[Haoleb]

Hello. Well im want to build the Grado Ra-1 battery powered amp and i have schematics and stuff but i am having a hard time figuing out what op amp to use, id like to be able to get something at radioshack if i could just to make sure i can get one working before i order a nice Burr Brown or something. If someone can please help me that would be much appreciated. Here is a link to the schematics and stuff i found. I know how to build electronics at a amature level but havent any experience with stuff like op amps. So yea. thanks.

http://www.geocities.com/rubin_jpk/rubin/page_4.html

 

[PeterR]

You'll need to use the same opamp (from New Japan Radio I think), or it won't be a RA-1 clone.
The RA-1 circuit itself is the most generic opamp circuit you can think of, same as a CMoy. So if you plan to use another opamp, head over to headwize and read up on the CMoy (if you haven't already done so), then go to tangentsoft.net and read tangent's cmoy and opamp articles...

 

[jeffreyj]

PeterR, you give the CMoy a bad name by lumping it with the Grado RA-1!!!

The op-amp is the very rare NJM4556 (rare because it blows!) made, as PeterR said, by NJR corp (aka JRC, NJM, etc.. depends on whose translating, I guess). It was specifically designed to drive lower impedances than the well-regarded if long-in-the-tooth NE5532. However, it doesn't even seem to achieve statistically significant gains over that venerable chip when both are compared driving a ~100 ohm load (I don't recall exactly what the load impedance was, but I could swear it was 120 ohms).

The volume pot is about as cheaply made as they come, but those DC blocking capacitors - which an op-amp with superior DC specs would not require - are fairly nice; easily exceeding the cost of all of the rest of the parts, including the pc board, put together.

One thing that ought to strike a chord of curiosity is: why, if this amp is so simple yet so expensive, is the market not flooded with copies?

Things that make you go hmmmm....

 

[Squalish]

The NJM opamp is available through mouser for about 30 cents.

 

[Haoleb]

Thanks for all the help guys. I want to build this thing but have in the back of my mind the headroom airhead still, because its small and has the signal processing.

 

[Squalish]

Pretty much anything is supposed to trounce the airhead, RA-1 included. I'm sure it's an improvement on most portables' headphone jacks, but it's looked down upon on head-fi. Don't forget that the RA-1 was considered a good deal even among people that had several amps, up until someone took it apart and discovered the $20 of parts inside(much less in bulk).

 

[Haoleb]

Being that the airhead is 120 bucks that i dont have, and i can make the grado for 20 bucks in parts im gonna make this grado and just put it in as small of case i can fit it in i guess. Its such a simple device, just getting all of the parts together is going to be a PITA.

 

[jeffreyj]

Squalish: $0.30 at Mouser, huh... Looks more like $0.29; get your facts straight!

Note that I made no comment as to how it sounds - that's because I have no idea! Yep, no idea at all.

But I find it downright immoral, repugnant, even, to charge so much money for so little... R&D, parts quality, etc.

Reading pretty much any thread at diyAudio, or especiall AudioAsylum (got the name right on that one) should convince you that psychology plays as much a role in how good a piece of equipment sounds as raw specs do. If you buy an amp that is beautiful, to be sure - made of Mahogany, sporting a huge machined aluminum volume knob, 'Grado' in gold leaf across the front - and then you find out that the op-amp inside costs $0.29 from Mouser... well, it would probably be extremely difficult to keep on thinking the amp was the cat's meow, now wouldn't it?

And, frankly, I couldn't blame that person because I'd probably get sick knowing I just spent $350 for a block of wood with $10 worth of parts inside.

But if you spent $10, as it is worth, you might find it to be a very satisfying expenditure, indeed.

Haoleb, you can get all of the parts from Mouser, so go for it. If you want to try to duplicate the excess of the input capacitors, get the Vishay caps, part number 75-735P505X9100L ($5.18 ea.) The performance of the op-amp really calls such excess into question, so a more practical choice might be the Cornell-Dubilier part, 5989-100V4.7 ($1.62 ea.)

Xicon 1% resistors work just fine and for a panel mount volume control, you'll need a dual-ganged audio taper pot; part number 531-PC16DC-10K ought to do the job quite well (no, it's not top of the line, by any means, but it is quite serviceable and probably better than what's in the RA-1, anyway)

I'll leave the rest up to you, especially sourcing the "Bronx" Mahogany and aluminum volume knob

 

[Squalish]

A few months back I bought the RA-1 parts that still languish in my 'to-do' table. Now that summer is here and I have some free time...

Anyway, we determined some of the closest parts to what is actually in the RA-1 a few months ago. The input caps are either Aeon or Solen - look here, $5 for the pair. The input caps and the opamp are really the only two distinguishing features, but if you want the pot, it appears to be the same one as RS#271-1732.

It's actually closer to $40 than $20, but most of that is in the offboard components

 

[Haoleb]

i got all the parts together in my shopping cart at mouser. Gonna get the pot at radio shack and a box and the rest from mouser. after all is said and done it will probbly be arund 40 bucks. so your are very correct.

 

[PeterR]

Quote:

PeterR, you give the CMoy a bad name by lumping it with the Grado RA-1!!

Sorry

So if you build a CMoy using a NRJ4556 opamp, what will be the difference to a RA-1?

Quote:

Note that I made no comment as to how it sounds - that's because I have no idea! Yep, no idea at all.

I know that amp, and I must say the sound is a lot better than it looks on paper. Not the be-all end-all of headamps, but it complements the Grado headphones very well.
Quote:

I'd probably get sick knowing I just spent $350 for a block of wood with $10 worth of parts inside.

I think that's been discussed at length in various forums (fora?), so I don't want to get into this again. But DIYers often make the mistake of looking at the parts costs only, not what the costs will be when a product finally arrives in a shop window with a lot of people trying to make a living from it...

 

[was ist los?]

Heh, actually, i prefer my ra-1 clone (biased to class a) over my mint with my partial d-25s turbo.

 

[uniuniunium]

Quote:

Originally posted by jeffreyj Xicon 1% resistors work just fine and for a panel mount volume control, you'll need a dual-ganged audio taper pot; part number 531-PC16DC-10K ought to do the job quite well (no, it's not top of the line, by any means, but it is quite serviceable and probably better than what's in the RA-1, anyway)

where would one find 1% Xicon resistors, I've checked Digikey, Mouser, and PartsExpress, none seems to carry them.

 

[Squalish]

http://www.mouser.com/catalog/614/323.pdf

 

[jeffreyj]

Quote:

Originally posted by uniuniunium where would one find 1% Xicon resistors, I've checked Digikey, Mouser, and PartsExpress, none seems to carry them.

Squalish answered you for me in his characteristically terse style

Xicon resistors are nothing fancy - just generic metal film resistors. While there are certainly substantial differences in performance between the different resistor types, I am not at all convinced that one could tell the difference between two amps, all else equal save one uses Vishay-Dale resistors while the other uses Xicon's.

At any rate, try page 323 on Mouser catalog #614 for the Xicon resistors or page 317 for the Vishay's.

Good luck with your clone!