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Amp Tests (1 of 2)
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<blockquote data-quote="John Roberts" data-source="post: 31678" data-attributes="member: 126"><p>Re: Amp Tests (2 of 2)</p><p></p><p></p><p>I'm not sure if that is wrong, or just awkward, but class D and switch-mode are two ways of saying the same thing (saturated power devices). In fact many class D power amps liberally borrowed from earlier switching power supply technology. The main difference is class D audio amps had to be made faster, lower noise, and lower source impedance (not to mention capable of sinking and sourcing current). </p><p></p><p></p><p></p><p>Clever perhaps, ingenious not so much (IMO). I think yamaha did a variation on this in some cheap power amps and powered mixer modules some time ago. IIRC the Yamaha uses bipolar devices for their switching supply and was marginal for output current over time at 2 ohms, but they may have improved it with later generations. For MI it worked well and saved on heat sink and transformer size. </p><p></p><p>From a theoretical or engineering perspective class AB is not some gold standard for audio amplifiers (in fact there are good and bad implementations of all topologies), and this hybrid approach is effectively wasting power in that extra class A/B stage used to filter out switching noise, etc**. While they save some on heat sinks, and secondary breakdown (VxA) issues with bipolar output devices. That class AB output stage has to handle the full drive current which is still relatively heavy lifting for bipolar devices. It is nice that they can use proven mature technology in the output stage where the rubber meets the road (class D screws up in different ways and involves a learning curve). </p><p></p><p>IMO as switching devices get faster, (and higher power) there is no (good) reason why a pure class D can not be made as good as the best analog or hybrid amplifier, and save that extra power wasted and extra cost of using that superfluous class AB stage. I am aware of a well respected lower power class D platform (Hypex). I haven't personally bench tested or experienced the current crop of high power sound reinforcement class D so won't opine one way or the other.</p><p></p><p>I will not argue theory over real world results. LG make amps that sound good and are relatively efficient, so that should be good enough. If it sounds good it is good... if it doesn't it ain't. </p><p></p><p>JR</p><p></p><p>** I designed a small amp with a tracking supply back in the '80s and this isn't trivial. if you make the rail fast, it couples through the miller capacitance of the output devices and causes distortion, if you make the rail too slow you need to provide too much safety margin to prevent the amp outrunning the rail at HF and lose efficiency.. not trivial. Knowing how hard this is to do I am impressed by how well they did. I would be even more impressed by pure class D.</p></blockquote><p></p>
[QUOTE="John Roberts, post: 31678, member: 126"] Re: Amp Tests (2 of 2) I'm not sure if that is wrong, or just awkward, but class D and switch-mode are two ways of saying the same thing (saturated power devices). In fact many class D power amps liberally borrowed from earlier switching power supply technology. The main difference is class D audio amps had to be made faster, lower noise, and lower source impedance (not to mention capable of sinking and sourcing current). Clever perhaps, ingenious not so much (IMO). I think yamaha did a variation on this in some cheap power amps and powered mixer modules some time ago. IIRC the Yamaha uses bipolar devices for their switching supply and was marginal for output current over time at 2 ohms, but they may have improved it with later generations. For MI it worked well and saved on heat sink and transformer size. From a theoretical or engineering perspective class AB is not some gold standard for audio amplifiers (in fact there are good and bad implementations of all topologies), and this hybrid approach is effectively wasting power in that extra class A/B stage used to filter out switching noise, etc**. While they save some on heat sinks, and secondary breakdown (VxA) issues with bipolar output devices. That class AB output stage has to handle the full drive current which is still relatively heavy lifting for bipolar devices. It is nice that they can use proven mature technology in the output stage where the rubber meets the road (class D screws up in different ways and involves a learning curve). IMO as switching devices get faster, (and higher power) there is no (good) reason why a pure class D can not be made as good as the best analog or hybrid amplifier, and save that extra power wasted and extra cost of using that superfluous class AB stage. I am aware of a well respected lower power class D platform (Hypex). I haven't personally bench tested or experienced the current crop of high power sound reinforcement class D so won't opine one way or the other. I will not argue theory over real world results. LG make amps that sound good and are relatively efficient, so that should be good enough. If it sounds good it is good... if it doesn't it ain't. JR ** I designed a small amp with a tracking supply back in the '80s and this isn't trivial. if you make the rail fast, it couples through the miller capacitance of the output devices and causes distortion, if you make the rail too slow you need to provide too much safety margin to prevent the amp outrunning the rail at HF and lose efficiency.. not trivial. Knowing how hard this is to do I am impressed by how well they did. I would be even more impressed by pure class D. [/QUOTE]
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