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lingDAC - cost effective RBCD multibit DAC design
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Old 12th July 2018, 05:08 AM   #1
abraxalito is online now abraxalito  United Kingdom
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Default lingDAC - cost effective RBCD multibit DAC design

Update, October 2019

This thread was originally created to talk about lingDAC which is a stack of four 5*5cm PCBs comprising a multibit DAC based on two TDA1387s which is able to drive some moderate impedance headphones directly with up to 2VRMS output. The fourth (power supply) board isn't shown an an early picture nor in the earliest BOM, it was added during the course of the thread.

Prior to the establishment of the thread, a few 1st generation lingDACs (v1, the first generation having just 3 PCBs in the stack) were sent out to interested parties for listening reports.

LingDAC has at least one feature which make it a bit hard to DIY, especially for those with little experience. That being the filter requires fairly accurate inductors which necessitates an inductance meter being used to select 'good' ones from a batch. Or the filter's capacitors can be tweaked in value to match a slightly off-value inductor, this calls for simulation skills in Spice and a capacitance meter, again not really amenable to beginners. Because of this major drawback I decided to create a design more suitable as a starter DAC, this being called 'PhiDAC'. PhiDAC is introduced in post #126, December 2018 : lingDAC - cost effective RBCD multibit DAC design

PhiDAC has a much simpler single stage filter based on a large number of MLC inductors and only occupies a single PCB, 8*5cm. Instead of discrete transistors it uses AD8017 CFB opamps for its active circuitry. It calls for a single rail PSU of 9V-12V. This is a DAC rather than a DAC-AMP, its not designed to drive cans. PhiDAC was designed with components cheaply available on Taobao and hit a BOM cost just below $3 - some packs of ten kits were sold to interested builders.

The last design, PhiDAC SE rectifies this last weakness - its essentially the same circuitry as PhiDAC but using AD815s in place of AD8017s. The greater thermal capacity of AD815s means a much bigger physical package so the PCB size grew to 6*10cm and needs a single supply of 12-15V. The board doesn't contain the necessary electrolytic decouplers, they are mounted beneath on smaller auxiliary PCBs called 'pants' (opposite of 'hats'). PhiDAC SE hasn't had a complete release of all manufacturing information nor have I costed it but I'd guess it would come in around $5 with Taobao-sourced components. Here's a link to where I formally introduce it : lingDAC - cost effective RBCD multibit DAC design


Towards the end of the thread I'm doing experiments on using multiple paralleled DACs (given they're so cheap it seems an obvious route to explore) and eventually settle on a way to exploit them successfully - but the gory details of that journey will go into another thread. I'll include the link here when that thread's opened : Grossly parallel multibit DAC adventures


Original post, July 2018

I've been working on DAC designs using TDA1387 for several years now, both in helping modify existing designs and coming up with my own solutions.

'lingDAC' has satisfied me in listening to such an extent that I feel its worth sharing the whole design here as I feel I'm close to reaching the end of the road with what's possible when beginning with the TDA1387 (famous last words!).

A few bullet points to introduce this DAC :
  1. designed for Red Book CD source material hence 16bits and 44k1
  2. no-oversampling design means no digital filter is used
  3. a steep analog filter is used instead of the digital filter to kill images
  4. the design is aimed at reaching the best SQ, not best measurements
  5. lowest possible BOM cost commensurate with still sounding good
  6. designed as a board stack for maximum DIY flexibility, boards are 5*5cm

I need to tidy up the schematics before posting them, I'll add them to this post as they're rendered presentable.


Returning later I see I'm told I'm unable to add attachments to this post so guess new info will go into subsequent posts.

@kokoriantz has collected together pdfs of schematics - for lingDAC here (3 boards) : lingDAC - cost effective RBCD multibit DAC design and for PhiDAC (single board), here : lingDAC - cost effective RBCD multibit DAC design
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Last edited by abraxalito; 12th October 2019 at 06:20 AM.
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Old 12th July 2018, 09:58 AM   #2
DRONE7 is offline DRONE7  New Zealand
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Old 12th July 2018, 10:25 AM   #3
abraxalito is online now abraxalito  United Kingdom
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Here are the three boards required to build a lingDAC - from the left the DAC, filter-I/V and buffer stages. A fourth board for power supply is in the works, the aim being to be able to run from a very cheap USB 5V wallwart. For now the first two boards need a 9V supply and the third, 7V.
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Old 12th July 2018, 01:51 PM   #4
BesPav is offline BesPav  Russian Federation
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Please, let us know analog filter order and approximation function.
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Old 12th July 2018, 02:38 PM   #5
abraxalito is online now abraxalito  United Kingdom
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The order of the analog anti-imaging filter is 5 - that is two inductors in series positions and three capacitors in shunt. Its not a standard textbook function, rather somewhere between Chebyshev type 1 and Cauer (Elliptic).
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Old 12th July 2018, 03:53 PM   #6
rickmcinnis is offline rickmcinnis  United States
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I have been wanting to return to digital but not wanting to spend a fortune.

ABRAXALITO is always a step or to ahead so I want to build one of these.

Looking forward to your revelations!
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Old 12th July 2018, 04:02 PM   #7
randytsuch is offline randytsuch
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lingDAC - cost effective RBCD multibit DAC design
I was very fortunate as Abraxalito sent me one of his first lingDACs a couple of months ago.

I have been slow to try it out (Sorry Abrax), but am getting close now. Real life and laziness have slowed progress :/

I received the three main boards, and have put together a power supply using three lifepo4 batteries. Power supply is about 90% finished, just need to actually hook up the batteries to it now, but it does have three working 3.3V regs.

So PS will output 10V, and then Abrax included diodes on my power input to drop it down to around 8V to power the three boards.

Lately have been making some changes to my digital playback system which has a soekris r2r dac, the original 1021 with a bunch of mods mostly related to power.
Been spending some time listening to it as my baseline.

Hoping to hook up the lingDAC this weekend, then will let it break in some and then compare to my soekris.

Randy
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Old 12th July 2018, 05:07 PM   #8
sumotan is offline sumotan  Indonesia
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Congrats Abrax,
Im an old man, soldering those smd parts is going to kill me. Lol
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Old 12th July 2018, 06:01 PM   #9
wcwc is offline wcwc  United States
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Looks interesting.
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Old 12th July 2018, 06:50 PM   #10
rickmcinnis is offline rickmcinnis  United States
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Quote:
Originally Posted by sumotan View Post
Congrats Abrax,
Im an old man, soldering those smd parts is going to kill me. Lol
I am hoping he might find a way to offer populated boards!!!

(thanks for your note sumotan - still trying to figure out which way to go - but have long wanted to try something from the mind of abraxalito)
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