...Anyone know how to do this?

I read about it years ago...but I don't remember what book it was in...

Basically you take a 100w power amp and hook up some resistors and you've got a very powerfull headphone amp.

Its an old studio trick so I was hoping someone here would know...

I really need the headroom that this would offer.

thanx!

texhouston wrote:...Anyone know how to do this?

Basically you take a 100w power amp and hook up some resistors and you've got a very powerfull headphone amp.

It will all depend on what kind of phones you plan on using. If you're using 600 ohm studio headphones, you can actually get away with plugging them directly into your (solid state) power amp. An amp that can put 100 watts into 8 ohms will only put a max of about 1.5 watts into 600 ohm headphones. That's quite a lot for headphones, and you can make them crackle and die if you crank the amp, but the advantage is that you can basically string as many headsets across the amplifier speaker outputs as you want without changing the sound/power going into each set (and you can make them go LOUD). If you add a resistive network at the output to trim the power down to a few hundred milliwatts then you to some extent lose the ability to parallel sets, unless you build an individual network for each headphone output.

Someone will probably tell you to wire a resistor in series with each output since, unlike normal speakers, most headphones are designed to be able to be driven by slightly high source impedances (like tens to hundreds of ohms depending to some extent on the model), but for simplicity you can probably just wire them directly if you just remember not to turn up the amp more than maybe 1/2 of the way up, or basically more than you have to to just make your ears bleed.

If you want to be able to plug consumer 8 ohm headphones in, then its a whole nother story, you'll definitely have to cut the max. voltage level somehow. You can do it with resistors, but another alternative is to use a 70V line to speaker transformer like they use in multiroom PA systems. I don't know why I mention that...I guess it's maybe more expensive than resistors and not necessarily "better" since you've got plenty of power to throw away in resistors, but for some reason I feel like everybody just has a box of a few dozen 70V line to speaker transformers sitting in their closet waiting for someone to figure out a really good, interesting use for them the way I do. This is probably not a very valid assumption. But just thought I'd throw it out there.

Ned

If you're looking for a donor amp, I just took my Roland out of use in my home studio.
It's a Roland 120 (not JC, like the guitar amp).
Simple and nice, and I don't need it, so I'm planning on selling it cheap. Like all Roland stuff from their golden era, it's really nicely built.

-A

Thanks Ned!

I'll give this a shot, all my headphones are 600ohms and I need to string multiple pairs.

Alex, I've got enough amps but thanks for the offer.

ned knows all things electronic- seriously seriously.

Now that somebody was nice enough to stick up for me I feel I should go back a tiny bit on what I said. I mean, what I gave you was technically probably bad advice. It's true you can "get away with it", but I just want to be sure it's clear that you have to be very very careful you don't ever accidentally plug a low impedance set of phones into your box or ear/headphone destruction is guaranteed. The right way to do it would definitely be to add protective series resistors to each output, but if 600 ohms is carefully assured, you don't technically need to.