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Old 8th May 2011, 10:33 AM   #1
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Join Date: Jun 2010
Question Input DC offset? (TA2020)

Hi All,

Just cased a TA2020 pcb from Helder audio. While I was measuring/checking everything I noticed something that may be perfectly normal, however, would like to check in case it could harm my preamp.

Upon turning on the amp (without speakers and source) there is a 2.5v dc voltage between Input and Input Ground. Draining I and Ig with a resistor and this input offset goes and stays at 0v (draining the input capacitor I assume?)
Turning off the amp the voltage reverses:
- if voltage between I and Ig was the 2.5v from turn on, it drops to 0v
- if voltage between I and Ig was zero because I drained with resistor, voltage drops to -2.5v

With no source and speakers connected I can trim the dc offset on the outputs to zero.

Should I be worried? Or is it normal for input cap to charge at power up? And why does the voltage reverse after power down?

Many thanks!
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