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3.3v power to Digi+ Pro

Dom Verity

December 13, 2016 12:29

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I'm planning to provide a low-noise 3.3v regulated line to the D+Pro as per the knowledge base entry, but I'm wondering about the GND - I assume this shares the common ground with the 5v rail that powers the Pi/Digi+, so is there any need  to connect the ground to P5?

My choice is between powering my 3.3v LDO from the same 5v LPSU that I'm using on the Pi, or having a second 5v LPSU just to power the 3.3v reg (albeit taking mains AC from same tranformer). If I do the latter, I have two grounds in play, I'm not sure what the implication of that would be... Any ideas?

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38 comments

• 0
  
  HiFiBerry team December 13, 2016 14:58

  Hi,

  in general, all potentials are in respect to a given ground potential. If you use separate power supplies, GND has to be connected for both. 

  Best regards,
  Daniel

• 0
  
  Dom Verity December 13, 2016 21:08

  Thanks Daniel, I just wanted to sanity-check. I have some work to do to get the other power supply running and source the regulator, but I'll post the results when I get it running.

  Cheers, Dom

• 0
  
  Dom Verity January 01, 2017 19:41

  Here it is, my Digi+ Pro with BNC and indepedent LPSUs for 5v and 3.3v (amb sigma11 circuits). The casework is a bit rough, but hey, I'm a software guy ;) It's feeding a Schiit Gungnir Multibit via PiCorePlayer - very impressed with the sound so far!

  
   

• 0
  
  michael vogt February 10, 2017 08:04

  hello,

  i also want to try your setting here:-)

  is this a digi+pro rev 1.2?

  have you unsoldered r3?

  and have you cut/bend any of the gpio pins on the raspy?

  i ask because some people in this forum say this doesn´t work with rev 1.2 anymore...

  but you made it:-)

  thank you for your answer.

  michael

• 0
  
  Dom Verity February 10, 2017 18:37

  Hi Michael, let me answer your questions:

   

  is this a digi+pro rev 1.2?

  -- yes

  have you unsoldered r3?

  -- yes

  and have you cut/bend any of the gpio pins on the raspy?

  -- no, why would this be necessary?

  Best,

  Dom

• 0
  
  michael vogt February 11, 2017 07:58

  hello dom,
  thank you for your help!
  i read the gpio problem here in this forum, but now i think sergey could be wrong.
  a last question: is the bnc port input you soltered the one of hifiberrys online shop or which one you have got?
  thank you again:-)
  michael

  "Bugaev Sergey January 30, 2017 02:09
  so i will comment myself )

  REV 1.2 uses +3.3V from RPI only for eprom U3 (autoconfig, HAT compatibility etc)

  +5V needed only for toslink

  +3.3V for wolfson 8804 generated by LDO U2 from +5V header P3

  so external +3.3V feature is really questionable, and will not work as advertised here in forum by Hifiberry

  if you remove the zero ohm resistor R3 it will only disable the eprom but with +5V still connected (from RPi) there will be two sources of +3.3V one is onboard LDO and the second is your external +3.3V form P5 - bad picture (("

• 0
  
  Dom Verity February 11, 2017 13:07

  Hi Michael,

  It is indeed the BNC connector from hifiberry, though I'm sure others would be fine.

  I just followed the instructions for doing the 3.3v mod, but having looked at the board more closely, I wonder whether Sergey is right. I've asked hifiberry for clarification, I'll post back if I get anything.

  Dom

   

• 0
  
  michael vogt February 12, 2017 21:26

  hello dom,
  may i ask you which psu's you have used in your setting. fine audiophile parts
  i see here:-)
  thank you !
  michael

• 0
  
  Dom Verity February 13, 2017 11:19

  Daniel @ Hifiberry confirmed to me that the LDO needs removing, I will do this in the next few days.

  The PSUs are AMB sigma11 circuits http://www.amb.org/audio/sigma11/ - I tend to use good quality parts but I've not deliberately used 'audiophile' parts as such, there may be some Nichicon Muse electrolytics on there, but only because that's what I had lying around from an previous amplifier build, I'm not convinced that fancy parts would make an audible difference here.

• 0
  
  michael vogt February 13, 2017 12:17

  hi dom
  thank you for the link:-))
  would you send me a picture/description which ldo you've removed, when it's done?

  michael

• 0
  
  Dom Verity February 14, 2017 19:48

  Here is the board with the LDO at U2 (just beneath the P5 header) removed, works great:

   

  

• 0
  
  michael vogt February 14, 2017 21:57

  hi dom
  thank you again !!!
  i'll try your setting!
  p5 uses 3.3 v (plus is pink)?
  p3 uses 5v and feeds the raspberry also thru the gpio's?
  thats right?
  michael

• 0
  
  Dom Verity February 14, 2017 22:11

  Hi Michael, all your statements are correct, yes. Good luck! Dom

• 0
  
  dankam77 February 15, 2017 11:19

  What hapens when:

  - I conected 3,3V to the p5 and 5V to the P3 but leave U2 LDO?

  WM8804 and clock are be powered by U2 LDO from P5?

   -  I conected 3,3V to the p5 and 5V to the P3 and unsolder U2 LDO?

  WM8804 and clock are be powered by 3,3V from P3?

• 0
  
  Jim White March 03, 2017 07:54

  Hi Dom

      I'm a sw guys, too. I just learned how to solder these months, and I soldered a linear  regular power on my digi+pro on P3(5V) few days ago. It does improve the sound after I soldered it. Now I wanna try your way, it's interested to me! 

