And what does "preforming tests subjectively" mean? Casual, uncontrolled listening, or controlled test conditions (for example as described in the ITU recommendations I referred to earlier)?
Nah - it means listening after having swallowed a load of 'propaganda' about 47k resistor noise and op amp output current needs
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Eeesh guys, probably best to take it down about 10 notches. This is a SQ vs. Measurements thread right now, and not so much an NC500 thread. :/
May be I missed something, can you give a link? The only picture I've seen so far (2 pages before) only tells that there is no mains harmonics above ~ -120dB when idle. This picture doesn't suggest anything good about noise floor. And I also don't think it is a THD+N measurement as there is neither 1kHz spike nor any signs of rejection filter.
Or is it is actually a discussion about how claims should and could be substantiated?
If they want to put in earplugs and watch the audio data dance across the screen of a spectrum analyzer when evaluating the amp, let them. It doesn't matter. What matters is if they are satisfied with the product or not.
That's a THD+N measurement, and that's all he provided. As I said earlier, any OEM who wants to use the circuit, will have to do their own measurements if they want more measured data.
Pretty much one in the same, wrt to subjective vs measurements. Anyhow, I'm not helping, so I'll peace out.
So we have 2 circuit designs, and 2 measured results provided by Nerdman. If his "Ultimate fix" circuit measured result is of THD+N like the measured result of the stock LM 4562 based buffer, this would mean he has one hell of a measurement system.
SGK says BS! Those measured results are not correct! Nerdman hasn't responded. So I guess from here to move forward one of the following things need to occur:
1: Nerdman chimes in to explain in detail how he came up with those measured results, and claims of 70mA being required from the NC-500's
2: Someone else builds the circuit (in real life) and provides measurement results.
3: Someone builds a completely different circuit and provides measurement results.
Here's the THD+N measurement of the 994 on its own:
SGK says BS! Those measured results are not correct! Nerdman hasn't responded. So I guess from here to move forward one of the following things need to occur:
1: Nerdman chimes in to explain in detail how he came up with those measured results, and claims of 70mA being required from the NC-500's
2: Someone else builds the circuit (in real life) and provides measurement results.
3: Someone builds a completely different circuit and provides measurement results.
Here's the THD+N measurement of the 994 on its own:
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This is becoming boring and tedious...I seem to have to repeat myself for bavmike.
Let's be clear. I challenged two statements: (1) that the 47k resistors were the dominant noise in the circuit and (2) that the "Hypex Amp needs current drive > 70mA"
Your words not mine
Let's be clear. I challenged two statements: (1) that the 47k resistors were the dominant noise in the circuit and (2) that the "Hypex Amp needs current drive > 70mA"
Your words not mine
Okay, maybe Nerdman will respond to this. The claim of 70mA being required does seem high, but I'm not going to argue with a guy who not only has produced an opamp that sounds stunning with the NC-500's, but has also backed it up with measured results.
Looking back in my emails from months ago I have found a measurement plot of the bone stock Hypex OEM LM 4562 boards after the resistor change. So now we can compare measured results of the “before” and “after":
Looking back in my emails from months ago I have found a measurement plot of the bone stock Hypex OEM LM 4562 boards after the resistor change. So now we can compare measured results of the “before” and “after":
Those are ~two orders of magnitude worse than stock Hypex LM4562 based buffers as found on the NC1200 or on the UcD boards... For the NC1200 you can find measured results in the datasheet and I doubt the stock buffer for NC500 is any different. For the UcD the main contributor of distortion is not the buffer but the noise floor is still as low as with the nCore. So, as 'measurements' in your post are a lot worse from the datasheets and from a general experience from users of those modules/amps, please stop posting them until you can describe the conditions and procedures in detail. There is definitely something very wrong with them. As you can't support those 'measurements' in any meaningful way - there is nothing to discuss.
Note that the data sheet 'recommended buffer' typology doesn't have the R14 2.2M resistor between the two 47k. Just ground R9 R13 in your drawing. I believe the equivalent references in Colin's Rev B are R6 and R11 - with R5 being the resistor not included in the rec design.
Not that these resistors contribute much noise (pV) to the buffer in a properly deployed circuit. Add 470u DC blocking caps and they'll contribute even less (any noise is low-pass filtered) and there will be protection against poorly designed/functioning source equipment.
The dominant noise sources are (Colin's rev B) R7 (3.3k), R9 (1.5K) R12 (3.3K). Their noise is amplified by the op amps. Improving on that requires a more complex circuit but it is possible.
Not that these resistors contribute much noise (pV) to the buffer in a properly deployed circuit. Add 470u DC blocking caps and they'll contribute even less (any noise is low-pass filtered) and there will be protection against poorly designed/functioning source equipment.
The dominant noise sources are (Colin's rev B) R7 (3.3k), R9 (1.5K) R12 (3.3K). Their noise is amplified by the op amps. Improving on that requires a more complex circuit but it is possible.
I agree with Igor. As I have said before the first plot is so bad there must be a lot more wrong. It certainly isn't the 47k resistors!
I'm just sharing Richards measurement results. If someone else has measured them as well, maybe they can share and we can compare.