How to setup power amp for subwoofer?

[yente06]

Hi,

I recently fixed my JVC ja-s11 (stereo receiver) and would like to use it as the main amplifier in my sound system. My current sound system consists of 2 tower speakers and 1 12" passive sub. The impedance of the sub is 4 ohms and has a rating of 300 watts (I think). Given that the receiver is a stereo receiver, I need a separate amp to drive the subwoofer. On the internet, a lot of people use power amplifiers to get the job done. So I was thinking of buying a Behringer NX1000D and using it in bridge mode because it's cheap (I don't want to spend too much money) and has a built-in DSP (don't know if I need it). My receiver doesn't have any pre-out connections, so I will have to use the rec-out to connect them together. I want to know if hooking up a power amp is different from hooking up a home receiver with RCA and if I have to buy anything else (or if you have a better suggestion). I have had bad luck in the past where almost no audio would come out of the speakers even tho the power amp (without DSP) was a lot more powerful than my home receiver.

Thanks in advance!

 

[lovinthehd]

If you use the rec-out it will be a fixed level line output, no volume control. Not a particularly good way to go. Just not a great combo of equipment to use together for your desired result. Power amp would need sufficient signal level to operate fully, a fixed level line out may well be insufficient. Does your integrated amp have any other options besides rec out?

 

[yente06]

If you use the rec-out it will be a fixed level line output, no volume control. Not a particularly good way to go. Just not a great combo of equipment to use together for your desired result. Power amp would need sufficient signal level to operate fully, a fixed level line out may well be insufficient. Does your integrated amp have any other options besides rec out?

Thanks for the reply,
No, my amp only has a rec out.

Will it theoretically work with a normal RCA connection (e.g. connecting a phone directly to the power amp) or is the signal strength of a phone not strong enough for a pro power amplifier? if so, do I need to use a preamplifier to get the desired result?

 

[lovinthehd]

Not sure how a phone would resolve your connection/use issues. Some phones/cd players/other sources may have sufficient ouput level to use directly with a power amp, tho it would depend on spec of both the source and the amp. You might use the system 2 speaker connections with speaker level to line level converters to connect to a sub amp, tho I have no particular recommendations as I've never needed to set something up like that. Maybe someone else has some specific recommendations along those lines....

 

[TLS Guy]

Thanks for the reply,
No, my amp only has a rec out.
View attachment 47217
Will it theoretically work with a normal RCA connection (e.g. connecting a phone directly to the power amp) or is the signal strength of a phone not strong enough for a pro power amplifier? if so, do I need to use a preamplifier to get the desired result?

You can not drive a sub with that receiver. You would need a sub with speaker level inputs, and these have pretty much disappeared. There is no way you can use a passive sub with that receiver.

 

[yente06]

You can not drive a sub with that receiver. You would need a sub with speaker level inputs, and these have pretty much disappeared. There is no way you can use a passive sub with that receiver.

I know, that's why I want to buy a power amplifier as I specified in the initial comment. I just want to understand the signal level thing, because a lot of people are talking about it. I've always just connected sources to the RCA inputs of amplifiers, but I guess it's different with power amplifiers?

 

[lovinthehd]

Part of the problem is you don't have but a fixed line level output on your integrated amp. That means that as you turn the volume knob on your integrated amp, the level of that output will not change, even if it is is of sufficient level to let another amp control full range of volume of the sub; you'll constantly be trying to level-match the speakers volume to your sub volume, which would suck. Pre-outs would have variable line level output, i.e. would change with volume knob of the integrated amp, thus maintaining a level match between speakers and sub as you change volume. Fixed line level output voltage tends to be lower than pre-out level, so there's the matter of achieving full use of the amp (by meeting its input voltage sensitivity requirements).

Only way I can think of to mickey mouse a setup like this is to use the second set of speaker terminals with a converter like I mentioned earlier....but really you just need a different combo of components that are intended to work well together.

 

[yente06]

Part of the problem is you don't have but a fixed line level output on your integrated amp. That means that as you turn the volume knob on your integrated amp, the level of that output will not change, even if it is is of sufficient level to let another amp control full range of volume of the sub; you'll constantly be trying to level-match the speakers volume to your sub volume, which would suck. Pre-outs would have variable line level output, i.e. would change with volume knob of the integrated amp, thus maintaining a level match between speakers and sub as you change volume.

Only way I can think of to mickey mouse a setup like this is to use the second set of speaker terminals with a converter like I mentioned earlier....but really you just need a different combo of components that are intended to work well together.

Like an av receiver? So I can use a subwoofer out? If I do it this way, can I just connect the RCA subwoofer out to the XLR inputs of a power amplifier directly, using an RCA to XLR cable?

 

[lovinthehd]

Like an av receiver? So I can use a subwoofer out? If I do it this way, can I just connect the RCA subwoofer out to the XLR inputs of a power amplifier directly, using an RCA to XLR cable?

An avr is a good way to go in that it has a proper pre-out for a sub's amp as well as bass management. Depends on amp as to how well an rca to xlr cable may work....some pro amps need a higher level signal. Might look at a Crown XLS instead, it has rca inputs and consumer friendly sensitivity levels. Or just get a sub with its own amp built in....what is this 12" passive sub you have?

