Headphones Question?

Discussion in 'General Electronics Chat' started by adrian.dmc, Feb 19, 2008.

  1. adrian.dmc

    Thread Starter Active Member

    Feb 22, 2007
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    Whats the input voltage for a simple headphones?
    It's possible to produce "music" with a DAC connected to the headphone directly?
     
  2. nomurphy

    AAC Fanatic!

    Aug 8, 2005
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    Generally, the max input voltage is based upon the rated wattage and impedance (8/16/32 ohms) of the particular headphones.

    V = sqrt (W*R)

    4V = sqrt(1W * 16 ohms)
     
  3. adrian.dmc

    Thread Starter Active Member

    Feb 22, 2007
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    I think you did not understand what i mean...

    I want to know if using a micro-controller, connected to a DAC (0 to 5V output) is possible to wire the headphones directly to the output of the DAC and hear reasonable sound.

    I made a program that analysis a *.wav file (8kHz, 8 data bits) and then sends that to the DAC. I can see that the output voltage of the DAC varies, but on the headphones there's only noise.
     
  4. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Then the data being sent to the DAC is wrong, or the headphones don´t recieve signal without DC component.


    What king of noise is it?
     
  5. adrian.dmc

    Thread Starter Active Member

    Feb 22, 2007
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    The headphones are connected between the DAC Vout and GND. Is this the problem?

    When I measure the voltage in the DAC output it varies correctly to what was supposed too but the headphone don't work accordingly.
     
  6. Audioguru

    New Member

    Dec 20, 2007
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    The DAC has a limited output current. It is probably clipping when it is overloaded by the low impedance of headphones.
     
  7. adrian.dmc

    Thread Starter Active Member

    Feb 22, 2007
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    But the DAC output only give a DC component.
    As I know, to have sound, we need a AC component, with a constant frequency, and what gives the different tones is the amplitude, right?

    I have a MX7224 but I don't find in the datasheet the maximum supported current, can anyone tell me what is it?
     
  8. beenthere

    Retired Moderator

    Apr 20, 2004
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    Use 10 ma as a good guess about the maximum current output from a DAC. It could easily be less. Driving low-impedance loads is a job for amplifiers. Your MX7224 is rated at +\- 10 volts into 2000 ohms - Mr. Ohm says that's 5 ma.

    And, true, a DAC will output a DC level for each digital input, but if you change the inputs fast enough, the output will start to resemble an audio signal. That is why audio is sampled at 22.1 Ksamples/sec per channel. When played back at that rate with a bit of filtering, it sounds lots like the original audio.

    One thing I noticed - you say you are playing a .WAV file @8KHz & 8 bits. Stereo .WAV files have the right and left channels alternated, so the effective playback rate is 44.2KHz. The usual word size is 16 bits, not 8. Are you sure the microprocessor sending the digital data to your MX7224 correctly? Is it compensating for the lower playback rate and number of bits? Or did the file get recorded at that rate and with that resolution?
     
  9. Audioguru

    New Member

    Dec 20, 2007
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    No.
    The pitch is the frequency and the loudness is the amplitude.
    when young, most people can hear frequencies from 20Hz to 20kHz.
     
  10. nomurphy

    AAC Fanatic!

    Aug 8, 2005
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    If you have 32 ohm headphones, and you apply 5V to them, that's:
    156mA = 5V / 32 ohms

    For 8 ohm headphones it would be:
    625mA = 5V / 8 ohms

    Can your DAC supply 625mA of current, or even 156mA? I doubt it.
     
  11. legac

    Well-Known Member

    May 4, 2005
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    Certainly you can do that with some specific DA chips. I have seen some circuits which use staking of 10 chips -PCM63 or TDA1541 I am not sure-. You can search internet using key word "staking DA drive headphone' or the like. Headphone inpedance is 32 ohms in general. That value is ideal to be used as I/V converting resistor for TDA1541.
     
  12. veritas

    Active Member

    Feb 7, 2008
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    nomurphy is right. In order to power a speaker (or headphones, in your case) using a microcontroller, you need to amplify the output.

    If you're not worried about the sound quality of the output, a simple NPN transistor amplifier should give you enough frequency response.

    A common collector amplifier won't give you any gain, but it will buffer the output of your microcontroller or IC and allow you to source enough current.


    *edit* Headphones generally take a very low voltage signal, so 5V would be completely unnecessary. You might have to attenuate your output.
     
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