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Cheap as Chips OPA1688 Low-THD Muscle Amp
Cheap as Chips OPA1688 Low-THD Muscle Amp
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Old 21st July 2018, 07:52 PM   #101
xrk971 is online now xrk971  United States
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Cheap as Chips OPA1688 Low-THD Muscle Amp
Quote:
Originally Posted by lineup View Post
There is a resistor R-int, 10k.
What does this do?
Is it really necessary?
Maybe not, but itís always good to provide a lower impedance load than the 10MOhm intrinsic impedance of the input of the buffers. If the inputs are JFETs, they need a way to drain off charge.
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Old 21st July 2018, 08:03 PM   #102
lineup is offline lineup  Sweden
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I see.
It feels it should be a little load on the output of the driving op.
So, it is surely correct having it.
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Old 22nd July 2018, 09:05 AM   #103
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Some measurements using a Cayin N3 DAP playing a 1kHz tone from a flac file. The Cayin has an OPA1688 as a source, so really can't be used to measure itself. But here is what this amp gets for 1Vpp and 2Vpp into 47ohms.
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File Type: png OPA1688-2x-Buffer-1.0Vpp-47ohms-FFT.png (81.8 KB, 329 views)
File Type: png OPA1688-2x-Buffer-2.0Vpp-47ohms-FFT.png (80.9 KB, 329 views)
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Old 22nd July 2018, 10:37 AM   #104
Shaq888 is offline Shaq888  Ukraine
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You know, if you spent time reading about Baxandal's/Cordell's "distortion magnifier" instead of wasting it on those pointless THD simulations, you would be able to do a better measurements.

Last edited by Shaq888; 22nd July 2018 at 10:44 AM.
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Old 22nd July 2018, 11:14 AM   #105
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Quote:
Originally Posted by Shaq888 View Post
You know, if you spent time reading about Baxandal's/Cordell's "distortion magnifier" instead of wasting it on those pointless THD simulations, you would be able to do a better measurements.
It is good to be smart and have knowledge. It is even better to be kind and respectful to others.
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Old 22nd July 2018, 11:29 AM   #106
Shaq888 is offline Shaq888  Ukraine
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Quote:
Originally Posted by SomekPoland View Post
It is even better to be kind and respectful to others.
I'm returning exactly as much respect as I was given earlier. Beside that respect I'm giving a useful information. How could this be a bad thing?

Last edited by Shaq888; 22nd July 2018 at 11:48 AM.
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Old 22nd July 2018, 11:30 AM   #107
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+1 @SomekPoland
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Old 22nd July 2018, 11:38 AM   #108
Shaq888 is offline Shaq888  Ukraine
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What is a more respectful way of saying "I don't care" in you opinion?
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Old 22nd July 2018, 12:24 PM   #109
lineup is offline lineup  Sweden
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It is fun to make them simulations.
They do not hurt noone.
But the value is somewhat limited.

Actual measuring is a whole other thing.
For example using oscilloscope to watch squarewaves.
As well as listening to some music with the devices you have built.
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Old 22nd July 2018, 12:35 PM   #110
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They do "hurt" if they are done wrong, because they are misleading in this case.

Last edited by Shaq888; 22nd July 2018 at 12:40 PM.
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