TOPPING NX1 Portable Headphone Amplifier Impressions Thread

Discussion in 'Portable Headphone Amps' started by h20fidelity, Dec 26, 2013.
  1. skeej
    Last edited: Aug 15, 2017
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  2. sharpi31
    IMG_0052.jpg IMG_0421.JPG I received my NX1s today. Looking at Toppings frequency response graph the bass is >2db down at 20Hz. Sure enough this appears to be largely due to undersized coupling caps between the volume pot and gain stage (1uF into 9.4Khz resulting in a -3db point of 16.9Hz). The good news is that there is no DC bias on the coupling caps, so it should be possible to bypass them (rather than find some way to replace them with larger capacity caps within the small amplifier case). I measured less than 1mV DC offset on the outputs with the caps in place - I'll short out th coupling caps and remeasure, to ensure the level doesn't become problematic.

    It's worth addressing this issue (by bypassing the existing caps or replacing with larger ones) as the phase response of the amp is compromised significantly above the -3db frequency. The normal rule of thumb would be to set the coupling caps to have a -3db point of 1/10 the lowest frequency you're aiming to reproduce (so 2Hz if you want clean 20Hz playback).

    Update: all works fine with iPad Pro source and bypassed coupling caps. I'm measuring 0.5mV and 0.6mV on the NX1s outputs. Bass definitely bigger and tighter (not over the top, just less softened).
    Last edited: Sep 7, 2017
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  3. photosonic
    Just curious, how do you bypass the coupling caps.
  4. sharpi31
    I left the caps in place and soldered a thin wire from one pin to the other (to short them out of the circuit). I actually used the legs of two spare resistors, as it was easy to tin one leg with solder, hold in place and then solder to the existing cap legs (then trim off the resistor body and other leg). You could alo remove the caps and install a wire from one PCB hole to the other.

    I should mention that this does leave your amp and headphones exposed to the risk of DC on the source input connection. With the caps in place no DC gets to the NX1s gain stage, so a DC offset from the source wouldn't be amplified and fed to headphones (possibly damaging them). Removing or bypassing the caps is the best option for audio quality, but does remove a layer of protection. Another option would be to install replacement coupling caps of higher capacity (10uF or more) - this would retain the protection from DC, but remove the problematic roll-off and phase shift in the bass. The problem with this option is finding coupling caps of 10uF or greater that won't degrade the sound and will fit within the tiny NX1s case (tantalum need a DC bias so won't work here, bipolar electrolytics would work but don't sound great, film caps are probably too large).
    bsoplinger likes this.
  5. Toretoshark
    I'm doubting on buy it or Fiio A1 amp, which one is better to use with my Huawei P8 and Ipod classic 80Gb ? Topping seems to have better equipment so induce cable and accesories but I do not know nothing about the quality of sound and power.
  6. skajohyros
    Just from the specs the nx1s is better. Definitely more powerful and I believe the hardware is better. My nx1s is coming on Tuesday hopefully.
  7. photosonic
    Interested to hear about what you think of the NX1s.
    I have a love/hate for the NX1s. It pumps out clean and non-distorted sound. It's also shielded and I
    don't hear any RFI noises from my phone. I hate how bad it rolls off sub bass frequencies though. I wish the bass boost affected lower frequencies because when switched on, it becomes a little too boomy in the upper bass area. I'm going to keep it and maybe switch out to different coupling capacitors inside the amp. I've heard this fixed the sub bass roll off.
    Last edited: Sep 17, 2017
  8. Toretoshark
    And do you have Fiio A1 too?
  9. skajohyros
    Let us know the results if you try the mod. I like to tinker.
    I got the nx1s mainly for my beyer dt990 250 ohm which is a bit too bassy for me. Hope it works out well.
  10. skajohyros
    Do you need to connect all 4 legs of the caps?
  11. sharpi31
    You connect the two legs of both caps (one wire link between the legs of C33 and one wire link between the legs of C34)
  12. skajohyros
    After that do you connect c33 to c34?
  13. sharpi31
    No - the two channels need to be kept separate
  14. skajohyros
    Thanks mate.
  15. skajohyros
    Thanks mate. Just did it and enjoying an upgraded nx1s.

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