, I got a subwoofer with a physical crossover in an otherwise cheap-*** Magnavox SRS system, and the signal from the receiver's SUB port doesn't need to be amplified as strongly as I had worried.

Based off of this, I'm not sure how to best go about connecting this to any of my Technics receivers.
If I were to just connect the sub to the Remote posts, would it be better to buy a split RCA cable and run both the left and right channel leads into the sub, or would it be better/easier to only run the left channel? My concern is if a song has a stereo-shift for some low-midrange instrument, the punch from it might be noticeably cut out when it shifts to the right channel (or whatever channel I don't wire to the sub). Is this likely, or is anything that the sub is going to accept going to be too low to be featured any channel-bouncing?

If I went for the split-off-the-iPod method, I was thinking of using a split miniplug, with one connected to the miniplug-RCA leads that normally go into my stereo and the other to a single mini-to-RCA lead to the sub. I've never used miniplug splitters before; will it reduce the amplification from my iPod (does it have to split the power between both leads) or will it still preamp at the same level it does if I just ran the stereo lead into it directly?

Also, between those two, I'm not sure which would be the best route to take, both sound quality and sub-amp-safety wise.
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Old 8th September 2005, 05:31 AM   #4
Stocker is offline Stocker  United States
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For sub-amp safety, go with the splitter. This is the route I would try first, before risking blowing the input to the sub's amp with a full-on speaker level signal. Also, the other receiver amp is available for doing whatever else, like some speakers somewhere else in the house, or some el-cheapo surround sound effects or whatnot.

As for the ipod, you *may* have to turn it up a little more, but you also may not notice at all.

For sound quality, get some of CSS's new FR125S drivers in a TL and measure the thiele-small parameters of the subwoofer driver you have, and make it into a box that will pick up where the other drivers leave off. Otherwise, let's face it (we've likely most all done it) this set of solutions is sub-optimal, but very much good-enough.

I wouldn't worry too much about the left-right quandary with a mono feed to the sub, unless it just kills you to listen to it on your favorite songs.
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