Annyone know where I can get some small device that takes maybe like a double A battery that boosts the signal that comes out of the headphone jack. The volume doesn't get very loud from the iriver slimx 350. Or any other suggestions?

This might be what you're looking for. I've never tried it so I can't say if it's good or not.

Dougal's got it right. A headphone amp is what you're looking for. I'm not sure of cost or any names to recommend though... check out head-fi.org and click on "Amp Forum" for more info.

- Matt

Most RadioShacks sell an el-generic cheap headphone amp & splitter for $20 (same model as boostaroo). A friend of mine uses it with her slimx & Koss A250s (and my grado SR-125s), and it works. In addition to a volume boost, the sound is a bit better too IMO (clearer bass). Just a quick & cheap option.

I just bought the XIN SuperMicro (Dougal's link) about a month ago. It's an incredible little amp that costs $159, runs on a single aaa battery and uses the line out (not headphone out) of your iRiver. You'll love it; it will drive most any headphone, even the lower impedance ones, and will sound great. I use it out of my iPod or my son's iRiver SlimX imp350.
Ted_B

For that money I'd go with a total airhead, of for even less, and airhead. (I used to use one before I got my cosmic)


http://headphone.com/layout.php

If you are handy with a soldering iron, you could build one of these:

http://sound.westhost.com/project70.htm
http://sound.westhost.com/project24.htm

The first one (a class A discrete design) has has cheap PC boards available and should have excellent sound quality (I have built and enjoy Rod's DoZ preamp). The second one doesn't have board available, but uses opamps so the small number of components should make it easy to build on Veloboard.

They won't look as elegant or be as small as most commercial offerings, but the sound quality should be top class.

Just a word of warning - neither of the circuits are suitable for battery operation (unless you mean a rechargable...) Thjey focus on sound quality, not on going easy on the power (that's what class A means...)

One thing to note with the Boosteroo is that if the volume is cranked up on my iRiver IMP250, with the Boosteroo inline, you can hear the CD spinning up / down, and the laser moving about. Also with my old Minidisc player it picks up the mechanical movements... But the thing is £20 or so, it does what it says on the tin, and as soon as the music starts at that volume, you certainly cant here the above

True. Looks like I didn't read the original post well enough. When going for low power, manufacturers use all sorts of techniques that aren't generally available to the hobbyist. Designing for low power is generally harder than designing for good sound and if Xin (et al)'s battery life figures are true, then I am truly humbled.

Or, with a little less effort, you could try these.. desigined for battery use and good quality sound:

Tangent's audio page

He has the basic design by Cmoy... and the ones that he and a group of others have developed.. (the META42, PIMETA, and PPA) Lots of help and info on building one, they sell PC boards and hard to locate parts for easy assembly.

I believe the Xin is a modified version of one of these.. made with surface mount parts for ultra tinyness.

Pretty easy kits to build..

I replaced my Total Airhead with the SuperMicro. I have nothing against Tyll's products over at Headroom. They are good products and they have great customer support. However, for the amps in question...No comparison. The Xin amp is much more refined, much more detailed, and at the same time much more slam; seldom are these characteristics found in the same amp for under $500. Xin is a DIY freak. I'm a believer.
Ted_B