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Old 5th April 2012, 02:15 PM   #2321
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Quote:
Originally Posted by greenalien View Post
As soon as you hook up an AC power supply, there's the potential for creating EMC emissions right there - think of it as a 50 or 60 Hz oscillator.
True enough but that's a compliance issue for the supply, not the amp.

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No telling what frequencies of harmonics may be created in the circuit. This does imply that CE certification may be needed.
Can't see how a purely linear amp can create EMC emissions issues. But there is more to CE marking than just EMC emissions - its quite possible to self-certify and provided you show 'due diligence' (i.e. have a good pre-prepared story for why you believe its benign) then you're fine.

EMC susceptibility is another issue from emissions and is an aspect of CE marking usually but in practice you're free to set your own performance (degradation) criteria.
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Old 5th April 2012, 04:46 PM   #2322
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Quote:
True enough but that's a compliance issue for the supply, not the amp.
No, because the AC carries on into the amp, where various components interact with it before it becomes DC.

If the external power supply was DC output, no problem, but no use for the O2.
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Old 5th April 2012, 04:52 PM   #2323
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Ah that's my misunderstanding then - I'd forgotten the O2 contains a half-wave rectifier - it could be responsible for some conducted interference back to the mains, as diodes generate some RF on switching off. But realistically that's only an issue for significant currents, not at the small signal levels in a headphone amp.
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Old 5th April 2012, 08:40 PM   #2324
BlueRob is offline BlueRob  Mexico
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I just read the review....it is a bag of mix feelings and somehow contradictory statements that I don't fully understand, honestly gives me the impression that the review was written in a rush or something.

In some sentences it gives me the impression that this guy does not have the O2 background clear and it kind of lost me saying that the Mini3 sounds good (despite what RS stated and measured) I have it here and its like comparing bananas and apples.


What I do agree with is that this is amp that favors some phones and other don't, but matching equipment is not a new subject. The other thing that I do find true is that and amp that measures good does not mean it is going to sound good...measuring and listening should be side by side but obviously what sounds good to one might sound bad to other, again not a new subject either.

As I said before I`m quite happy with this amp, and is very likely that there are other amps with better sounding features and different signatures but there is no secret with that either.
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Old 5th April 2012, 10:12 PM   #2325
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I'm pretty sure that the O2 was used on high gain with a 1.5V source at one point, clipping the input stage. The reviewer then asks in the comments something to the effect of "Is the design that great if it sounds so bad on high gain?"

Errrgh...apparently preliminary research into how the operate a product you're reviewing is considered beneath them. On the other hand, so is proper volume matching most likely and the most basic controls against involuntary bias, so yeah...(Never fear, according to their "On Sound" section bias is for lesser mortals. Here I quote: "I don’t deny that Placebo is a real phenomenon. But accusing us of being fooled by placebo when we are giving our impressions is an entirely different thing. And just because someone, not us, in a completely different listening environment, has been proven to be fooled by placebo doesn’t proof that we are suffering under the same psychological phenomenon when we are doing our reviews.")

An amp that measures well, assuming it genuinely does measure well all-round, will sound the same as any other well-measuring amp under blind conditions. This is how we would expect it to be, this is how it is to the best of our collective knowledge. Nothing has ever been presented under controlled conditions to suggest otherwise.

Why people persistently imagine that the differences they hear under sighted listening conditions are best explained by not existing and proven science (bias ect) but what basically amounts to magic, God only knows.
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Old 5th April 2012, 10:13 PM   #2326
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Quote:
Originally Posted by greenalien View Post
@Lorriman - thanks for the heads up on the Superlux HD681 - currently 19.49 from Amazon http://www.amazon.co.uk/Superlux-HD6...7092021&sr=8-1
lots of interesting reviews, got to be worth a try, so I've ordered a pair.
GReenalien: what did you make of those superluxes?

