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Discussion Starter · #1 ·
So I am replacing an old surround system with a broken speaker with a bar, but want to keep the sub from the old equipment. The bar has a 3.5mm sub output that I guess has to go to a powered subwoofer. Now I assume I can get a m/m 3.5 to rca adapter and remove the rca jacks and tape the wires together, but will still need power. Does that mean I have to have an amp between them? Could someone point me in the right direction of what I'm looking for and what it would run me?


THanks
 

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Yes, you need a power amplifier to drive the sub. The cost will depend on the needed performance. What is the sub model? Or its general details -- driver size, box size. Any clues.
 

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Discussion Starter · #3 ·
Thanks for your help! I'm not home but I'm 95% sure the system is a Sony DAV-C700. From what I looked up it's dimensions: Subwoofer : 7.9 in x 4.3 in x 3.9 in / 1.9 lbs.

Speaker: 1.0 x Subwoofer - 2-way - External - 50.0 Watt - -9880.0 Hz - 6.0 Ohm - Wired

Driver details: Subwoofer : 1.0 x Tweeter driver - 70.0 mm

Does that help?
 

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Sony claims the amplifier for the sub is 100W. It's a small sub, and almost any power amp will handle it. The trick will be in spending very little, since if you want to spend a little more, you can buy a self powered sub with better performance for around $200.


Parts Express has a " plate amp " that will work for around $50. I'm sure there are various other suitable options.
 

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Quote:
Originally Posted by nstong /forum/post/20886100


So in that set up could I just plug the rca directly into the low level input and then speaker wire out?

Yes.

Quote:
Do I need to get a specific subwoofer amp?

No. Any regular audio power amplifier will work.
 

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Discussion Starter · #7 ·
So I got this
http://www.amazon.com/gp/product/B0002YUMY8

Less powerful than what you suggested, but from the reviews it seemed like people used it for similar applications and it would be good enough. Hooked it up, and if I blast the volume, I can barely hear the audio coming through the subwoofer. So does that mean I'm under powering the signal? If I use the old sony 5.1 as an amplifier with a source directly into that it works, however when I connect the sound bar's sub out to it it doesn't. Is the sub out normal audio out? If not isn't this just a regular input on this amp?
 

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Quote:
Originally Posted by nstong /forum/post/20902056


Hooked it up, and if I blast the volume, I can barely hear the audio coming through the subwoofer.

Hooked it up how? What is the signal source? How is it connected--to which input of the plate amp? How is the plate amp connected to the Sony sub?

Quote:
If I use the old sony 5.1 as an amplifier with a source directly into that it works, however when I connect the sound bar's sub out to it it doesn't. Is the sub out normal audio out?

The Sony's DVD unit has all the amplifiers built in. It outputs a speaker level signal to drive the sub. It can drive the sub directly and needs no further amplification.


But your original post stated: >>So I am replacing an old surround system with a broken speaker with a bar, but want to keep the sub from the old equipment.
 

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Discussion Starter · #9 ·
Right I just used the sony system to make sure the sub worked, and it does. I connected the rca sub woofer out(just thought it was 3.5mm before got it) from the sound bar into the right low level rca in and then connected speaker wire from the right speaker out to the sub...
 

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Quote:
Originally Posted by nstong
Right I just used the sony system to make sure the sub worked, and it does. I connected the rca sub woofer out(just thought it was 3.5mm before got it) from the sound bar into the right low level rca in and then connected speaker wire from the right speaker out to the sub...
If you want to test the plate amp with the Sony system, you'd need to connect the Sony's wires to the speaker-level inputs on the amp, not the RCA inputs.


The RCA inputs are for line level signals, which are some 30 dB lower in level.
 

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Discussion Starter · #11 ·
So if I connect the speaker level inputs from the sony it works just as a pass through right? The goal is to get rid of the sony, so I connected the sub out from my sound bar to the amp, and the speaker level output to the sub. Isn't the point of the amp to amplify the line level coming out of the soundbar so that I can use the sub? When I set it up that way I don't get much. My problem is probably that the amp isn't powerful enough right?
 

