10 V DC on audio in pin OK?
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iinself
diyAudio Member

Join Date: Dec 2012
10 V DC on audio in pin OK?

Hi,
beginner question - I am trying to assemble a TDA2050 amp kit. I am seeing a 10V DC on my audio in for a Vcc of 20V for this attached circuit, is it ok? - especially for my android phone

Also I see a 10K pot at the audio in but they did not supply a pot nor is it marked on the PCB (attached). Would appreciate if someone would take time to explain.

Thanks
Arvind
Attached Images
 circuit dia enlarged.jpg (83.4 KB, 56 views) pcb-front.GIF (191.9 KB, 55 views)

 19th January 2013, 04:47 AM #2 adason   diyAudio Member     Join Date: Nov 2004 Location: Maryland no
 19th January 2013, 05:08 AM #3 sandyK   diyAudio Member   Join Date: Apr 2007 Location: Sydney Arvind Connect a 10K resistor across the Input terminals in place of the non supplied potentiometer, and measure again. You may be seeing capacitor leakage with your DMM , or perhaps have a faulty C3 or C4 Regards Alex
 19th January 2013, 05:46 AM #4 minsik   diyAudio Member   Join Date: Mar 2011 Location: Adelaide South Australia When posting please specify precise information to help in people helping you. ie Input? One can assume the pcb input terminal, or the IC input terminal, or the input relating to a component? If its the input to the IC Pin1, then this is correct with a 22k voltage supply and the input bias divider network of 2*22k should be 10V. (Also by nature of the dc gain of the ic and 100% negative dc feedback the output voltage on IC pin 4 and negative input pin 2 will all be 10V. ) If you mean the input to the pcb ie pin 2 of the non supplied pot then as previous poster said, put a 10k to ground and measure again with nothing input connected. The DC path to ground will have zero volts on it unless the caps are faulty. when connecting any other device to the input it depends on what they are outputting as reference to ground. Measure them before connecting to the amplifier. Of course if there really is 10V dc present from the connected device and the dc on the positive side of the input caps is slightly lower then you have reverse bias on the caps. Not a good situation and can lead to failure of the cap and destruction of the IC. Also I point out a cct drawing and possible wiring mistake. the input coupling cacpacitors look like they should be in parallel and going between the pin2 of the pot position and the pin 1 of the ic input pin. C4 is shown as connecting to the input bias network of R1 and R6 but this is a mistake and and will seriouslt affect the freq responce limiting to a low pass cct. Perhaps you meant to draw the two capacitors in parallel and NOT connected to R 1 and R6 ???? If the cct is correct then the 1uf c4 is connected from the input via c10 to ground greatly providing a nice path for higher frequencies to ground. ie shorting them out. Hope this helps.
 19th January 2013, 07:01 PM #5 iinself diyAudio Member   Join Date: Dec 2012 Sorry about not being clear enough. Thanks for the suggestion - I put the 10K resistor and the amp works now !. BTW I am using my computer 12V 10A output from my computer PSU via a DC DC boost converter (150W, 24V) and I am not noticing any distortion - at least not to my hears, I am no audiophile. Another thing, the Lepai 2020A+ sounds louder and nice, for \$20, it is nice. Thanks again. Arvind

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