Has anyone on here had a chance to hear the new CLAS db yet? I'm curious to know if the new chip sounds better then the old CLAS.

Hey pirates. I'm looking for more knowledge. I am quiet ignorant on what is desirable in a portable headphone amplifier. For example what should I be looking for, what would be the difference between getting the UHA-6mkII or the ALO Rx Mk3B.

Any good reading material on how I should be judging such amplifiers? Especially in regards to supra aural headphones (I love my dt1350's) with higher than IEM impedance. I think the dt1350 has 80 Ohms.

I would like to become educated on the topic before sinking my pirates treasure chest into a purchase. I would appreciate your knowledgeable direction  Thanks! 

So, we know which headphones you are likely to use, a few more pieces of information might be helpful...

What do you plan to use as a source?  Are you thinking of adding a dedicated DAC?

Are you looking to have a truly portable (small) set up, or something more "transportable" (think brick)?

Assuming the 1350's are your primary, do you plan to use IEM's as well?

I think you can see where I'm going with a few of these questions, they will help narrow what amps are right for you.

Well, that is where we are headed.  Just getting the basics because that sets the stage.

For instance, you want something that's going to fit in your  pants pocket, you had better start looking at much smaller options than the MKiii, unless you have some large pockets.  Maybe more along the lines of the Pico slim...

I ask about IEM's because a lot of portables out there are terrible maches for highly efficient IEM's and will leave you with a noisy sound floor and difficult gain control and potentially channel splitting at low volumes.

These are the kinds of things to consider so you can short list, set a budget, and then start comparing the nuts and bolts to see what's best.

So here is my simplified take on the portable market. It is best to think of them as modular because many of them use variations of the same theme.
The modules would consist of the following:
1.   Lets start with the most important bit, the amplification module itself.  Someone can correct me if I am wrong but as of this time, all the portable amps are based on some or other opamp. The chosen opamp varies and some even allow the “rolling” of opamps  to enable the user to find the poison they prefer.
a.   There are some tricks used –
i.    adding in buffers which could either be discrete or another chip. The value of a buffer is that it adds to the amplifiers ability to supply current needed in some situations. ( we will not discuss voltage swing versus current abilities for high and low impedance headphones )
ii.   Biasing the chips into “Class A” Tangent has written on this http://tangentsoft.net/audio/opamp-bias.html
iii.   Adding tubes into the mix – not many portables do this as it actually takes much more effort to get all the voltages for the tube and keep things compact. ALO, Millet and GoVibe are the only ones I know of.
iv.   Balanced
 My problem with any opamp is that it has about 110dB of gain and thus requires huge amounts of feedback to pull the output back down to anything that is practical ( ie going from million x to 8x ). It is just the nature of the beast but high feedback amps have inherent signatures which low or non feedback amps don’t. Don’t get me wrong, I am not one of those people who feel feedback is evil, I just prefer not using massive amounts of it if it can be avoided.  I have hopes that we will see a discrete , low feedback portable, we can but keep the dream alive.
2.   Power supply. This is probably the part that most people give little to no consideration when thinking about amplifiers but is actually a crucial part of portable amplifier design. Some use highly advanced power supplies ( the chip tech has made some incredible advances for our portable landscape ), some use simple rail splitters , obviously all use a battery. Most all portables today include a dac and thus USB is pretty standard. Some can charge from the usb, others need an independent jack. Ground planes probably fall into this module too so worth visiting here. Ground plane isolation is either done by careful/clever design, some amplifiers “float” the ground plane while others use an active ground plane ( eg mini 3 ) to separate the signal ground from power supply ground via an active buffer.

3.   Input options. As mentioned, USB dac is pretty much par for the course. I have not investigated the chips used but there are essentially 2 options, use a chip like the pcm2704 which has a usb receiver and dac incorporated into a single chip, or use 2 chips, one to receive the usb signal and a higher acclaimed dac chip which generally do not have built in usb input. Most have an analogue input option too. As many DAC chips put out a balanced signal option, the trend for portable balanced amps is increasing. This is a subject unto itself.

This should be enough food for thought.

..dB