[kerelybonto]

The META42, CHA47, and CMoy can be built in battery-only, DC-only (out of an AC-adaptor like those available at RadioShack), or battery-and-DC configurations. The Creek OBH-11 is DC-only. The Fixup amps, HeadRoom AirHead, and Meier Porta Corda are battery-only.

kerely

 

[darkclouds]

Kerelybonto:

The Airhead and Total Airhead both have 5V DC input so they can be used with a walwart or batteries.

 

[kerelybonto]

Hmm, okay. Sorry about that. I checked the specs/pics on HeadRoom's site and didn't see them. Someone might want to check to make sure I'm right about the Porta Corda too.

kerely

 

[fiddler]

The Porta Corda can also be used with an external supply, anything between 5VDC and 24VDC or something like that.

 

[tangent]

Nit: The "META42" is a PCB design, not a circuit design. The circuit doesn't have any formal name that I know of. There are several amps out there built on similar circuits to that represented on the META42 PCB, yet they're all quite distinct. (ppl's portable amps, aos's DAC, Fixup's tiny amps, some of sijosae's recent confections...)

 

[eric343]

If you can afford it, get the Gilmore. I haven't heard it, but Kevin seems like such an insane perfectionist that I'd bet money it's one of the best dynamic headphone amps out there - period.

Otherwise DIY a META42 or have Tangent or JMT build you one. (if Tangent's still taking orders, that is)

 

[Andrew LB]

Ok, those of you who have both the Meta 42 and the the CHA47, what are the pros and cons of each? I definately want something that is AC adaptable since ill probably have them hooked up all the time and dont want to have to deal with batteries.

 

[tangent]

A CHA47 is a Hansen circuit board that is modified so that the four op-amp channels on-board are wired up in parallel instead of in series. (The normal Hansen configuration has a crossfeed between the series op-amp channels; the CHA47 sacrifices on-board crossfeed.) The effect is to double the maximum output current of the amp, which is a good thing. Unfortunately, in my experience the CHA47 circuit is a bit picky about the op-amps it will tolerate, and although it's better than a standard CMoy amp, it gets expensive when you start using more expensive op-amps because it requires four op-amp channels.

The META42 also boosts output current vs. a simple CMoy type op-amp amplifier, but it uses buffers instead of doubled op-amps to accomplish this. Dedicated buffers are designed for boosting output current, whereas doubling op-amp channels is a bit of a hack. Also, buffers are cheaper than extra op-amp channels except at the low end of the op-amp scale.

The META42 board has some other refinements relative to the Hansen board, mainly in the way of a better power supply. The topology used on the META42 circuit is also superior: it's much more stable than the CHA47 circuit, which means you can use more kinds of op-amps in it.

The CHA47 circuit board is smaller than the META42, so a mint tin CHA47 is possible. The META42 board is about twice as large as the Hansen board.

The biggest reason I dislike the CHA47 design is that it requires modifying the Hansen board. Six of the resistors get stood up on their ends; four of the resistors have one wire each attached to their upper end, and the other two have 3 wires each attached to them. The result is somewhat brittle, physically: it's easy to break these "tombstoned" resistors or the wires running to them. It's just the nature of board-hacking. A properly-assembled META42 is much more durable.

A low end CHA47 can be a bit cheaper than a low-end META42, but it won't sound as good. A high-end CHA47 will be more expensive than a similarly-configured META42, and it still won't sound as good.

Disclaimer: I had something to do with the production of the META42, so I may be biased.