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My humble Discrete DAC
My humble Discrete DAC
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Old 14th February 2019, 07:24 AM   #21
tru168 is offline tru168
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Quote:
Originally Posted by xx3stksm View Post
Nice job. I appreciate your original approach since it's unique.
I want to ask one question. Why do you use discrete R2R instead of monolithic one like TDA1541 ? If you have many troubles in selecting matched resistors, monolithic is a better solution.

I used to use pcm1704 for several years. After being obsolete, I needed to find an alternative chip or system. Discrete one was out of my sight because of difficulty to have well-matched resistors. Industrial DACs can have 16bit monotonicity ,e.g. ltc2642. I designed my R2R DAC with ltc2642. It was pretty good because I used it for two or three years. It sounded a little bit different from pcm1704 though I intended true copy sound of pcm1704. I still don't know the reason why. LTC2642 was brighter than pcm1704. I preferred a soft pcm1704 tone to ltc2642.

Is your decision based on listening(your ears) or measuring data? LTC2642 has better THD performance than pcm1704 but has a slight glitch. But glitch of ltc2642 is probably the lowest(0.5nVS) in audio application R2R DACs. I would say discrete one has a much large value at least 10 times. My hypothesis is that glitch can change sound color like enhancer in a video system. The more glitch, the more vivid. Some like sharp and clear sound while some like soft and warm one. I prefer the latter.
Hi,
I build this R2R just for fun at first place, and want to learn more about discrete R2R using normal parts and I enjoy tweaking the DAC very much. Of course , I also have a lot of others DAC using others DAC chips. I owned TDA1541 for many years, and also built PCM1704 before. All those monolithic ICs are perform really good. I did measure performance for all my DIY projects for the past few decades, and always end up by fine tune to suit my ears, and I would say, I prefer listening test, and also compare them in front of our local audiophile friends for blind test or passing around among local audiophile friends and ask them to compare and give feedback. From a Japanese audiophile friend , he said there're several similar kits appeared in your country for the past 10+ years? do you have any chance to listen to one yet?

Last edited by tru168; 14th February 2019 at 07:33 AM.
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Old 14th February 2019, 08:19 AM   #22
lcsaszar is offline lcsaszar  Hungary
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I also experimented with an R-2R discrete DAC, see attachment. It took simultaneous data from an SAA7000 (from a Marantz CD-74), but the project has never been completed. Some ideas might be useful, though. E.g. I provided a calibration facility through an internal word generator for the 8 MSBs and Bourns variable resistors. The declither also has to be worked out yet.
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Old 14th February 2019, 08:39 AM   #23
tru168 is offline tru168
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Join Date: Apr 2016
Quote:
Originally Posted by lcsaszar View Post
I also experimented with an R-2R discrete DAC, see attachment. It took simultaneous data from an SAA7000 (from a Marantz CD-74), but the project has never been completed. Some ideas might be useful, though. E.g. I provided a calibration facility through an internal word generator for the 8 MSBs and Bourns variable resistors. The declither also has to be worked out yet.
Nice. looks like my first version
keep it up and thanks for sharing !
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Old 14th February 2019, 09:08 AM   #24
xx3stksm is offline xx3stksm  Japan
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My humble Discrete DAC
Hi,tru168.
Yes, there are many DIY boards available, which include R2R and DSM, at a reasonable cost in Japan. But I prefer to design myself because I can have a free hand in my PCB, e.g. number of layers, DAC chip, and power configuration. I had been an engineer in a mixed-signal application for 20 years. So, my design tends to use a digital solution based on FPGA. That's why I usually use a monolithic chip though it's possible to employ FPGA which may have better performance than a shift register(74HC595) solution because output driver of FPGA are well-matched and have very low ringing and fast rise and fall time.

My current project is a little bit unfamiliar to DIY since it has a BGA package.
Two way DAC(multibit and DSM)from scratch with input options(SDmicro,toslink and IIS)
If you want to dive into a digital solution, BGA is hard to avoid. I need to populate 8 PCBs to have a real listening test. It's my long and winding road to the door which may lead me to heaven or hell.
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Old 14th February 2019, 09:37 AM   #25
tru168 is offline tru168
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Join Date: Apr 2016
Quote:
Originally Posted by xx3stksm View Post
Hi,tru168.
Yes, there are many DIY boards available, which include R2R and DSM, at a reasonable cost in Japan. But I prefer to design myself because I can have a free hand in my PCB, e.g. number of layers, DAC chip, and power configuration. I had been an engineer in a mixed-signal application for 20 years. So, my design tends to use a digital solution based on FPGA. That's why I usually use a monolithic chip though it's possible to employ FPGA which may have better performance than a shift register(74HC595) solution because output driver of FPGA are well-matched and have very low ringing and fast rise and fall time.

My current project is a little bit unfamiliar to DIY since it has a BGA package.
Two way DAC(multibit and DSM)from scratch with input options(SDmicro,toslink and IIS)
If you want to dive into a digital solution, BGA is hard to avoid. I need to populate 8 PCBs to have a real listening test. It's my long and winding road to the door which may lead me to heaven or hell.
Yes, indeed, DIY are more fun. BGA are hard to handle especially for a hobbyist with very limited equipments. Thanks for sharing and I'm reading your post now.
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Old 14th February 2019, 09:37 AM   #26
xx3stksm is offline xx3stksm  Japan
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My humble Discrete DAC
Quote:
Originally Posted by lcsaszar View Post
I provided a calibration facility through an internal word generator for the 8 MSBs and Bourns variable resistors. The declither also has to be worked out yet.
It's an interesting project! Internal calibration for R2R is challenging facility. I also designed some ideas at the desk but have never implemented it into a real PCB. I luckily have had another solution to do the same thing. AD9717(high-speed 14bitDAC for RF), which is my current DAC chip for audio application, has an internal calibration system though I don't know the mechanism in detail. It consists of 32banks of 512 resolution DAC. Each 512 resolution DAC has its own calibration register(probably gain control).

You can adjust the register through SPI. Recent high-speed R2R DAC employs such architecture, where distortion mainly depends on the difference between 32 banks because each 512 resolution DAC has little distortion. I guess the calibration register adjust the gain of each bank. If you can find an excellent combination, you have -100dB THD. If you are unsuccessful, you have -80dB THD. This can be regarded as super well-matched registers(0.001%) and normal -matched one(0.01%). I would say -100db THD in R2R DAC is the best score. But I'm not positive it has the difference in SQ.
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