[Possum]

Do note that the 42 amp (as with the META42 board) and the 47 amp (as with the CHA47 configuration) were designed for different purposes, so saying one is definitely better than the other is kind of a blind statement unless you specify where/why.

The designer of the circuits of both amps, Apheared, himself said the 47 is for his Grados, and the 42 is for his HD600's, but was too aggresive for his Grados.

Note though, that the META42 board can accept changes to components (op amps and maybe buffers) to change this aggresiveness, since the board implements common op amp/buffer configuration(s), but then the circuit wouldn't be a 42 anymore.

 

[Audio-Me]

So call it E43-42 vA.M

It does not matter what it's called since I'm not having any emblems, engravings, stickers, etc of any sort on there anyway. I am waiting for a minimalist overkill portable amp...

Call it erics diy amp, EDA42. Hehe, whatever.

 

[eric343]

Possum: By CHA47 I meant a Hansen board, not a A47. The Hansen board is actually a Levallois Cmoy-variant, not the A47.
See Addendum #2 to the article: http://headwize.com/projects/showpro...2b_add_prj.htm

 

[Possum]

The circuit the Hansen board was based on shouldn't be incorrectly referred to as the CHA47. CHA47 is the Apheared 47 circuit, using only part of the Hansen board for easy component placing without having to deal with component wiring. I don't remember what people usually call the Levallois circuit on Hansen board now, since people usually seem buy the "JMT amp" or "CHA47," but it's kind of backwards and misleading to refer to the Levallois circuit on Hansen PCB with the name CHA47.

See this article for an explanation of a Apheared 47 circuit:

http://headwize.com/projects/apheared_prj.htm

See your own link for the circuit and board that are not the CHA47.

 

[tangent]

So many topics in this thread already...

Batteries: I tested the protoboard prototype for voltage with the AD823, and it will run at 4V with my toughest test. This is the same test that says the OPA2132 requires 10V to sound its best, while many people run it on less than 9V with excellent results. This test is tough.

What this really tells us is that with the META42 the base opamp's voltage requirement dominates. The buffers will run at very low voltages, despite the datasheet's claims.

Cost: Find a builder in the Marketplace forum and ask. No one can give a single number for this because the design is flexible enough to allow at least a 4x cost difference between bare-bones and the version with bells, whistles and gongs. And of course different people want different compensations for their time. The bare boards will be available, too -- an announcement on the details will appear in a more appropriate forum. In any case, haggles over configurations and prices don't belong in this forum.

Openness: The schematic has been made public, the base design is well-understood, and much of the design process has also been public. One could clone what we've done without much trouble, if one so wished. I have personal reasons for holding back a little bit. In practical terms, though, I don't think it really matters. The design is as open as it needs to be.

META42 vs. CHA47 I will be doing some comparisons along these lines when I get the prototype boards in at the end of this week. Details will appear on the META42 web page kindly linked to by A&M above.

Possum's right, though: much of the character of the amp will come from the opamp you use.

What's left is a matter of refinement: the META42 has a better power supply circuit than the Hansen board, it gets its improved current drive from true monolithic buffers instead of paralleling the opamps, and it's multi-loopable so it should have lower audible distortion. Also consider that the META42 allows for crossfeed and other processing stages that are too difficult to do on a CHA47. You'd have to switch to protoboard to get an A47 with crossfeed with a reasonable amount of work.

 

[eric343]

As usual, you said it best, Tangent.

 

[puppyslugg]

neruda:

"hey JMT, are you going to try out this amplifier? Any thoughts about making them for the rest of us? "

If I am not mistakened, JMT put in a request for about 5-10 boards and some 20(?) buffers. So I would assume......