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The Sub-$200 Portable Amps Shootout – 13 (+11) amps compared - Page 8

post #106 of 451
Objective2 isn't really a pOrtable amp.
post #107 of 451
Quote:
Originally Posted by clairyvic View Post

Objective2 isn't really a portable amp.

How about over-sized semi-portable headphone amplifier?

post #108 of 451

Lol, it needs to fit in my skinny jeans. Which is why I want either the t3 or e11 or some other such small amp that's the best for drive a 50 olm headphone (meaning at least100 mw at 50 olms according to the maker).


Edited by clairyvic - 9/9/12 at 8:37pm
post #109 of 451
Quote:
Originally Posted by MeeHungLowe View Post

I think one of the challenges for new amp buyers is the difference between high current, high voltage & high gain.  I know it confuses me!  All I know is that low-impedance headphones tend to hiss and sound bad if the amp's gain is too high - but I really don't know why - I'm guessing it is because gain is actually a voltage increase?  And if the amp gain is too high for a low-impedance 'phone, then you can overdrive the 'phone (supply too much voltage) - is that correct?

 

High gain (high multiplier of input voltage) causes high voltage, but there's a separate important measure, clipping voltage, which is the maximum voltage supplied by the amplifier regardless of gain. Low gain is usually better than high gain, since gain amplifies input noise and many potentiometers have channel imbalances most pronounced in the lower part of range. Switching to higher gain is only recommended if the audio is too quiet. (almost always)

Low impedance headphones require an amplifier with exceptionally low current noise and higher maximum output current - they tax the current stage more than the gain stage. Too low maximum current will cause current limiting and sagging, which causes harmonic distortion.

Reducing current noise is usually harder than reducing voltage noise and requires careful circuit layout and design.

post #110 of 451
Quote:
Originally Posted by PurpleAngel View Post

How about over-sized semi-portable headphone amplifier?

 

I wonder when someone's going to make a smaller smd version.

post #111 of 451
Quote:
Originally Posted by Evshrug View Post


Ok, going back to this post I am quoting... The reason we know (or are learning) what the stats mean is that we want to match an amp to our headphone. The whole voltage/current requirement isn't that difficult to wrap your head around.

Not really, a good amplifier will do well both with highly sensitive IEMs and far less sensitive headphones, within limits.

Usually the main source of limitations is at the higher impedance end due to the battery voltage - most amplifier producers are loathe to include step-up circuits, as they are expensive, usually power hungry and require even more care in circuit design to not introduce their switching noise into audio. Similar, but much less pronounced problems are faced by designs using charge pumps to synthesize the other rail (negative voltage) for the opamps.

 

The low impedance IEMs on the other hand can be affected by high output impedance of the amplifier. This will cause frequency response changes in concert with natural impedance curve of the device, which mostly affects balanced armature IEMs, esp. multi BA; and lack of electrical dampening, which will mostly hurt dynamic driver and orthodynamic quality, causing harmonic distortion.

Moving armatures are inbetween with regards to both of these effects.

 

So, the ideal generic source would provide: relatively high maximum output current (for very low impedance IEMs and orthodynamic headphones), near zero output impedance (for BA IEMs) and high maximum voltage (for high impedance headphones). Obviously enough power to drive something high impedance.

--

 

Rebuilding O2 into SMD should be relatively easy, as all of the components have SMD versions. It won't be too much smaller though.

The main source of girth in O2 is the two 9V batteries. Replacing them with li-ion or something else thinner (which could be laid above the PCB) would require replacing the power management circuit altogether - most of the bottom part of PCB. (near the batteries) Needs care to not break the performance.


Edited by AstralStorm - 9/9/12 at 11:43pm
post #112 of 451
Thread Starter 
Quote:
Originally Posted by Armaegis View Post

I wonder when someone's going to make a smaller smd version.

NwAvGuy prohibits any modification to the design without his consensus (in the GPL) though...
post #113 of 451
Quote:
Originally Posted by ClieOS View Post


NwAvGuy prohibits any modification to the design without his consensus (in the GPL) though...

 

No, the GNU GPL permits modifications.

 

The O2 is released under a "Creative Commons Attribution-NoDerivs 3.0 Unported (CC BY-ND 3.0)" license. Although real license interpretation requires a lawyer, I doubt this CC license prevents shrinking the board or using SMD parts.


Edited by HamilcarBarca - 9/10/12 at 6:02pm
post #114 of 451
Thread Starter 
Yes, you are right. It is under CC. However, here is what the guy said: "...the O2 is offered only under a “no derivatives” license. Put simply, you can’t modify it or use it as part of a different design and then offer it to others without prior approval. This is to help prevent inferior versions of the O2 that might disappoint whoever buys/builds them. Even the PC board design is an essential component of the O2’s performance and changing it could have dramatic consequences...." If course, one can always choose to disregard this sort of things...
post #115 of 451

Exactly - the author of such a PCB/layout would have to contact NwAvGuy to get his approval. Nobody prevents using the same design principles, similar components, then calling it differently though.

Perhaps you could even call the design inspired by O2.


Edited by AstralStorm - 9/10/12 at 6:56am
post #116 of 451
AstralStorm,
You're right about the O2-inspired design... I'm also not a real lawyer (wouldn't want to be, tend to get so technical about EVERYTHING in life), but someone could come along, make a few changes, and call their amp something different. I mean, that's basically what happened with Fred_Fred_2004's 3-channels amp, right? Mini^3 inspired?
Also, in regards to your reply to my post, it seems like we mostly agree... just in different words. I was basically taking a stab at a shorter, layman's explanation of "proper" amping so that clairyvic could make his own decision. Since he/she kinda glossed over his needs, I was trying to just give him a general answer. An answer besides "just buy one and see if you like it," lol!
post #117 of 451
ClieOS, any possibility of doing that tube amp review? Also, this would probably be irrelevant to the portable amps shoot out, but have you heard of the Indeed G3 Tube Hybrid or Bravo V2 tube hybrid desktop amps? I have suspicions that they'll suit Q701's better than a FiiO E11 (though the top picks for the sub-$200 round up should do nice as well...)
post #118 of 451
Thread Starter 
Quote:
Originally Posted by Evshrug View Post

ClieOS, any possibility of doing that tube amp review? Also, this would probably be irrelevant to the portable amps shoot out, but have you heard of the Indeed G3 Tube Hybrid or Bravo V2 tube hybrid desktop amps? I have suspicions that they'll suit Q701's better than a FiiO E11 (though the top picks for the sub-$200 round up should do nice as well...)

BL-2's review has actually been posted a week ago, you can find it here:
http://www.head-fi.org/t/627659/impression-tube-amp-bl-2-portable-miniature-tube-amp-from-china

Never listen to those eBay desktop tube amp before. I haven't had much use of desktop amp (plus I already have a hybrid amp from FireStone Audio) so I never think of picking one up.
post #119 of 451

I was looking at the Leckerton Audo site and noticed that the UHA-4 can be ordered with a couple different output OP amps.  The one in the review was done with OPA209 what is the difference between that and the standard AD8610ARZ that seems to come standard.

 

Thanks for any input you can give

 

Mike

post #120 of 451

I have to hand it to iBasso.

I recieved a D-Zero a week ago and it had quite a bit of noise in the DAC section(amp section is silent using with ipod). I contacted iBasso and they sent me out a new one right away. I recieved that one yesterday and I have to say, it's a nice little amp/DAC.

Dead quiet, great sound quality, and more than enough power.

I guess I'll use one with the ipod and the other with the computer...

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