i've build 15w amp from TDA 2030 but currently i measure from input line to ground (measure are performed from audio jack), reaching 400 mV, my question is:

-is that normal? how i can remove it? even with decoupling cap it's still 400 mV and what is this called? Input offset votage and current?

-can i use another voltage divider in between 1 uF cap decoupling and pin 1 to the ground to remove it?

-how much current and voltage that emmited by amplifier circuit are acceptable for phone or any media player?

This is the image that i use, the red one is the first voltage divider that come default and i thought it was the source of problem?:

enter image description here


It seems to me that the voltage would disappear if you put a high-ish value resistor (say, 1M) between the input and ground, before the 1uF decoupling capacitor, to give the input a ground reference.

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  • \$\begingroup\$ Is the 100k res connected to input still used? So i have 2 connected resistor on input right? \$\endgroup\$ – aji Jan 10 '15 at 10:03
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    \$\begingroup\$ The existing 100K resistors are after the cap. Mark is suggesting 1M on the input side of the cap. Also, if the cap is electrolytic, consider changing it for a lower leakage type of cap. \$\endgroup\$ – Brian Drummond Jan 10 '15 at 11:48
  • \$\begingroup\$ what is lower leakage type of cap? and this is getting frustrated, after trying to reassemble it on the breadboard it seems the voltage wasn't 400mv but reaching 7 volt and keep discharge when i measure it. it seems that there's something wrong with the cap, and actually how much voltage that "seems right"/acceptable \$\endgroup\$ – aji Jan 11 '15 at 9:19
  • \$\begingroup\$ Aji, you must take care when reading the circuit diagram. There is no 100k resistor connected to the input in the original circuit. Where two lines cross each other without a dot, there is no connection between them. \$\endgroup\$ – Mark Hadman Jan 11 '15 at 14:37
  • \$\begingroup\$ Adding 1M res make input muted \$\endgroup\$ – aji Jan 22 '15 at 1:39

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