[stevebeyer@mac.c]

I am a newbie and confused about the portable power amp possibilities. I am using an ipod as a source and I still don't have the headphones selected. My question is what are the pros and cons of the the DIY amps.... the cmoy, mint, ppa, pimeta.... and the comercial versions. Is the cross over feature something that is really makes a big difference? I am not sure I am really even know what features I should be looking in an upcoming purchase. Thanks in advance for your help.

 

[jnewman]

A few people like crossovers, most don't. You can always get one very cheap that you can put inline between your source and amp later if you want one and there isn't one in your amp (if you can't find anyone to make you one, I'll do it for you for cost of parts + shipping).

The CMoy is a very basic design - it's almost just signal going into an opamp going to your headphones.
The MINT is actually pretty close to being a modified CMoy - it adds a buffered output, which supplies more current to the phones and gives a fuller sound, especially in the bass region.
The PPA is more advanced and adds a "ground channel," which improves response and detail - the ground channel draws the ground current and keeps the output stage from having to push it. This amp also has the most possible options for upgrading components and altering the circuit.
The PIMETA is, to some extent, a simplified version of the PPA, retaining the ground channel but losing many of the configuration options.

The PPA is the best of these in an absolute sense, but is not really portable - you can get one that runs on batteries, but the standard is 12 NiMH AA's - a portable PPA is more like "luggable" and is huge.
The PIMETA is the best of the options that are really possible in a portable configuration. The MINT is fairly simple and can be made much smaller than the PIMETA - small enough to fit in a mint tin. The CMoy is simpler still.

The most popular portable commercial amps are probably Ray Samuels' SR-71 and Xin's designs - his newest (and probably the best) is the Supermono. You could also look at the Meier audio Porta-Corda and the Headroom amps. There are too many to really talk about here - look around in the forums for reviews.

 

[Talonz]

Great explanation jnewman, I learned something there.

 

[drewd]

Regarding the MINT, it's actually more than just a modified CMOY. It's a modification of the venerable META42. Beyond the buffers (which are a big improvement on their own), the MINT also adds the ability to bias the opamp into class A mode, something that many opamps can benefit from (most of the Burr Brown opamps come to mind) by improving their linearity and it uses Walt Jung's multiloop feedback system that keeps the majority of the feedback local to the opamp and just a small amount global from the buffer. This reduces distortion and noise by keeping the resistor values in the signal path low.

The fact that you can fit all of this into a tiny little mint can (hence the name: META42 in a tin) is a pretty amazing feat!

-Drew

 

[jnewman]

Quote:

Originally Posted by drewd Regarding the MINT, it's actually more than just a modified CMOY. It's a modification of the venerable META42. Beyond the buffers (which are a big improvement on their own), the MINT also adds the ability to bias the opamp into class A mode, something that many opamps can benefit from (most of the Burr Brown opamps come to mind) by improving their linearity and it uses Walt Jung's multiloop feedback system that keeps the majority of the feedback local to the opamp and just a small amount global from the buffer. This reduces distortion and noise by keeping the resistor values in the signal path low. The fact that you can fit all of this into a tiny little mint can (hence the name: META42 in a tin) is a pretty amazing feat! -Drew

That's true. I guess the multiloop system is the biggest difference - adding a CRD to bias the opamp isn't terribly unique and doesn't work nearly as well as a cascode. Those're all things you can add to a CMoy, but I guess it wouldn't be a CMoy anymore

.

 

[drewd]

Quote:

Originally Posted by jnewman Those're all things you can add to a CMoy, but I guess it wouldn't be a CMoy anymore .

Of course, since a CMoy is so simple, darned near everything is a modified CMoy, so you do have a good point!

 

[Zanth]

If you want options galore...then going with the new supermono from Xin would offer everything you want with the flick of a switch. It also sounds incredible! I have yet to hear the SR71 but from what I have read the sound is to die for, though it does not offer many features, just pure sound. No bass boost, no gain switching (I think) and definitely no cross-feed.