Composite ICs

00940 · 16th December 2005, 03:24 PM

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.

lineup · 16th December 2005, 04:30 PM

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.

ken.berg · 17th December 2005, 03:01 PM

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.

- bkb

peranders · 18th December 2005, 05:52 AM

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.

18th December 2005, 05:52 AM	#4
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	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. __________________ /Per-Anders (my first name) or P-A as my friends call me

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16th December 2005, 04:30 PM	#2
lineup diyAudio Member Join Date: Dec 2005 Location: the north	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.

17th December 2005, 03:01 PM	#3
ken.berg diyAudio Member Join Date: Nov 2003 Location: Tempe, AZ	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. - bkb

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