Electronics > Beginners
Microphone bandpass with unity gain design question.
alexg:
Hi All, I am designing audio signal processing circuit, the idea is that signal from microphone will go through band pass filter, then be full wave rectified in the end. I broke it into two tasks and task1 is to filter the signal and make it ready to be received by full wave rectifier which will be task2, I am focusing on task1 at the moment
I am thinking to start with this basic circuit (illustration 1) and change components a bit:
It is important that gain of this circuit will be 1 (unity gain), I want signal from mic remain not amplified, just filtered. High Pass Frequency >= 1000Hz, Low pass frequency <= 15000Hz
Illustration 1 - circuit reference from internet:
Illustration 2 - modified circuit with changed component values and different op amp
R1 and R2 have matching values so that gain will be -1
C1 value chosen so that combined with R1 it forms high pass filter with cutoff about 1000Hz
C2 chosen so that conbined with R2 it will form low pass with cutoff frequency about 15000Hz
OpAmp of the choise is: MCP601 - datasheet here: http://ww1.microchip.com/downloads/en/DeviceDoc/21314g.pdf
Microphone will be biased so that in silence it can swing rail to rail with loudest sounds, I suppose it won't be exactly rail to rail some clipping will happen close to 0 and Vcc but the idea is the bias it to squeeze the best Vpp swing of the signal.
Once I can get this circuit to work I will further send it into Op Amp based full wave rectifier.
Does it look okay?
Audioguru:
An LM358 is much too noisy (rumble and hiss) to be a mic preamp. It also produces high amount of crossover distortion that might mess up your measurements.
It has trouble with all audio frequencies above a few kHz.
alexg:
--- Quote from: Audioguru on July 24, 2018, 08:16:58 pm ---An LM358 is much too noisy (rumble and hiss) to be a mic preamp. It also produces high amount of crossover distortion that might mess up your measurements.
It has trouble with all audio frequencies above a few kHz.
--- End quote ---
I mentioned that I am replacing it with MCP621, will it be better choice?
HB9EVI:
still a good and affordable choice for audio is the venerable NE5534, or the LM833... the microchip opa are very good for digital proposes (adc, dac handling), but I wouldn't use them for audio
alexg:
--- Quote from: HB9EVI on July 24, 2018, 08:41:46 pm ---still a good and affordable choice for audio is the venerable NE5534, or the LM833... the microchip opa are very good for digital proposes (adc, dac handling), but I wouldn't use them for audio
--- End quote ---
Thank you, but there is a catch in my case, some criteria I want to meet for this circuit is side and power consumption, well, besides necessary filtering. My choice has fallen to MCP601 is because it is available in small package, and its power consumption is about 230uA. MAX4466 seems to be tailored specifically for Audio application and is very small and very efficient but I am not sure it can be used for the circuit above, i.e. as op amp in inverting configuration, can it?
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