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high vac at speaker terminals rotel rb1070
high vac at speaker terminals rotel rb1070
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Old 3rd January 2012, 10:26 AM   #1
chefsinc is offline chefsinc  Australia
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Join Date: Jun 2006
Location: Perth Suburbs. Western Australia
Default high vac at speaker terminals rotel rb1070

Dear Hi Fi Gurus,

I am having some issues with my Rotel RB 1070 power amp. I have measured the vac on the speaker terminals at idle nothing connected and it is giving me 92 volts on the right side and 38 volts on the left side.
there is no dc voltage at all on the terminals. I had to replace a 10ohm resistor in series with a 0.1uf cap going to ground at the terminals as it got toasted. the new resistors get hot but so far have not burnt out.

As a newbie to how electrical circuits work I would like for some comments or suggestions on how to fix it.I can send it off to the repair man but I think that would be passing up an opportunity to learn something new.
I would welcome any suggestions on this.

thank you very much in advance.

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Old 3rd January 2012, 10:30 AM   #2
jaycee is offline jaycee  United Kingdom
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Location: Norwich, UK
It sounds like the amplifier is oscillating. The resistor/capacitor on the output terminals is called a Zobel network, and the resistor burning out is a sign of oscillation.
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Old 3rd January 2012, 10:57 AM   #3
DF96 is offline DF96  England
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If it affects both channels then it could be a grounding fault. Look for loose connections.

Oscillation could also be caused by the Miller capacitors failing, but it is unlikely that they would fail in both channels at the same time.
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