General > General Technical Chat
What's the real reason that laptop batteries are made not-accessible?
ogden:
--- Quote from: magic on December 12, 2021, 11:00:35 am ---Fun fact: whenever there is an integrated amplifier in something, they point out how it is capable of driving "professional high impedance headphones" but don't mention "consumer low impedance headphones" too much :)
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High impedance pro headphones need much higher output level to achieve specified sound pressure level. Owners of low impedance consumer stuff most likely don't care - their headphones are overdriven or not :D
NiHaoMike:
--- Quote from: SilverSolder on December 11, 2021, 11:41:10 pm ---Does that solve ground loop issues though? Other than using optical coupling of some kind, I can't think of an alternative to a transformer for that.
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With sufficiently well matched resistors, the CMRR of a differential amplifier is more than good enough.
SilverSolder:
It will be interesting to see how this chip/phone compares to a dedicated audio player. I'd be surprised if it comes close to Wolfson WM8740 DACs coupled with a good external amp - but it has a chance of being quite decent! :D
David Hess:
--- Quote from: SilverSolder on December 11, 2021, 11:41:10 pm ---
--- Quote from: NiHaoMike on December 11, 2021, 11:20:28 pm ---
--- Quote from: SilverSolder on December 11, 2021, 10:50:21 pm ---A good hack for circumventing this problem in a car is to use an audio signal tranformer to galvanically isolate the signal between the source and the destination device. Miracle cure, in many cases.
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Opamps and a few well matched resistors are a lot cheaper than a decent audio transformer.
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Does that solve ground loop issues though? Other than using optical coupling of some kind, I can't think of an alternative to a transformer for that.
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It is not galvanically isolated like a transformer or optical coupling is, but a difference or instrumentation amplifier does remove the ground loop. I have done it this way many times.
--- Quote from: NiHaoMike on December 12, 2021, 12:31:11 pm ---With sufficiently well matched resistors, the CMRR of a differential amplifier is more than good enough.
--- End quote ---
Just 1% resistors for a worse case common mode rejection of 34 dB is usually good enough. Only a moderate amount of common mode rejection is required in most cases to make a huge difference.
SilverSolder:
--- Quote from: NiHaoMike on December 12, 2021, 12:31:11 pm ---
--- Quote from: SilverSolder on December 11, 2021, 11:41:10 pm ---Does that solve ground loop issues though? Other than using optical coupling of some kind, I can't think of an alternative to a transformer for that.
--- End quote ---
With sufficiently well matched resistors, the CMRR of a differential amplifier is more than good enough.
--- End quote ---
I will definitely try that (thanks @David Hess as well).
The audio transformers sold for this purpose on Amazon did not measure well... to put it mildly! :D It shouldn't be hard to make an op amp work better than that...
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