connections for a sub

[dekaliber]

Is it possible to connect both an integrated stereo amp and an A/V receiver to a subwoofer, and have them drive it independently?

The integrated is an NAD M3, and uses a set of RCA pre-outs to connect a sub. here's the diagram from the manual:

The receiver is a Yamaha RX-V1800, which uses 1 RCA connection for the sub. There is also 1 RCA connection for an input.

Most subs I see only have 1 set of RCA inputs, so would I have to just disconnect one source to plug in the other? I also see that they have 1 set of RCA outputs. What's that for?

Ideally, I'd like to use only my M3 for listening to music. Would it be possible to run the set of pre-outs into the subwoofer input (going from 2 RCAs down to 1)? How would that work, anyway?

 

[TLS Guy]

Is it possible to connect both an integrated stereo amp and an A/V receiver to a subwoofer, and have them drive it independently?

The integrated is an NAD M3, and uses a set of RCA pre-outs to connect a sub. here's the diagram from the manual:

The receiver is a Yamaha RX-V1800, which uses 1 RCA connection for the sub. There is also 1 RCA connection for an input.

Most subs I see only have 1 set of RCA inputs, so would I have to just disconnect one source to plug in the other? I also see that they have 1 set of RCA outputs. What's that for?

Ideally, I'd like to use only my M3 for listening to music. Would it be possible to run the set of pre-outs into the subwoofer input (going from 2 RCAs down to 1)? How would that work, anyway?

It is possible, but you will have to build a switch or switch/buffer amp.

If you have a sub that has left and right ins, that are buffered, (not directly commoned) you can make up a switch box.

If the sub has only one RCA input, or the inputs are directly commoned, you will need to design and build a buffer amp and switcher.

You can not connect any of your NAD pre outs together or you will have mono throughout your system.

In order to connect your pre out together, you need to design a circuit for a dual channel op amp chip and connect left and right together at the outputs of the op amp buffers.

If you can't accomplish this, then the answer to your question is no.

If your sub has only one RCA input you will only be able to use the bass from left or right outputs, but not both, unless you buffer. Your NAD is really set up for driving speakers requiring biamping, not subs.

The RCA output is for daisy chaining subs.

 

[dekaliber]

I'm probably going to get an SVS or Hsu sub with L and R RCA inputs.

Actually, here's a question in general -- why would a sub have 2 inputs anyway? Usually it's only one driver and bass frequencies would pretty much omnidirectional anyway.

So, would I be wrong to assume that I can just connect one of the pre-outs on the NAD to one of the inputs on the sub and the sub out on the receiver to the other input on the sub? I'm not 100% sure how the crossover on the NAD would work, but it sounds like the frequencies below the threshold are output from pre-out1 and the frequencies above are output from pre-out2 (jumpered to the main ins). Oh wait, I guess the L and R channels might have different low frequency signals. I suppose that means the L and R inputs on the sub simply combine the signals from both channels.

What about the speaker level inputs and outputs on subs? How are those used? Would I be able to chain my front speakers to those and leave the RCA connection for the receiver?

 

[TLS Guy]

I'm probably going to get an SVS or Hsu sub with L and R RCA inputs.

Actually, here's a question in general -- why would a sub have 2 inputs anyway? Usually it's only one driver and bass frequencies would pretty much omnidirectional anyway.

So, would I be wrong to assume that I can just connect one of the pre-outs on the NAD to one of the inputs on the sub and the sub out on the receiver to the other input on the sub? I'm not 100% sure how the crossover on the NAD would work, but it sounds like the frequencies below the threshold are output from pre-out1 and the frequencies above are output from pre-out2 (jumpered to the main ins). Oh wait, I guess the L and R channels might have different low frequency signals. I suppose that means the L and R inputs on the sub simply combine the signals from both channels.

What about the speaker level inputs and outputs on subs? How are those used? Would I be able to chain my front speakers to those and leave the RCA connection for the receiver?

An LFE output from a receiver is a buffered common output of the bass from the left and right chanels.

A sub with left and right inputs, usually provides a buffered input that will combine left and right channels, so that you can use a device such as your NAD that does not have buffered left and right outputs. If you connect the NAD output together, then the NAD will output mono at the speakers, because of the absence of a buffer.

You could connect your receiver LFE out to one of the sub RCA ins, and connect one of the NAD pre outs, to the other. You would have to choose if you want to output the bass from the left or right channel of the NAD. You can not have both, without building a buffer.

