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August 26, 2011

Miu Audio RA-1 Portable Headphone Amplifier

Miu Audio, a recent sponsor on HeadFi.org, offered some freebie kits on their HeadFi sponsor thread a few weeks ago. Of course I was happy to take them up on the generous offer, there are few things more enjoyable than dropping  a few components on a PCB and cranking up the soldering iron.

Miu Audio operates in Shatin, Hong Kong and has been producing gear since 2004. They've created a number of rather interesting looking CD players, as well as an impressive looking little portable tube headphone amplifier, speakers and other audio components.

The Miu Audio iH Tube Headphone Amp
The kit I received was purportedly less exciting than the iH Tube Headphone amp, but still a very capable little machine. The board was noted to be the RA-1 v1.1, which leads me to believe the circuit would be similar to the famous RA-1,  a cute little headphone amplifier housed in mahogany by Brooklyn's Grado Labs.

The Grado Labs RA-1 Headphone Amplifier
Included in the kit was the circuit board and a number of parts in plastic bags, each labelled individually. It may have been nice for the labels to include additional information like capacitor voltage ratings, just in case a potential kit builder wanted to substitute something in the kit without having to track down the schematic and do some math.

The Miu Audio RA-1 v1.1 Circuit Board
Being the compulsive builder than I am, I always measure resistors before dropping them on a board. In rare instances there are mis-marks, slight drifting of vintage carbon comps, or resistors that fall out of their tolerances. I did notice that the resistors in the kit that were supposed to be 100K (100,000) ohms were actually 100 ohms. Simple mistake I'm sure, but it saved me from having to troubleshoot and potential smoke ;) I opted to order some compact Vishay half watt metal film resistors that were a mere 4mm long. They're slightly fatter than the resistors included in the kit, but still fit just fine. I also opted to drop on a gold plated op-amp socket I had in the parts bin rather than the nickel plate included with the kit.

Board with OpAmp socket and resistors fitted

Once these steps were completed, the rest of the components were dropped on piece by piece. This is a very quick build and should be easy to complete in less than an hour.

Completely Populated Board
At the recommendation of another HeadFi member, I replaced the stock op-amp with a Burr Brown 2134AP Op Amp. While the amp isn't the last word in control and detail, it has a pleasing amount of bass and was fun to listen to with my modded and recabled Panasonic RP-HTX7-R1 headphones.

Here is the amplifer dropped into a Godiva Chocolate tin, which seems to be the perfect size!

Completed amp in a Godiva Tin

If you like miniature headphone amps in tins, check out my post on the JDSLabs CmoyBB in an Altoids tin.

Need a custom cable for your portable amp or device? Contact Zynsonix Audio for some great options.

The Fine Print:
Please remember that building circuits and performing circuit modifications can be dangerous to you and/or your surroundings and should only be performed by a certified technician. The owner of this blog and all associated parties can not / will not be held responsible if you attempt a build or modification posted above and cause physical harm to yourself or your surroundings. Many electronics contain high voltages that can kill, and mods, if performed improperly, can be a fire hazard. Please keep this in mind. 

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