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Old 20th August 2003, 12:13 PM   #1
cdl is offline cdl  Denmark
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Default New high quality opamps...

LC Audio has now discontinued their AD825 upgrade, stating that the there are better chips on the market now.

http://www.lcaudio.dk/com/ad825.htm

However, they donīt state which chips they have in mind.

Of course, "better" is subjective, depends on usage, design taste etc.

But does anyone have an idea which opamps they might be talking about?

Or experiences with newer opamps in preamp circuits?

I will be using it in a preamp based on a single opamp. Just one single stage after the volume pot to drive the rather lowish (10k) input impedance of my power amp.

(presently using OP37, as I had some lying around... i know they aren't top of the league!)


I will try out the AD825's, but any other recommendations? AD8610?
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Old 20th August 2003, 04:37 PM   #2
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Default Re: New high quality opamps...

Quote:
Originally posted by cdl
LC Audio has now discontinued their AD825 upgrade, stating that the there are better chips on the market now.

http://www.lcaudio.dk/com/ad825.htm

However, they donīt state which chips they have in mind.

Of course, "better" is subjective, depends on usage, design taste etc.

But does anyone have an idea which opamps they might be talking about?

Or experiences with newer opamps in preamp circuits?

I will be using it in a preamp based on a single opamp. Just one single stage after the volume pot to drive the rather lowish (10k) input impedance of my power amp.

(presently using OP37, as I had some lying around... i know they aren't top of the league!)


I will try out the AD825's, but any other recommendations? AD8610?
IMHO I think you got it right. The AD8610 is probably a better part than the 825.

OP37s are quite good, and you better listen to both before making your choice. At least that way you will be listening to the one your prefer and not the one anyone will say sounds better.


Carlos
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Old 20th August 2003, 04:53 PM   #3
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Default Re: Re: New high quality opamps...

Quote:
Originally posted by carlmart


IMHO I think you got it right. The AD8610 is probably a better part than the 825.

There's another new option which you should probably consider: AD8065.

It's less noisy, has good PSSR and settles fast.


Carlos
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Old 20th August 2003, 06:04 PM   #4
cdl is offline cdl  Denmark
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Default Thanks!

Thanks a lot - will keep you all posted on what I find out.

I had some hassels with the OP37 in the beginning, was in doubt if they could be used at all as they are not unity gain compensated.
The first version definately sounded "funny" somehow - boombox-type bass and white noise in the trebles.

I thought capacitive load might be a problem; decided to bypass resistor in feedback loop with 30pF as recommended several places. Was not a succes, and made the thing produce DC offset (?!? don't really understand why).

So I removed the caps and increased the resistor in series with the output (recommendation from AD) which was a very big improvement. Maybe the load was simply too small?

I haven't got around to intense listening tests yet; but my impression is that the bass still isn't quite right - a little inflated and resonant, but not deep.
I guess I will try increasing the output resistor a little more, and add more decoupling caps (presently only using 100nF's).

Cheers - cdl
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Old 20th August 2003, 07:45 PM   #5
PMA is offline PMA  Europe
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OPA627 gives perfect combination of low noise, DC accuracy, speed and low distortion. According to my measurements distortion is about 20x lower than for AD825 and noise is also lower.
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Old 20th August 2003, 09:06 PM   #6
cdl is offline cdl  Denmark
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Hmmm - and OPA627 even comes in DIP package so I can just plop it in ... definately a must-try if I can lay my hands on some!

...oh better check the pin connections first...

/cdl
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Old 21st August 2003, 12:39 AM   #7
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Quote:
Originally posted by cdl
Hmmm - and OPA627 even comes in DIP package so I can just plop it in ... definately a must-try if I can lay my hands on some!

...oh better check the pin connections first...

Pins are almost exactly the same on the OP27/37 and OPA627. Perfect drop-ins, except for the DC trim you will probably not use.

There is another difference between them: the OPs are all bipolar types, and the OPA627 has a FET input.

The 27/37 types are more sensitive to power supply quality, and will probably respond more dramatically to improvements there.

The 37 should be used on greater than x5 gains, but neither should be used with more than x10 gains.

But the 627/637 types should bring improvements all along, do not hold any doubts about that.

It would be an easy way to upgrade what you have now, with minimum fuss.


Carlos
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Old 21st August 2003, 02:55 AM   #8
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OPA627's are a good choice. Subjectively, they sound very clean and effortless as long as the outputs aren't overdriven
(i.e. >600ohms) If greater load driving capabilities are needed, you can use the BUF634 in the feedback loop to drive very low loads and retain good distortion characteristics
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Old 22nd August 2003, 07:27 AM   #9
cdl is offline cdl  Denmark
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Thanks for the tips - have used the last couple of days ordering engineering samples

Some of them should be arriving today, so with a bit of luck I will experiment in the weekend!

Does anyone know of any changes to a standard opamp circuit that should be made in order to accomodate the current-feedback types?

B.T.W. those SOIC to DIP adapters are painfully expensive at Farnell - cost as much as the opamp itself!

/cdl
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Old 22nd August 2003, 09:03 AM   #10
cdl is offline cdl  Denmark
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Oh, and while I'm at it I might as well get rid of those nasty NE553X's in my CD player as well - now that I'm ordering lots of opamps anyways!

I really would have expected something better inside that CD, but well, at least they didn't use 741...

cdl
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