Steampunk USB-Powered Desktop Head Amp (agdr audio OPA1688 Parallel Super CMOY)

Discussion in 'Headphone Amps (full-size)' started by WoodyLuvr, Oct 21, 2018.
  1. WoodyLuvr

    Finally completed my Steampunk USB-Powered Desktop Headphone Amplifier. I used agdr audio's OPA1688 Parallel (Dual Chip) Super CMOY head amp board and it is performing wonderfully! Many thanks to @adydula for assisting me in more ways than one with this build... very much appreciated good sir!

    The power module consists of a RECOM RW-0509D DC-DC Converter which converts the 5V from the USB cable to the required 9V. Please kindly excuse the shotty soldering and gluing... I battle severe hand tremors.

    Still waiting on one final part to arrive... a 19mm wide brass volume knob.

    Without further ado my creation...

    The copper tomb... no EMI/RFI getting in this here amp!








    CTS Black Aluminum Heat Sink 40mm x 40mm x 9.5mm


    Heat Sink Insulation & Grounding Pad
    Last edited: Oct 22, 2018
    headpfizer and smallcaps like this.
  2. adydula


    Great looking amp! does it sound to you?

    Smiling here!

    WoodyLuvr likes this.
  3. DavidA
    Cool looking amp and like Alex noted above, HOW DOES IT SOUND :ksc75smile:
    WoodyLuvr likes this.
  4. WoodyLuvr
    Thus far, it is dead silent even with the volume pot at max volume.

    Here are some details and specs:

    "OPA1688 Parallel Super CMOY dual-chip headphone amplifier with a real ground and a headphone relay for zero turn-on or turn-off thump and essentially zero (250uV) DC output offset voltage. Uses two of the brand new Texas Instruments OPA1688 ( ) headphone driver chips in parallel for 150mA output per channel (6x the output of most op-amps). Ultra low distortion with extremely low idle current for long battery life. Uses 2 9V batteries with a real ground and "solid state relay" technology - no virtual grounds or rail splitters to distort the sound." - agdr audio

    150 mA output per channel
    zero output impedance (yes, 0 Ohms)
    unity gain

    Last edited: Oct 22, 2018
  5. WoodyLuvr
    This RECOM RW-0509D DC-DC CONVERTER POWER SUPPLY MODULE has been running now for more than 36 hours and running very cool coupled to a 40 x 40 x 9 mm aluminum heat sink. Easily handled with bare fingertips. I am pleased to say the least!
  6. adydula
    The OPA 1688 is a very nice op amp.....and its nice to see TI making a chip designed especially for this area of our hobby.

    AGDR did a great job designing this amp in its form factor and I was elated to wire it up and it worked wonderfully for me.

    I actually built three of them in AGDR's development phases....I still have a prototype and a single 1688 version. Sonically they are identical.

    I dont know if AGDR is still selling the pc boards..but you can PM him over at

    Some of the soldering is indeed challenging!!

    Last edited: Oct 22, 2018
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  7. WoodyLuvr
    Volume knobs finally arrived from China and I decided on this bronze metal one.

    DavidA likes this.
  8. WoodyLuvr
    Now in it's place sitting beside "UV Siamese 2" Silent Fanless SFF PC

    DavidA likes this.
  9. WoodyLuvr

    Oh my this little amp sure is powerful!

    I have had to set foobar2k music player down to -16dB so it won't blow up my 32Ω Nhoord Reds or 300Ω Blurs! It pushes both drivers way too hard especially on a few prominent sub-bass tracks that I have (e.g. Gustav Holst: The Planets, Op.32/H.125: vii. Neptune, the Mystic; Andante Original Ending - Mark Elder; Hallé Orchestra & Choir or Jóhann Jóhannsson's Sicario: ii. The Beast).

    System volume (Win10) is still set at 100% though.

    Full Specs for agdr Audio OPA1688 Parallel Super CMOY
    Output Current (peak): 150 mA per channel
    Output Current (rms): 106.05 mA per channel
    Output Impedance: ~0 ohms
    Voltage Gain: 1x ("unity-gain amplifier")
    Voltage Cut-Off Level: 8.4 V nominal
    Voltage Swing (peak): 7.4 Vdc
    Voltage Swing (rms): 5.23 Vrms

    So this 'little dual-chip head amp that could' should be able to handle not only the power hungry HE6 driving them up to 105 dB SPL but the mighty AKG K1000 as well... albeit only driving it to 97 dB SPL which is still doable for all but the most dynamic/heavy sub-bass pieces.

    HiFiMAN HE6

    AKG K-1000
    Last edited: Nov 5, 2018
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  10. DavidA
    I'm so glad that you show sound technical info since lately there are so many that say you need an amp with 1.21 GW of power for even average headphones on some threads but I've found that its more of a synergy effect that tends to make one amp pair better with some headphones over other amps. My Teac UD301 headphone output only has 100mW but even it is enough for my HE560 and LCD-2f but there are still those that are recommending amps of >4W for them.

    FWIW I wish I had the time and knowledge to build an amp like you or another Head-Fi member who let me try a powerDAC (a bit like a Mojo) that he built for driving a HE400i but it has enough juice to drive even my HE560 which needs a bit more grunt to get to my listening levels.
    WoodyLuvr likes this.
  11. WoodyLuvr
    Concur, I don't get most of those "more power required" recommendations you speak of nor do the audiophiles that I know here in Thailand whom are very high level electrical engineers! Now there are a few (very few) headphones out there that are indeed power hungry and do require a higher voltage swing to perform well but not the amounts that are being readily recommended. So what it comes down to with insensitive headphones like the HE6 and K-1000 is not so much about the need for extreme wattage but rather the quality amp and it's power supply (synergy being part of that of course).

    Look at the recommended specs for your HiFiMAN HE-560:

    Nom. power rating: 2W (estimated)
    Max. voltage: 10V
    Max. current: 210mA
    Max. S.P.L.: 119dB
    Impedance: 45 Ω
    Efficiency: 86 dB/1mW (99dB/1V)

    So your HE560s only need 251mW, 75 mA, and 3.4V to reach 110 dB SPL. Your TEAC UD301 is driving your HE-560s perfectly fine providing 106 dB SPL and there is enough dynamic headroom there to handle sub-bass demands. As per the bottom portion of the table a 4W amp hooked up to your HE-560s would be very unwise... feeding your cans over 13.5V @ 300mA which is way beyond the recommended specs for your cans.


    The only headphones I can think of that truly would require a ~4W amp to reach ~110 dB SPL would be the almighty AKG K-1000... they require ~182 mA @ ~21.8Vrms! However again, with only 40mW @ 18mA and 2.2V the K-1000 can be easily driven to a very listenable 90dB SPL with all but the most dynamic and sub-bass heavy tracks.

    So where does one draw that line of diminishing returns in regards to a higher wattage amp and better yet wouldn't one rather focus on better build quality and power supply than seeking higher wattage?
    Last edited: Nov 5, 2018

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