In-Line white noise generator?

Discussion in 'The Projects Forum' started by EvilVargon, Apr 4, 2016.

  1. EvilVargon

    Thread Starter New Member

    Apr 4, 2016
    6
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    I've been looking for a white noise generator circuit that I could put in line to a 3.5mm jack. I was wondering if the jack has enough power to generate the noise, or how I would implement the battery otherwise. Any help would be appreciated.
     
  2. Sensacell

    Well-Known Member

    Jun 19, 2012
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  3. Papabravo

    Expert

    Feb 24, 2006
    10,163
    1,796
    Jacks by themselves have no ability to generate power. Power comes from a battery or from a power supply derived from the AC mains. The circuit above has a single output and no input. As such it may not be suitable for an inline application. Maybe you could elaborate on your idea so we have a better idea what you have in mind.
     
  4. EvilVargon

    Thread Starter New Member

    Apr 4, 2016
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    I was hoping to have a module that puts a white noise generator on a 3.5mm extension cord. This is meant to be used with phones. A battery would work, but I would be limited in size with about a AAA battery
     
  5. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,546
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    To clarify, you are asking about a small circuit, self-contained and battery powered, that generates a white noise electrical signal, with enough current to drive headphones directly, connected to a 3.5 mm headphone jack.
    Yes ___
    No ___
    If yes, what are the headphones? Do you know the DC resistance or AC impedance? There is a big difference in the output signal power required for studio-grade over-the-ear headphones versus $1.99 ear buds.

    Is this an acoustic masking application?
    Yes ___
    No ___
    If yes, the "right" way is to have two independent circuits, one for each ear, so the left and right signals are not identical.

    1.5 V severely limits your circuit options, output power, and output fidelity (yes, noise has fidelity). Any way to fit in a single 9 V transistor radio battery? What are the max size limits of the box the circuit fits in?

    ak
     
    Last edited: Apr 4, 2016
  6. EvilVargon

    Thread Starter New Member

    Apr 4, 2016
    6
    0
    Yes, I intend for this to be a small self contained circuit connected by the 3.5mm jack.

    I plan to be able to use this as a general purpose and do not know the impedance of the earphones. Generally $50 earphones, not studio headphones that require a DAC.

    Yes, this is intended for acoustic masking.

    I do not have a size requirement per se, but I intend on having this be portable. Possibly able to clip onto your shirt.
     
  7. Nykolas

    Member

    Aug 27, 2013
    87
    31
    I believe EV thinks of pink noise, or random noise shaped for sound masking stems. White noise would be highly annoying very quickly! If the earphones have an impedance of 32 Ohms and require 100mW to drive the RMS voltage needed would be about 1.8 V. Multiply by a crest factor of 5 the amplifier needs to deliver 9Vpp. If you have space for only an AAA battery you need to up-convert the 1.5V battery voltage to about 15V for the amplifier to deliver clean sound. E
     
  8. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,546
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    Depending on things like how many, and how long it must run on one battery, and how loud it needs to be, this could run on a lithium coin cell, with a different circuit.

    The circuit in post #2 is a classic with many variations. Generally speaking, they all require over 6 V to operate because that is the nominal reverse breakdown voltage of a small signal transistor base-emitter junction. Not a serious problem because of the type N battery, about half way between an AA and AAA in diameter, about 1/2 as long, and 12 V. Or the circuit can be reworked for a lower voltage.

    Complexity = life. The circuit in post #2 is a class A output stage, the least efficient of all and the least complex. A major problem is its very asymmetrical output impedance. A simple AB stage has better performance and can be tweaked for minimum static current, but you're up to 3 transistors plus whatever the noise source is. Or search for a low power headphone amp chip. Digi-Key has hundreds to choose from.

    ak
     
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