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Help !!! Opam for my cmoy ...

post #1 of 18
10/25/07 at 8:40am
Thread Starter 
Hi,

I'm about to DIY my first CMOY but still wonder if I can use AD8397ARDZ and OPA690ID in place or not? Because I really do not like the OPA2124 or OPA2227.
Thnx in advance
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post #2 of 18
10/25/07 at 8:56am
You should stick with the OPA2132 or the OPA2227. Both of those are available in DIP-8, work without a hitch in the basic CMoy circuit, and they are cheap$.

You may be causing yourself nothing but potential frustration if you try an SOIC chip as your first project. You're also on the fine line of the OPA690's voltage limit (+or-5VDC). When you use the voltage divider in the CMoy, it will break a single 9V battery into +or-4.5, but there are a lot of things that could go wrong along the way, including a fresh battery or a rechargeable with a fresh charge. Two 9V batteries would be out of the question.

Filburt often disagrees with this point, but IMHO, the AD8397 is out of the question. Look at the Mini3 and note all of the capacitive de-coupling, ferrites, and the output resistors. This chip is not made for a CMoy and will cause you nothing but trouble.

You should look to whatever you can do to insure success with your first DIY headphone amp. Built following Tangent's tutorial, success is almost 100% guaranteed. Deviate from that as much as you propose and you may have the project become your first and last DIY experience.
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post #3 of 18
10/25/07 at 12:03pm
If you want a good sounding amp, I can understand your frustration. OPA2132 isn't that good, and a 3 channel amp do sound better. If it's not worth the effort doing some tweaks and learn to solder SOIC, you shouldn't hang around the DIY forum at all.

But since you do, I'll guess you're willing to learn. If you think you're up to making an amp like Mini3, i.e. with active ground, go ahead. You could make life much easier by buying a Mini3 board, and it's not more expensive than a good stripboard.

What phones are you using?

If you want to do it the hard way, why not try AD8066/LMH6642. I like this combination. Very detailed and spacious but a bit cold. You could use AD8397, but you have to be prepared for some tweaking to get it to work properly unless you use a Mini3 board. Read about PINT at tangentsoft.net. All this fuss about AD8397, it's not that hard to get it to work, but... AD8397 ain't that good either. And when it comes to OPA690, how many of you have actually heard this amp. I mean compared it to anything else.
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post #4 of 18
10/25/07 at 12:29pm
Thread Starter 
Quote:
Originally Posted by NelsonVandal View Post
If you want a good sounding amp, I can understand your frustration. OPA2132 isn't that good, and a 3 channel amp do sound better. If it's not worth the effort doing some tweaks and learn to solder SOIC, you shouldn't hang around the DIY forum at all.

But since you do, I'll guess you're willing to learn. If you think you're up to making an amp like Mini3, i.e. with active ground, go ahead. You could make life much easier by buying a Mini3 board, and it's not more expensive than a good stripboard.

What phones are you using?

If you want to do it the hard way, why not try AD8066/LMH6642. I like this combination. Very detailed and spacious but a bit cold. You could use AD8397, but you have to be prepared for some tweaking to get it to work properly unless you use a Mini3 board. Read about PINT at tangentsoft.net. All this fuss about AD8397, it's not that hard to get it to work, but... AD8397 ain't that good either. And when it comes to OPA690, how many of you have actually heard this amp. I mean compared it to anything else.
It's exactly that I want to use the core of Mini3 in the Cmoy
I don't realize that it's such a difficulty to use other opam
I'm looking for some warm, bassy opam because my DAP is cowon d2 and ety er4p, which are sooo bright
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post #5 of 18
10/25/07 at 1:14pm
Quote:
Originally Posted by Lil' Knight View Post
It's exactly that I want to use the core of Mini3 in the Cmoy
I don't realize that it's such a difficulty to use other opam
I'm looking for some warm, bassy opam because my DAP is cowon d2 and ety er4p, which are sooo bright
If that's the case, then an OPA2132 or 2134 is right up your alley.

You know, the FOTM (Flavor Of The Month) thing gets out of control around here a lot. Just because there's a lot of good amps available these days, doesn't mean a CMoy with an OPA2132, OPA2134, or OPA2227 sounds like cr*p - it doesn't. It will still beat the pants off of any portable CD player and will do the same with iPods and such if using loaded headphones.