 

[lovinthehd]

Or just get a sub with it's own amp and speaker-level (aka high level) inputs.....they're still out there.

 

[TLS Guy]

Like an av receiver? So I can use a subwoofer out? If I do it this way, can I just connect the RCA subwoofer out to the XLR inputs of a power amplifier directly, using an RCA to XLR cable?

As Lovin just told you. You idea, may or not work.

The problem is that line voltage (RCA) is 1 volt full modulation. XLR balanced is 2.2 Volts. Some power amps have a switch to alter the sensitivity of the XLR input to switch between 1 and 2.2 volt sensitivity. An RCA to XLR plug is called a floating line. We have had problems from previous posters who have run into trouble doing what you want to do.

In any event you do need a unit with a sub preout. Only pre/pros have RCA and XLR preouts. Most amps also have a choice of RCA and XLR input. The other issue is that if you use that Behringer in Bridge mode it needs to see 8 ohms. This always applies to bridging when you do it, you need to double the impedance of the load. I'm not a fan of bridging for multiple reasons.

 

[yente06]

An avr is a good way to go in that it has a proper pre-out for a sub's amp as well as bass management. Depends on amp as to how well an rca to xlr cable may work....some pro amps need a higher level signal. Might look at a Crown XLS instead, it has rca inputs and consumer friendly sensitivity levels. Or just get a sub with its own amp built in....what is this 12" passive sub you have?

Thanks, I don't really know what sub I have. I got a speaker from my friend and build an enclosure for it. The speaker itself doesn't have a brand or serial number, I just know it's rated for 4 ohms.

 

[yente06]

As Lovin just told you. You idea, may or not work.

The problem is that line voltage (RCA) is 1 volt full modulation. XLR balanced is 2.2 Volts. Some power amps have a switch to alter the sensitivity of the XLR input to switch between 1 and 2.2 volt sensitivity. An RCA to XLR plug is called a floating line. We have had problems from previous posters who have run into trouble doing what you want to do.

In any event you do need a unit with a sub preout. Only pre/pros have RCA and XLR preouts. Most amps also have a choice of RCA and XLR input. The other issue is that if you use that Behringer in Bridge mode it needs to see 8 ohms. This always applies to bridging when you do it, you need to double the impedance of the load. I'm not a fan of bridging for multiple reasons.

Yeah, I got a bit confused by Behringer. They say the lowest each channel can go is 4 ohms, but they also say that bridge mode supports 4 ohms, so I don't know what to believe. Maybe It does support 2 ohms on each channel because the non-D variant does.

 

[TLS Guy]

Yeah, I got a bit confused by Behringer. They say the lowest each channel can go is 4 ohms, but they also say that bridge mode supports 4 ohms, so I don't know what to believe. Maybe It does support 2 ohms on each channel because the non-D variant does.

I would not trust Behringer and their gear has a reputation for blowing up. I would avoid that.

 

[TLS Guy]

Thanks, I don't really know what sub I have. I got a speaker from my friend and build an enclosure for it. The speaker itself doesn't have a brand or serial number, I just know it's rated for 4 ohms.

Stop spending money on this insanity! You don't know you even have a sub. Just because a speaker is 12" does not make it a sub driver. You can not build a box and call it a sub. You have to know or be able to measure the Thiel/Small parameters of the driver, and design and build the box specifically for that driver.

You need a lot of education before you go spending money. You are headed to poor money down the drain and get nowhere.

 

[lovinthehd]

Thanks, I don't really know what sub I have. I got a speaker from my friend and build an enclosure for it. The speaker itself doesn't have a brand or serial number, I just know it's rated for 4 ohms.

Would need to know the driver you put in what kind and size box to even have an idea what kind of sub you have there. Sounds like you just need a new sub, rather than buying an amp for what you have but if you have details to consider....

 

[lovinthehd]

As to bridging an amp the general idea is don't generally, just get one suited to the use to begin with. While the Crown XLS will run 4 ohm bridged (or 2 ohm without) and have done so, I'd definitely take Behringer spec a bit more pessimistically in general when it comes to their ratings (they tend to be vague/inflated).

 

[Pogre]

Thanks, I don't really know what sub I have. I got a speaker from my friend and build an enclosure for it. The speaker itself doesn't have a brand or serial number, I just know it's rated for 4 ohms.

Uhh, that's not gonna do what I think you think it's gonna do...

If you don't even know what driver that is there's no way you could have figured out what size cab to build for it. You should abandon this project before spending a penny on it.

 

[lovinthehd]

Yeah driver diameter alone doesn't mean a whole lot....

 

[yente06]

Uhh, that's not gonna do what I think you think it's gonna do...

If you don't even know what driver that is there's no way you could have figured out what size cab to build for it. You should abandon this project before spending a penny on it.

I already build it, but it was a while ago. I know you should calculate the perfect cab size, but I had some MDF laying around and my friend was going to throw away the sub anyways, so I decided to just try something. It worked out really well, it sounds really good. I don't need THE perfect sound system and I am a student so I don't have a lot of money. I want to upgrade in stages. My sub amp is dead at the moment, so first I want to upgrade the amp. If I don't like my sub in the future I will upgrade it.