Subwoofer Connection to Integrated Amp - AVS Forum
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Old 06-14-2013, 10:08 AM - Thread Starter
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Sorry if this question is borderline (or outright) dumb, but I honestly don't know how to make line-level connections from an integrated amp to a subwoofer. So please indulge me.

Background

I currently have a 5.1-channel system with separates. I configure digital bass management in the A/V preamp, and I connect to the subwoofer via the LFE output. I get all that. Thing is, I'm thinking of dropping to two-channel with an integrated amp, and I'm not certain what to do.

Potential Amp

I think I might like the new Rotel RA-1570 because it has certain things I want: adequate power, an electronic volume control and an asynchronous USB input. One thing it does not have is a subwoofer output, but it does have both L/R main outs and L/R ins/outs with jumpers.

Subwoofer

I have a B&W ASW700. Like most subwoofers, it accepts both line-level and speaker-level inputs, and it has both line-level and speaker-level outputs, and its low-pass filter can be bypassed (which it currently is, because I'm using digital bass management upstream).

So how would I connect this stuff to an integrated amp?

Option 1?

My first thought was that I use a Y-connector to sum the main outputs and route that to the subwoofer (with the subwoofer's low-pass filter switched in). Then I noticed that the subwoofer's back panel (which I almost never look at) has L/R inputs, so I figured I could run both L/R line-level cables to the subwoofer and let it sum the channels. This would work, correct? The only down side I see is that the subwoofer would be running underneath the satellites, meaning the main amp would not be relieved of full-range duties. I would have the option of switching the subwoofer out, though, by simply turning it off

Option 2?

Then I noticed that the integrated amp has jumpered line-level inputs/outputs. Sooooo ... it would appear to me that I could pull the jumpers (thus disconnecting the preamp section from the power-amp section), run the amp's line-level preamp output to the subwoofer, then run the subwoofer's line-level output back to the amp. This way, I figured, the subwoofer would be acting as an electronic crossover, as it would send a high-pass signal back to the amp, thus relieving the amp from amplifying low frequencies (below 80 Hz or whatever). It would seem to me that 120 top + 500 bottom would play pretty damn loud with my system and in my room. The only downer I see is that, with this setup, I could never switch the subwoofer out without rewiring.

Sorry for the length, but do I have all this right?
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Old 06-14-2013, 12:08 PM
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Option 2
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Old 06-14-2013, 01:09 PM - Thread Starter
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Quote:
Originally Posted by Ratman View Post

Option 2

Well .............

I've since gone to talk to a local dealer buddy of mine, and he says that Option 2 actually won't work -- he says that pulling the jumpers actually disables the power-amp section and is intended for using the integrated as a preamp. Really? I need to look at the manual and see if that's true.

Meanwhile, he also said I could put the subwoofer in a tape loop. But that wouldn't work, because the output level is fixed! (That didn't occur to me when he said it, but it has since.)

Then ... he also told me that Rotel is set to introduce a new two-channel preamp with (apparently) the same basic features as the new RA-1570 integrated (meaning a USB input and an electronic volume control), so I may yet stick with separates. This would definitely allow me to connect the subwoofer between the preamp and power amp, but, again, I'd have no ability to switch the subwoofer in and out.
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Old 06-14-2013, 02:43 PM
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Option 3: Insert line level xover into pre/power loop and run high pass output to Rotel and low pass to sub.
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Old 06-14-2013, 03:36 PM
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Quote:
Originally Posted by Brownstone322 View Post

Well .............

I've since gone to talk to a local dealer buddy of mine, and he says that Option 2 actually won't work -- he says that pulling the jumpers actually disables the power-amp section and is intended for using the integrated as a preamp. Really? I need to look at the manual and see if that's true.

Meanwhile, he also said I could put the subwoofer in a tape loop. But that wouldn't work, because the output level is fixed! (That didn't occur to me when he said it, but it has since.)

Then ... he also told me that Rotel is set to introduce a new two-channel preamp with (apparently) the same basic features as the new RA-1570 integrated (meaning a USB input and an electronic volume control), so I may yet stick with separates. This would definitely allow me to connect the subwoofer between the preamp and power amp, but, again, I'd have no ability to switch the subwoofer in and out.

