Mono mix at the speaker?

[Dartagnan]

Hey guys,

How do I mix a stereo pair of speaker-level outputs to mono?

I've got a cheap receiver with no stereo/mono switch and a single 8-ohm speaker I'd like to use for bedroom music.

I'm guessing it's doable with a few resistors, right? How, exactly?

[Netlist]

Connect the speaker between the two ‘hot’ outputs.
No problem at ‘bedroom’ level.

/Hugo

[Dartagnan]

Really? Just connecting both leads to the red terminals will work??

Would this cause any probs if I ever turned it up?

[SY]

I don't think that will work. What you'll end up with is just the L minus R. Think of a mono signal; it will be common mode and the speaker will ride up and down on it, but there will be no potential difference between its terminals.

Best to do this at line level.

[Dartagnan]

Since I'm using the reciever's on-board tuner, a line-level mix isn't an option.

Isn't it possible to do at speaker level? What if I twist the black leads together, add say 4 ohms to end of each red lead, and twist them together?

[sprucemoose]

nope, cant just connect across the + terminals. that gives you a difference signal, which is the basis of the "Hafler effect", an ambiance recovery tecnique used in the '60s and later to provide a rear channel from a stereo source. works great for some program material, especially live rock. chicago at carnegie hall sounds great!

sm.

[Dartagnan]

nope, cant just connect across the + terminals. that gives you a difference signal, which is the basis of the "Hafler effect", an ambiance recovery tecnique [snip]

Yeah, I tried the + terminal suggestion last night, and the effect was sort of metallic and echoey...definately a contrived ambiance...

Hmm. It seems this isn't as easy as I thought it would be. Is there no good way?

I don't mind losing a bunch of sensitivity--the receiver is 100w/ch, and I'll only be playing soft music...

[SY]

Since I'm using the reciever's on-board tuner, a line-level mix isn't an option.

Sure it is. Two minutes spent with a soldering iron and a couple bits of wire will get you what you want.

[Dartagnan]

Great! How and where??

[SY]

Well, without your receiver's schematic or a block diagram, I can't tell you the easiest way. But I can tell you a sure-fire way.

Go to the volume control. It will almost certainly be a dual potentiometer. Check the value. Let's say it's 10K. Since you're not interested in cranking this up all the way, we can sacrifice a little bit of gain. Disconnect the feed wires to the top of the potentiometer sections. Add a 2K or 3K resistor to each wire, connect the other end of the two resistors together, then solder that other end to the top of the pot section corresponding to the channel you want to use for your mono speaker. If the balance control comes before the volume control in your receiver, you'll have to do this connection there instead of the volume pot, noting that the feed wires will come in to opposite ends of that control, not the same end like the volume pot.

If you're just using the tuner as a source, you can do something like this at the tuner output- trace where the tuner outputs are, disconnect them from the rest of the circuit, add the series resistors, tie the resistors' far ends together, then reconnect to the channel you want to use.

The resistors can be 1/4 or 1/2 watt. Matching is not terribly critical; 5% will do.