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Quote:
Originally Posted by nstong /forum/post/20907866


So if I connect the speaker level inputs from the sony it works just as a pass through right?

No. Even though it takes a speaker level signal in, and outputs a speaker level signal to drive the subwoofer, it is using the amplifier inside the plate amp. That a) offloads the amplifier driving the amp -- it's driving a high impedance now, and b) the plate amp can apply signal processing like combining L/R signals into mono and a low-pass filter before feeding its amp.

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The goal is to get rid of the sony, so I connected the sub out from my sound bar to the amp, and the speaker level output to the sub.

Right.

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Isn't the point of the amp to amplify the line level coming out of the soundbar so that I can use the sub?

Yes.

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When I set it up that way I don't get much. My problem is probably that the amp isn't powerful enough right?

It's not a question of power, but gain. While none of these amps state the gain, one would assume it has enough to do the job.


Let's confirm: You took the 3.5 mm sub output signal from the soundbar and connected it to the RCA Low Level input jack? And you turned up the gain control? And set the frequency to highest (to start)?


If the level is too low, what is the soundbar (brand/model)? Does it have an internal output gain trim setting -- as is common on AVRs? If so, that should be turned up.


If it is still too low, you can use a "Y" cable to split the signal so it feeds both amp inputs in parallel. That will add 6 dB level.
 

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Discussion Starter · #13 ·

Quote:
Originally Posted by Roger Dressler /forum/post/20908679


Let's confirm: You took the 3.5 mm sub output signal from the soundbar and connected it to the RCA Low Level input jack? And you turned up the gain control? And set the frequency to highest (to start)?

Yes this is the set up I have tried (although the soundbar has an rca out). The soundbar is a vizio vsb200, very cheap and I don't think I can increase the output. I'll have to get a splitter. How does the split work to increase it if I am only outputting to one speaker?


Also I'm not sure what's going on, if I set up the sony speaker out into the speaker in on the amp I can get it run the sub woofer, but the gain does nothing, and it sounds the exact same with the amp off... Is there something wrong with the amp?
 

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Quote:
Originally Posted by nstong /forum/post/20908872


Yes this is the set up I have tried (although the soundbar has an rca out). The soundbar is a vizio vsb200, very cheap and I don't think I can increase the output. I'll have to get a splitter. How does the split work to increase it if I am only outputting to one speaker?

The plate amp sums the L and R inputs together, so if you feed both of them, it doubles the signal, and that's a 6 dB increase.


Before you try the splitter, first check the output connections as below. The Vizio is clearly intended to drive a subwoofer amp just like the one you have.

Quote:
Also I'm not sure what's going on, if I set up the sony speaker out into the speaker in on the amp I can get it run the sub woofer, but the gain does nothing, and it sounds the exact same with the amp off...

That's a bad sign.

Quote:
Is there something wrong with the amp?

Maybe. But let's check the output connections. Look at this picture of the amp.


In the lower right corner is a bundle of red/black wire with terminal connectors on it. This is the amp's output wires, normally intended to connect to the spade terminals on the woofer driver. in your case, you have to connect them to the Sony's subwoofer wire. Is that how you have it?
 

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Discussion Starter · #15 ·
haha nope! I knew it had to be something stupid that I was doing wrong. I thought the speaker outs on the front we're for a sub or two. I was reading about ways to set it up where you use the sub outs for your other speakers, but I didn't think my cheap $35 amp would have those. Anyway everything else makes a lot of sense now. Thanks for sticking it out and figuring out the what I was doing wrong.
 

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Quote:
Originally Posted by nstong /forum/post/20909960


haha nope! I knew it had to be something stupid that I was doing wrong. I thought the speaker outs on the front we're for a sub or two. I was reading about ways to set it up where you use the sub outs for your other speakers, but I didn't think my cheap $35 amp would have those. Anyway everything else makes a lot of sense now. Thanks for sticking it out and figuring out the what I was doing wrong.

I knew we would get there, eventually!
 
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