I have repaired one these, in a Mordant Short Sub woofer. I replaced the17TL072DTS with a TL072BCD and it mostly works but has an audible tone. The new op amp has a lower input offset voltage (3mv) than the original ST Microelectronics TL072CDT (10mv). Would this lead to a lower audible tone? How can I push this beyond audible and will the amp still work if I do?
Does anyone know what the original Hz was?
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Looking at the output on pin7 of IC1 I see a very distorted triangle. My slow brain finally realise this may be an offset problem, since the L072BCD has a different offset to the TL072DTS. Adjusting R10, with a paralleled trim pot cleaned up the triangle and the noise went away. replacing R10 with the new measured resistance appears to have fixed the issue. Time will tell.
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