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Audio and Video Talk
The Vintage Audio Section
Any amp geniuses here willing to give advice?
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<blockquote data-quote="marantz123" data-source="post: 847115" data-attributes="member: 16849"><p>Hi Rick</p><p></p><p>No expert or genius, but just a little bit of experience and some thought about this. Had a Technics Z200 that had similar symptoms wrt the distortion. Low and behold, I also tested everything, including transistor and diode junction resistances (very important), gain and junction type tests in diode mode..all fine. In 25 years, I have never had to change a small value ceramic cap...was told that they rarely go faulty..never had a bad one....until this Z200 appeared. I had a 10pF measuring 20nF....that was causing the distortion...i think it was even presenting itself as a short at Hz where it shouldnt be. I changed a few others out (of the same type) as didnt trust them. Even the channel that was working ok sounded so much better with new ceramics...I was surprised.</p><p></p><p>If you havnt tested them, or even if you have, under the current circumstances where you have checked everything else, & still killing semiconductors, I would consider replacing the ceramics to rule them out. They test ok, look ok, but when operating under Hz, or if they took a hit a some point, can be unreliable. (The ceramics in the AC power section should be ok though). Theres only a few on there, with C405 in a possibly important position, in the path of your 'output resistor pair'. Also check that zobel capacitor, even though a larger value. NPO/COG or X7R /Z5U dielectrics are decent for the small values. Its a shot in the dark for me as I havnt worked on your model of amp as yet, but my circumstances were similar to an extent.</p><p></p><p>Good luck</p><p>Marantz123.</p></blockquote><p></p>
[QUOTE="marantz123, post: 847115, member: 16849"] Hi Rick No expert or genius, but just a little bit of experience and some thought about this. Had a Technics Z200 that had similar symptoms wrt the distortion. Low and behold, I also tested everything, including transistor and diode junction resistances (very important), gain and junction type tests in diode mode..all fine. In 25 years, I have never had to change a small value ceramic cap...was told that they rarely go faulty..never had a bad one....until this Z200 appeared. I had a 10pF measuring 20nF....that was causing the distortion...i think it was even presenting itself as a short at Hz where it shouldnt be. I changed a few others out (of the same type) as didnt trust them. Even the channel that was working ok sounded so much better with new ceramics...I was surprised. If you havnt tested them, or even if you have, under the current circumstances where you have checked everything else, & still killing semiconductors, I would consider replacing the ceramics to rule them out. They test ok, look ok, but when operating under Hz, or if they took a hit a some point, can be unreliable. (The ceramics in the AC power section should be ok though). Theres only a few on there, with C405 in a possibly important position, in the path of your 'output resistor pair'. Also check that zobel capacitor, even though a larger value. NPO/COG or X7R /Z5U dielectrics are decent for the small values. Its a shot in the dark for me as I havnt worked on your model of amp as yet, but my circumstances were similar to an extent. Good luck Marantz123. [/QUOTE]
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Audio and Video Talk
The Vintage Audio Section
Any amp geniuses here willing to give advice?
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