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Another B4 Thread

Discussion in 'd.i.y.' started by keithsnaim, Jan 27, 2012.

  1. Colinb

    Colinb pfm Member

    I will take 4 please

    Thanks

    Colin
     
  2. DuncanF

    DuncanF pfm Member

    Please send me an e-mail.
     
  3. DuncanF

    DuncanF pfm Member

    Guys, I've moved all details of the group buy to it's own thread. Please only post queries on that thread.
     
  4. Suffolk Tony

    Suffolk Tony pfm Member

    Many thanks Duncan.
     
  5. PigletsDad

    PigletsDad pfm Member

    Not having a NAP, I can't say myself, but I would expect the turn-on and turn-off thump to be small.

    Of course, best practice is always to turn the power amp on last, and turn it off first.
     
  6. mudlark

    mudlark nearly half a clue

    Hi binne,

    I've got a b4 into a nap140. There's a bit of a minor thump when turning the lot on with the wall socket switch. Nothing alarming.

    Pulling the power sulead to the b4 no noise. Plugging it the B4 after the 140 on slight thump, but muted. However, my build has the pots in to reduce the DC offset to a minimum.(R3 R104) See parts list.(BOM) I'm guessing, but a low DC offset would reduce any thump. (Please correct this if I am wrong)

    Mike
     
  7. keithsnaim

    keithsnaim Gone Fishing

    Thanks for the info Mudlark. Just got 2 of the boards from Quasarelectronics. Could they be improved by using Hexfred's instead of the 1N5401 diodes?.

    Regards Keith
     
  8. mudlark

    mudlark nearly half a clue

    Heaven knows. You will have to ask a clever /knowledgeable person about that. When I built mine I asked if the board was Ok. It is way over specced as they are designed for power amplifiers. Power supply noise rejection is good and if using the on board regulators again I have had comments that they are fine.

    ESP audio say that fast diodes aren't needed in 50Hz power supplies.

    If you want to go better than the boards then it's ask specific questions of those with super ears rather than me.
     
  9. keithsnaim

    keithsnaim Gone Fishing

    I am waiting for the Hackercap group buy Pcb's to appear. Carl recommends the use of Qspeed/Hexfred diodes in the build. Just wondered if they could be used in one of these boards too.
    I was thinking about the 6A or 8A version. RS stock these too.
     
  10. mudlark

    mudlark nearly half a clue

    I don't know, but the hacker is a power amp and the B4 draws little power. having said that I am going to try a Qspeed power supply with my headphone amplifier B4.
     
  11. keithsnaim

    keithsnaim Gone Fishing

    Thats true, Carl informed me that it would be suitable for the B4 using low current Qspeeds because they are quieter.

    By the way , the B4 sounds superb in its present form using a salvaged power supply from an old stack system so it can only get better.
     
  12. binnie

    binnie Binnie

    Thanks PigletsDad and Mike for your answers :)
     
  13. cromodora

    cromodora foshfishfie

    I'm finally getting round to stuffing the B4 board and am wondering the following:-

    1. Is R3 meant for a variable resistor?
    2. Has anyone put a volume pot at the output instead of the input of a buffer?
     
  14. PigletsDad

    PigletsDad pfm Member

    Yes, R3 is a trimmer, for adjusting offset to zero, if you don't use output capacitors.

    Volume control after B4 is not ideal - the whole point is to give consist drive conditions from variable resistance of the volume control. I suppose if you had some ancient source device that couldn't drive the volume pot, it might make sense to buffer before the pot, but any even vaguely modern source has no problem.
     
  15. cromodora

    cromodora foshfishfie

    Thank you for replying PD.

    What I'd like to do is put together a phono preamp with volume control and using the B4 as buffer after the phonostage. Attenuator will be a Dantimax relays-and-resistors type set to 10Kohm input impedance.

    This is what Nelson Pass said about building his B1 buffer.

    If you put a buffer in front of a volume control, the control’s low impedance looks like high impedance. If you put a buffer after a volume control, it makes the output impedance much lower. You can put buffers before and after a volume control if you want.


    Wouldn't it be better for SNR to have the full output of the phonostage sent to the buffer and then attenuate betore sending it out to the poweramp?
     
  16. PigletsDad

    PigletsDad pfm Member

    Which phono stage? Most will drive the 10K attenuator without any problem. SNR is not a big issue as the noise from the front of the phono stage completely dominates.
     
  17. cromodora

    cromodora foshfishfie

    Its the Phonoclone.
    What would be the drawback putting attenuation last in such a chain?
     
  18. PigletsDad

    PigletsDad pfm Member

    The output impedance varies with attenuation. Putting the buffer after the attenuator fixes that.

    Phonoclone is op-amp based, and will drive the attenuator without problem. Putting buffer between it and the attenuator will have no benefit.
     
  19. cromodora

    cromodora foshfishfie

    Thanks for the explanation, PD.
     

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