Even so, your statement of using ety's and sounding soo bright is a good fit for the warm opamps noted above. They get a bad knock these days when plopped in a circuit with high-powered power supplies and hot rod buffered output stages. However, in a CMoy, those opamps will sound warm, detailed and tube-like sweet. Just lower the gain by substituting different resistor values (detailed in Tangent's tutorial) and you'll be fine.

P.S. Lowering the gain, which is something you probably need to do with IEM's, makes it even more important that you stick with the ultra-stable opamps listed above, IMHO.
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post #6 of 18
10/25/07 at 1:57pm
If you don't like the sound of TI's OPA IC's you can try the AD8620 from analog.com ro the AD8066. IMO, they sound better in buffered designs, but give them a try. You should also look for the aparhead ( iI'm not sure if that's the correct speling. Basicaly it uses 2 dual opamps where the first IC takes care of voltage gain stage and the second one acts as the current gain stage. It is said to be a good design with grado's and other current hungry cans as it provides more current than the cmoy. A search in the forums should give you plenty of threads with schematics and board layouts.

Show us the results when you're done.

Manuel
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post #7 of 18
10/25/07 at 2:11pm
get an opamp that is unity gain stable as it's unlikly you will want ANY gain with IEM's

* to get no gain wire the output directly into the inverting input creating a special case non inverting amplifier with a feedback resistor of ohms and a resistor to ground of infinite. gain= 1+(0/infinity) is 1 and therfore you have unity gain
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post #8 of 18
10/25/07 at 2:31pm
OPA690 is a single opamp, so you can't use it in a CMoy. A 3 channel config, isn't a CMoy anymore, IMO.

You may want to check out the OPA2107 as well and possibly the OPA2604.
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post #9 of 18
10/25/07 at 3:31pm
Does it matter what it's called? If you want a better sound go for the active ground. My recommendation is worthless for you. AD8066/LMH642 is on the bright side of neutral. It's like tomb said, OPA2134 should be "your kind of sound". OPA2107 has the same sound signature, only better in every way.

For ground channel, OPA551 is very mellow and kind of sweet sounding.

I'd say, add an OPA134 or OPA551 as active ground channel. If you're not happy with the result, then you should start opamp rolling. Or...

An alternative is to add buffers to the output, like Sijosae's or LMH6321. It'll make the sound a little bit sweeter, and it'll drive your low impedance phones better. If you like the sound signature of OPA2134, but unhappy with the low resolution, you could add the class A tweak - resistor or a constant current source from opamp output to negative rail. Then you've built yourself a PIMETA.
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post #10 of 18
10/25/07 at 4:08pm
Quote:
Originally Posted by holland View Post
OPA690 is a single opamp, so you can't use it in a CMoy. A 3 channel config, isn't a CMoy anymore, IMO.

You may want to check out the OPA2107 as well and possibly the OPA2604.
Cmoy's original article on headwize used 2 single opamps. I would agree on the OPA2107.

The AD opamps mentioned previously will be kind of bright. The AD8397 is IMHO bright as well (at least in a mini3-fied PINT).
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post #11 of 18
10/25/07 at 5:48pm
Quote:
Originally Posted by Pars View Post
Cmoy's original article on headwize used 2 single opamps.
That's correct. For some reason I was under the impression OP bought a "kit". I don't know how I got that impression, so I am mistaken.
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post #12 of 18
10/25/07 at 6:23pm
IMHO, voltage requirements are too high to use an OPA2107 in a CMoy. Minimum PS voltage is spec'd as +or-4.5V. That pretty much tears it for a CMoy unless you run with two 9V, but it's still a poor ratio for any portable/battery powered amp.
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post #13 of 18
10/25/07 at 10:06pm
You CAN run an opa2107 on 18 volts, but it doesn't really start to sing until at least 24 volts, imho. I run 'em at 30.

Why hasn't anyone suggested the ad823?
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post #14 of 18
10/26/07 at 3:27am
Quote:
Originally Posted by ericj View Post
Why hasn't anyone suggested the ad823?
Because it's a turd.
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post #15 of 18
10/26/07 at 8:50am
Quote:
Originally Posted by ericj View Post
You CAN run an opa2107 on 18 volts, but it doesn't really start to sing until at least 24 volts, imho. I run 'em at 30.
Yep. I love the OPA2107 in the SOHA - plenty of volts there.

Quote:
Why hasn't anyone suggested the ad823?
I think because the AD823 has only 15ma output current. It's very possible that it will clip a lot in a non-buffered circuit like the CMoy - might be why some don't like it.
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