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iBasso PB-2 Pelican fully balanced portable, DB-2 Dac . . HiFlight recommended op amps page 16. .

Discussion in 'Portable Headphone Amps' started by jamato8, Dec 13, 2010.
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  1. snellemin
    I searched and didn't find one in any low C rate. For the stock battery to have 700 mah, the C-rate must be like 10 and below. Which also translate to ripple current under load. That is why I had an improvement in my previous PB2 when I swapped stock cap to a dual cap setup. With me swapping out to the smaller capacity higher c-rate, noticed a cleaner sound output and loud levels. I have no need to swap out the stock cap.
  2. zilch0md
    Thanks for this info. I've used RC LiPo batteries with ridiculously excessive continuous current ratings for the loads in question - a Meier Corda Stepdance portable headphone amp (15VDC max) and a TBI Audio MG3 Millenia power amp (24VDC max). In both cases, I wrote the designers (Jan Meier and Jan Plummer (coincidentally having the same first name), and they both conveyed that unless a "dust bunny" or some other impurity encourages an "air arc" to short two traces on a PCB, it's highly unlikely that a LiPo battery which can deliver 350 Amps continuous without overheating is going to damage their respective products.

    YMMV - proceed at your own risk - but I routinely use these high-amperage RC LiPo batteries and haven't had a problem (yet) with those two amps.

    Last edited: Oct 25, 2017
    snellemin likes this.
  3. plutonim
    Hi everyone,
    a few weeks ago I swap my Centrance mini M8 to a set of ibasso pb2 + db2. I liked the possibility of replacing the op-amp, the 32V output swing and the DIY design. No battery was inside, so I tested PB2 with an external 16V power supply.

    First of all, I measured the supply voltage to the op-amp - it was +/- 8V, which fully corresponds to the input voltage of 16V. Accordingly the maximum output amplitude voltage swing can not be greater than 16V (+/- 8V), and this is correctly only for rail-to-rail op-amp. But how do they state the output amplitude swing of the 32V if even on one wire of the balanced output the maximum amplitude peak can be + 8V, and on the other output, in the opposite phase, minimum -8V. Therfore the amplitude of 16V on the balance output is obtained.

    I began to understand the power circuit in order to increase the voltage. Making modification of the FiiO X7 amplifier I realized that the higher power supply of the op-amp, the better sound at the output.

    For a long time I could not find the microcchips names with erased labels, but when I make a reverse engineering of the PB2 PCB, the idea of power supply inmplementation became clear. The PB2 power supply is taken from an external source or internal battery, and the middle point is created by the microchip divider. Thus we obtain from a unipolar input voltage a bipolar supply of the op-amp. Since the characteristics of this chip allow to feed it with voltage up to 40V, I tried to connect an external power source 24V from the photo printer. !But before connecting it is necessary to change the input capacitor to a higher voltage, I replaced it to 2200u35V! The sound quality increased significantly. The resolution and depth became amazing.

    After that, I decided to raise the voltage as much as possible. For this, I bought two LiPo 4S 14.8V 1000mA 70C batteries and connected them in series. It turned out about 30V at the input of the amplifier and the power supply of the op-amp became +/- 15V. Just in case, I changed all the tantalum capacitors in the power supply rails, since the marking is flawed and it's not clear what maximum voltage they can withstand, replaced it to 220u16V.

    And on this input voltage has burned a 2.2 Ohm resistor that limits the starting current when the power is turned on. Therefore, it must be replaced by a more powerful or greater resistance. It can not be short-circuited, since when the power is turned on, a strong current surge occurs when the capacitor is charged and the power switch contacts are burned.

    Now the amplitude output swing of the amplifier can reach 30V. And the sound of the amplifier became unbeatable. All the same, the power supply of an op-amp for good sound should be not less than +/- 12V.



    Now I am working on DB2 modification and it became sounds much better.

    PS Sorry for my "Google translated" English :)
    zilch0md and snellemin like this.
  4. zilch0md
    Wow! I very much enjoyed reading your story of modifying the PB2 for MORE POWER! :)

    It's obvious that you have some excellent skills. I'm envious. :)

    I had once concluded that no matter how high the voltage applied to the external DC input jack, the op-amps only see the voltage coming out of the PB2's internal power supply. Do you agree?

