NAD 1240 Preamp & subwoofer connection question

[drbiggles]

Hey everyone!

I don't post here very often, mostly in the Speakers forum. A friend who's not able to be here, asked me to stop by and see if you had any answers for him. Please help!

The subwoofers in question may be Cambridge ASW-1's. I do know they're powered and a stereo pair.

He knows about installing the subwoofers to the Tape Outs. But he wants to have the volume knob on the preamp to also adjust the volume of the subwoofer. More specifically, "what's up with the two separate pairs of outputs on that particular preamp." If those 2 sets of outputs work for 2 amplifiers, why not the 2 powered subwoofers?

"The NAD 1240 has two pairs of outputs, 1 and 2. Each set has a R and L channel. Output one goes to the power amp. I was trying to use output two R and L to go into the R and L of a stereo pair of subwoofers. Every time I plug into output 2, it mutes one of the main speakers. When I unplug from output 2, the speaker is back on, normal stereo operation. Is this normal? I can only guess that the preamp, somehow, when you use both outputs simultaneously, thinks you are adding a second power amp and bridges both to MONO automatically so that output 1 becomes R and output 2 becomes L. This would explain why I lose one of the main speakers via the power amp. It's sending everything to the subwoofer. Is this correct or is the preamp not working properly?"

Biggles

 

[whoaru99]

There isn't enough info for me to understand what's at fault, but I doubt it's the preamp.

First thing I'd do is just connect the two cables that you want to use for the sub. Plug them into the 2nd preamp outputs but don't connect them at the far ends.

If the sound still cuts out then swap the cables left and right. If it follows the cable then you have a bad cable. If the sound works fine either way, then it's probably something with the sub(s) or how you're trying to connect to the sub(s). Speaking of which, how, specifically are the subs being connected? If running a stereo pair of subs then then left pre out should be connected to the left input of the left sub, and the right pre out connected to the left input of the right sub.

 

[drbiggles]

Thank you Whoaru99 for your response, it's hugely appreciated!

"Let me rephrase the question. I am specifically wondering if anyone knows whether the function of the NAD 1240 preamp outputs changes if you use both simultaneously. In other words, you can use either bank 1 or bank 2 (a bank consisting of a stereo pair, R and L) individually, but what seems to happen when you use both bank 1 and bank 2 together is that they cease to be two sets of stereo pairs. What happens when you use both is that one of the channels that the main speakers are connected drops out. Why would that happen when you plug into the second set of outputs? Unplug from the second set of outputs and both main speakers are on again."

Biggles

 

[whoaru99]

My gut says both pair are intended to be used simultaneously if needed.

The manual appears to be available in the NAD archives. Have you checked what NAD says about it in the manual?

 

[drbiggles]

I have, it states that it can run several amplifiers in parallel, and it states that can run "powered" speakers having built-in power amplifiers. Another paragraph for the same Preamp Outputs section is about connecting surround sound or ambiance processors.

Biggles

 

[whoaru99]

I gave a look too. It says you can use both, is a somewhat indirect way. Says if you don't want your main signal to go through a surround processor then connect one set of outputs to the main amp and the second set of outputs to the surround processor.

 

[drbiggles]

Exactly. And the original question remains. Maybe the preamp is broken, or maybe it's a question for NAD.

Biggles

 

[whoaru99]

Maybe, but least likely.

Have you tried what I suggested?

 

[drbiggles]

Hey,

Yes sir! Cable swapped and test good.

Biggles

 

[whoaru99]

Not sure what that means.

With just the cables plugged into the 2nd preamp outputs, not looped together, not connected with any sort of "Y" cables, no subwoofers connected, the free ends of the cables just laying on the floor, the output 1 still cuts out?

If still cutting out, it's both channels, or just one channel cuts out?

 

[drbiggles]

What I meant by the cable tests good, is that he tried it on another system and the cable is fine. He tried a different pair of cables that test good, and the same issue happens.

It's not that you lose a channel. It's that when you attempt to use the second output, instead of having two separate right and left channel amps, one amp turns into the right channel and the other amp is the left. It's as though the preamp decides for you that you're bi-amping your speakers.

Amplifier is on the number 1 output, subwoofers are on the number 2 output. When the subwoofers are connected, the amplifier loses it's right and left channels and just goes to a Right or Left channel only. Then, the subwoofers take on the other channel.

Biggles

 

[Eminence1963]

I think there is a problem with that preamp or them sub woofers are doing something funny to them outputs. I would plug in another amp and try that first before you start seeing magic smoke. Meaning try a set of amps, ditch the subs for now until You or he figures it out.

