Mark: did you actually read the attachments. A little challenging to read due to the scan but as a reference point not worth bothering. Walt's comments are interesting. If only people these days were able to describe things as well. The internet has killed the art of considered communication.
Okay, read. Agree there is some lasting truth to Walt's words, as it has turned out.
Unfortunately, it takes time and editing to compose thoughtful prose. I find it does, anyway.
The internet, on the other hand makes it easy to impulsively shoot from the hip with words that will soon be lost among all the other noise out there.
I don't think it is just the internet either. Writing with pen in hand rather than using a text editor requires one to organize one's thoughts more thoroughly prior to starting. It almost fundamentally changes the way humans think, seems to me.
EDIT: And as you can see -- already edited!
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We should test components as a system because this is how we listen to components. Now, however, we only test a DUT in isolation. Then we attempt to listen to it in our systems. One difference from system to system is interfacing and how it affects cmr. Surely, the audible differences people report about an amp is due to these kinds of interfacing changes in cmr and other parameters.
In 1992 I showed a simple test and way to adjust cmr for preamp to power amp interfacing. "Balancing Differential Circuits" Fig 2 is measured before and after data.
View attachment BDC2.pdf
View attachment BDC1-B.pdf
This cmr change alone made an audible difference in accuracy with this pre-power interfacing combination [IMO]
THx-RNMarsh
In 1992 I showed a simple test and way to adjust cmr for preamp to power amp interfacing. "Balancing Differential Circuits" Fig 2 is measured before and after data.
View attachment BDC2.pdf
View attachment BDC1-B.pdf
This cmr change alone made an audible difference in accuracy with this pre-power interfacing combination [IMO]
THx-RNMarsh
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Dan, I looked at that document. They say they found some capacitor distortion that people could hear down as low as .008%. Naturally, they say they found some at a higher levels too. In addition, they say that simple linear-ish or stationary modeling of capacitor harmonic distortion generation could not match the perceived sound of real capacitor distortion, and that possibly Volterra functions could be used for more accurate modeling. They say capacitor distortion is pretty nonlinear.
However, and it is a big however, for something which is seemingly proffered as a PhD dissertation, the general quality and depth of work seems rather unimpressive. I don't know if others get the same sense.
However, and it is a big however, for something which is seemingly proffered as a PhD dissertation, the general quality and depth of work seems rather unimpressive. I don't know if others get the same sense.
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Notice the enthusiastic response to the AD712 upgrade, then compare it to JC constantly referring to his need to replace it due to some review. You see if you depend on these anecdotal stories after awhile anything is true.
I know. Did you read it? I can't see someone getting out of Stanford CCRMA with something like that, not even close. Then again, maybe it's just my take on it for some reason.
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IMO.... I see just debating points again. I have no doubt that the ad712 was an improvement in that gear. I also have no doubt that JC could do better. Or even today a better OPA would be better still.
THx-RNMarsh
Well, it wasnt available in 1992. However, I am not sure at $6 each and the need to run signal thru 4 opamps per channel is going to improve anything But cmrr.
Improved cmrr is only 90 db vs the 65db I got just with matching input Z of simple diff input..... better cmrr could happen with matched diff load Z and matched transistors....and have a lot fewer active devices to run signal thru and same lower cost.
THx-RNMarsh
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Richard, can we be honest that you complaining about $6 opamps given your otherwise high-$ builds seems a little, um, ironic? Why not just out and say you don't have a good technical reason to dislike it but you do anyhow?
It's not exactly trivial getting 90 dB CMRR over wide bandwidth. Admittedly if one is looking for the fourth or fifth zero in THD+N, then it's problematic, but 90-65 db is 25 dB, which means you're still 1/20 as good. 65 dB with a bunch of hand tuning might be just fine (probably is for home use!) but give credit where due.
It's not exactly trivial getting 90 dB CMRR over wide bandwidth. Admittedly if one is looking for the fourth or fifth zero in THD+N, then it's problematic, but 90-65 db is 25 dB, which means you're still 1/20 as good. 65 dB with a bunch of hand tuning might be just fine (probably is for home use!) but give credit where due.
I dont like it because I can do 90db as well with less fuss. 4 opamps? Even for 1 dollar.
The point is that these are the type of things which go un tested -- system testing approach would show more issues like the cmrr is an example.
If a company makes both preamp and power amp, they ought to do well together. Maybe not so well with mixed brands with less than optimum interfacing.
Since the reality is that people do mix brands and they do not all use that InGenius brand for input, what I showed is for DIY to get best results with thier combo.
THx-RNMarsh
https://ieeexplore.ieee.org/document/5227874/
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