O2: High Performance Portable/Home Amp

[axon01]

Originally Posted by WalkGood

I don’t want anyone to freq out but this thread has gotten off topic on various levels and we will be working on purging most of the off-topic posts. With that said, I urge members to stay on topic ...

Why do you want to remove off topic posts?

Your site is the only place where we can discuss what has been going on.

My suggestion would be to please leave this last line of communication wide open.....

Axon

[CrowdAds]

[SpaceTimeMorph]

Originally Posted by Beduin

From now on, I will just trust the products made from the inventor of Objective 2, or the products he has tested with his equipment, and given good remarks.

Definitely, just don't get caught up in giving too much faith. NwAvGuy makes good points because they are logical, scientific, and are quite easily verified; giving complete faith in Him (ha) is slightly contradictory to what is trying to be accomplished.

Originally Posted by NwAvGuy

Thanks for all the positive comments everyone. As for "reference grade" I have to say unless someone packages the O2 in a big heavy chassis, with an internal power supply, massively thick front panel, huge solid metal volume knob, etc. it won't every seem "reference grade" to many audiophiles. And, to be fair, I can understand that. There's something to be said both for build quality and aesthetics.

Can't wait to start soldering this thing together. There is some room for polish. However, it shouldn't be too hard to accomplish since the amp is contained on a standalone board. Making room for a DAC, a remote interface, RCA inputs, etc... should be relatively easy. As far as aesthetics, someone mentioned a wooden case they were going to have built (sweet). I saw something on the head-fi DIY section where someone had taken wooden cutting boards, sanded them down and polished them and fitted those to the sides of a case; which should be possible for the BM-080 case. Shouldn't be too hard (or expensive) by any means to make this thing look a little bling. I would think a corollary of "good sound for cheap" would be "good sound... and can still make it look awesome for cheap."

[WalkGood]

Originally Posted by axon01

Why do you want to remove off topic posts? ...

There is nothing wrong with this thread except it needs to be about the O2, this will not turn into a flame war or open season on headfi. I am not the only mod working on this thread, that you haven't noticed what happens in the background is a compliment to the staff here at abi. But I assure you that sometimes we make minor cleanups or deletions numerous times a day.

[SpaceTimeMorph]

NwAvGuy, have you gotten a chance to work out all of the details with the desktop version where the board would be turned backwards? Is it going to be as simple as just mounting it differently or are there other things to take into account here?

[kilermachinegun]

I just can't wait for a DIY kit to be released. This amp's gonna be huge

[TimYoung]

I'll buy one if you have a complete model 'cos I dunno anything about DIY.

You can make it a business like this guy http://www.jdslabs.com/ who builds portable amps and sells it on ebay for UK.

I would say most casual users would want a proper thing rather than having to build it yourself. And making it look good would help a lot as well.

[Anonanimal]

Originally Posted by TimYoung

I'll buy one if you have a complete model 'cos I dunno anything about DIY.

You can make it a business like this guy http://www.jdslabs.com/ who builds portable amps and sells it on ebay for UK.

I would say most casual users would want a proper thing rather than having to build it yourself. And making it look good would help a lot as well.

Part of the design intent from the start was that it would not be a commercial venture, so I can't say I'd expect the designer to go this route. That being said, I think it's a good thing and puts the focus on engineering know-how rather than profit.

If this amp ends up sounding as good as it measures, I can say that I fully expect a number of people and/or businesses to offer their own versions of it, as it's under a creative commons license.

[NwAvGuy]

I'm told my critics are attacking the O2 on the basis the input stage can be overloaded. But they're stretching the truth. They're talking about the O2 running on BATTERY power but using an AC powered home source. How likely is that?

In reality, the O2 can handle 99% of all home sources when it's running on AC power at the default 3X gain. And it can also handle 100% of portable battery powered sources I know of when running on batteries. So where's the problem?

And for the 1% fringe case, it's very easy to modify the gain of the O2 to suit any unusual needs. The benefits of the O2's gain structure easily outweigh the 1% that might encounter a problem and need to tweak the gain.

The O2 is very much designed for the real world. Everything is a trade off involving performance, cost, complexity, etc. The O2 is designed for optimal performance for 99% of the applications. If my critics want to argue the 1% case, that seems fairly desperate.

I've also always made the gain issues, including input stage overload, very clear on my blog. The information is there for anyone concerned about the issue.

[khaos974]

So I think this should be made clear (clearer) and the article should be revised to state

-the max input level on battery for a 2x/3x/7x gain before input clipping
-the max input level on AC for a 2x/3x/7x gain before input clipping

and while we are at it, post the calculations for those results or point to them if they are already posted). It's not like consumer gear nicely stick to + 4 dBu or even -10 dBV, is it?

[odigg]

Would this amp be stable with a gain of 1? It would make for a pretty nice pre-amp. One would just have to add a remote control motor...

[NwAvGuy]

The O2 is completely stable at 1X gain. That's in the last article. I've provided, in the parts list, resistor values for gains from 1X (no resistor) to 12X.

In the article I've provided the guidelines, and calculations for maximum input levels. It's pretty simple. On battery power the max input level is 5/X and on AC power it's 7/X where X is the gain factor. So with 2X gain, the O2 can handle 2.5 V RMS input on battery and 3.5 V RMS on AC power.

A few critics, at least one of which is a commercial interest with a competing product, have tried to make a big deal out of something that's really not a big deal. 99% of users won't have any clipping issues with the O2 on the low gain setting.

