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Super Cmoy!!! Using the new TI 1688

Discussion in 'Portable Headphone Amps' started by adydula, Jun 19, 2016.
  1. adydula
    I just completed a new Cmoy amp using TI speciffically designed for headphones op amp the 1688. AGDR just designed a circuit based on the cmoy with TI 1688.
    A mint-tin CMOY headphone amp like no other!  Uses the brand new Texas Instruments OPA1688 and (optionally) OPA1622 headphone driver chips.  Ultra low distortion with extremely low idle current for long battery life.  Uses either throw-away 9V batteries or lithium rechargeable batteries.

    Texas Instruments has just released a brand new generation of headphone chips, available only in surface-mount packages.  These chips have many benefits over the older chips:
    The lowest Total Harmonic Distortion and Noise (THD+N) of any headphone chip to date
    Extremely low quiescent (idle) current for low power draw and long battery life.  Up to 1/6 the draw of some older op-amps.
    High output current levels.  The OPA1688 is rated for a maximum of 75mA per channel, while the OPA1622 is good for 150mA per channel.  Most older op-amps in CMOYs are only rated at 20-25mA.
    High capacitive load drive with no output resistor.  Most op-amps used in CMOYs were never intended to drive the levels of capacitance found in headphones and headphone cables, resulting in oscillations unless series output resistors are used tp isolate the load.  The new TI chips are designed to drive headphone CLOADs directly, with no output resistor.

    So if you ever had a penchant to muck with some DIY...take a look!
  2. adydula
    Here are some pix of the amp and build....

    Tiny board with most of the stuff on the other side of the board.
    Notice the very very tiny comparator chip, it was indeed a chore to solder!!

     This was posted last Sept by an TI Engineer you can follow these new developments at the vendors bazaar area at the DiyAudio site....
    Seems like these new op amps designed for headphone amps will start creeping into head amps!!

    The Cmoy like amp i built has one 1688, plans to have two of them for a really beast of a Cmoy!! LOL!

    Last week TI released a new audio Op Amp, the OPA1688 (http://www.ti.com/product/OPA1688)

    For those that are interested, the basic specs are:
    Gain Bandwidth Product: 10 MHz
    Slew Rate: 8 V/us
    Power supply voltage range: (4.5V to 36V or +/- 2.25V to +/- 18V)
    Power supply current: 1.6mA
    Input voltage noise: 8nV/rtHz (1kHz)
    Input current noise: 1.8 fA/rtHz
    Input offset voltage: +/- 0.25mV (typical)
    Input bias current: +/- 10pA
    Input voltage range: 100mV below V- to 2V below V+ (reduced specs outside of this range)

    What's really interesting about this device is the output stage linearity, which makes it a good choice for driving headphones. For example, if you're using an OPA2134 in a CMOY-type headphone amplifier, the OPA1688 would be a big improvement in both distortion and power consumption.
    Systems Engineer - Texas Instruments Precision Analog / Audio Products
    Harry Manback likes this.
  3. adydula
    How does it sound...well the answer is just superb!!.
    Compared to other amps I have built its just as good as the others!
    I have several o2's, schitt amps, many other DIY amps, and this little TI 1688 cmoy is just as good as the others...
    There are also plans for a higher power amp, stay tuned!
  4. adydula
    If your want to build one check them out over at diyaudio.com
  5. Minerman
    Having a sight problem always becomes an issue with this sort of DIY project unfortunately I always have to buy any headphone amp of any sort  to enjoy the sound,  it took me a few hours  just to re-solder the negative wire back in place after it came adrift on my 18v askew lab Cmoy so would never be able to do this but it sounds like a great little amp to listen to I normally use a pair of Beyerdynamic  DT770  250ohm headphones which seem pretty good with the askew but batteries tend to run out after a few hours so this type of amp may be the saviour
  6. adydula
    Contact martin at agdraudio.com I believe he will make and sell you one?
    timb5881 likes this.
  7. timb5881
    I am going to have to check this out. Love my old cmoy, still use after 8 plus years.
  8. adydula
    I have built three versions of AGDR's cmoy and they all have worked first time, no real adjustments, they just work.
    Its a real easy amp to build except for the TPS 3701 part, which is a challenging solder job, AGDR does sell these at cost over at AGDRAUDIO.COM
  9. stellarelephant
    How does the sound signature compare to that of the original CMOY design with the older op amps...like the latest JDS Labs version?
  10. rickso234

    TI's OPA1622 is available on a populated evaluation PCB, including the surface mount components and a 3.5mm output jack for $25. The board's 2" x 2.125" and will fit in an Altoids tin.
  11. stellarelephant
    Cool. Have you heard it in this configuration? I found this thread about it, authored by the same guy who designed the Super CMOY... http://www.diyaudio.com/forums/headphone-systems/297019-ti-opa1622evm-headphone-driver-eval-board-unboxing-hookup-part-1-a.html He said it sounded good with a little work.
  12. dhruvmeena96
    Can we use opa1622 in this setup, just for being sure....as i was told, this is a cmoy optimised for 1688.

    I read opa1622 has a lot better specs
  13. dhruvmeena96
    Yo @adydula Alex

    I want to ask how to connect OPA1622 to my agdr cmoy..
    What modifications I have to do to...

    And yah...I changed all resistor to Texas instrument tx2575 and some capacitor upgrade (not the snake oils, normal caps but even better value and performance).

    These do sound better than many amps I have listened this far.

    And yah,,, I forgot

    I am also making graphene battery with same volt rating as stock NiMH but small form factor and increased life cycle and man...

    Right now that's a DIY project which is going on with my friends..

    And I was not able to successfully send agdr a message...diyaudio showed me message sent failed...

    Three times in row
  14. adydula
  15. dhruvmeena96

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