  What should I do next ? Should I remove the regular power first? Seems it still connect to an external power on P3(5V) 
  
  1. unsoldered r3
  2. unsoldered U2
  3. an external linear regulated power supply to P5(3.3v)
  4. an external linear regulated power supply to P3(5v)

  Anything else?

   

• 0
  
  Jim White March 03, 2017 08:00

  This link doesn't mention unsoldered U2? what does it effect?
  https://support.hifiberry.com/hc/en-us/articles/213227645-Digi-Pro-power-separately-from-the-Raspberry-Pi

• 0
  
  Dom Verity March 03, 2017 21:43

  Hi Jim,

  I'm not sure why the hifiberry page hasn't been updated with the information about U2, which is a 3.3V voltage regulator (so-called LDO)

  I believe that older versions of the board used the 3.3V supply from the RaspberryPi GPIO (which has it's own 3.3V regulation, but probably pretty noisy), whereas this newer version takes the 5V supply and puts it through U2, which, in theory, provides a cleaner 3.3V supply, so for normal use, I'm sure this is an improvement.

  For our purposes, if we just supply our 3.3V to the P5 header with U2 in place, the power going to the WM8804 is our 3.3V volt rail in parallel with the 3.3V from the LDO . So that we are powering the chip purely from our linear power supply, U2 must be removed.

  Best, Dom

• 0
  
  Scott Kramer March 04, 2017 00:36

  Maybe Daniel chickened out & thought there'd be too many pop'd digi's after everyone put 5V on the 3V ;D But yeah, probably big improvement for people just dropping it in and keeping it stock!

  Edited by Scott Kramer March 04, 2017 01:02
• 0
  
  Jim White March 04, 2017 00:41

  Thank you for answering me so clearly!
  
  So these four steps only, right?

  1. unsoldered r3
  2. unsoldered U2
  3. an external linear regulated power supply to P5(3.3v)
  4. an external linear regulated power supply to P3(5v)

• 0
  
  Dom Verity March 05, 2017 13:16

  @Scott it would have helped if P3 were the 3v one and P5 were the 5v one ;) I wrote on the board and my connectors with a sharpie to avoid this mistake.

   

  @Jim That's what I did!

• 0
  
  julien gueib March 05, 2017 16:43

  Hi guys,

  Shouldn't R3 be taken out even if you don't use an external LPS? The way the board ships, it gets 3.3V from GPIO AND from the 5V attached LDO.

   

  Edit: took it out... sound isn't worse ;)

  Edited by julien gueib March 05, 2017 17:19
• 0
  
  Jim White March 06, 2017 07:13

  Hi Dom
      If I use RCA for my output only, will these settings still improve quality for me?

  Edited by Jim White March 06, 2017 07:13
• 0
  
  Dom Verity March 06, 2017 16:48

  Hi Jim,

  Which settings are you referring to?

• 0
  
  Jim White March 07, 2017 01:24

  Hi Dom

      Well, the settings just like you do~ I want to try it! but I am not sure if these will improve the quality for RCA output

  1. unsoldered r3
  2. unsoldered U2
  3. an external linear regulated power supply to P5(3.3v)
  4. an external linear regulated power supply to P3(5v)

  Are these for BNC or TOSLINK only?

• 0
  
  Dom Verity March 07, 2017 20:32

  Jim,

  The SPDIF signal in all cases comes from the same circuit (WM8804, clocks etc) powered by the 3.3v. The TOSLINK transceiver is powered by 5v, as is the Pi itself, which you needn't power via the USB port if you apply 5v to P3.  

  Assuming the power you provide is cleaner than what the stock board had to begin with, and assuming that power supply noise is a major contributor to distortion of the output signal (i.e. the distortion is not dominated by some other effect like clock jitter) then in theory, the better power should be an improvement. Will that improve be audible? Only you can answer that I'm afraid!

  Dom

• 0
  
  Jim White March 08, 2017 00:53

  Hi Dom

      I got it! Thank you for always answering me so nicely. Thanks!!

• 0
  
  Paul Kavsek March 20, 2017 15:28

  Hi, thank you for this discussion and posts, after some research this made most things clear to me. 

  I have now a D+Pro system running with no changes to it so far. I made listening tests between optical and cinch output.

  I prefer the cinch, so I am thinking of giving there an extra 3.3V PSU

   

  My question is, if I am not using the TOSLINK at all, can/shall I stay with the standard 5V PSU on the Pi?

  Or shall I also replace the 5V as Dom described in his circuit

  Paul

• 0
  
  HiFiBerry team March 21, 2017 05:46

  You can ALWAYS stay with the standard power supply. I see a lot of people trying to upgrade the power supply. Note that we already saw cases in which people have damaged their boards. There is strictly no warranty for modified boards. BTW: The Digi+ Pro already uses an onboard linear power supply.

  Back to your question: If you don't use TOSLink, 5V are not needed. 

  Best regards,
  Daniel

• 0
  
  Jim White April 10, 2017 05:34

  Hi All

      If I don't use TOSLINK, could my steps be simpler? no need to solder P3?

  1. unsoldered r3
  2. unsoldered U2
  3. an external linear regulated power supply to P5(3.3v)
  4. an external linear regulated power supply to P3(5v)

• 0
  
  Ricky Terzis July 18, 2017 18:33

  Hi..i am a new user here. As per my knowledge all potentials are in respect to a given ground potential. If you use separate power supplies, GND has to be connected for both. Also the Digi+ Pro already uses an onboard linear power supply.

  Edited by Ricky Terzis September 01, 2017 20:05