op amp Reducing noise in audio circuit (optical pickup + op amp)

Posted on Feb 6, 2014

Except that I`ve added a passive high-pass filter after the output of the op-amp, to eliminate DC (since I am using 0V and +12V as my V- and V+, respectively). I use Rf=500K Ohm (is this way too much ). In addition, I have an LED adjacent to the photodiode that serves as a light source. The LED is powered by 5V and the op-amp is powered by 12V, bo

op amp Reducing noise in audio circuit (optical pickup + op amp)
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th from a PC power supply. The photodiode and LED are connected to the circuit using a 2m long guitar cable ("PL"). The circuit works and produces audio signal when I modulate the intensity of the light shining on the photodiode, but my problem is that the signal is very noisy. I can hear/see two types of noise: Electrical noise similar to a noisy electric guitar pickup. I suspect that it originates in the long cable (or the tip of it, where the photodiode and the LED are conected) collecting ambient electromagnetic noise. This noise is present all the time, even when no light is shining on the photodiode. Another noise is present only when a signal is generated, i. e only when I modulate the light intensity. I suspect it is a result of amplifying thermal noise, since my gain is very high. Improving the signal to noise ratio at the source, i. e by optimizing the physical conditions (ambient light, precision of the position of the photodiode, etc. ).

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