Somebody recently asked me what I do for a hobby. Well, if you discount playing piano or producing music, and making coffee, there isn’t much time left for me to do much else. However, before the Christmas break I resolved to begin a real hobby project during my time off. (Incidentally, “resolved” is used here in the truest sense of the word, as I do not believe in using a significant but arbitrary time measurement milestone to prompt a lifestyle change.)

You see, I had been reading online about various different hobby electronics projects. My interest in all audio related things caused my interest to be piqued at the idea of building a headphone amplifier. More specifically, a CMoy headphone amplifier, based on the excellent circuit published by a guy by the name of Chu Moy at Headwize. In actual fact, the tutorial and schematic I’m using comes from Tangent.

The rest of this fixation will simply journal my first electronics experience for a while and provide a description of the Australian distributors and construction methods I used. If that sounds interesting to you, read on.

So, after reading up extensively (and marvelling at the apparently simplicity of the CMoy’s design) about a fortnight before work finished in December I ordered some hard-to-find electronics bits from Farnell InOne. Actually, there were only two bits – $26 to purchase and ship only the op-amp and a pot. Ah, even hobby audio is expensive!

Most of the other bits I got from Dick Smith Electronics, and a couple of bits from Jaycar. There are a few things which make lean towards DSE as my preferred vendor for this kind of gear. The first is that they’re everywhere. The second is closely related – all the stores have some level of stock of basic electronic components. The third is that their stock counts are reliably updated on their website on a per-store basis each day at 2am (and the Jaycar website sucks in comparison). And last but not least, particularly for this particular electronics novice on this particular project, is that they stock the exact same protoboard used in Tangent’s tutorial. (It’s DSE catalog item H5608.)

In fact, I think the only parts I’ve actually elected to buy at Jaycar are some film caps (as they are rated closer to the circuit’s specified values than the DSE ones) and a box-type double-gang 10K pot (which appears to be made by Noble, in their X3B93GPHPN series which Chu Moy refers to on his project page). When I was buying the op-amp I was so excited to find the Alps 10K pot at Farnell that I did not think to confirm it was double-gang. So, if you or someone you know needs a 10K single gang Alps pot, I’ve got one going cheap!

I haven’t done any soldering since about year 10 at school – that’s six years ago now. We built an egg timer in our Tech classes, etching a PCB and everything. Back then at St Peter’s College they had just built a new technology centre, so we were using drill presses, vacuum extracted temp controlled soldering iron stations and top range testing equipment. Here at home, I have none of these luxuries. Before this weekend I didn’t even have a decent iron. Learn from my frustration – if your soldering iron’s tip is charred and black and won’t hold any solder no matter how much you push on there, stop right now and go get a new iron. Mine cost $21 on sale, and it has replaceable tips compatible with a much more sought-after line of soldering stations from DSE: future proof.

When planning the amp I bought enough components to completely build two, apart from the single expensive op-amp from Farnell. So, with firm resolve on New Year’s Day, I sat down at the dinner-cum-project table and, using my dodgy iron, I built a whole board, taking approximately 6 hours from start to finish. Then I tested it. Ugh. Generous hiss even without any inputs connected. You should see the back of it – it’s charred and fluxy and blobby and disgusting. The new iron (along with a Helping Hands alligator clip stand to minimise the frustration of only having two hands of my own) allowed me to put together a board in about 2 – 3 hours on Friday night, including a very enjoyable self-education phase with the multimeter at the end of the power supply section’s construction. This one sounded blissfully quiet with no inputs connected, and helpfully amplified every part of my input signal completely, including about 10% hiss and line noise.

The amp itself, however, can’t be faulted. In testing it I had what appeared to be some trouble with the right side of the amp – buzzing and humming much like a ground loop. I tested every connection, potential difference and resistive path with my trusty meter, with the power applied and disconnected, and with the chip in and out of its socket. It’s here that I must praise the Burr Brown OPA213x – I’m sure I punished it by inserting and removing it about a dozen times, and by probing its leads with the meter incessantly. After dealing with computer parts quite a lot, I’m pleased to say that this little op-amp seems to suffer handling with ease. Tangent speaks truly when reviewing the Burr Brown OPA2132 & Co. op-amps: they sound superb and do excellent work under poor conditions. In a true test of character and display of irony, it turns out that my right channel alligator clip was earthing with the sleeve on the output jack from my CD player, which was a completely usual cause for ground-loop buzz.

I’m stuck now because I don’t have a dual-wiping pot to finish the job with a volume control. I’ll head down to Jaycar this week and grab a handful of them, along with some other bits and pieces. Then I’ll sell this one on eBay, order a bunch more op-amps from Farnell and go around again a couple of times. I want to get my experience and troubleshooting level up before I embark on a PIMETA journey…