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| how to isloate audio ground from the amplifier |
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| Adhith:
OK understood Sir. I'll let you know once I'm finished with the circuit |
| Adhith:
First I apologize for the long delay for the reply. I was preparing for exams and stuffs and thus couldn't focus on my hobby project. I have now build the op amp based filter and changed to the transistor to the darlington. But the circuit is not working at all. All wires were double checked still not working. I taped a wire from pin 5 and connected to the the audio then its working and i think the problem is with the filter circuit. I'm attaching the new circuit that i used. What could be the reason?? the diodes at the end is for a different sort of function to turn on the LEDs and there is is no problem with that function Since the LM358 has two op amps and I need only one for my purpose, i could totally leave the pins for the other opamp right?? In the second pic of the opamp block diagram I leaved the pins 1, 2 and 3 and used the other pins of the second opamp |
| Audioguru:
The circuit does not have a filter. Maybe you mean that the "peak detector circuit" is not working? Then a part is defective or its pins are connected backwards. Since you have two opamps but one is not used then it should be disabled. With its pins disconnected then it has a voltage gain of hundreds of thousands and probably oscillates at a high frequency causing interference to the opamp you are using. To disable an LM358 opamp make its voltage gain= 1 by connecting its (-) input to its output and ground the (+) input. |
| Adhith:
Yeah sorry ...I meant the peak detector .Its not working either. Used another LM358 by setting the unused op amp to gain 1 and still nothing. My soldering is proper and neat so I think the possibility of shorting the traces won't be a reason . My concern is towards a fault in the initial circuit layout that I have designed. I have attached a screenshot of my design with this. The layout is bit congested and may be annoying but it would be great if you could help with it. I'm also attaching the actual pic of my circuit also 1) the green trace between the components indicates the orientation in which the components are arranged and does not indicate a bottom copper connection trace. 2) the long green trace connecting the two +12v pad indicates that the pads are connected externally with a wire. 3) The pins 1,2 and 3 of the LM358 are cutoff and thus it don't have a through hole on the PCB board. This is done to provide a way for the other traces to run through its bottom side. The output pins side works fine since I have tested it separately, so I think the things at the left side could be taken as the area of analysis. |
| Audioguru:
Your circuit board appears to be connected correctly but I do not see how the 47k pot is connected. Use a digital multimeter set to measure DC volts: 1) With no input signal then pin 5 of the LM3915 should be close to 0V. 2) With an audio input signal of a few volts then pin 5 of the LM3915 should show the positive peak voltages of the signal. EDIT: It looks like the 120k resistor is connected to pin 1 and pin 2 of the opamp that are shorted together, and both the 120k and 100k input resistors are connected to pin 3 of the opamp that is shorted to ground. |
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