The Objective2 (O2) Headphone Amp DIY Project

[haejuk]

Can't you use the low current op-amps and low gain resistors to make the O2 work well with IEMs? I plan on trying that with mine once all my parts arrive.

[cecil0405]

Thanks for your reply!

[nezbleu]

Originally Posted by greenalien

@cecil0405 - the O2 isn't really suitable for in-ear type headphones of the sort shown in your picture - but both those and the items featured in the video appear to be triumphs of style over substance...

While I'm not a big fan of that brand of headphone, there is nothing inherent in in-ear phones that makes them "unsuitable" for use with this or any other amp. I have used my UltimateEars IEM's with my O2 and it is a nice combination. The UE's are quite low impedance and so benefit from the very low output impedance of the O2. Sound is definitely better than without the amp, and much better than the same IEM's driven from a CMoy.

Cecil: those phones are widely available, so listen to them, and compare to some other good brand-name headphones.

[greenalien]

there is nothing inherent in in-ear phones that makes them "unsuitable" for use with this or any other amp

I have always found in-ear type headphones to be very easily driven and easy to overdrive into distortion, hence the reason for suggesting that they weren't suitable for use with the O2. I had never considered adding a zero-gain O2 into the chain, and it's interesting to know that it improves the sound.

[sgrossklass]

If you plan on driving IEMs, definitely include a gain setting of unity (i.e. gain setting resistors not equipped on this position). As mentioned, this tends to be ample. I'd easily consider the O2 the best inexpensive amp for such a task, as it is dead quiet and not particularly bothered by low impedances while having an output impedance of just half an ohm.

[nezbleu]

That kind of depends on your source, doesn't it? Using the headphone-outs of my MP3 player (Sansa Fuze or Sansa Clip) I find it useful to keep the volume control of the player at a lower level (to conserve battery power) and let the amp apply some gain. In fact I usually have the gain switch in the "high" position and the volume control past 12 o'clock, either with IEMs or my AKG full-size cans. I just keep the volume lower on the player.

Greenalien, you are right that most IEM's can be driven to uncomfortably loud levels without an external amp. But then, so can most over-ear phones. But some IEM's still present a difficult load despite their efficiency (16 ohms or less), and the output stages of lots of portable devices suck. A good amp can improve sound quality, even where sound quantity is more than adequate.

[ethanolson]

If it were me and my IEMS (Shure E2c, 16 Ohm) then I'd check out the O2 mods thread and change the high gain to 2x or less and then put the voltage divider circuit from the mods thread on the low gain setting. That way I'd be able to dip below unity gain on the O2 for redbook sources.

Also, it's worth noting that my Shure IEMs are not nearly as loud as my less efficient 55 Ohm AKG headphones with their 30mm driver when played straight from my laptop's headphone port. I believe it's because of the current draw that my IEMs impose on the circuit. Current is often a limiting factor in many electronics but is where the O2 shines.

I also put in an email with RS last year about reducing the voltage offset because I surmized that the offset was enough the have instances of all push and no pull, or vise versa. He explained how to do it. I'll have to dig up that email and share. He did also indicate that he thought it still didn't matter, though.

In case you're wondering, I use my IEMs straight from my laptop in one setting and I use my DAC/Amp combo with my AKGs in the other.

[vitop]

This looks like a great project for me and my son. I just bought him some headphones and I'd like to get him an amp he can use with the stereao as well as his iPod. Are there any PCBs around? If so, I'd like to get two. Are there any recommended cases? This site was a great find!

[lorriman]

Originally Posted by vitop

This looks like a great project for me and my son. I just bought him some headphones and I'd like to get him an amp he can use with the stereao as well as his iPod. Are there any PCBs around? If so, I'd like to get two. Are there any recommended cases? This site was a great find!

I was a newbie builder who succeeded (no prior soldering experience nor any electronics knowledge). I'll briefly give a few words that might help.

Assuming the lowest common-denominator that you are as much as a newbie as myself:

There's a lot of detail that needs to be absorbed to get this right. Unless your son is infected with your enthusiasm and drive or is quite geeky then you might find he has motivation problems to get to the end. I really wanted to do this project but the scale of it caused some procrastination. Perhaps what might work is for you to do the research and absorb the info and then to act as guide as he solders and tests. OR you could treat it as a business: you put up the money and he spends it so that the project is more 'owned' by him; and he comes to you for more money which he then has to justify before you give it. Anyway, the point is that it's a sufficiently large project that the human factor could make a significant appearance, I think. You may end up doing most of it your self (definitely fun though so that's not a bad fall back).

(selling on ebay: unfortunately the two pro sellers have, IMO, seriously underpriced their offerings which makes the profit from selling a bit marginal. People are getting bargain O2 amps. IMO a proper costing including rationalised factors for returns/risks would have resulted in more like £250+ for each amp. This is what happens when business/costing isn't taught at school even though simultaneous equations are, which are very useful in business.)

I got three kits with the intention of building three but also having spares in the case of disaster. I spent 300€ on boards, parts, cases and power supplies, DMM, anti-static wrist-strap etc. It's a lot but I intend to sell two amps (selling on ebay would quite likely thrill the socks off your son). Also I spent £37 on the recommended solder station (which I regret: I should have spent a little more for a lead-free capable station) and a couple of tips sizes; worth every penny since I've fixed so many things since around the house. I had an 'incident': the electrolytics departed this mortal life prematurely. I replaced them: all is well. Since then I've built up a list of other bits I want to buy so that I won't get hammered by postage when I replace the electrolytics in order to build the third amp. Two boards is a good idea: ripping out the electrolytics could have easily damaged the board and needed a restart.

I would really recommend reading the whole of this thread and book-marking individual posts as you go along.

One discovery: at least one resistor doesn't measure its rating when soldered in place. For whatever reason R25 (I think) measures differently whereas if I remember correctly all the others measure their rating. I thought I must have damaged the resistor (perhaps by too hot soldering) and ripped it out. I tested the new one, soldered it in and it measured the same wrong rating as the previous?!?!?! It turns out that once in place a resistor can measure differently. The first resistor had been fine all along.

I wrote a little more here: O2: High Performance Portable/Home Amp - Headphone Amplifiers (Portable) - abi>>forums

[swalter]

Originally Posted by vitop

This looks like a great project for me and my son. I just bought him some headphones and I'd like to get him an amp he can use with the stereao as well as his iPod. Are there any PCBs around? If so, I'd like to get two. Are there any recommended cases? This site was a great find!

Hi,

we have all parts in stock needed to build this little jewel, cases will arrive tomorrow and be listed straight away.

Stefan