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DC on the mains |
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Graham Slee
Admin Group Retired Joined: 11 Jan 2008 Location: South Yorkshire Status: Offline Points: 16298 |
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I think it does, but "downunder friend" doesn't quite see things my way, and so I tend to keep my mouth shut, but this time it's different. It is difficult to "see" the workings of this, yes, even for me, but something that would otherwise steal transformer magnetising current each half cycle, isn't going to be much good for the amplifier it's powering. By "centering" the waveform, then the relationship of mag current to reservoir capacitor charging current becomes "even". OK, the reservoir charging current is per every 100Hz (120Hz elsewhere) and the musical waveform is everywhere else, and the current drawn each conduction angle is not the mag current, which occurs at a different angle within the 180 degrees, but DC is not DC in the strictest sense. All analogue amplifiers are cap coupled as "downunder friend" does actually say, yes, even the DC coupled amps are cap coupled, because the current into the reservoirs only conducts for part of the mains cycle. At all other times they are supplying energy all by themselves. So if the signal demands current (which it does) and the mag current is offset, then it's out of balance compared to the next 10mS. The relationship to mag current is due to the non-linear capacitive filter rectifier load, and transformer winding harmonics, which can increase the mag current, unless it isn't there because of interference. So basically, the naysayers say it can have no effect. That depends on whether you over analyse things like I do, or you deny that little things have any effect. It used to be said that if you look after all the little things, then big things would follow. Perhaps I'm old fashioned in that respect. Anyway, the 1W distortion fell from 0.009% to 0.007% so something about it works. |
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Graham Slee
Admin Group Retired Joined: 11 Jan 2008 Location: South Yorkshire Status: Offline Points: 16298 |
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Or even the reduction in noise.
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That none should be able to buy or sell without a smartphone and the knowledge in how to use apps
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CageyH
Senior Member Joined: 30 Apr 2012 Location: Toulouse, Franc Status: Offline Points: 1678 |
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I am a great believer in “every little helps”.
My amplifier is based on the LM3886, and apparently has the following specs: Output power: 360 W (4 Ω) – 240 W (8 Ω). Ultra-low 0.00026 % THD+N (140 W, 8 Ω, 1 kHz). Ultra-low 0.00048 % THD+N (100 W, 4 Ω, 1 kHz).
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Kevin
European loan coordinator, based near Toulouse, France. |
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Graham Slee
Admin Group Retired Joined: 11 Jan 2008 Location: South Yorkshire Status: Offline Points: 16298 |
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With that amount of NFB - about 30dB available at 20kHz for a voltage gain of 20 - then distortion and noise simply vanishes (fig.47 LM3886 datasheet). The point though is what it does within the first watt, where most of the detailed listening takes place. No matter how good a circuit is, external factors can be more prominent. Not that a power supply should be considered an external factor, but is often considered that way.
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That none should be able to buy or sell without a smartphone and the knowledge in how to use apps
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