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OK, I have a few questions about the CHA47 that I purchased from JMT a while back. I am pretty much a complete newbie when it comes to DIY, so please bear with me.

First of all, what would be a good way to significantly improve the sound of this amp (not that's it's not great already) without a complete overhaul of the amp? More specifically, I am thinking about swapping out the two OPA2134's for higher quality ones such as the AD823 or OPA637. Would this work, as in requiring no other mods?

Secondly, I have essentially zero soldering experience at this point, so would it be safe for me in the first place to even attempt doing this?

In any case, if I were to do this, where would be a good place to obtain a decent de/soldering iron and solder? I've seen some at my local Rat Shack and Ace Hardware, but are these up to snuff for the task? Or is there somewhere else I should look?

Thirdly, when I feel like I want to build a higher quality amp (such as the META42) by myself, would it be possible to just put together the parts on the board, then swap it out with the old board and hook everything back up (this is with a standard PacTec case)? If so, I'd imagine it would make the contruction a whole lot easier.

Finally, is this all worth it in the first place?? My entire headphone system currently consists of Teac MC-D80 source, and a pair of Senn HD-495's, with Monster IL 400 MK II IC's, which is also hooked up to a SBLive. Hardly what you'd call a "high-end" system at all. If I were to do any of the above, would this really make a worthwhile difference for the price and time?

Thanks a lot for your help. This is a great board, and I've learned a lot of new things. Now it's time to zero in and get something done! Any advice would be appreciated.

 

[attnet]

A little o/t, but I felt it wasn't worth another post. Would getting the Senn HD-280's be a better upgrade than persuing the above project? They seem pretty appealing to me, especially the isolation, since I work next to my somewhat noisy computer a lot. Any tips appreciated.

 

[tangent]

Quote:

I am thinking about swapping out the two OPA2134's for higher quality ones such as the AD823 or OPA637. Would this work, as in requiring no other mods?

The AD823s might sound a touch weak driving those headphones directly. If you had high-impedance headphones (100 ohms or higher) I wouldn't worry, but below that, you might notice a loss in the bass slam.

For the OPA637s, you will have to use a gain of 5 or more to be sure you don't get oscillation. The higher the better, which is at odds with the requirement to have a reasonable sweep on the volume knob. It's a balancing act... Also, you will need to give this chip at least 12V, which means you need to be using the PacTec HML-ET, not the standard version, and the batteries have to be wired in series, not in parallel.

Quote:

where would be a good place to obtain a decent de/soldering iron and solder? I've seen some at my local Rat Shack and Ace Hardware, but are these up to snuff for the task?

Read this article:

http://tangentsoft.net/audio/new-diyer.html

Quote:

would it be possible to just put together the parts on the board, then swap it out with the old board and hook everything back up (this is with a standard PacTec case)?

This will work, assuming there's enough slack in the wiring. Knowing JMT's neat wiring habits, though, I suspect you'll find that half of the wires don't reach the holes they need to.

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Finally, is this all worth it in the first place?

DIYing is generally not cost-effective. You almost never get it right the first time, and either you succeed and get bitten by the tweaking bug, or you fail and end up with an amp that doesn't work and you decide not to pursue the hobby any further. Either way, you would have been better off buying an amp built by someone else, either commercial or DIY-by-someone-else. At least that way you get something known to work and you don't have to go buy a bunch of tools.

Having said that, if you can afford it, I highly recommend DIYing.

It's educational, and you can tweak the amp to your tastes. Just don't do it to save money, especially at the low end.

 

[attnet]

Thanks for the reply tangent, and I think I still am interested.

So what Opamps would work for my setup then, that would still improve the sound substantially?

 

[tangent]

Quote:

what Opamps would work for my setup then,

I will answer direct questions about specific op-amps, if I've used the chip and if those questions aren't answered here:

http://tangentsoft.net/audio/opamps.html

...or in the datasheet. I won't answer general open-ended questions like that one. Sorry.

 

[attnet]

OK, what would happen if you dropped in two single opamps into the (technically) quad amp design?

 

[tangent]

There are adapters that take two single-channel chips and allow them to plug into a dual-channel DIP-8 socket. One is for SO-8 surface mount chips and is from BrownDog, and the other is for DIP-8 chips, and I offer it.

Which reminds me: there's a point with the CHA47 where I think you hit a wall in terms of price/performance due to the doubled chips. The only purpose of doubling chips is to increase the amp's output current, which is a job better done by a buffer. Why this matters: upgrading a CHA47 to OPA627APs means buying four of them plus adapters, which will run almost $75, with shipping and all; instead, you could spend $40 in a META42 for just two OPA627APs and an adapter plus a pair of EL2001 buffers. Point being, the META42 design works better when you're using expensive op-amps. When the chips are cheap (under $7 or so per channel), the CHA47 isn't much different in cost, and can be cheaper.