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DIY For Audio
Repairing Rotel amp - one channel cooking, one chill
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<blockquote data-quote="ludo" data-source="post: 777261" data-attributes="member: 691"><p>If you leave the 910 Ohm resistors out of the circuit (or if they have gone open circuit due to overheating) the amp can still work. </p><p></p><p>What those resistors do there is to keep the 2SB631/2SD600 switched on permanently, so that they do not contribute to the crossover distortion that the output stage generates (around the 0V point). </p><p></p><p>One can expect better crossover behaviour with only the output stage transistors switching off around 0V than from output stage and its drivers switching off nearly simultaneously around that point. So the 910 Ohm resistors remove some of the chaos at crossover. You may not see it on a scope, but I'm sure you will see it on a spectrum analyser. And you'll hear it on some material.</p><p></p><p>If it is running cool I suspect open circuit 910 Ohm resistors. Can't be anything else really.</p><p></p><p>If it looks like a trap because it is. Well spotted :thumbs:</p></blockquote><p></p>
[QUOTE="ludo, post: 777261, member: 691"] If you leave the 910 Ohm resistors out of the circuit (or if they have gone open circuit due to overheating) the amp can still work. What those resistors do there is to keep the 2SB631/2SD600 switched on permanently, so that they do not contribute to the crossover distortion that the output stage generates (around the 0V point). One can expect better crossover behaviour with only the output stage transistors switching off around 0V than from output stage and its drivers switching off nearly simultaneously around that point. So the 910 Ohm resistors remove some of the chaos at crossover. You may not see it on a scope, but I'm sure you will see it on a spectrum analyser. And you'll hear it on some material. If it is running cool I suspect open circuit 910 Ohm resistors. Can't be anything else really. If it looks like a trap because it is. Well spotted :thumbs: [/QUOTE]
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DIY & Tutorials
DIY For Audio
Repairing Rotel amp - one channel cooking, one chill
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