AD825: class-A operation + bypassing/snubbing - diyAudio
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Old 12th February 2010, 08:27 AM   #1
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Default AD825: class-A operation + bypassing/snubbing

I'm thinking about class-A'ing some AD825s in a portable (battery-pwr) headphone amp and, perhaps, a non-portable D/A processor IV section. If you've class-A'd this op-amp was it worth the fuss (or does it do almost as well -- or better -- on its own)?
Also, how about bypassing/snubbing this guy, in a manner similar to the one suggested for another model, the OPA2132 -- or does it do almost as well -- or better -- on its own?
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Old 17th February 2010, 07:53 AM   #2
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Is your post a statement or question?

AD825 is pretty good as it is. Aren't you satisfied with it?
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Old 17th February 2010, 09:30 AM   #3
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ClassA and battery powered make me ask "what are the priorities in the design?"
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Old 19th February 2010, 05:59 PM   #4
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Quote:
Originally Posted by AndrewT View Post
ClassA and battery powered make me ask "what are the priorities in the design?"
"Portableness" and best SQ attainable per limited-size PCB footprint.
The AD825 seems to be more pwr-hungry, at least in my headphone amp, than other op-amps I've tried, so class-A may not be so desirable after all.
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Old 19th February 2010, 06:59 PM   #5
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Quote:
Originally Posted by hollowman View Post
"Portableness" and best SQ attainable per limited-size PCB footprint.
The AD825 seems to be more pwr-hungry, at least in my headphone amp, than other op-amps I've tried, so class-A may not be so desirable after all.
The 825 needs about 6-7mA from the supply which is typical of the 'audio' opamps. If you want less power consumption, there are others, but not 'audio' types (whatever that means).

Try the OPA890

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Old 16th August 2010, 02:49 AM   #6
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Did AD ever (un)officially put out a dual version of the 825? If not, what spec- and/or sound-wise is the closest approx. (again, I need a dual). This 825-like dualy may very well come from another manuf. (Linear, TI/BB, National, etc.).
Thx!
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Old 16th August 2010, 03:23 AM   #7
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Stick with the AD825, Hollowman, you are on the right track. This is the best overall audio op amp that I have found, in my experience. I wish it were quieter, but for line level it works just fine. You can buffer the output if you want.
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Old 16th August 2010, 11:05 AM   #8
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Quote:
Originally Posted by john curl View Post
Stick with the AD825, Hollowman, you are on the right track. This is the best overall audio op amp that I have found, in my experience. I wish it were quieter, but for line level it works just fine. You can buffer the output if you want.
Thx John! I agree and that's why I asked about a possible dual version if one exists. Reason: I can't install a BrownDog-type adapter into the tiny DAP (an "iPod") I'm modding. I.e., not a lot of real-estate in there for two SO8 opamps. The BrownDog SOIC-to-SOIC 2-to-1 is one of those tall vertical jobs (which adds up to about four of the DAPs in thickness!)
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Old 16th August 2010, 11:26 AM   #9
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Default Low-noise 825?

Quote:
Originally Posted by john curl View Post
I wish it were quieter, but for line level it works just fine.
Yeah, I was thinking about this a while back. I haven't seen AD or any other manuf put out anything (at any price) that will retain the bennies of the 825 and, concurrently, be quiet(er). Is there some sort of topological barrier in monolithic opamp construction that won't let us also eat our cakes?
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Old 16th August 2010, 03:21 PM   #10
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It appears that the source or emitter degeneration added to make it into a properly working video amp, makes it noisy. It uses the same sort of topology as low noise IC's. However, this resistor degeneration also raises the open loop bandwidth significantly, and I think that is the key. (Watch me get ---- for saying this. ;-) )
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