Last time we had finished the desk and were looking forward to built in cupholders and high speed dial up. Perhaps we will get to those later but for this week, we are starting a headphone amp that is more commonly associated with Altoids tins. The Altoids (Chu Moy designed) thing is a cool idea but the intitial "I cant believe they put an amp in that altoids tin" thing wears off eventually so we wanted to consider a longer term, more designed approach.
At first we thought we would just build it right in to the table, but over the past couple of weeks, the leftover wood from the build has been calling out to us... "Generic Unplggd writer, use me." After coming across the Grado RA1 amp some time ago, we felt it was possible to get some of the same natural beauty but with a less techy, much less expensive and much more purpose built look. By using the same wood as the table, we get a blending effect that integrates nicely and can be taken out for use at the local wifi enabled Lollicup.
Now back to the interior design of the amp. If Legbrace Fetishists can have a huge internet community these days then so can DIY headphone amp builders (You didn't believe that link would actually go to such a site? ...seriously.). The Chu-Moy or Cmoy DIY amp is a big thing in DIY audio. There is quite the following and from what we can tell, it appears that anyone can use the design in any way they want. Chu Moy is largely credited with the initial circuit concept, but many have developed it further and prebuilt amps and kits abound. He has a site called headwize.com where you can witness the mayhem.
photo from evilfire.com
We went the full, from scratch, DIY route but that may not be for everyone. Try Ebay or here for a prebuilt model and then stick it in a new box... if you want. Hey, that Altoids tin is super portable and not too many outside "the community" know about it- maybe just keep it there. Anyway, it suffices to say that the amp gives your headphones much fuller and yes, be careful, louder sound. Almost any headphone will sound its best with one of these giving it some extra juice.
If you do the DIY version, check out Tangentsoft's site for the best tutorial on how to make it happen. Lots of suggestions and pics and most importantly: alternative parts for when you can't find what you need at Radio Shack.
The first thing we did was try to estimate how much space one of these little amps would take up with a 9V battery attached. The little circuit boards are no bigger than 1.75" square and the battery makes the package just a little bigger so we glued up a 4.5"x4.5"x1.5" block from the leftover table wood with a 3"x3"x3/4" cavity in it.
As you can see from the image above, we just drilled holes in the 4 corners all the way through one piece of wood, cut between them with a jigsaw, and then glued it to the other, undrilled piece. This created a cavity which doesn't go all the way through as you can see from the below photo-
Then we went to tangensoft's site and printed out the list of parts needed to make the circuit board. The actual microchips had to be ordered through Digi-Key which is no big deal, just get the part number (Digi-Key #OPA2132PA-ND) and call them and tell them you want that part number. You dont have to answer engineering equations or give them your Mensa ID number (Mine is 123...45...6...A..).
After receiving the chips (you only need one, but we are making a few of these) and running out to Radio Shack for all the ends and odds, you can solder up the board and start fitting it in. We used a dremel tool to make a little recessed home for it and it fits awesomely.
After finding a place for the circuit, we moved on to the plugs for the headphone cables. We decided to use the larger 1/4" format since this is going to be for our lovely set of Grado SR-125's - Grado headphones have been mentioned a few times here at Unplggd.
We decided on a fun star pattern around the holes- we wanted flush mounted plugs even though they come with nuts to basically screw them in... just didn't like the look. Not enough fun stuff in electronics; always so serious. The star shaped holes will be filled with an opaque epoxy and will look grey. The switch and LED will be on the bottom where they won't be seen.
Tune in next time for the cover plate on the bottom and for sound! That's right; music!