DAC Schematic Review and Layout Suggestions - WM8804 and PCM5102A - diyAudio
Go Back   Home > Forums > Source & Line > Digital Line Level

Digital Line Level DACs, Digital Crossovers, Equalizers, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 13th July 2014, 02:09 AM   #1
diyAudio Member
 
df audio's Avatar
 
Join Date: May 2014
Smile DAC Schematic Review and Layout Suggestions - WM8804 and PCM5102A

The information on this first post is outdated (I've made changes)! The final details are as follows:
  • Built-in linear power supply with external transformer and pre-reg (no USB!)
  • PCM5102A DAC, WM8804 with transformer-coupled SPDIF input (coaxial)
  • Four LP5907 regulators to feed the AVDD/DVDD supplies of the chips
  • 3.5mm and RCA outputs
Schematic and layout is avaliable on later posts. I'll link to the final version here after I've tested and confirmed that the board actually works.

--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Ok, so here's my first DAC project! I've got the schematic here, but I would prefer to hear your suggestions first before actually laying it out on a PCB. The circuit is a simple one, using a Wolfson WM8804 (coaxial SPDIF input, isolated) to send I2S signals to a TI PCM5102 DAC. Regulation is provided by 2 TI LP5907s (low noise and PSRR) connected to a USB 5V supply. Most of the actual circuitry is simply from the datasheet (I don't have the skill to come up with my own.

Currently, I've seperated the digital and analog supplies using 2 regulators (it looks like the right way to go), but there have been mixed reviews on the internet about whether or not I should have seperate analog and digital grounds, or just a single flat ground plane. SMD looks like the way to go, and most likely I'll be using thru-hole for the large caps and the connectors. Everything else seems fine - but I'm concerned with the high frequency I2S signals (and special considerations) needed to avoid interference.

I'm also a bit unsure about my power supply, as there's no detailed information on the ripple and noise on a USB input. The 100uF cap there is just a guess and may not be optimal. I've also heard mixed reviews on ferrites - some people love them and stick them everywhere, others avoid them altogether. Maybe someone here can help sort this out?

While I won't name names, I've seen several posts here where some of the members have extensively revised a beginner's board to fix all their "problems". After looking at those posts, I think I have a resonable idea of what a 2-layer DAC board should look like - but before I start I think it would be best to get some ideas first...

Schematic:
Click the image to open in full size.
Download link (PDF)
Attached Files
File Type: pdf Schematic 1.pdf (40.8 KB, 20 views)

Last edited by df audio; 14th September 2014 at 07:04 PM.
  Reply With Quote
Old 16th July 2014, 03:59 PM   #2
Mull3t is offline Mull3t  United States
diyAudio Member
 
Join Date: Apr 2012
Location: Gamehendge
Looks cool. I wish I could add something other than... are you considering adding a way to access the i2s lines? or is this SPDIF only?
  Reply With Quote
Old 16th July 2014, 04:17 PM   #3
diyAudio Moderator Emeritus
 
jean-paul's Avatar
 
Join Date: Sep 2002
Location: Germany
Hi some tips:

- Your design needs beads/coils in the supply lines. People avoid parts that they don't know well and that cost extra money. Trust me, you need them.
- Use termination resistors at the right side of I2S.
- A larger electrolytic cap after the regs close to the DAC chip may be a good idea.
- Since PCM5102A has no free running external clock source possibility you could experiment with a low jitter XO for the 12 MHz (no crystal). It should not make a difference with a PLL but you could try and compare.
- You should remove the power on switch to the AC side of things as switching DC is a bad habit.
- While you are at it you could include a rectifier and large filter cap so the design will be ready for use when using a small power transformer.
- In that case make C19 a 2200 µF 16V.
- The USB connector indicates the use of a switching power supply (which are good, disclaimer etc) but a linear supply will make your design better sound wise. Just test and compare.
- Be prepared for ground loop issues if you just just a computer USB port for supplying power to this DAC.
- After having made the same decision like you on our Subbu V3 I would now include a PCB mount BNC connector straight on the PCB. No wiring !
- Same counts for RCA jacks, soldered straight to the board leaving only the power supply AC wiring to be necessary. There are some very nice quality versions available for that purpose !
- Least possible wiring as wiring does not make things better.
__________________
It's only audio. Official member of the Norske Brillegeit Gang.

Last edited by jean-paul; 16th July 2014 at 04:39 PM.
  Reply With Quote
Old 18th July 2014, 08:43 PM   #4
diyAudio Member
 
df audio's Avatar
 
Join Date: May 2014
Two things:

The problem with a high C19 is high inrush current via USB - I'm already exceeding the 100uF limit already.

What do you mean by "remove the power on switch to the AC side of things as switching DC is a bad habit"? I don't have AC at all on my board...

