Building a stereo headphone box

[suncrush]

Ok, so I am setting up a stereo amp system using a pair of Micro Terrors.  The amps have headphone jacks, which is an important fact.

I'd like to set up a box that takes the signal from each amp's headphone output, converts it back to mono, and sends it to a common headphone out.

Now, I'm trying to figure out how to do this without totally screwing up the impedance, or doing anything nasty to my amp.

The wiring is easy.  The headphone jack just takes a mono signal and copies it to each side of a stereo out.  You could either just patch both sides back together into a mono signal, or you could pass one side and ground the other.

Once you've converted each signal to mono, you just wire up to a stereo jack.

But, what horrible amp-exploding thing am I not thinking through?

[thermionix]

The wiring is easy.  The headphone jack just takes a mono signal and copies it to each side of a stereo out.  You could either just patch both sides back together into a mono signal, or you could pass one side and ground the other.

I don't think you need to ground anything out, and you're probably over-thinking this.  Just take signal from either tip or ring from each Terror.  Flip a coin, doesn't matter.  And you already know how to combine them at your new, actually stereo, headphone jack.

If you really want to get fancy, you can disengage the ring connections in both amps' headphone jacks, and run standard guitar cables (tip + sleeve only) to your new combiner box.

^ That's assuming the Terrors have 1/4" headphone jacks.

[Kipper4]

No possible phase issues then?

[suncrush]

I'm mostly concerned about the impedance, since each amp will be driving only one side of the headphones, rather than both.  Not a problem?

[suncrush]

No possible phase issues then?

It would be really weird.  I'm sure the stereo out is just a splitter.

[anotherjim]

It has a solid state amp so impedance isn't much of an issue. Besides, you could have 30R or 250R or whatever impedance headphones. Does the user manual specify?
You should be safe to common the socket sleeve/ground of each amps headphone jack -  continuity test that the sleeve is hard wired to ground in the amp.
Phase issues? Only if you try to connect the tip or ring connections together between the amps. Keep one amp for left and one for right and you should be ok.

[vigilante397]

Jim beat me to it. Micro Terrors are hybrids with a solid-state power section so impedence isn't a big issue, plus the headphone driver is separate from the speaker driver, so it will be expecting an even higher impedence. It will be fine.

[feddozz]

I don't get it. Why do you need combine 2 amps for this? Isn't one headphone out enough?

[davent]

To convert the stereo out of my old shuffle ipod to mono i made up a patch cord to combine the signals.  Two 12r resistors in series, left channel to one end of the string and right channel to the other, the node between the two resistor feeds each output channel.

http://www.diystompboxes.com/smfforum/index.php?topic=111946.msg1031736#msg1031736

dave

[suncrush]

I don't get it. Why do you need combine 2 amps for this? Isn't one headphone out enough?

It's a mono amp. I'm using two in parallel to amp stereo effects. I hooked the tip and ring of one jack to the tip of a headphone jack, and re other to the ring. Grounded both to the headphone ground. Worked like a charm.