Combining pre-out signals

[dekaliber]

A quick and probably dopey question -- what happens when you combine the L and R channels of a pre-out on an integrated amp with a Y cable (2 male to 1 female RCA)? Logic tells me that the 2 signals would get fused into one mono signal, but I'm wondering if there are subtleties to the electronics that my lack of knowledge with circuitry may not have grasped. Would there be any degradation from the 2 signals interfering with each other in the same wire?

I'm asking because I'm considering hooking up a subwoofer to the stereo amp, and the only way to do so is via the second set of pre-outs.

 

[markw]

Aside from the possibility that the entire signal path (not just the one to the subwoofer) will be mono, there's the possibility of phase issues between the two channels cancelling some of the signal.

 

[dekaliber]

I just heard back from Bob Moran at NAD and he suggested this may short the class A preamp outputs. Good thing I asked around before trying it. Stupid idea I guess!

Maybe I'll give the speaker level inputs on the sub a try.

 

[Adam]

Hi. This wouldn't happen to be in regards to the 20-39 PC-Plus that you have on order, would it? That has left and right line-level inputs, so you could connect it directly to both pre-outs on the amp.

You're probably talking about a different sub, but I wanted to mention that just in case. No reason to solve a problem that you might not have.

Adam

 

[dekaliber]

Hi. This wouldn't happen to be in regards to the 20-39 PC-Plus that you have on order, would it? That has left and right line-level inputs, so you could connect it directly to both pre-outs on the receiver.

It actually is. What I wanted to do was connect both my stereo amp and AVR to the sub at the same time. TLS guy suggested using a headphone amp as a switch, but I was curious if there was another solution. I may give the speaker level inputs a shot. Do you have any other solutions, short of plugging and unplugging different jacks between watching movies and listening to music?

 

[Adam]

Ahhh. I remember seeing that thread, but I didn't follow it because it because I headed back to work this week. I'll give it some thought and write some more tonight or tomorrow.

 

[TLS Guy]

It actually is. What I wanted to do was connect both my stereo amp and AVR to the sub at the same time. TLS guy suggested using a headphone amp as a switch, but I was curious if there was another solution. I may give the speaker level inputs a shot. Do you have any other solutions, short of plugging and unplugging different jacks between watching movies and listening to music?

Do not connect the speaker level outputs together, that will really blow things up.

You need to understand the concept of buffering. I used the headphone amp as a buffer amp, not a switch. I gave you the solution. If it were me I would buy a dual channel MOSFET opamp chip and make my own buffer, but the headphone amp will do the job, it will just be bigger and have controls you don't need.

If you want to drive a sub with your new NAD unit, and direct bass of both left and right channels to your sub you will have to buffer, anything else may cause damage or give inferior results.

 

[rijaak]

preouts bad too?

so you can't fuse the preouts either? Not just speakers outs?

 

[rijaak]

what about line level outs from two different amps? any danger there?

 

[TLS Guy]

what about line level outs from two different amps? any danger there?

Again, do it through a mixer or buffer amp.