It's important to extend this to how much voltage typical headphones need. The popular Sennheiser HD600/650 need about 2.5 V RMS at the most. The O2 is capable of more than twice that even on battery power. So there's no need to have high amounts of gain that risk clipping with typical headphones. The O2 has plenty of reserve with all but the most extreme headphones.

[odigg]

I agree with you that a 2X gain is probably best for the low gain. Somebody has already built the amp with a point to point design, and has driven it to clipping by using a DAC with a 2.5Vrms+ output with 3.1X gain.

A 2X low gain would address this issue for most any product. The gain is also enough that it would drive a wide range of headphones if the source is even a little bit hot. Also consider that many IEMs get to really loud volumes plugged into many PMPs, so 2X will work for those as well.

Finally, a comment on the article. I know the answer to many questions is RTFM, but the article is so long that it's easy to miss something or get confused. I know you have a "Caution" section, but you could really bring it out a little more (using blinking red lights? ) and stress that people should first use 2X gain first to see if that is enough.

Remember that many people who will build (or simply buy/borrow and test) this amp own those 1% products. They'll criticize the amp. They might technically be in the wrong by setting the gain to 3.1X without thinking about it, but the criticism will still stick.

[NwAvGuy]

Thanks Odigg. I'm strongly considering changing the default low gain to 2X or possibly 2.5X. But, being realistic, the ad hoc standard for home gear is 2 V RMS output. I'm not aware of many sources that don't have a volume control capable of more than 2.25 V RMS.

I'll work on making it even more obvious in the article.

[Marvin the Martian]

Damn....I shut down the computer at 4:45PM yesterday afternoon to leave for work....I just logged into Head-Fi and apparently the O2 thread has 59 new posts since then! This should be interesting.....

[NwAvGuy]

Originally Posted by Marvin the Martian

I just logged into Head-Fi and apparently the O2 thread has 59 new posts since then! This should be interesting.....

Yeah, it's interesting what some people will say when they know the target of their criticism cannot respond. I strongly encourage my critics to post their concerns here or on diyAudio where there can be a genuinely open discussion. Otherwise, they're just throwing rocks from behind a wall.

[maverickronin]

Originally Posted by NwAvGuy

Thanks Odigg. I'm strongly considering changing the default low gain to 2X or possibly 2.5X. But, being realistic, the ad hoc standard for home gear is 2 V RMS output. I'm not aware of many sources that don't have a volume control capable of more than 2.25 V RMS.

In the grand scheme of things, the number of sources like that is probably minuscule but they seem to be pretty popular on head-fi and in similar circles.

I think its one of those psycho-acoustic tricks used to sell you stuff. Its like the story of the dishonest audio salesman who gooses the volume a tiny bit when you're not looking to sell you on some stupid trick like fancy cables. If the difference is small you'll think that the louder one sounds better instead of just louder and I think that boutique DAC manufacturers have done something similar by increasing the level of their outputs. It slowly creeps up over time and next thing you know there's this completely insane chart on 6moons explaining what 'phones will work from a Schiit Lyr with a 1V, 2V, 5V, and 10V source.

OMGWTFBBQ doesn't even begin to cover it...

[NwAvGuy]

Well, worst case, even someone who might buy a pre-assembled O2 and has some unreasonably "hot" source can just clip the gain resistors reducing the gain to 1X. In that case the O2 will handle a whopping 7 V RMS of input which is well beyond anything I know of without a volume control can ever produce. Problem solved.

Hopefully rational folks can see the O2 critics are way out on a limb trying to find any fault they can. I've used the O2 with half a dozen different sources and it hasn't been close to clipping/overloading with any of them. In real world use, it works very well and sounds amazing.

[Beduin]

Well, I see that most of the people critizising your Objective 2, don`t dare to discuss their argument with you, instead they just hide under the Head-Fi banner, where you are not allowed to write. I think you will also see that some of these diy`ers will build your Objective 2 not following all your specs. Then they will tell it didn`t sound any good.

[maverickronin]

Actually I thought of another reason why thy might be angry.

A lot of people in the head-fi-zone view different DACs/sources as things that can and should have different flavors or sound sigs so when you call it "one size fits all" but they find out that they can't use it with their 3VRMS DAC or 5VRMS tube output stage CD player without some forethought or modification they feel cheated. To them its like some headphones are randomly incompatible or something. Unfortunately they haven't noticed that they're the ones in the minority with the unusual and out of "spec" equipment.

[khaos974]

Originally Posted by maverickronin

Actually I thought of another reason why thy might be angry.

A lot of people in the head-fi-zone view different DACs/sources as things that can and should have different flavors or sound sigs so when you call it "one size fits all" but they find out that they can't use it with their 3VRMS DAC or 5VRMS tube output stage CD player without some forethought or modification they feel cheated. To them its like some headphones are randomly incompatible or something. Unfortunately they haven't noticed that they're the ones in the minority with the unusual and out of "spec" equipment.

I would disagree with this, the target of the O2 is obviously audiophiles, most people will be happy with ibuds and those who care a little more about sound quality without being audiophile will buy $100/200 headphones and will plug them directly into their portable device or whatever headphone jack they have on their computer.

Today, the mere fact of buying a headphone amp is reserved to audiophiles, who tend to have semi exotic gear. Boutique equipment is the norm among audiophiles, especially in the very low end and the very high end, it's sad but nevertheless true.

So I think that not taking into account the penetration of boutique equipment among audiophiles is a small oversight. The funny thing is that the very first guy to build an O2 (point to point) did run into input clipping.