    If so, you must be bypassing the charger to increase the supply voltage seen at the op-amps. Your schematic is very smartly drawn, but I'm not smart enough to interpret it. :)

    When reading the datasheets for many different op-amps, I've noticed that they sometimes include charts that show supply voltage vs. THD + N and, quite often, the lowest (best) THD+N is achieved at a supply voltage that is a little bit below the maximum allowable supply voltage for a given op-amp. I recall seeing charts where something like +/- 15V produces lower THD+N for an op-amp that can handle up to +/- 18V, for example.

    It is possible, however, that the difference in THD+N is so negligible, that any improvement in dynamics or bass control that comes with higher output power to the headphones, will outweigh any audible increase in THD+N.

    I would very much appreciate your thoughts on this and please tell us what headphones you are using - that are responding so positively to an increase in power.

    Also, are you happy with the DB2 Boomerang DAC? I bought it and returned it along time ago, finding it to be too warm for my tastes.


  5. plutonim
    No, it is not correct. The more input voltage on the DC input jack, the more voltage on the op-amp. The input voltage divided by 2 like in this scheme with virtual ground https://tangentsoft.net/elec/vgrounds.html (look at the VFB OPAMP-BASED VIRTUAL GROUND DRIVER).
    Thus , the power supply voltage on the op-amps equal the input voltage divided by 2 (Vopa=+/-Vin/2) I started to test increasing voltage by using laptop power supply 19V (+/-9.5V op-amp) and there is no any problem with electronic components, but the sound improvement was audible. Only the input big capacitor was replaced for more voltage.

    My excellent headphone is XBA-Z5, and I don't need to increase the power, but it is necessary to increase the op-amp supply voltage, because, how you said - to increase THD+N.
    And I found that charge controller can support 4S batteries, and I want to set up four elements 3.7V 450mAh inside the PB2
    Later I'll tell you how it would be.

    It WAS very warm and turbid untill I replaced WM8740 DACs to WM8741. The sound became exciting , so lively and transparent.

    And now the WM8741 are supported 192/24 and DSD64, therefore I want to change later USB interface to that module

    Last edited: Oct 27, 2017
    Mshenay, zilch0md and snellemin like this.
  6. zilch0md
    Amazing! You are taking the DB2/PB2 duo to a performance level never seen before. Congratulations on your planning and successful execution.

    I had never attempted to measure the supply voltage at the op-amps themselves, when I (incorrectly) concluded that increasing the input voltage at the jack had no audible impact. Apparently, I had made a false assumption that the battery charging circuit was limiting the supply voltage to the of-amps. I was afraid to increase the input voltage at the jack by much.

    Your DB2 mod is VERY appealing. I'm really nvious of your skills, again!

  7. snellemin
    Pretty cool mods there man. I'm interested in the 4S lipo mod and the charging within in the stock unit.
  8. zilch0md

    I could never have soldered those WM8741 pins so neatly.
  9. plutonim
    Microscope and sodering station, it's my job :wink:
    I'am listening MUSES02 and dummy buffers on the PB2 output. It's enough power for my Z5 and the sound very lively.
    Also I have Sparkoslabs SS3601 and they sounds much better but they are unstable. I'll check and fix it later when I have some time.

    I bought four batteries now and when I get them I'll make mod and tell you what to do, but you must have some soldering skills.
    Last edited: Oct 28, 2017
    snellemin likes this.
  10. snellemin
    Soldered some caps on spare dip sockets to be used with the Bursons. Sounds nicer with the 8 buffers. That 4s Lipo mod would be nice as the next step up.
  11. zilch0md
    I love seeing this stuff! :)
    Mshenay likes this.
  12. plutonim
    sparkos very nice with dummy buffers, I'm waiting MUSES03 to set it in the output :wink:
    zilch0md likes this.
  13. snellemin
    What capacitor value did you swap out the stock one from? Have you found a source for the Muses03?
  14. plutonim
    snellemin likes this.
  15. snellemin
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