I'm afraid my equalisations were a bit out. I assumed Q and Bandwidth (BW) were identical but in fact they aren't but rather sort of inversely proportional, sort of. If you are still interested then the corrected q numbers for rockbox are : (restrained bass) 1db 70Hz q=1, -8db 8000Hz, q=1.4, -8db 12300Hz q=2.4, and then treble -4 for treble heads and -7 or less for everyone else. Apologies for that.

Without these equalisations I think a simple treble of -10, as recommended by Innerfidelity, results in a merely OK, good value headphone.
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Old 5th April 2012, 10:40 PM   #2327
Turbon is offline Turbon  Sweden
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Quote:
Originally Posted by Turbon View Post
The O2 sound perfectly OK in my ears so I'm a happy camper.

Brgds
I camp with HD-650's an UE-Tripple-Fi10's. Even my cheapish Philips sounds quite nice with the O2.

Nah, audio is a very personal experience so how can anyone tell me that I'm wrong in one way or another? This doesn't imply that I consider the rewiver to be wrong in his experience - his ears arn't my ears. Just listen and enjoy - then make your pick.

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Old 5th April 2012, 11:11 PM   #2328
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Quote:
Originally Posted by sofaspud View Post
I find the O2 itself more objective than the review. Which is quite alright.
If I were to give advice to the reviewers, I would say don't write things like, "...its transparancy [sic]. There is no coloration what so ever, it is very neutral sounding..." and follow that with, "...the bass... is missing some punch and impact. But the bass isn’t the only thing bothering me actually, there also is something bothering me with the mids . They sound a bit thin."
Or
"A good feedback from a pair of good ears to further improve the design and the tuning would definitely help." Whose ears?? And of course this implies that either a) the designer hasn't good ears, or b) he didn't listen to his own amp.
Mike's magic ears!

Quote:
Originally Posted by BlueRob View Post
I just read the review....it is a bag of mix feelings and somehow contradictory statements that I don't fully understand, honestly gives me the impression that the review was written in a rush or something.

In some sentences it gives me the impression that this guy does not have the O2 background clear and it kind of lost me saying that the Mini3 sounds good (despite what RS stated and measured) I have it here and its like comparing bananas and apples.


What I do agree with is that this is amp that favors some phones and other don't, but matching equipment is not a new subject. The other thing that I do find true is that and amp that measures good does not mean it is going to sound good...measuring and listening should be side by side but obviously what sounds good to one might sound bad to other, again not a new subject either.

As I said before I`m quite happy with this amp, and is very likely that there are other amps with better sounding features and different signatures but there is no secret with that either.
He's not a very good writer and his opinions seem completely arbitrary except when he's reviewing HiFiMAN equipment he's always positive (one of his sponsors).

If a headphone sounds better with an amp that distorts vs. an amp that is transparent I would sell that headphone in an instant. . .


Last edited by Etilletas; 5th April 2012 at 11:13 PM.
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Old 6th April 2012, 08:55 AM   #2329
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@lorriman - I'm very happy with the Superlux HD681 - I found them a bit harsh on first listening, but they have improved with time and are now more mellow - I didn't realise that some headphones need to be 'run in'!
I've certainly heard better headphones, but not for 20 - and they are comfortable to wear, which counts a lot in their favour.
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Old 6th April 2012, 09:49 AM   #2330
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Quote:
Originally Posted by gkanai View Post
Just received my JDSL O2 and power adapter from Mouser today.
Question for O2 owners: does the unit have to be on to charge? How do we know when the batteries are fully charged?
answer 1: No, the O2 does not have to be on to charge. If the AC power is plugged in, the batteries are being charged.
(longer) answer 2: Well, I'd say we don't really know. A person can make a pretty good estimation, though. The O2 was designed so that as the battery reaches full charge, the current to the batteries is significantly reduced. At full charge only a small maintenance charge is applied to the batteries. In this way, the charger can be left connected to the O2 without fear of cooking the batteries. But I wouldn't recommend leaving the AC connected for indefinite lengths of time without using the amp. If you are planning to use the amp, leave it charging for a day. If you are using it a lot, leave it charging overnight.
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