decoupling AD825
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jarthel

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Can I decouple this opamp by connecting the capacitor to -/+V? What capacitor value can I use?

I assume the audiocom and LCAudio AD825 upgrades uses this method.

Thanks

Jayel
 
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tangent

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Power supply bypassing works the same for all chips -- a cap from each power supply pin to ground. ("Decoupling" usually refers to putting a cap inline with an AC signal, like C1 in a CMoy amp.)

The type and size is a matter of much debate, but a common setup is to put a 0.01 to 0.1uF ceramic cap as close to the chip as you can. If that doesn't help, add 1-10uF of tantalum or film capacitance in parallel, farther from the chip.

Do this only if you have to. In my brief experience with the 825, it hasn't been necessary.
 
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jarthel

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Thanks Tangent. But....

If you look at the AD825 upgrades from LCAudio and Audiocom, they have the capacitor sitting in the PCB. From what I can remember, there's no ground pin in the AD825.

The only other logical place for them to connect the decoupling cap is to connect it to -/+V.

I'm not talking about decoupling in general but talking about the AD825 upgrades.

Thanks


Jayel
 
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tangent

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The LC modules have a pad on them to which you solder a wire, which then goes to circuit ground in whatever you plug the module into. It's a bit ugly, but that's the only way they could have done it. That's one reason why Morsel didn't do such a thing on the Brown Dog adapter -- it's just plain ugly, and with good modern op-amps, it tends to not be necessary.
 
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jarthel

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Ah I didn't see this ground pin.


Thanks


Jayel
 
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morsel

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I wrote an extensive reply to this thread many hours ago but it poofed.
Tangent covered most of the points. Adapters with onboard caps and ground tether will not fit in many places the BrownDog adapter fits. I have yet to hear from anyone who had problems with opamps on a BrownDog adapter. My advice is to not worry about bypass caps.

Tangent, decoupling = bypassing. Jarthel is right. C1 in a cmoy is a coupling cap, not decoupling. The semantics are confusing.
A coupling cap conducts the signal you desire. A decoupling or bypass cap conducts the signal you are trying to be rid of.
 
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morsel

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Ah, I see you posted the same question to multiple forums. My reply didn't poof, it is on Headwize. Snort!
 
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