Can I run multiple headphones off one Crack amp?

[Pfenning]

So I took the plunge this morning and bought Crack and Speedball along with several other items. Man am I pumped! So can I add a second headphone jack, so my wife or friends can listen at the same time? Will it degrade the sound quality or over load the circuit?

Pfenning

[xcortes]

It depends. What impedance headphones are you using?

And ideally you would use identical cans or at least of equal sensitivity.

In the past I purchased tw identicl sets of HD600 so that my wife could listen along with. She never did. That's good 'cause now I'm using Sony MDR R10s and I couldn't afford a second set.

[Pfenning]

I currently own some Sennheiser HD 545 Reference cans. These are a little on the low side of the recommended ohm range, but I planned to use them till I can find some with the correct ohms (and price). I've been looking to snag some good used Sennheiser HD 580's or 600's, or some Beyerdynamics 770, 880, or 990's. How critical would it be to have a matched set? I was thinking if I could pick up a couple different ones, I could sample them long term, and have some to share when others wanted a listen. If I want to drive 2 pairs, should I have bought the smack?

Pfenning

[porcupunctis]

If you run two headphones in parallel, your amp will see about half the ohms of only one set.  The actual formula is the inverse of the sum of the inverses of each headphone.  The Crack will do the job even if the overall impedance is lower than optimal.  It is a very robust amp.  The worst that may happen will be some loss of bass.  A couple of 300 ohm cans in parallel will still offer more than the 120 ohms recommended.

You may need to crank it up a little more for the same volume, though.

[Pfenning]

Is it as simple as just adding a second jack in parallel off the first jack? I just ordered it yesterday, so I don't have the instructions yet. I think I'll give it a try. Thanks for the information.

Pfenning

[Laudanum]

If the majority of listening will be with only one person at a time, I would be inclined just to buy or build a Y cable and just install the single jack.  Just my 2 cents.