Lumped THD has little correlation with sonics... do you have some spectrum graphs?
dave
Hi Dave,
Yes I did have a lot of spectrum-based graphs for that amplifier... but alas they are all on my computer at National. I have been trying to purchase a used AP2 cascade for my home lab to make my own measurements but have been unable to find one at a price an "Out of work analog/audio applications engineer" can afford!
However I might be able to dig up a few graphs. Which parameters/settings would you like to see most?
One other thing, during our listening tests we found that if the entire THD line, like in the graph I showed, dropped an equal amount from low to high power out it was always an audible improvement! But it had to be a constant difference from low to high power. There were also some things we looked for in the spectral plots, which had to do with the shape of the peaks of the individual harmonics from 20 Hz to 20kHz (or 200kHz).
Mark / Audioman54
Yes I did have a lot of spectrum-based graphs for that amplifier... but alas they are all on my computer at National. I have been trying to purchase a used AP2 cascade for my home lab to make my own measurements but have been unable to find one at a price an "Out of work analog/audio applications engineer" can afford!
However I might be able to dig up a few graphs. Which parameters/settings would you like to see most?
One other thing, during our listening tests we found that if the entire THD line, like in the graph I showed, dropped an equal amount from low to high power out it was always an audible improvement! But it had to be a constant difference from low to high power. There were also some things we looked for in the spectral plots, which had to do with the shape of the peaks of the individual harmonics from 20 Hz to 20kHz (or 200kHz).
Mark / Audioman54
AP2 FFT for LME49811 mono amplifier
Planet10,
It took a hour or so to find this FFT AP2 file for a LME49811 mono power amp and it is not a perfect file because I don't have all the setup data for it. I believe it was a 0dB (which was 1%THD for us) 1kHz sine wave into an 8 ohm load. See the attached AP2 Plot.
Sorry but this is the only one I could find.
Mark / Audioman54
Planet10,
It took a hour or so to find this FFT AP2 file for a LME49811 mono power amp and it is not a perfect file because I don't have all the setup data for it. I believe it was a 0dB (which was 1%THD for us) 1kHz sine wave into an 8 ohm load. See the attached AP2 Plot.
Sorry but this is the only one I could find.
Mark / Audioman54
Attachments
So that is near full power? Pretty good.
More important is what it looks like at realistic power levels and how it changes when you turn up the wick.
A family of curves from about 50 Hz to 5kHz, at power levels from ~ 10mW to a watt or 2.
dave
From recently measuring a Gainclone I'm more curious how it changes when the frequency is wicked up. The LM3875 chip's distortion spectrum gets 'toothy' fast.
SE class A amps don't have crossover distortion of class B (and to a lesser extent class AB) or the RF and posible noise issues of class D. However the better question would be is SE class A worth the extra power consumption and cost (big transformers and heatsinks). I would say for >10Watts it's not worth it, for headphone amps for non portable usage definatly worth it. For anything inbetween it depends ^ ^
Personally i voted YES, as the best sounding most pure amp i have built so far is a single ended monster hybrid. However, i think classD is fast catching up and as soon as we learn how to truly remove all background noise and carrier leakage the classD mode of sound reproduction will become king. For the moment it is just a prince in the shadows of the mighty CLASS A ( and rightly so too )
I doubt this, however, nature likes to play long-term tricks. So, I'll be excited to see a Class-D replacing Class-A as the king. So far Class-A is honest with the input signal and easy on our ears, sonically, I see no logic in having a sheet full of "record breaking" specifications between the speaker and me, there is already so much air to deal with... what a pity, I cannot hear the music without air, perhaps I could place a voice coil on my eardrums, may be it is possible, but I have neither enough money nor courage to try this. Nelson Pass have both,
but he seems to like the air between speakers and his ears more than anything.But I love to see changes.
It's just my opinion but from my nearly 40 years messing with audio, the power supply makes more difference than the amp configuration. If you build 2 identical amps with different power supplies the one with that has the tightest regulation and lowest output impedance will always sound better.
In most cases any well done amp with a very good power supply will sound better than the most exotic design with an unregulated power supply or one with a higher output impedance power supply.
Bruce
In most cases any well done amp with a very good power supply will sound better than the most exotic design with an unregulated power supply or one with a higher output impedance power supply.
Bruce
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