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New Portable Amp - "Pocket Class A" by xrk971 - now available as complete PCB

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  1. jonmbarlow
    I purchased this amp recently, after a lengthy hold-up at customs I finally got my hands on this amp and have spent some time with it so here are my impressions......

    Firstly I must say that the ordering process is either done via etsy or eBay, I ordered via etsy and found it a simple process....shortly after my order was placed the maker of the amp xrk971 got in touch to enquirer about the headphones that I would be using with the amp, my favourite kinds of music and my preferred sound signature....never before have I had such a personalised experience purchasing such an item and it raised my expectancy that this amp would deliver the sound signature I was looking for.

    I purchased rechargeable 9v batteries and a charger to go with the amp, I went for the blue version, the amp arrived very well packaged and after a quick charge of the batteries it was ready to go.....

    I told xrk971 that I like a bass presence in my music and this amp delivers the bass in a way that I'm not particularly accustomed to.....I use Uapp via my Shanling m2s and s8 and have always had to have the bass dialled up near to the max to get the sound I desire.....With this amp the bass was immediately distorted and I had to turn it right down to the neutral level, my instincts told me this was a bad thing but how wrong was I, you see this amp is custom made to suit my musical tastes so this amp is delivering what I consider the perfect amount of bass without having to alter the frequencies hardly at all....volume wise I shifted the gain up a little and this amp has got my fidelio x2's singing like I have never heard before (and I own a mojo) also my Lz a4's have gone up a level which I didn't think possible.

    If anybody is considering purchasing one of these amps or anything else from xrk971 I cannot recommend it highly enough.
    Last edited: Aug 24, 2017
    stellarelephant, tarhana and xrk971 like this.
  2. stellarelephant
    This amp indeed delivers incredible bass like nothing else I have heard. I also love the fine details it brings out. I have been considering the M2s as my next DAP...good to hear you like the combo.
  3. xrk971
    Thanks for your review Jonmbarlow. Glad that the amp is living up to your expectations. It seems to be able to drive a wide variety of headphones well.
  4. BucketInABucket
    Just a question. Are those 9V batteries wired in series or parallel?
  5. xrk971
    In series to provide about 16v to 18v full rail voltage for single ended operation.

    Btw, Campfire Audio Andromeda has been reported by about 5 users as working superbly with this amp. I assume Lyra would be excellent match as well.
    Last edited: Oct 6, 2017
    DBaldock9 likes this.
  6. BucketInABucket
    I'd assume an 18V lithium battery would do the trick too, right?

    Ooo, I have a Lyra 2, I'm seriously considering buying one of these amps and pairing it with a Nuansa P1.
    DBaldock9 likes this.
  7. xrk971
    If you can get the 18v lithium ion battery to fit in the tin. Otherwise works in a bigger case too. What I have done is use a 3.7v 3600mAHr LiPo cell and a DC step up converter. The followed by a small capacitance multiplier to reduce noise and allow a soft start mechanism. If you are handy and into DIY'ing it is all described in the threads on DIYAudio.

    Else. Just use a pair of EBL 9v rechargeable Lii-ion cells (4 for $21 including wall charger). Those last 4-5hrs per charge.

    Just google EBL 9v Amazon.
    DBaldock9 likes this.
  8. xrk971
    Thanks for the likes Dbaldock!

    Have you gotten anywhere in your quest to make a balanced drive SE Pocket Class A amp?

    I have been working on a new design for a desktop amp that will amaze you guys. Hugh Dean of Aspen PLC, Melbourne is doing the layout as we speak. We will offer it as a product as a collaboration from both our shops. It's a single ended push pull amp. Or SEPP - sort of the holy grail in amps. Uses SE topology, but has the oomph and snap of a push pull. Of course pure Class A and can drive up to 1.2w into 8ohms. Has very low distortion (lower than usual SE Class A) and what it has is dominant 2nd order and little 3rd

    It will come in a nice aluminum case with analog VU meters. XLR and 1/4in TRS jacks.

    Stay tuned.
    DBaldock9 likes this.
  9. DBaldock9
    Check your PM... :ksc75smile:
  10. Lost Cosmonaut
    Last edited: Apr 6, 2018
  11. xrk971
    The HD650's are 300ohm and high sensitivity. Basically the PERFECT headphone to pair with this amp. The amp was designed and optimied around a 270ohm impedance so 300ohms is perfect.
  12. Lost Cosmonaut
    Last edited: May 23, 2018
    DBaldock9 likes this.
  13. DBaldock9
    I've used my Pocket Class A amp with Beyerdynamic DT-831 Headphones (250Ω), and it's a good sounding combo.
  14. xrk971
    There was a list from a while back from all the people that have tried this amp and reported good results. needs to be updated, but here it is again:

    - AKG K240 (Bogde)
    - HD600 with Apollo 8 Blackface (John H. personal communication to xrk971)
    - LCD-2 (70ohm) (Morde)
    - DT990 pro (Bogde)
    - DT880-250 special ed. Chrome with Focusrite Solo 2G (xrk971)
    - DT770-250 (pcgab)
    - MA900 (Bogde)
    - MDRV6 with Focusrite Solo 2G (xrk971)
    - HD800 (modified) with Yggdrasil (Funch)
    - HD800 (Bogde)
    - HD598-50 (StellarElephant)
    - HD598c (Bogde)

    I have had a lot (at least 6) that have paired this amp with Campfire Audio Andromeda (16ohms but very high sensitivity) and love the results.

    - Campfire Audio Andromeda (many people)
    - KZ ZS5 (4 way dynamic and bal) (xrk971 - this is a superb sounding combo, one of the best)
    - Status Audio OB-1 (xrk971 and several others)
    - DT831 (dbaldock)

    I have even listened to the Focal Utopia with this amp at the last Head-Fi Schiitstorm meet in Gaithersburg, MD and they sound awesome together. Also, LCD-X, HiFiman Edition X, Sony MDR-Z1R. So to add to the list:

    - Focal Utopia
    - LCD-X
    - HiFiman Edition X
    - Sony MDR-ZR1
    Last edited: Oct 14, 2017
    all999 and kukkurovaca like this.
  15. Lost Cosmonaut
    Last edited: Apr 6, 2018
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