• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

NAD Preamp switching to Mono with Y-connector

M

Martin Rola

New Member
I have a C160 preamplifier, and I just noticed something odd. When I use a Y-cable out of either of the preamp outputs to connect to a subwoofer that has a single RCA input, the amp switches to a mono mode (or at least a partial mono). For example, if I pan all the way to the left, it works as expected without the Y-cable attached. As soon as I connect the Y-cable, both speakers get sound. The same result happens even if I use the passthrough output on the amplifier (bi-amping with two Parasound HSA-750s in stereo mode). The effect occurs on both the high frequency and low frequency connections to the speakers. If I use a single cable out of only one of the outputs, the system operates as expected. It happens even if the Y-cable is not connected to the subwoofer, so it is not triggered by the sub. I've tried various Y-cables as well. Does anyone have any idea what may be causing this?
 
Register to hide this ad
You cannot use Y cables to “combine” outputs (like lift and right) - it is essentially like creating a short circuit between the differing output of the left and right channels.

It probably won’t harm the preamp in small doses, but should not ever be done.

Subs that have separate left and right inputs have an internal summing circuit to combine left and right to internally create the mono signal for the sub, it isn’t an internal Y cable.

You can “split” outputs all you want with Y cables, but you can’t ever “combine” outputs.

You could drive the sub either with speaker level outputs of the stereo amp, or just use either left or right preamp outs to drive the sub mono input (you will only get bass from one channel, but that is a 95% solution for most music).
 
Yup, that's pretty much it. If you think about it, how could the outputs be directly connected together, yet remain separate? Answer: Can't.

Fortunately, one can construct a sufficient mono summing adapter from just a few inexpensive parts. Refer to Rane's "Why not Wye?" paper.
 
And the shorting of outputs happens within the Y cable itself, which is why it goes to mono even when the Y cable output is not plugged into the sub”s mono input.
 
that's to be expected. if you combine the left/right signals at any point n the signal path, the entire signal becomes mono
 
Thanks for everyone's quick feedback! I knew that the Y connector would sum the outputs for the subwoofer, but what surprised me is that it also summed the outputs for the 2nd separate preamp output that is driving the main speakers. Almost every post online suggest to use a Y-connector to sum the L&R outputs when driving a subwoofer if you don't have an LFE output, which seems to make sense because you'd want the low frequencies from both channels sent to the sub if they are different. I just didn't expect that putting a Y on one of the pre outputs would cause the 2nd pre out to also sum. Even NAD suggests to use a Y connector on their own technical support page. I may end up just connecting a 2nd matching sub which will take care of the problem, but this still seems odd since the approach is recommended by a lot of manufacturers. I'm just using the left output now -- at least I got my soundstage back!
 
Martin Rola said:
Even NAD suggests to use a Y connector on their own technical support page. I may end up just connecting a 2nd matching sub which will take care of the problem, but this still seems odd since the approach is recommended by a lot of manufacturers. I'm just using the left output now -- at least I got my soundstage back!
Click to expand...

Maybe you can post a link to NAD's recommendation. I suspect what they were saying is that you can use a Y-cable on both the left and right outputs and use one side of the split Y cables to connect to your amp left/right inputs and the other side of the split Y cables to connect to the sub's left and right inputs. It could not have been to combine both left/right into any mono input.
 
Martin Rola said:
Thanks for everyone's quick feedback! I knew that the Y connector would sum the outputs for the subwoofer, but what surprised me is that it also summed the outputs for the 2nd separate preamp output that is driving the main speakers. Almost every post online suggest to use a Y-connector to sum the L&R outputs when driving a subwoofer if you don't have an LFE output, which seems to make sense because you'd want the low frequencies from both channels sent to the sub if they are different. I just didn't expect that putting a Y on one of the pre outputs would cause the 2nd pre out to also sum. Even NAD suggests to use a Y connector on their own technical support page. I may end up just connecting a 2nd matching sub which will take care of the problem, but this still seems odd since the approach is recommended by a lot of manufacturers. I'm just using the left output now -- at least I got my soundstage back!
Click to expand...

If the 2nd outputs were separately buffered, maybe simply Y-ing them might work.

But, most 2nd outputs are little more than internal Y connections so whether you short together L/R of the 1st or 2nd pair produces same result.
 
whoaru99 said:
If the 2nd outputs were separately buffered, maybe simply Y-ing them might work.

But, most 2nd outputs are little more than internal Y connections so whether you short together L/R of the 1st or 2nd pair produces same result.
Click to expand...

I was thinking that also, and I noticed that the C160 actually has an attenuation level control for the second preamp output (making the prospect of buffering more likely, though unless it had both gain and attenuation, it isn't necessarily buffered).

Even with buffering, it doesn't seem like a great idea to tie them together, but it is possible. I'm curious to see what the manual says.




2B99oer__59672.1542325676.jpg
 
Yeah, I've never seen many suggestions to directly Y together outputs. There's a lot of context I think is often missed or misunderstood in found information.

Made a very quick run through a manual. I didn't see any suggestion to Y together outputs, but maybe I missed it.
 
Last edited:
I've never seen any KNOWLEDGEABLE sources suggesting using a "Y" splitter to join the right and left channels to make a mono output. i strongly doubt NAD suggested this.
 
You are correct, I was misinterpreting something in one of the posts. There is a technical support post on the NAD site that is for doing this to an amplifier, but it is a bit different context. In that case, it referred to connection one side of the Y to the sub and the other back to a pre-in, which doesn't apply in my case. The sub is a Paradigm PDR-10 v3 which also has speaker level inputs (but no pass through outputs). I didn't think it would be a good idea to bi-wire the outputs of the amp I'm using for the low/mid drivers into these speaker level inputs, but if that would be OK, please let me know. Otherwise, I'll just run with the single channel to the sub for now until I get the 2nd sub going.

Thanks everyone, this was very helpful.
 
Thanks - that makes sense. I should have known that. You would think someone like me with a MSEE would have know this - especially since I now remember doing a lab study on the response of 80s DCM Timeframes for a project!!! I'm obviously out of practice and didn't stick with the analog circuit stuff!! But if you need to know anything about a robot, I can certainly help you there!!

All of you have been a big help.
 
peterp1 said:
You cannot use Y cables to “combine” outputs (like lift and right) - it is essentially like creating a short circuit between the differing output of the left and right channels.
Click to expand...

Its not a short persay but it is paralleling both channels together. SInce it is line level, a "Y" connection acts more like a stereo/mono switch. Won't hurt anything but I am assuming the OP's sub is one from a 5.1 surround system where the sub output from the receiver is only a single output jack. Should probably work fine with a genuine sub which uses stereo line level low inputs.
 
cademan said:
Its not a short persay but it is paralleling both channels together.
Click to expand...

I understand first thing that comes to mind with "short" is short to ground. But, technically, a short is just a relatively low resistance connection between two circuits where the resistance between is normally much higher. So, while the signal isn't shorted in the sense of like shunted to ground, the two channels are shorted together by the Y cable.
 
Some pre-amps have separate buffered outputs. Those you can wye to gether. I use to do something similar with the line outputs of my C-28 which were totally different that normal outputs you use to feed your stereo amplifier. Doing that however cancels the stereo ambient information contained on the recording. It can also reduce the bass volume depending on the relation ship between the two stereo channels in reference to the source of the bass sound. .
 
You must log in or register to reply here.
Back
Top Bottom