You can't have your cake and eat it to:

(1) If you go with the preamp then you'll most likely get 2 sets of pre-outs--one set for the amp and one set for the sub and no way to take the bass out of the satellites.

(2) If you use an integrated/receiver with jumpers then you need to feed the signal back into the amp somehow. This means you need to feed the signal into the sub and then out of it (which will utilize its high pass filter at whatever setpoint it has--assuming it isn't adjustable and assuming it doesn't degrade the sound in any noticeable fashion). Or, use two y-adapters out of the pre-out from the integrated and feed one set of L/R back into the amp and one set into the sub (same as having two sets of pre-outs).

(3) Or, get an outboard crossover/processor that offers separate outputs and loop it between the pre-out/main-in, but the above will work without any additional gear--only extra cables.

B.
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Old 06-14-2013, 05:20 PM
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According to the manual of the Rotel ra985bx.......similar to the 1570.....?




Preamp/Power Amp Jumpers 18

These connectors, labeled ”Pre Out” and “Main In”, are normally
connected by a set of solid metal jumper connectors. They provide a convenient insertion point for virtually any type of signal
processor. To use these connectors, pull out the jumper connectors. Using high quality cables, connect the “Pre Out” connectors
to the inputs of the signal processor. Connect the outputs of the
signal processor to the “Main In” connectors.
One of the most common uses for these connectors is to incorporate a surround sound processor into the system. Typically the
front channel outputs from the signal processor are connected to
the “Main In” of the RA-985BX. The other outputs from the signal
processor are connected to other power amplifiers and speakers



Wouldnt your plate amp be considered a processor?
Dont see why this wouldnt work.
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Old 06-15-2013, 04:59 AM
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Absolutely correct.
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Old 06-15-2013, 06:54 AM
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Option 4. Stick with an AVR, even for 2 channel. Why spend more for a system that does less? Do you expect better audio quality?

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Old 06-15-2013, 05:08 PM - Thread Starter
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Quote:
Originally Posted by Brian B View Post

(2) If you use an integrated/receiver with jumpers then you need to feed the signal back into the amp somehow. This means you need to feed the signal into the sub and then out of it (which will utilize its high pass filter at whatever setpoint it has--assuming it isn't adjustable and assuming it doesn't degrade the sound in any noticeable fashion).

My subwoofer has two sets of line-level outputs, one high-passed for satellites and the other full-range (labeled "Link") for connection to another subwoofer. I wouldn't expect either would degrade the signal in any audible way.

Quote:
Originally Posted by Perry R View Post

According to the manual of the Rotel ra985bx.......similar to the 1570.....?

Preamp/Power Amp Jumpers 18

These connectors, labeled ”Pre Out” and “Main In”, are normally connected by a set of solid metal jumper connectors. They provide a convenient insertion point for virtually any type of signal processor. To use these connectors, pull out the jumper connectors. Using high quality cables, connect the “Pre Out” connectors to the inputs of the signal processor. Connect the outputs of the signal processor to the “Main In” connectors. One of the most common uses for these connectors is to incorporate a surround sound processor into the system. Typically the front channel outputs from the signal processor are connected to the “Main In” of the RA-985BX. The other outputs from the signal processor are connected to other power amplifiers and speakers."

This is exactly what I thought those jumpers did. As I mentioned above, it would seem as though I could insert a subwoofer into the same path, and it would siphon off the low frequencies. Thanks for the reference.

Quote:
Originally Posted by Nethawk View Post

Option 4. Stick with an AVR, even for 2 channel. Why spend more for a system that does less? Do you expect better audio quality?

For starters, I use an A/V preamp, not a receiver, and have so for nine years, because I hate the way almost all receivers are laden with gimmickry. But your point applies to an A/V preamp just the same. (And, yes, I know some A/V preamps are overloaded with features, but mine certainly isn't.)

The answer is that I listen to two-channel music about 90 percent of the time, and I want to simplify and consolidate -- fewer boxes, fewer cables. The idea of ditching the surround and center speakers and their associated cables is very appealing to me. Plus I want to use a computer as my primary music source (lossless), so I need a USB input. (And, yes again, I'm aware that I could add an external DAC, but that'd be one more box, albeit as smallish one.) I'd consider another A/V preamp with a USB input, but I don't know of any yet. Considering USB inputs are starting to show up on AVRs, its quite possible that they'll become standard on A/V preamps as well.

