Crawls Backward (When Alarmed)

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CMoyBB Headphone Amp DIY Begins!

I know.  What the heck happened to the Red Pepper fuzz face build?  Well, it's just delayed a bit.  It was shunted aside for a quicker and less fussy build.

I commute to my job working for The Man via subway.  And on and off over the years, I've had various appliances to listen to music to on the train.  No matter what the device, I've found the sound quality a bit lacking and the incessant background noise an issue that the puny output stages in those devices can't cope with. 

In the last year or so, I've discovered the cult of headphone amplifiers - promising a bit more volume as well as much better fidelity.  The concept is simple - run your device into the headphone amp, then go from the amp to your headphones. Recently I acquired a Sansa Clip Zip, and this was my excuse chance to build a headphone amp to go with it.

There is a mildly large group of enthusiasts for these things, and subsequently there are a number of different DIY and commercial designs out there.  I wound up going with the CMoyBB.  This is based a popular CMoy design cooked up by Chu Moy.

This particular version is offered in completed and DIY form from JDS Labs.  I pondered buying a complete one, but decided there was no fun in that.  By building my own, I'd get a feel for the circuit, and be able to tweak/mod it as if I wanted to.

I bought the PC board, jacks and opamps from JDS Labs, and sourced the other components from Mouser and my own stash of parts.  The JDS site has a complete step-by-step guide, including a layout diagram.  With those on the bench, I set out populating the board.

The board is very nicely made.  JDS offers them in green or red.  I went for the red.  Very cool. 

It's easy to build.  The only issue I ran into was with the output capacitors.  The value is 1uF, and the Bill of Materials specifies 63v rating.  I had some good quality WIMA caps, but they are rated for 100 volts.  Unfortunately, the lead spacing was a little too wide as you can see in the picture.


My simple (stupid?) solution was to solder a bit of component lead onto the bottom of the board where the 'outboard' leads should go, and then solder them to the capacitors. 

This worked fine.  The caps stick over the edge of the board a tad, but that's not an issue in mounting the board into the 'cabinet' later.

Stuffing the board took about 45 minutes or so.  I had one goof - the opamp wasn't fully seated so the amp didn't sound right at first.

I also put the LED into the spot where the dropping resistor should go.  I realized it after I'd put everything else in - easy fix. 

Above is the completed board up and running.  I did one mod right off - I set it up to run off 2 9-volt batteries in series - making 18 volts.  The stock amp uses an OPA2227 opamp, which can run on 9v.  But I'm going to experiment with some other opamps which reputedly sound better.  A couple of those need 10+ volts.  The JDS board is set up to run either 9 or 18 volts, so this was an easy change.

The other 'mod' I did was upgrade the 470uF filter cap to a Nichicon "audio" cap.  Who knows if that will make an audible difference?  But it's worth the 30 cents extra over a standard Vishay cap to try it.  

I tested it on the bench with an El Cheapo® clone of a Sony FM Walkman and some mediocre headphones.  It actually had nice bass!  Very promising so far.


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    January 5, 2014 at 11:56 AM
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