The Objective2 (O2) Headphone Amp DIY Project

@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.
 
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.
 
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.
 
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.
 
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.
 
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
 
Last edited:
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
 
<more cut to condense space>

(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.)

<more cut to condense space>

1. the o2 was designed and release OSHW and most of what you called "pro" sellers respected that and sell it at thin margins, to keep in the spirit of OSHW. Also with the boards and parts readily available it keeps everybody's price around the same ball park

2. As of yesterday the exchange rate

UK£ 250 = 402.284808 Canadian dollars

The cost to buy the parts for the standard bill according to the BOM is about $75 plus $25 shipping, so roughly $100-$125 to get some other odds and ends..

you said they should sell it for at least $400.. which is a 400% markup.. I am sure they are savvy business people, but they are not going to gouge their customers either

3. The other day I picked up my Benchmark DAC1 USB for $800.. and it has a built in DAC that was compared to the upcoming ODAC.. there is no market for a $400+ o2..

-joe
 
1. the o2 was designed and release OSHW and most of what you called "pro" sellers respected that and sell it at thin margins, to keep in the spirit of OSHW. Also with the boards and parts readily available it keeps everybody's price around the same ball park

2. As of yesterday the exchange rate

UK£ 250 = 402.284808 Canadian dollars

The cost to buy the parts for the standard bill according to the BOM is about $75 plus $25 shipping, so roughly $100-$125 to get some other odds and ends..

you said they should sell it for at least $400.. which is a 400% markup.. I am sure they are savvy business people, but they are not going to gouge their customers either

3. The other day I picked up my Benchmark DAC1 USB for $800.. and it has a built in DAC that was compared to the upcoming ODAC.. there is no market for a $400+ o2..

-joe

I totally understand where you are coming from. But as a business proposition it's really terrible. You are working for not so far off an employees wage while taking all the risk and admin. I also don't think the spirit of the OSHW is really affected by a fair, boutique price. It's not really, yet, a mass produced, pile-em-high-and-sell-em-cheap product. When/if China gets involved, then yes, £140 will be a fair price, even less maybe.
 
I can't speak for the rest of the builders, but this is not my main bread-butter, I have a normal day job

I custom build for people because I enjoy their comments about how much they enjoy it etc.. and the kits I sell go to people who otherwise can't buy at the volume i buy at to get the same discounts.. I make a few bucks here, lose a few bucks there, it's all awash

-joe
 
I feel I ought to address this in addition to what I already wrote:

But in summary : this isn't suitable as a thin margin offering.

2. As of yesterday the exchange rate

UK£ 250 = 402.284808 Canadian dollars

The cost to buy the parts for the standard bill according to the BOM is about $75 plus $25 shipping, so roughly $100-$125 to get some other odds and ends..

you said they should sell it for at least $400.. which is a 400% markup.. I am sure they are savvy business people, but they are not going to gouge their customers either

These parts costs are high. A reseller of just the parts would expect 25% markup for thin margins. A repackager, like jokener, more I reckon. Then on top is labour, admin (a significant cost), regulatory adherence, equipment, overheads and RISK +others. It all piles up. The final markup on a boutique item should be around 100%. I would take an educated guess at $200 for parts/admin/regulation/overheads/depreciated equipment/accountant etc. So $400 could be about right.

Compared to a Benchmark DAC1 USB for $800? Tricky comparison because that is a 2nd user price and it has a DAC. But the spec of the amp is roughly the same as the O2 so its 2nd user price might notionally be about $400 minus the DAC so the O2 at $400 still has a good price for a new item.
 
I can't speak for the rest of the builders, but this is not my main bread-butter, I have a normal day job

I custom build for people because I enjoy their comments about how much they enjoy it etc.. and the kits I sell go to people who otherwise can't buy at the volume i buy at to get the same discounts.. I make a few bucks here, lose a few bucks there, it's all awash

-joe

Totally! Which is a completely different proposition to a normal business. I'm not criticising the pro sellers, by the way; I was just mentioning that as something to sell on ebay its not a great way for me or that guy's son to make money due to the underpricing.
 
The O2 has never been intended as a way for someone to make shedloads of money by just assembling and selling them. Of course, there's nothing to stop you trying, but there are plenty of people who are happy to make £20 - £30 on each one, selling them for £100, as several people already do. It's not difficult to build - no more than an hour's work if you are a competent, experienced builder, so talk of selling them for £400 a time is just a pipe dream.
You should also consider that it's probably only a matter of time before some enterprising far-eastern manufacturer redesigns the whole thing as a surface-mount board and starts turning them out, ready-built, for a bargain-basement price - after all, the design is out there for free, proven to work and highly respected as a great design - and once that happens, anyone holding stocks of components could end up taking a big financial hit.
Furthermore, the O2 isn't the only headphone amp on the market, there's plenty of competition...
 
The O2 has never been intended as a way for someone to make shedloads of money by just assembling and selling them. Of course, there's nothing to stop you trying, but there are plenty of people who are happy to make £20 - £30 on each one, selling them for £100, as several people already do. It's not difficult to build - no more than an hour's work if you are a competent, experienced builder, so talk of selling them for £400 a time is just a pipe dream.

Well, yes, but I meant £250/$400; my mistake. I don't think there was any intention either way. You could do as you wished and it just turned out this way which is a bummer for those who would have liked to making some kind of living off such a marvellous device but great for the semi-pro hobbyist doing it more or less for fun. But commercially/business-wise £30 for each is practically slave-labour. I mentioned the other costs and £30 doesn't cover them.

You should also consider that it's probably only a matter of time before some enterprising far-eastern manufacturer redesigns the whole thing as a surface-mount board and starts turning them out, ready-built, for a bargain-basement price - after all, the design is out there for free, proven to work and highly respected as a great design - and once that happens, anyone holding stocks of components could end up taking a big financial hit.

Absolutely, and that is part of the risk factor that has to be included in the costing (though doing so could be tricky to quantify). The price should be much much higher.

Furthermore, the O2 isn't the only headphone amp on the market, there's plenty of competition...

I wonder about that. Measured amps, HIFI sound, with high power and established credentials? The nearest competitor is likely the Violectric v90 which is $450. (though it seems like RS compares the O2 to the v200 which is $800).