Changes in "sound quality" (however you define that) have nothing to do with any of this.
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Old 06-15-2013, 05:50 PM
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Quote:
Originally Posted by Brownstone322 View Post

I use an A/V preamp, not a receiver, and have so for nine years, because I hate the way almost all receivers are laden with gimmickry. But your point applies to an A/V preamp just the same... ...The answer is that I listen to two-channel music about 90 percent of the time, and I want to simplify and consolidate -- fewer boxes, fewer cables. The idea of ditching the surround and center speakers and their associated cables is very appealing to me. Plus I want to use a computer as my primary music source (lossless), so I need a USB input. (And, yes again, I'm aware that I could add an external DAC, but that'd be one more box, albeit as smallish one.) I'd consider another A/V preamp with a USB input, but I don't know of any yet. Considering USB inputs are starting to show up on AVRs, its quite possible that they'll become standard on A/V preamps as well.

Does your AV preamp have bass management? Ability to set crossover points and phase and sub distances? That's all you really need it if you want a 2.1 system.

Or alternatively you could do what I do now - which is use JRiver media player as it has many great room correction features and its own bass management. I use JRiver's bass management instead of my AVR's now because JRiver has much more flexibility with adjustable crossover slopes and such. My AVR's crossover slopes were non adjustable. You got what you were given.

So now my music collection is on a PC > JRiver > audio goes out over the HDMI video card as a 2.1 digital channel signal > to the AVR which can play straight to my speakers and subs with its own bass management disabled. Very simple and no more boxes than necessary.
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Old 06-15-2013, 06:50 PM
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One man's gimmickry is another's necessary feature, just sayin'. Apologies if I offended, it seems all other options are workarounds, and if you want to simplify then we're back to option 4.

I could be wrong, but I believe USB is not a component interconnect, most are used with a smartphone, thumb drive, etc. My AVR is directly connected to my receiver via sound card, analog RCA, but then I send audio to two zones, so analog is a necessity. Toslink is another option.

Good luck to you.

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Old 06-15-2013, 07:02 PM
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Quote:
Originally Posted by Nethawk View Post

I could be wrong, but I believe USB is not a component interconnect, most are used with a smartphone, thumb drive, etc. My AVR is directly connected to my receiver via sound card, analog RCA, but then I send audio to two zones, so analog is a necessity. Toslink is another option.

Good luck to you.

On that particular Rotel there are two USB inputs...one in front for a portable device and another on the back for computer input--two separate source inputs.

B.
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Old 06-15-2013, 08:35 PM - Thread Starter
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Originally Posted by kiwi2 View Post

Does your AV preamp have bass management? Ability to set crossover points and phase and sub distances? That's all you really need it if you want a 2.1 system.

Yes, it has all the basic things you'd expect in an A/V preamp. It'd actually be an excellent basis for a two-channel system (I use it that way anyhow), except I really want an asynchronous USB input for computer-based audio, which is still an emerging configuration. In fact, I can only name a handful of components that have such a thing -- a couple of AVRs (from Pioneer and Cambridge Audio), a couple of two-channel integrated amps (from NAD and now Rotel) and a very expensive two-channel preamp from Classe. But I think it'll become more and more common.

One thing is certain, though. An A/V preamp is much better suited for subwoofer integration and bass management, which was my original point of interest in this thread.

Quote:
Originally Posted by Nethawk View Post

One man's gimmickry is another's necessary feature, just sayin'. Apologies if I offended, it seems all other options are workarounds, and if you want to simplify then we're back to option 4.

No offense taken, of course not. But I think you know what I'm referring to. AVRs have been engaged in "feature wars" for years, and I have to wonder if their owners know what half that stuff is, let alone how to configure it and use it. I mean, "height" and "width" channels? To each his own, I guess. (It's not only AVRs; the Marantz A/V preamps are much the same way. Techno overkill for me)

Quote:
Originally Posted by Brian B View Post

On that particular Rotel there are two USB inputs...one in front for a portable device and another on the back for computer input--two separate source inputs.

Correct -- an asynchronous USB input and high-resolution DAC (up to 24/192), much like a stand-alone DAC.

Thanks to everyone who replied.
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