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Old 7th July 2015, 01:10 AM   #1
riven67 is offline riven67  United States
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Default Info needed on adding subwoofer to tune amp

Title should say tube amp not tune!!! Sorry for the typo.

OK so I have this odd little amp from 1959-62? It's a Manhasset 2020p from a local company called Shell Electronics. Its odd in that it has a Rca jack labeled binaural out.
I was able to read a sale brochure online somewhere over a year ago (can't find it now) that said it was both channels at line level out so you could attach another amp and speaker for a third channel. I am hoping to use this for a subwoofer as the speakers I currently have are sadly lacking in low end.

My question is where does the signal go through a filter? In the sub or normally is it done in the amp before passing to the sub? Sorry but I'm a newbie still wet behind the ears!
If its done in the amp on modern equipment , is it possible to add a filter/crossover either inside my amp or on the jack externally so that the sub gets the proper frequency.

Any help will be appreciated!

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Last edited by riven67; 7th July 2015 at 01:13 AM.
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Old 7th July 2015, 01:18 AM   #2
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The cheapest solution is just allowing everything through to the sub.

You can put active crossover in the amp or a passive crossover in the speaker box itself.
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Old 7th July 2015, 01:31 AM   #3
riven67 is offline riven67  United States
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Originally Posted by nigelwright7557 View Post
The cheapest solution is just allowing everything through to the sub.

You can put active crossover in the amp or a passive crossover in the speaker box itself.
Right but if I pass everything to the sub won't it try to reproduce all frequencies? I don't mind spending some time and cash to make it work right. Which is the easier to execute? I'm still trying to get my head around crossovers. I guess the simplest solution that will sound OK but still only pass low end to the sub is what I'm looking for at this point. Thanks

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Old 7th July 2015, 01:34 AM   #4
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You can put an active filter between line level out and your external amplifier.
You can pick them up on ebay.

Or put an inductor in series with your sub to reject higher frequencies.
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Old 7th July 2015, 01:38 AM   #5
rayma is offline rayma  United States
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Quote:
Originally Posted by riven67 View Post
Its odd in that it has a Rca jack labeled binaural out.I am hoping to use this for a subwoofer
as the speakers I currently have are sadly lacking in low end. is it possible to add a filter/crossover
either inside my amp or on the jack externally so that the sub gets the proper frequency.
The single jack is likely just mono for a center channel, and then would be perfect for a single subwoofer.
You can add a low pass filter if you want, but you need to know more about the components to do that.

Last edited by rayma; 7th July 2015 at 02:03 AM.
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Old 7th July 2015, 01:45 AM   #6
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What you actually do will depend on the type of sub woofer you use. Many modern subs have a built in solid state amplifier. These can be had for pretty cheap used in good condition. Most of them have both a line input as well as speaker inputs. For the speaker inputs you simply run a wire from each speaker to the back of the sub's speaker inputs. Combining and filtering is done in the sub. Same for the line input. If you purchase a sub woofer like this, get one that has a phasing switch. This makes it very easy to select the proper phase. One way will have more bass which is the correct phase. Otherwise you have to switch wires and listen for the best bass.

If you just want to use a third amplifier and a bass speaker, you could either just rely on the speaker's inability to reproduce the highs. Or you could run the signal through a low pass filter at the bass amplifier input. You'll loose a small amount of signal this way, but the bass amplifier will make up for it.

An electronic crossover is more complicated and expensive and, for the little Manhasset amp you have, doesn't seem worth it. They are meant for true biamping rather then just a single sub woofer.
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Old 7th July 2015, 02:08 AM   #7
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A technique that frequently works well is to allow the main speakers to play "full range", hang the SW's speaker level I/Ps in parallel with the main speakers, and adjust the controls of the SW to fill in "underneath". Many SWs have speaker in and speaker out connections that can be used in "daisy chain" fashion, but I suggest you try the parallel arrangement 1st. BTW, when the parallel method is employed, 16 AWG OFC zip cord is adequate as the cabling from amp to SW.

The advantages of speaker level connections over line level connections are no worries about finding a correct connection set on the main amp and that the amp built into the SW will pick up some of the tube sonic signature.

Are you planning on DIYing the SW or are you buying something "off the shelf"?
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Old 7th July 2015, 02:48 AM   #8
lexx21 is offline lexx21  United States
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Using a couple of opamps I built a differential amp feeding a linkwitz filter. I set the filter to roll off at 60hz. I have the output both channels of my preamp feeding the diff amp so as the volume changes, so will the volume from the sub. It's pretty easy to build that on a perf board and you can find the schematics all over the net. No real need to buy one unless you just want to save time.
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