Speaker level inputs are for connecting an amp output to the sub and using the subs internal crossover. I don't see that would help you, I don't think you could use them at the same time, without adjusting the sub every time you switched. Buffering the NAD preouts is definitely the way to go for best results.

What you could do is buy a line level mixer and use it as a buffer to buffer and mix the NAD preouts. The most elegant solution however would be to build a buffer to combine the left and right outputs of the NAD. Op amp buffer circuits are very simple, with a low component count.

 

[TLS Guy]

This will do the trick for you. You can use this headphone amp as a buffer for the NAD.

Connect the NAD preouts to the headphone in. Common one of the right left headphone outputs and connect the common connection to one LFE in on the sub. Connect the receiver LFE out to the other sub LFE in.

You could use a Y connector on one of your NAD pre out and connect the receiver LFE out to the other side of the Y, but the output of the NAD channel connected with the receiver LFE would be loaded by the receiver output. You would loose about 3 to 6db on the NAD channel connected to the Y.

Using the headphone amp as your buffer is the best solution, if you don't know how to build a simple buffer.

 

[dekaliber]

I thought headphone amps only have a single 1/8" or 1/4" jack? How would I connect the 2 RCAs up to that? Is there a Y-type cable out there?

 

[TLS Guy]

I thought headphone amps only have a single 1/8" or 1/4" jack? How would I connect the 2 RCAs up to that? Is there a Y-type cable out there?

You will need two of these to go from your NAD pre outs to the headphone amp.

You will need one of these connected to a headphone out.

Then you just need a mono RCA to RCA cable from that connector to your sub.

 

[dekaliber]

You will need two of these to go from your NAD pre outs to the headphone amp.

You will need one of these connected to a headphone out.

Then you just need a mono RCA to RCA cable from that connector to your sub.

Maybe I'm missing something really obvious, but how do you get the 2 preouts from the NAD to the 1 input of the headphone amp?

 

[TLS Guy]

Maybe I'm missing something really obvious, but how do you get the 2 preouts from the NAD to the 1 input of the headphone amp?

Sorry, I thought the input was dual TRS mono, which is usual, but on this one the input is 1/4 inch TRS stereo, so you need this http://www.audiogear.com/cgi-bin/shopper.cgi?key=ADPT-2RCFQSM&preadd=action to connect to phone amp input.

This sort of thing is no problem for me as I solder up my own leads as required, which is the easiest and quickest.

 

[dekaliber]

Okay, cool! Thanks again for all your help. I'll give it a shot when I get my sub...

 

[Adam]

You could use a Y connector on one of your NAD pre out and connect the receiver LFE out to the other side of the Y...

I believe that this is what I was thinking about today. To make sure that it is, here's what I was thinking:

1. Connect one of the NAD pre-outs to one of the line-level inputs on the SVS sub
2. Connect the other NAD pre-out to one input of a Y-adapter
3. Connect the subwoofer output on the Yamaha to the other input of the Y-adapter
4. Connect the other (single) end of the Y-adapter into the remaining line-level input on the SVS sub

I think that this type of connection would work fine, except that you would want to make sure that you didn't send an output from the Yamaha and NAD at the same time.

 

[TLS Guy]

I believe that this is what I was thinking about today. To make sure that it is, here's what I was thinking:

1. Connect one of the NAD pre-outs to one of the line-level inputs on the SVS sub
2. Connect the other NAD pre-out to one input of a Y-adapter
3. Connect the subwoofer output on the Yamaha to the other input of the Y-adapter
4. Connect the other (single) end of the Y-adapter into the remaining line-level input on the SVS sub

I think that this type of connection would work fine, except that you would want to make sure that you didn't send an output from the Yamaha and NAD at the same time.

The problem with that solution is that the channel of the NAD connected to the Y will be loaded by the output impedance of the Yamaha in parallel with the sub input impedance. That will lower the output of that channel at least 3 db, and more likely 6 db.

The correct technical solution is a buffer amps, from the NAD and summing the signal at the buffer amp outputs.

The other problem the nature of the input buffer of the sub is an unknown quantity, and he still might run into trouble.

It seems he is trying to set up a superior system, and he should do his set up paying attention to optimal engineering principles. He will achieve best results with buffering.

 

[Adam]

It seems he is trying to set up a superior system, and he should do his set up paying attention to optimal engineering principles.

Excellent point. I think that we can all agree on a solution here - buy another SVS.

 

[TLS Guy]

Excellent point. I think that we can all agree on a solution here - buy another SVS.

That is the high cost solution. I think using the headphone amp as a buffer will work very well, even if a little awkward.