Headphone Amp Project - Pics

Discussion in 'Archived Threads 2001-2004' started by Michael_Hml, Feb 9, 2003.

  1. Michael_Hml

    Michael_Hml Stunt Coordinator

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    I've been hanging around over at Headwize and Head-fi recently, and decided to build the "CMoy Pocket Headphone Amp" - except not worry to much about it being pocket-sized.

    I just finished my first attempt... actually, kind of my 2nd, but my first *completed* one. The first one's got a more complex PS and I'm waiting for parts, so I built this today.

    Everything went very well - couple of stupid mistakes that took a few minutes with a meter and a good loud "Doh!" to resolve. It's all pretty much stock to the project guide, plus 1uF orange drop caps for the input caps and an extra 470uF cap to buffer the power supply.

    The most fun was the enclosure. :)

    I put up some pics at:

    Mike's First CMOY

    -Mike
     
  2. Chris Carswell

    Chris Carswell Supporting Actor

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    [​IMG] cool [​IMG]
     
  3. Rick Guynn

    Rick Guynn Second Unit

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    Why did you change the input caps to 1uf instead of .1uf? Won't this change the high-pass freq? I was just wondering as I recently completed one of these myself. The only mod I made to mine was to use the TI voltage-splitter chip in the power supply.

    RG
     
  4. Aaron_Smith

    Aaron_Smith Stunt Coordinator

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    Looks nice- great enclosure. I built a cmoy about 2 years ago and it was a great project-- one of the coolest things I learned was how different op-amps can sound, even when their specs are nearly identical. Those burr-brown op-amps that they all talk about are pretty nice but I love the sound of the national semi LM6172; much smoother. I have since replaced the op-amps in my CD player with the 6172's, and the difference was just as big.
     
  5. Michael_Hml

    Michael_Hml Stunt Coordinator

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    Rick,

    Using a 1uF cap drops the corner frequency to 1.5Hz instead of 15Hz. It's one of the recommended values to use, but generally full-size 1uF film caps are just too large for the tiny cases most people put the CMoys in.

    -Mike
     
  6. Rick Guynn

    Rick Guynn Second Unit

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    Ah, I went with increasing R2 to 1 Meg instead, which is *supposed* to do the same thing if I understood the guide correctly.

    RG
     
  7. Chris Tsutsui

    Chris Tsutsui Screenwriter

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    Wow that looks so clean cut, nice job.

    When I made my pocket amp I simply designed it off a circuit diagragm so the back of my breadboard looks like a triple layer freeway intersection. I did add a cool looking green LED to indicate "on".

    My pocket amp

    I've actually used the pocket amp to power some GR-Research AV-3s when I jerry rigged it. It didn't sound that good at loud volumes. [​IMG] My one quirk is that there is a very suble amt of hiss that's noticeable in a quiet environment when using headphones. How's the hiss on your model?
     
  8. Michael_Hml

    Michael_Hml Stunt Coordinator

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    Chris,

    Thanks! I don't get any hiss at all - I can hear a slight buzz with no input signal if I turn the amp up all the way, but it's silent up to uncomfortably loud listening levels. The circuit does have an optional resistor to reduce hiss, but I found that I didn't need it.

    Nice job on yours as well. What chip are you using for the amplifier in that project?

    -Mike
     
  9. Chris Tsutsui

    Chris Tsutsui Screenwriter

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    2 little LM386 ICs.

    The amp has adjustable gain up to 21dB, so it can deliver 95dB SPL into headphones from the E40 at "average" record level. "Average" record level is 8dB below digital max level. Output level with 80mV in is .95V.

    Size: 1.5 x 3 x 5 inches more-or-less
    Weight: 5 ounces (includes Nimh battery)
    Distortion: 0.2%
    Freq Response: 5Hz to >110kHz (-1dB)
    Max Output level: 1.7Vrms
    Noise: Slightly Audible
    Output Power: 375mW into 8-ohms
    Input Impedance: 33Kohms, minimum
    Running Time: 6-8 hours depending on volume
    Circuit Desc: Uses two LM386 power amp chips, 10-caps, 5-resistors.
    Controls: Volume, On/Off switch
    I/O's: Input pigtail, mini-phone out. DC power in, LED on.
     

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