 

[whoaru99]

What I meant by the cable tests good, is that he tried it on another system and the cable is fine. He tried a different pair of cables that test good, and the same issue happens.

It's not that you lose a channel. It's that when you attempt to use the second output, instead of having two separate right and left channel amps, one amp turns into the right channel and the other amp is the left. It's as though the preamp decides for you that you're bi-amping your speakers.

Amplifier is on the number 1 output, subwoofers are on the number 2 output. When the subwoofers are connected, the amplifier loses it's right and left channels and just goes to a Right or Left channel only. Then, the subwoofers take on the other channel.

Biggles

I could not find much detail on the subs mentioned. Is there something unique about them?

To me this sounds like some sort of problem due to the subs combining the outputs.

If one is trying to run a stereo pair of subs, normally you'd connect just one output to each sub. For example, the left pre out to the right input (yes, right input*) of the left sub, and the right pre out to the right input of the right sub. Is that how it is?

I do not believe it is a problem with the preamp, and if cables have been changed then it's not a problem with the cables.

That leaves how the cables are connected to the subs and or some idiosyncrasy of the subs themselves.

Is it possible to get a sketch of how the subs are connected, and pictures of the back panels/connections & adjustments on the subs?


*for a single connection most mfg. seem to designate the right input, but check the sub/doucumentation.

 

[drbiggles]

I think there is a problem with that preamp or them sub woofers are doing something funny to them outputs. I would plug in another amp and try that first before you start seeing magic smoke. Meaning try a set of amps, ditch the subs for now until You or he figures it out.

Agreed. Traditional sleuthing. Check all bits with known good components and work your way back.

I could not find much detail on the subs mentioned. Is there something unique about them?

To me this sounds like some sort of problem due to the subs combining the outputs.

If one is trying to run a stereo pair of subs, normally you'd connect just one output to each sub. For example, the left pre out to the right input (yes, right input*) of the left sub, and the right pre out to the right input of the right sub. Is that how it is?

I do not believe it is a problem with the preamp, and if cables have been changed then it's not a problem with the cables.

That leaves how the cables are connected to the subs and or some idiosyncrasy of the subs themselves.

Is it possible to get a sketch of how the subs are connected, and pictures of the back panels/connections & adjustments on the subs?


*for a single connection most mfg. seem to designate the right input, but check the sub/doucumentation.

Yup, simple connection. #2 Right pre-out to right input of sub and #2 Left pre-out to the left input of the sub. He was unsure of the model number of the Cambridge subs. This is why it was so frustrating because it is a simple connection with equipment that worked fine on other systems. Although, he never did try using the second pair of pre-outs on the preamp in the past. Getting a digital image of the setup isn't possible at the moment. That makes me kinda crazy too.

After we closed the doors here last night, I emailed him with a simple solution. I haven't heard back to see if that worked. Instead of using the #1 pre-outs for the amp and the #2 pre-outs for the subs, I suggested splitting the two. Meaning, put the right side of the amp on the #1 pre-outs, and the left side on the #2 pre-outs. Do the same to the subwoofer. Considering the results he was getting, this should actually work.

Biggles

 

[whoaru99]

Dunno...hard to say if it will work since we don't really know the root cause of the problem.

This situation feels familiar to me inasmuch as working 3rd or 4th party to resolve a problem. Often takes a long time and incurs frustration for all involved, for something that probably could be identified in a short time on-site.

Not picking on you personally, or this situation in particular, more just a rant. You'd probably not believe the number of times I've heard "Yeah, we checked everything...it's all OK." Only to end up having to make a trip and find in 15 minutes that the problem was one of the first things we asked them to check. I'm not talking about working directly with end users, these are supposed to be trained repair technicians.

 

[drbiggles]

Good Morning Whoaru99,

Maaaaan, I'm with you 900% and I get it. I've put in a lot of effort and time not to be That Guy here on AK. And I knew better when I sat down and started this thread. The only thing that caused me to press forward is that I know the guy and he's really gone out of his way to help me in the past. And so, I went ahead and posted his questions knowing full well it was probably going to go south not too far down the road. My next thought is that these 3rd and 4th party questions/post should be considered to be banned in the future. But I don't believe that's fair either. I'm sure there have been a decent amount of these questions where something good has come out of it. Sometimes it works, and some times for whatever reason, it does not work out well.

Carry on and hope your day and weekend go exceptionally well.

Biggles

 

[whoaru99]

Oh, sorry, my implication was not that this sort of thing should be banned from discussion. Only that it can be time consuming and challenging to work through.

 

[drbiggles]

Ha! That thought wasn't something I got from you, that was all in my head.

Biggles