[tangent]

Quote:

You mention a capacitor to control the opamps' occilation, could you elaborate?

I'm talking about small (0.1uF or so) film or ceramic caps near the op-amp's power pins for bypassing. That is, connected between power and VGND. In the META42, C4 and C5 serve this purpose.

Quote:

I really don't understand the technical explanations of how to pick parts that well

Sorry, but this is a technical subject. The idea is that you'll rise to the challenge and learn a lot in the process. If you don't want to take the time to learn how the amp works and how to tweak it, the META42 might not be the right project for you. I'm not trying to be harsh, just realistic. If the amp doesn't work the first time, how will you fix it if you don't have a basic understanding of how it works?

 

[JMT]

Perhaps you should walk before you run. Build something that will teach you the technical aspects of this. Fail, and learn from your failures. Quote:

and seeing that the meta42 is "easy" to build

"Easy" is a relative term.

 

[Kal525]

lol, ok guys, thanks for the kick in the ass, i guess it's back to more reading and questions then. I guess i won't have this before xmas. I have to start studying for finals in a week and i don't know if i'll have a parts list together by then, hopefully i will.

 

[CaptBubba]

Quote:

Originally posted by tangent I'm talking about small (0.1uF or so) film or ceramic caps near the op-amp's power pins for bypassing. That is, connected between power and VGND. In the META42, C4 and C5 serve this purpose.

I thought you were referring to adding a cap in the feedback loop of the opamp to reduce bandwidth. I already have a good number of small bypassing caps on the amp (~150nF/opamp and ~200nF/buf634). I figured these would mostly help the amp by keeping it from being current-starved on transients, but could they be causing the chips to occilate?

I may just switch out the opa637s for something else. Anybody willing to trade another chip for them? Single package opamps only, preferably something by a different manufacturer (AD would be nice...). I already have the following opas: 134a, 227, 228. I knew I should have just gotten the opa627 instead. They work great, but I prefer to listen to lower volumes.

 

[Kal525]

i am gonna worry about the headphone jacks and case at the end, for now i am going to assume this will be a portable amp and just work on the innards.....so 3x EL2001s no stacking, AD620, JFET cascode set, multiloop configuration with the resistances marked in the schematic, R8 and R9 jumpered, no C5, and i'm still not sure on the values for C1 or C4 and the the other capacitors and diodes, i will post more specific questions later tonight, in the meantime if anyone wants to give me some freeby recommendations for these values feel free

 

[Kal525]

Alright, this is a parts list that i am thinking of compiling so far with the help of tangent's site and the replies to this thread. Please let me know if there is anything i am missing or anything you would add. Everything you see is what i am using from the circuit diagram on tangent's site.

I am still unsure of a few things. The value i should pick for R7, and the value i should pick for C4. I stuck with what was already on the diagram for C2 and C3, hopefully this is a good configuration, i'm not sure what other configs will do, but since this is a portable amp, this is probably one of the smaller configurations. Also, where should i get the resistors from, and what kind should they be, i didn't really understand the section on tangent's site tittled "are 1/8w resistors sufficient?" so i could use some help in this area.


The only other thing is the LED. I want a blue LED, but there was none listed on the site. If anyone could recommend one to me, with a respective value for RLED, that would help. Thanks.

 

[jasong]

here:

C1:
0.47 ìF 100V+ metalized polypropylene film capacitor
mouser number 1429-1474

C2/C3
470 ìF 16V 12.5mm tall
mouser number 647-UPW1C471MPH
(fits small cases)

C4
Wima MKS-2 6.8µF/50V
from Tangent

D1
Crowbar diode, 40V 1A, DO-41 package
mouser number 511-1N5819

These will work for a 9-volt portable.

--Jasong

 

[tangent]

Regarding your parts list:

- You left out the pot, which value would influence the proper value for R2. As always, the details are in the docs.

- Make R7 100 ohms.

- Make R10 1K.

- C1 is too large for the v2 boards. I suggest the 0.22uF Panasonic ECQP (polypropylene film and foil), from DigiKey. I imagine the 0.47uF metalized polypropylene jasong mentioned probably fits without fuss, too.

- Jasong recommended the 6.8uF version of the Wima cap. That's what I'd use even though the 10uF would also work for a low-voltage powre supply, simply because the 6.8 is a lot cheaper and the improvement in the 10uF is not that great.

- You say you are "not sure" about the purpose of a buffer. A buffer passes the signal it gets as input unchanged in terms of voltage (that is, gain is 1) but a good buffer will be able to put out more current than your average op-amp, and they'll also be designed for driving difficult loads that might give an op-amp problems. This relieves the op-amp in the META42 of the problem of driving the headphones itself, which allows it to sound better and gives you more choices in op-amps. The virtual ground buffer is there to relieve similar strains on the TLE2426, which, like your op-amp, is not designed for driving high current loads.

- I've updated the parts list, adding white and blue LEDs that I've used successfully. Sorry, I haven't done the research to find alternatives to the parts from DigiKey. Doesn't mean they don't exist, just that I haven't tried to find them yet.

