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Raspberry Pi-Fi sound cards modifications PCM5102 PCM5122

I tried several of the hifi sound cards for raspberry pi, none of them are designed correctly, result poor audio quality
this can be fixed quite easy so you can enjoy the full featured high definition DAC

ORIGINAL, PIFI 1.0 for a pi1, but here connected to a PI3
this one uses PCM5102 DAC chip
Many P1FI and similar DAC boards use a little 10 by 5 mm switchmode module it is called mornsun B0505S
the circuit : it takes in 5V and make 5V again, now with tons of hispeed ripple, then a little sot23 3.3V regulator works overtime
to make a usefull supply for the dac, the ground from PI is broken hi-frequency wise with a ferite bead called R8 on pifi 1.00
this means the ripple currents from the switchmode converter, generate voltages peaks over the ferite,
and since this is ground split, it is perfectly the same as adding this 1V noise directly to clock data latch signals !!
The solution :
brake off the mornsun converter, burn it, blow it up, what ever you feel like, (i am not going to say fully here what I plan to do with mine)
once removed, under it you find pads for shorting in and out, pin 2 and 4,
then short the ferite bead, or remove it, add a short wire, now enjoy perfect stable audio !
and see your DAC board got a perfect clean VCC and also nothing is added to the clock data latch signals.
and more cool, you can poke arroind with clock data latch as much as you like now, it will not harm audio
since perfect margin is restored.
OMG what a terrible day.. good it is over now..

here are all my error fixes and improvements together:
M1 switchmode module REMOVE, under it, add 1 ohm resistor, in-out
M1 output pins, ADD 220uF 10V electrolyte (local 5V input to the 3.3V regulator is now super clean)
R8 FERITE BEAD, ground problem, remove, ADD 0 ohm WIRE instead
R21 for IR-remote , remove no need to feed clean voltage to stuff we dont need.
B1 ferite bead smd in series with 3.3v regulator, remove, add 0 ohm instead, the regulator perform better when it can "see" the output.
C1 smd cap input 5V side to ground plane !! REMOVE IT, no need to feed input side noise directly to our nice audio ground.
C20 tantal cap, remove, useless part, all they give is bad MTBF
C9 10uF cap left side, remove, add 220uF 10V instead.
more info : the 1 ohm resistor in series with input, drop is 37mV so we know the whole board draw 37mA

all noise on 5V input, go directly to ground plane of DAC board, AND all noise from DC/DC module in-out difference,
is added directly to digital input signals due to R8 ferite bead !! VERY BAD DESIGN.. but easy to repair.

any noise from 5V input, can not go into the ground plane of DAC board due to the 1R resistor

PIFI version 2.0 same problem to fix

this one uses PCM5122 DAC chip
REMOVE the DC/DC converter it is USELESS, all it do is add noise to your dc supply.
REMOVE the ferite called R8, ADD shortcircuit
ADD tiny resistor from DC/DC converter input to output footprint under the say FB2,
I used 1 ohm, but any value 1-5 ohms will be fine.
change C9 from 10uF to 220uF (voltage rating is not important 10-16-25-50V what ever)
I also added 220uF on the DC/DC module output pads (suck holes clean first) this way 5V in, is now super clean.
REMOVE C1 (you dont want to couple input dc ripple current into audio board ground)
REMOVE C20 (add bad MTBF and is useless)
DO this even if you hear no clicks or noise.

clear info on resistor and capacitor location.

ALL pifi modules using switchmode and ground path ferite as shown here, NEED the fixes explained on this page.


2016-2017 Thomas Scherrer OZ2CPU
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