O2 Headphone Amplifier Project

O2 Headphone Amplifier

I made this! It is a headphone amplifier for use with my Sennheiser HD650 headphones.

I’d love to be able to claim that I designed it, too, but that wouldn’t be true. It was designed by NwAvGuy and sold as a self-assembly kit by headnhifi.com. All I did was buy the parts and put them together.

Read on to see what’s inside and how I got on …

After reading the long and detailed assembly instructions, I was expecting this to be a tricky project. There were dire warnings about the consequences of mis-handling static sensitive components and plenty of detail about testing using a multimeter to avoid the possibility of damaging one’s expensive headphones.

In the end, though, everything went very smoothly. I bought most of the parts from headnhifi.com which turned up all present and correct, nicely packaged and on time. I sourced the batteries from ebay and the power adaptor from Maplin. Assembly was straightforward, the only hard part for me, being slightly colour blind, was identifying which resistors were which. In the end I used my multimeter to work it out.

I’m already pretty comfortable with a soldering iron, so it didn’t take me too long to solder all of the parts to the board. The static sensitive components need to be handled with care, but the instructions are very clear on how to do that.

Once assembly is complete there is a comprehensive guide to testing the board with a multimeter. Mine’s an old one with an analogue needle display but it did the job just fine and my board passed with flying colours.

I used a pair of old white Apple ear buds for the initial test, just in case anything had gone wrong. They have such horrible sound quality that I’d not have been too sad to break them, aside from it meaning my project had a fault. I really can’t understand either why Apple supply such rotten headphones with their products or why people continue to use them. Not that I thought Apple’s products sounded all the great even when used with better headphons, for that matter.

Here’s what my amplifier looks like inside:

O2 Headphone Amplifier

This is a rather blurry shot of my soldering work. It’s not the greatest, but it does the job.

O2 Headphone Amplifier

If you’ve read this far you are probably looking for the answer to the million dollar question - How does it sound?

The answer is: Fantastic! I was highly delighted with how this project worked out. I was using my headphones with the headphone socket from my pre-amp, so didn’t think having a dedicated headphone amplifier would make much difference. I was wrong on that score. Hard to describe the difference but the music seemed a lot more alive and comes with way more volume available than I could ever handle. Previously my pre-amp had to be turned up loud just to get the music to a listenable level with the headphones. This was potentially hazardous for my main speakers if I forgot to turn the volume back down again when switching back to them.

I wouldn’t say this is a beginner project. It is not really suitable for someone who has never used a soldering iron before (Try this - 126 LEDS + resistors later and you’ll know how to solder! My Mum’s still got the one I made.) but it’s definitely not so difficult you should be put off having a go.

However, if you don’t want to make your own there is a company that sells them ready assembled. Just be prepared to pay for the privilege!


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