- For battery use, I recommend either the 1N582x or the 10TQxx diodes for D1. Most often, I use a 1N5822.

Quote:

where should i get the resistors from, and what kind should they be,

It's simplest to use 1/4W generic metal films from DigiKey or 1/8W Vishay-Dale RN55Ds from Mouser. The latter are supposed to be better, according to people who've compared the two. I haven't, but the Dales are reasonably priced.

 

[Kal525]

ok, thanks for the critique. I'm not sure what you mean by the "pot" though. As far as i can tell i included all the parts in your circuit diagram except for CRD and ZNR which are used for making the LED get dimmer as the battery voltage drops, I would like that, but it sounds a little too complicated for me.

 

[tangent]

Quote:

I'm not sure what you mean by the "pot" though

Potentiometer -- volume control.

 

[Kal525]

oh, ok. I did not include that yet because i'm not sure of the case that i am going to use. And the size of the case will affect the size of the volume control that i use, right? I'm interested in the seethrough grey case that JMT uses. Do you know what part number this is? Also, how difficult is it to include both a 1/4" and a 1/8" stero jack for the output? And do you think it would be best to have the RCA plugs for the input, will that give me the most flexibility?

 

[Kal525]

I have another question. I stumbled upon a post in which Timoteus posted the following:

"If you liked your CMoy then I think you'll really like your new META42.

JMT built a META42 for me in the following configuration:

AD8620 op-amp
Alps Blue pot
Elna Cerafine PS caps
Vishay resistors
dual stacked 2001 buffers
Cardas jacks
Biased to Class A
Locking Neutrik jack
Blue LED

I don't know if this is the maxed out version you ordered but I'm sure it's pretty close.
The sound quality is crisp and clean. Silent background. Very fast and a great build too.

I'm using the Ety ER-4S and have plugged in my HD600 a few times to try them out. These are similar to what you will be using so I think you'll have similar results. I think the limiting factor for sound quality in my setup is the PCDP. If I hooked this amp up to a high quality source who knows...You should be pleasantly surprised and happy with your new purchase.
"

My question is, what is PCDP, and i thought that using an amp reduced the need for a quality source......meaning i could plug the amp into any old cd player and get good sound, is this incorrect? And if so, would a bigger home version of the meta42 be more suitable for me than a portable meta42? Also, what exactly would you consider maxed out? Is it possible to get a "maxed out" portable meta.....i'm guessing for it to be considered maxed out i would have to use stacked el2002 buffers, 1000 micro F power caps, and perhaps the 10 uF Wima cap, other than that i think i will have a similar setup.

I also had a question on capacitance values for C1. Why does JMT recommend 1 uF for portables, while tangent, you said i should go with .22 uF. Is there a huge difference, i just want to make sure i have ample protection for my headphones. Also, do i have to consider fluxuating AC current if i use AC power.

 

[JMT]

PCDP = Portable CD Player
Quote:

i thought that using an amp reduced the need for a quality source......meaning i could plug the amp into any old cd player and get good sound, is this incorrect?

That is incorrect. An amp is not going to make a poor source sound good. Ever heard the term "garbage in, garbage out?" If anything, it may enhance what you don't like about your source. It will, however make good headphones sound better. You can't make a Yugo into a Ferarri by using better plugs. Quote:

And if so, would a bigger home version of the meta42 be more suitable for me than a portable meta42?

A larger case means that you can:

1) Use dual 9v batteries
2) Use components with a larger physical size, ie: Elna Cerafine caps.
2) Use higher quality off-board components, ie: Alps Blue pots. Quote:

Also, what exactly would you consider maxed out?

Using the best components that you can.

 

[Kal525]

ok, if i'm using sennheiser hd600 headphones with this amplifier, is what i have selected as parts so far going to suffice, or should i sacrifice some portability so i can get better components?

 

[Kal525]

hey JMT, i was wondering if you would consider building one of these things for me. As it stands, i have 5 finals coming up in the next week and i need to focus on them, and perhaps over the summer, when i have had the benefit of my ECT and logic design classes and i have enough time to really sit down and understand each component fully then i will attempt to build my own. I could probalby do it now, but i would rather understand exactly what is going on when i have the time to learn, rather than this just being a soldering job.

I have definitely learned a considerable amount from this thread though, and i'm sure that will assist you in knowing what i want in the meta. If you don't have time, i understand, in which case i will probably have to convince my parents to donate some extra christmas money so that i can purchase a little or mg head. I really do not want to spend more than $200 on this thing, i just wanna be able to get the most out of my headphones.

You'll get a laugh out of this. I originally wanted to get a pocket pc for christmas but decided against it since it was too expensive. I figured that getting the best sounding headphones would be MUCH cheaper..........then i saw the $3000 blockhead amp, hmmmm, that's more expensive than the parts i used for my computer and my parents' computer combined, this is definitely an expensive hobby, my mom almost had a heart attack when i told her a top of the line amp costs $3000.

Anyway, if you can help me out let me know, or if you know someone who can that would be great too, i've seen your work though and i like it, and other people seem to be pleased as well.