Thanks for your thoughts and insights well appreciated.
I will ask the engineer again why he "signed them away" when he was fully aware that his found ratings for power at 8 and especially 4 Ohms are clearly below spec. Why he didn't investigate any further or supply any explanations about these ratings related to his setup.
The red one probably reach 600 Watts at 1%, we just don’t see the top part of the graph. The yellow reach it a 0.5%
I think that they are trying to say that the real numbers are better than the published ones 😅
It is interesting to see that at very low output levels the distortion goes up. I guess it is because it is a Push-Pull amplifier with relative low bias current (pr output device)?
A single ended amplifier (which by nature is class A) has lowest distortion at lowest output level (at least the curves I have seen published by NP).
I think this is one of the reasons they sound so nice. A lot of room / 3D information is to be found in mW output levels. Maybe even uW. That have been by theory for a long time.
The X600.5 is known to be a very good amp. Probably other PP-amps performs "much worse" like my old NAD. .....the sound of this NAD amp compared to all the amps I have built in this forum (incl. M2X which is a PP) is "harsh" and not nice to listen to for a longer period of time. I feel I get more 3D information from this small wattage class A amps.
A single ended amplifier (which by nature is class A) has lowest distortion at lowest output level (at least the curves I have seen published by NP).
I think this is one of the reasons they sound so nice. A lot of room / 3D information is to be found in mW output levels. Maybe even uW. That have been by theory for a long time.
The X600.5 is known to be a very good amp. Probably other PP-amps performs "much worse" like my old NAD. .....the sound of this NAD amp compared to all the amps I have built in this forum (incl. M2X which is a PP) is "harsh" and not nice to listen to for a longer period of time. I feel I get more 3D information from this small wattage class A amps.
Maybe......I have black curtains behind my system so my eye/brain can better pick up the 3D info from the music 🙂
I have often thought about the low levels in music (e.g. room reflections) how low levels they are (depends of speakers of course).
But a church room like this:
When an organ tone fades out. What levels are we down to when it is just audible?
mW or uW?
But a church room like this:
mW or uW?
I've noticed that also and I expected to be much flatter at low power levels.
I've had a couple of Levinson ML-2 mono's that had a very flat curve at low power levels as I remember correctly.
Although these amps took 400 Watts per chassis from AC for only 25 Watts at 8 Ohms they were also complementary amplifiers (PP).
These high wattage powerful amps probably have so many output devices that it would be not possible to run 3-4 A bias current through each of them to achieve a nice working point for each device?
If I had one with my speakers I would all the time be < 1W so this amp would make not much sense in my system (apart from a very good bass control).
If I had free choice of a Pass Labs power amp it would be the XA25.
Have you measured how much power you use when you play at preferred level?
You have some "hard to drive speakers" as far as I remember? ....so amp may be perfect for you.
If I had one with my speakers I would all the time be < 1W so this amp would make not much sense in my system (apart from a very good bass control).
If I had free choice of a Pass Labs power amp it would be the XA25.
Have you measured how much power you use when you play at preferred level?
You have some "hard to drive speakers" as far as I remember? ....so amp may be perfect for you.
Meper. The XA25 is a neat choice. It is the 25watt amp that ate it's spinach. I would love to hear the no degeneration thing.
Ok, I was comparing with your curves in SE amp specs like this:
https://www.firstwatt.com/pdf/prod_j2_man.pdf
Here the distortion seems just to drop with output level.
Does the analyzer here make a distinction?
It doesn’t drop with output level. It increases steadily and then rapidly towards the 1% level @ full output.
One graph however shows a drop in distortion between 200hz and 2khz.
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The J2 amps distortion drops with output level?
I was looking at graphs like this (0.007% at 100 mW or so (without any global NFB?)):
How low would this be at 1 mW? 🙂
I was looking at graphs like this (0.007% at 100 mW or so (without any global NFB?)):
How low would this be at 1 mW? 🙂
Maybe, 100 mW is quite loud in a sensitive speaker so maybe 1 mW is audible.
Should be easy to make an experiment......
Should be easy to make an experiment......
Are you referring to the figure in Waynes post? If so, I don't think the higher values at lower power really indicate higher distortion. With such measurements, the readings at lower power are usually swamped by the residual noise in the system (amp + test equipment), which then shows up as a signal relative to the fundamental test signal. The "straight line" decrease up to about 10 Watt is most likely just this noise effect and has nothing to do with non-linear distortion.
As is said, analyzer can't distinguish noise from the distortion. Both are deviation from the original signal. Visual difference between J2 and X600 distortion graphs comes from distortion difference at higher powers. J2 has high distortion and X600, actually has less than 0.001% up to 30W. Almost all measured below that level is noise. How so?
Let’s check what would be AP measured distortion of a zero distortion amplifier that has 100 uV output noise. As that noise level is constant, we have just to calculate simple ratios of output voltage at some power level and that 0.0001 V noise/distortion.
100 mW/8Ohm = 0.894 V -> 0.894/0.0001 = 8944
Now just calculating what percentage of our 100% signal is that 100 uV deviation 100% / 8944 = 0.011%
Using the same procedure, 100 uV noise contributes as 0.0035 at 1W and 0.0011 at 10W.
Comparing calculated points with the actual measured “distortion”, conclusion is clear. X600 behemoth has distortion less than 0.001 at any power level below 30W. 😀
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