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I need suggestion on building a guitar signal preamplifier
MUFF WIGGLER Forum Index -> Guitars, Basses, Amps & FX  
Author I need suggestion on building a guitar signal preamplifier
This is for a DSP project. I am trying to prepare my guitar signal for as best as possible ADC response in order to detect harmonics to the 5th of the highest note of the guitar (1175 Hz for 22 frets), which is about 5875 Hz. This means that I need to be sampling at about 58.75 kHz, which is possible with the microcontroller and it's DSP functions.

I am using an STM32F407 Discovery board.

So far, I have not come across any solutions that I am happy with.

Considerations that are important:

    Guitar output impedance: about 1M ohm.
    Anti-aliasing for the ADC
    Guitar signal of 500mV Vp-p max
    ADC input range 0-3.3V
    5V single supply
    Frequency range from 82Hz and 5875 Hz

Does anyone have any suggestions of a circuit that I can use? I have TL082, LM358 and LM741 opamps available, but I am open to other suggestions.

The goal of this element of the projects is to be able to use the first 5 harmonics and a sampled period of the guitar signal for further DSP.

This is what I have come up with so far - although I believe it's far from ideal.

This is a closed loop bode plot of the system. Couple of things that worry me are the massive phase differences at the corner frequencies, and the slope of the low pass filter and it's stop frequency. The cutoffs are at 10Hz and 10kHz

Any tips would be greatly appreciated.
I'm guessing you don't care much about sound quality (an LT1006 isn't a good choice for audio). Neither is an LM358. And a 741 is a horribly noisy antique. I don't see the need for an interstage cap. Anyway, there are better front end circuits to get the high input impedance (discrete FET, bipolar, bootstrap, etc.) that don't use a 1M feedback resistor. There are plenty of schematics for booster pedals than run off single 9V supplies. So it should be pretty easy to adapt them to 5V. Although I would use an op-amp for V/2.

Also, many guitars put out more than .5Vpp, but it looks like you are clamping the output.
how about the project now ?
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