Thanks.
  Reply With Quote
Old 19th July 2014, 12:58 AM   #5
diyAudio Member
 
df audio's Avatar
 
Join Date: May 2014
And Mull3t, this is SPIDF only (for computer and TV). I currently don't see any point of being able to access the I2S lines unless this is a modular setup.
  Reply With Quote
Old 19th July 2014, 09:52 AM   #6
fotios is offline fotios  Greece
diyAudio Member
 
fotios's Avatar
 
Join Date: Feb 2007
Location: Δραμα - North Greece
Quote:
Originally Posted by jean-paul View Post
- Use termination resistors at the right side of I2S.
Do you mean close to DAC? Or at the "right" (see proper or suitable or...) side of I2S bus?
__________________
Best Regards FOTIS ANAGNOSTOU
  Reply With Quote
Old 19th July 2014, 10:15 AM   #7
fotios is offline fotios  Greece
diyAudio Member
 
fotios's Avatar
 
Join Date: Feb 2007
Location: Δραμα - North Greece
Quote:
Originally Posted by df audio View Post
The problem with a high C19 is high inrush current via USB - I'm already exceeding the 100uF limit already.
A current limitting resistor (1.5 to 10 Ohms) could solve the issue. Although i believe that 100uF is more than enough.
Quote:
What do you mean by "remove the power on switch to the AC side of things as switching DC is a bad habit"? I don't have AC at all on my board...
Connecting or disconnecting the USB plug is the same like the function of a DC switch. I think the switch option is OK.
__________________
Best Regards FOTIS ANAGNOSTOU
  Reply With Quote
Old 19th July 2014, 10:34 AM   #8
fotios is offline fotios  Greece
diyAudio Member
 
fotios's Avatar
 
Join Date: Feb 2007
Location: Δραμα - North Greece
Quote:
Originally Posted by jean-paul View Post
- Your design needs beads/coils in the supply lines. People avoid parts that they don't know well and that cost extra money. Trust me, you need them.
Yes, that is correct. Put two ferrite beads in series with the USB Vbus and the USB gnd (ground is a return path for noise etc.) From memory, the ferrite bead should present a resistance of 50 Ohms - at least - at the frequency of interest. Here a type for the beginning: 2512066017Y1 - FAIR-RITE 2512066017Y1 - FERRITE BEAD, 0.08OHM, 1A, 1206, FULL REEL | Newark element14 Canada
__________________
Best Regards FOTIS ANAGNOSTOU
  Reply With Quote
Old 19th July 2014, 10:47 AM   #9
diyAudio Moderator Emeritus
 
jean-paul's Avatar
 
Join Date: Sep 2002
Location: Germany
Quote:
Originally Posted by df audio View Post
Two things:

The problem with a high C19 is high inrush current via USB - I'm already exceeding the 100uF limit already.

What do you mean by "remove the power on switch to the AC side of things as switching DC is a bad habit"? I don't have AC at all on my board...

Thanks.
Hi, just design a proper mains fed linear power supply instead of feeding this DAC poisoned Volts via USB. Switch can then be at the AC side of things....Reread my post another time please. Try to make your design as good as possible as it will be more expensive than ready made Ebay stuff anyway. Quality is all in the details !

*Please also use CLC filtering to the power supply pins of chips. L may be a coil or a bead.*
__________________
It's only audio. Official member of the Norske Brillegeit Gang.

Last edited by jean-paul; 19th July 2014 at 10:53 AM.
  Reply With Quote
Old 19th July 2014, 05:49 PM   #10
fotios is offline fotios  Greece
diyAudio Member
 
fotios's Avatar
 
Join Date: Feb 2007
Location: Δραμα - North Greece
A very nice thread regarding I2S bus "termination" resistors with excellent documentation here: I2S and digital signal path - in-line resistors?
Top posts written from real scientists - experts on digital circuits and digital audio.
One of the best threads i've ever read on diyAudio.
Take a look and in schematics of WM8741 DAC evaluation board: http://www.wolfsonmicro.com/media/77...tic_layout.pdf where a WM8804 spdif transceiver - configured in hardware mode like in your circuit - is used.
__________________
Best Regards FOTIS ANAGNOSTOU

Last edited by fotios; 19th July 2014 at 06:10 PM.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
TDA1543 Anarchist DAC PCB layout. Suggestions welcome. freax Digital Line Level 17 24th August 2014 04:47 AM
SPIDF DAC with DIR9001 and PCM5102A - Questions and Suggestions df audio Digital Line Level 4 19th May 2014 12:12 AM
XMOS/PCM5102a DAC vs Modded CD63 - New DAC loses - Why? dwjames Digital Source 4 18th January 2014 07:03 AM
WTB V2.6 PCB for ES9023 / WM8804 S/PDIF DAC –SUBBU DAC grufti Swap Meet 0 26th November 2012 05:51 PM
Schematic review, Coax SPDIF receiver-DAC-Volume pot Neutrality Digital Line Level 19 10th December 2011 06:40 PM


New To Site? Need Help?

All times are GMT. The time now is 12:35 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2