Maxed out META42
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Audio-Me

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What's the most all out configuration that you could make without tripping into dual mono looniness? (cost isn't an issue)

META42 with the final board:
opamp - AD8610
buffers - dual stacked EL2001
virtual ground driver - EL2001
power caps - Elna Cerafine 4 × 25V 220uf (Can you not use quad 470uf or 1000uf ones in the new board? Or is this already optimal?)
reservoir caps - Wima 10uf
resistors - tantalum
volume control - TKD stepped attenuator
input - WBT topline RCA jacks
output - Neutrik ¼" locking type
Power source - 24V Elpac linear PSU and 4 × 9V battery pack (dual parallel pairs in series)
case - die cast aluminum
plus all the good stuff of the new design like the rail splitter, class A operation, Fairchild FET cascode current source, full multiloop feedback mode, gold contact DIP-8 IC sockets, etc...
can you add a power regulator chip?

Please offer comments and suggestions (change or add anything?).
 
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Nezer

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Take the power supply off board and regulate it to +/- 15V (or whatever your opamp and buffers need). Also use a lot of 1000uf or better Cerafines. I'm looking at a pair 10,000uf 50V Cerafine ALAs that have been discontinued. In addition choke the power coming in from the trafo. Use an oversized Trafo capable of a LOT more than your going to ask from it, even considering the cap sizes.

Drop the external power into the Meta42 board at the buffer section and still run through the caps you list for the power supply above.

Perhaps upgrade the buffer on the power supply to an LM6122 or maybe an EL2009.

Stacking EL2001s would probably be overkill. You might try going for the EL2002s and stacking them instead if you want overkill. :wink:

Consider the OPA637 opamps. :wink: (At this point it's just a matter of taste)

Use a CRD in the bias circuit. Might not make any difference but by this point whats another $4?

Use a Jung multiloop and set gain to taste and limit bandwidth to around 100Khz (as Tangent documents).

Use Dale Vishay resistors in the audio signal (less critical in the power supply, but may as well while your going nuts).
 
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Audio-Me

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Hehe, this will be a travel amp (case size just needs to fit in a backpack or suitcase with the headphones and accessories), meaning I'll still need to be able to run it with a battery pack that'll last 4 hours minimum, will that be a problem with a bunch of 1F caps? What about the speed? Or would the wima caps take care of that? Could you tell me more about the EL2001 vs EL2002 and EL2009? (is EL2001 fine as virtual ground driver?) I'm set on the AD8610 opamp. Was hoping to try the Elna tantalum resistors. Is there a distinctive sonic trait of vishay vs tantalum resistors? What is CRD and Jung? Chips?
 
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Nezer

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If it's battery powered it can't be maxed-out as you're going to *HAVE* to make comprimises somwhere. ;-p

For the other questions about the CRD and the multiloop, read Tangnents notes on his website about these. He discusses all the options in detail.

With battery powered I think you're on the right trail but this thing is going to be huge with the stepped attenuator and heavy with the die-cast aluminium case.

I don;t think you're going to get much use out of 9V batteries. I would go down to AA and use NiMH. Alkalines lose the voltage toward like the last 15% of their life whereas NiMH don't. Of course, with NiMH 9Vs the best your gonna find is around 150-160mAH. 300mAH total into a current draw of about 30mA means about 10 hours of battery life. Maybe thats adequate for you?

If your concerned about weight and size drop that aluminium case and use something more sane. If not, load-up on AA NiMH and last a long time.
 
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puppyslugg

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I think ppl suggested using 2-el2001's in parralell for the virtual ground driver. This of course, will suck more juice out of you batteries.
 
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Audio-Me

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I'll be using NiMH no doubt. Now that I think about it, hrm, how about 15×AA?
Mine is already in a heavy brick like die cast aluminum case, just I am anticipating a much bigger case next time around, not a problem.
Most of its use will be with the Elpac PSU plugged into an outlet though.
.
Stacked EL2002 buffers, stacked EL2001 for driver, hehe, how's that sound? =P
 
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morsel

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Tantalum resistors are a waste of money. Dale Vishay, Holco, etc are fine. I'm not picky, I am using Radio Shack 1% metal film.

There is not room on the META42 for a voltage regulator, but as Nezer suggests you could use an off board regulated power supply. This implies AC power, not batteries. There are plenty of regulated supplies out there, or you can roll your own. If you get a dual supply you can omit the virtual ground circuit.

Elna Cerafine caps are no longer made, but perhaps Elna Silmic would be to your taste if you can find someone who sells them.

It is not necessarily a waste to stack output buffers, this lowers the output impedance and increases control of the buffers over the headphone driver coil. This is probably of greater benefit to low impedance headphones, but can improve the sound for any headphone. Realize that the virtual ground buffer has to sink/source the current from both channels, mitigated by the power supply caps. You may also want to stack the virtual ground buffer, but that decision is best made by the person building the amp, based upon test measurements with high level bass signals.

