DIY Classic 47 Headphone Amp





Today, I put together a small headphone amplifier called "The Classic 47." It was relatively easy to do and actually sounds pretty good once you get it all hooked up. It doesn't have great shielding though. I tried to drill out an Aluminum Project Box but I messed up the wholes and scrapped the idea, so next time...

First off, I purchased this kit on Amazon for $10.

https://smile.amazon.com/gp/product/B06XBMN5QK/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1

It's quite cheap, even cheaper on AliExpress, but I wanted it sooner.

All you need to build it is a soldering iron and some solder, and a 12V-18V power adapter.





The kit comes with all the necessary components to get going including an acrylic transparent case. The instructions are mostly in chinese but you can figure it out pretty easy using their circuit diagram and PCB drawing.




While I won't go over everything in detail, the basic gist of the build is to make sure you sort out all your parts and know which resistor is which. Then you match them to the PCB board location. 

I started with the shortest items and ended up the largest items (capacitors and the pentiometer). If you've never done this before, you basically just take each leg and bend it, and then place it through the PCB holes in the correct location. When there's a positive/negative, just remember that the long leg is positive.


Once the legs are through and the item is flush, solder the joint on the back Make sure you heat up the leg and hole location first with your iron and then add solder to the hole to avoid any cold solder joints.Then trim off the legs when you're happy.



This is what it looks like when all the components are soldered on.


Finally, put the Op Amps into the IC sockets.


Then you're ready to test!

Once done, you can assemble the case.


 


This whole project took 1-2 hours to do. I spent most of the time trying to make an aluminum box for it which ended up failing. So, really, it could be done even quicker if you've got some experience. I ended up attaching a Bluetooth Receiver to it and used my own volume knob from Radio Shack. I also found that using the iFi Ear Buddy really helped remove all the noise that the amp had. The noise isnt much of an issue while playing music, but you can hear it when no music is playing. The Ear Buddy also helps from cell phone radio interference as well.

Update: I switched to a USB cable for power and it is dead silent now! I'll have to try this again with a 3-prong ground cable (laptop charger for example) and see if that also eliminates any humming



And finally, here it is with my Focal Elex headphone and some crazy wiring configuration. Yea, that's my DIY balanced cable to 4-pin XLR, which is connected to my DIY 4-XLR female to 2.5mm balanced male adapter, connected to a 2.5mm to 3.5mm adapter connected to the Ear Buddy. :)


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