TNT-200, Overheating resistor at RCA input jack

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Vince Maida2014-01-01 21:36

I am having a problem (Both Channels)with the 4.7 ohm resistor that connects the circuit ground to chassis ground at the RCA input connectors overheating and burning out. I noticed on the Hafler version of the amp that the resistor/capacitor combo has been removed with a direct wire connection from circuit to chassis ground. The problem occurred while bench testing the amp into a 2 ohm load at 75 Watts RMS output. I have not looked into this further but it does not occur when the amp is just idling (DC condition) only under power (AC condition). I suspect a high frequency oscillation since the only other connections from chassis ground to circuit ground are the two 0.1uf caps from the output FETS source to chassis ground and the AC line chord. I have checked all the circuit grounds and have found no open circuits or high resistances (> .05 ohms). Has anyone encountered this and what might be the fix. Thanks for any help.


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