The EL2002 has a higher bias current. It is better for AC only amps. If you are going for battery operation, stacking EL2001 buffers draws less current than a single EL2002. The EL2008/2009 were discontinued a year ago, and are TO-220 packages, which are not 8 pin DIP compatible. They are rated for 1A, as opposed to the 100mA of the EL2001/2002. Great if you can get them, and I suppose they can be bent to fit. The EL2008 is the low bias version, EL2009 is the high bias version. All of this has been discussed over and over again in previous threads.

CRD = current regulator diode, really a FET with source tied to gate and a resistor to set the current.

Walter Jung is a famous opamp circuit designer. He wrote "The Op-Amp Cookbook" and designed the multiloop topology that the META42 uses.

I don't think anyone will be using 1F caps in an amp. The only 1F caps I have ever seen are low voltage reservoirs for keeping memory alive during battery replacement or brief power outages.

Judging by your questions, you might be better off hiring someone like JMT or Tangent to build you an amp. They have the electronic knowledge needed to make good choices. Please search previous threads here and on HeadWize, where most of the META42 conversations are going on.
 
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Nezer

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"Elna Cerafine caps are no longer made, but perhaps Elna Silmic would be to your taste if you can find someone who sells them. "

Talk to Erix... They are most certainly still made but they have discontinued many of the high-voltage models (none of which are of any real use in this application).

I'm in love with the Cerafines and think they are the ONLY way to fly.
 
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puppyslugg

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morsel:
Quote:

If you get a dual supply you can omit the virtual ground circuit.


How about hooking the reg. psu and virtual ground circuit thru a dpdt switch and connect it to c2-/cr2+, (to make use of the onboard bypass caps) and have the option of batteries or ac?

nezer:
Quote:

Consider the OPA637 opamps. :wink:


Is there a battle brewing between the opa637 vs ad8610?
 
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Nezer

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[QUOTEnezer:


Is there a battle brewing between the opa637 vs ad8610?
[/B][/QUOTE]

I dunno, wanna start one, punk? :wink:

Honestly I haven't heard the AD8610 yet and just test drove the 637 last night in my Corda under less-than-ideal conditions. Still it performed so great I think other opamps are going to have a hard time matching it. I'd love to be wrong though!


Hmm, I wonder if Analog will send me some three free samples of each of thier opamps if I ask.
 
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puppyslugg

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Quote:

Hmm, I wonder if Analog will send me some three free samples of each of thier opamps if I ask.


(LOL) My god, man! Have you no shame?!!


Analog Devices do offer free samples, though.

Lord, what have I done?
 
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What about for an all-out portable set-up to rival the Cosmic? Or is that what you guys have been talking about? This super-META42 probably could run off DC or battery power, right?!?!!

Audio&Me,

Is the META42 you have now semi-portable or tuggable/ movable? It runs of many AA's or many 9V's or what does it run from?
 
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You know, I was just thinking about this rather randomly, but didn't the Headwize/Head-Fi member Apheared come up with the designs for the CHA-47 and the META42 (otherwise referred to as A-42 and A-47)? Then where the heck is he when his amp, his very design, is being reincarnated and sold to the masses? He's a moderator isn't he? Shouldn't he be moderating or something? Seems odd for someone who seemed to be so deeply involved in designing very, very good amplifier designs to be almost never around nowadays on Head-Fi.
 
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puppyslugg

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the quality guru:

Quote:

What about for an all-out portable set-up to rival the Cosmic?


I don't know if the META was designed to 'rival' the Cosmic or not. But it will be interesting to see how it stacks up to the Cosmic and others. I think the META should be at the very least, 'respectable'.

Quote:

Is the META42 you have now semi-portable or tuggable/ movable?


Portabilty is a state of mind. What some consider 'portable', others may not. Seeing from your bio that you are a student, I assume that you are a young, strong buck. So maybe lugging around a couple of 12v car batteries may not be out of the question.



Quote:

It runs of many AA's or many 9V's or what does it run from?


There are many options on powering the META. I plan to run my META off 4-9v batteries in a series/parallel arrangement. Can't have too much power, can we? On the ac side, I will be using a linear regulated psu.
 
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Audio-Me

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Mine at its current state, runs off two 9V batteries in series. You could stash it in a backpack and hook it upto a portable cdp in front pocket with a flexible cable. But at this point, I want to use this as a lug from point A to point B type of amp where I use it stationary (as you can tell, this thing is going to go through a major transformation,
). Tangent makes them in small portable cases. I'd like eric to build me two more amps but in different enclosures.
 
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