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Chip Amps Amplifiers based on integrated circuits

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Old 16th December 2005, 04:24 PM   #1
00940 is online now 00940  Belgium
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Default Composite ICs

I was browsing through Jung's book (opamp applications) and I saw the schematic posted below (chapter 6, p202). It is claimed that such arrangement would : lower noise, boost open loop gain and isolate thermally the input section.

Has anyone built something like that ? Would it be interesting or not ? The idea would be to use an OPA549 or something like that.
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Old 16th December 2005, 05:30 PM   #2
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I have seen such circuit used in Phono RIAA circuit
mainly to get get very low noise, I suppose.

Will add one more stage to inside OP-amp stages.
And of course will be very high open loop gain.
This might not be always a good thing.
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Old 17th December 2005, 04:01 PM   #3
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A more technical and detailed explanation of the ides behind compound opamps is (again by Walt) found at http://waltjung.org/ED_Archives.html.

The idea is very popular with the headphone-amp-building folks who publish on headwize.com.

While I haven't tried it with a chip power amp, the line drivers in my system use the AD815 inside the feedabck loop of an opamp, and I can attest to better sound than either alone.

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Old 18th December 2005, 06:52 AM   #4
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00940, such design is a bit historical because nowadays there is not much sense to do this because the opamps are much better now but it works alright.

If you compare Walt's suggestion with AD797 I think the latter is better and definitely smaller/cheaper.
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