My guitar Pre-Amp stage/filtering and STM32F4

Discussion in 'Instruments' started by suzy, Jan 11, 2017.

  1. suzy

    suzy Newbie

    Jan 10, 2017
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    I am currently involved in an academic project which the topic is to design a Digital Tuner for Electric Guitars. My knowledge of electronic is very basic, so here I am.

    I need to pre-process the signal that goes out from the pickups of a common electric guitar, let's consider passive pickups so....we have an output voltage from 200mV up to 1V of peak, with also negative peaks (of the same magnitude).

    I have to use the STM32F4 (Discovery Board), so I need a very simple circuit that drives the On-Board 12-bit ADC, that takes, as inputs, signals with voltage between 0 and 3.3V. So I have to design a pre-amp circuit that amplifies and clamps the guitar's output.

    I want to underline that I have never realized an electronic circuit (a real one, not in the simulator) before. I am wondering about:

    1. STM32F4 provides some voltage sources (5v or 3v). Shall I use these sources or is it preferable to go with an external voltage source (e.g., batteries)?
    2. I have chosen an opamp that is not, let's say, "handy" because it needs 2 voltage sources: the TL082. What op-amp do you suggest me to use? (maybe with only 1 voltage source)
    3. I have tried to design a circuit by using LTSpice, but I don't know if it is correct at all. You can also notice that I have inserted a filtering stage (LP w/ cutoff freq. 2,2 KHz) and a "protection" Schottky diode before entering in the pin of the board.
  3. GangamStyle

    GangamStyle Member

    Oct 31, 2012
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    You throw a wide net, at least according to google ;D
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  4. Kobayashi Maru

    Kobayashi Maru Member

    Jan 14, 2014
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    In the MIDIbox forum,
    A lot of the DIY projects/builds use the STM32F4
    My MIDIboxSEQv4 (Hardware Sequencer) uses the STM32F4.

    Here is a link to the MIDIbox forum STM32F4 search page, where someone maybe able to help.

    Sorry I couldn't be of more use, I got someone to build my MbSEQv4 so I don't know very much about the STM32F4.
  5. type2002n

    type2002n Member

    Apr 5, 2012
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    About the opamp, you can use an old m387n, or better an mc14069, it's a cmos hex inverter, each one of the six inverters can be used as an opamp. It is extremely simple to use, +5...+9V on on the ic, and each inverter needs a 10mega resistor in parallel (between in and out). Gain is around 30dB per inverter.
    Last edited: Jan 12, 2017
  6. angie

    angie Kapellmeister

    Nov 26, 2012
    Likes Received:
    Hi! If your aim is only a digital tuner, noise is not an issue, so google for an inexpensive fet buffer that you can power with 5v maybe.
    I should not use tl082 here, but hey it's my noob opinion
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