Tuesday, December 15, 2020

nos TDA1541 tube DAC


I've become cynical of the latest is best mentality because in my 30 years of searching for sound that pleases my ears, I've always gone back to move forward. From this experience, I've learned to use planned obsolescence to my advantage by investing in old school components that have achieved classic status.

 There is a common denominator between the Philips TDA1541 DAC chip and the Western Electric 300B directly heated output triode vacuum tube. The former brought digital sound to everyone’s homes in the '80s, while the latter amplified talking pictures in movie theaters in the '30s. Both have also been rediscovered for their distinguished musical abilities.

This tubed TDA1541 sans oversampling multi-bit DAC evolved from my frustration with its bitstream and delta-sigma successors, revisiting and studying multi-bit CD players and DACs, performing Magnavox CDP + DAC mods, and other digital audio experiments.

!!!WARNING!!! 

The voltages in this circuit are potentially lethal! Build at your own risk!

If you are a metrics-obsessed audiophile who spends more time arguing in audio forums instead of listening to music because you can't trust your own ears and would rather buy a component approved by a hifi guru and/or his/her test equipment, STOP 🚫! You'll be offended by the contents of this blog, especially this project!

However, if you agree with Radiotron Designer's Handbook, 3rd edition published in 1940, that the THD metric should be abolished and better test procedures and standards established, you may proceed.😊

This project starts with the deconstruction of an already obsolete DAC board still available from eBay sellers. Since the TDA1541 chip has been out of production for over 20 years, I scavenge them from the CD player graveyard.


I incapacitated the analog section of the DAC board by removing the high speed/fast slew rate op-amps and low ESR signal capacitors, which will be replaced by a slower and harmonically more satisfying circuit from a bygone era. 

Non Over Sampling (NOS) measures like a broken component but my ears prefer musicality over accuracy, so the SA7220P chip was tossed and the circuitry bypassed. Speaking of accuracy, to what? I wasn't at the recording session, so I don't obsess about it.πŸ˜‰


This picture shows the spots where I tapped the right (AOR 6) and left (AOL 25) analog outputs of the TDA1541 chip. The DAC's delicate and jagged left and right analog output stream will be connected via shielded cable to a cutting edge I/V converter + vacuum tube smoothing circuit advertised and marketed by savvy Mad Men as retro-tech art.😎


I was very impressed by the sonic flavor introduced by the Western Electric 396A/2C51 in the buffer section of my 21st century Xiang Sheng DAC 01A. But in this particular application - gain stage + buffer -  the WE396A couldn't deliver the Carnegie Hall and Village Vanguard atmosphere I was trying to recreate. Caveat: the yellow WE logo doesn't offer a 100% satisfaction guarantee. 


So I rewired the B9A 9-pin sockets for a pair of 6CG7s, which I've already used successfully as a buffer for my TDA1543 DAC. These are the Noval-based equivalents of my favorite medium gain (mu)/medium transconductance (gm) 6SN7 octals, esteemed for their linearity as an audio amplifier. 

The circuit topology is very similar to my line stage preamp with the first triode section configured as a gain stage direct coupled to the second triode section wired as a low impedance cathode follower/buffer. No negative feedback is applied in the circuit to maintain signal purity. This tube circuit also functions as a sound processor, which is beyond the abilities of fast slew rate op-amps.πŸ˜„


I recycled a power transformer from a Heathkit mono FM tuner. Using a 6X4 tube rectifier, the rectified 480VCT  @ 60mA secondary feeds a capacitor input filter, then the B+ rail is split via 2 x 15H @ 30mA chokes to provide 295 volts of ripple free DC to each channel. The 6 volt DC supply, which lights up the 6CG7 filaments, is provided by a separate filament transformer. This archaic method of building a power supply enhances the DAC's tonal character!


Finally, I assembled the Back to the Future DAC on an organic 3/4" thick Baltic-Birch bread board. Even if it has a USB input, DSD, MQA and other so-called Hi-Res files are downsampled to 16-bit/44.1kHz PCM. That makes it 100% compatible with at least 90% of music streamed on the web. Since it makes my two-for-a-buck 4.75” silver discs from thrift stores and flea markets come to life, I don't ask for more.

Let's have some chips...



The reputation of this ubiquitous DAC chip was built upon regular production run TDA1541s, which can still be acquired for under $50. BTW, this is a DEM (Dynamic Element Matching - see TDA1541 FAQs) chip, not an R2R ladder DAC chip, as it's commonly misidentified. 

So there's no reason for angst if hand-selected and tested single and double crown S1 and S2 TDA1541A chips command SothΔ“By's prices or reside in private audio museums in Asia. Buyers should actually beware of high dollar re-stenciled regular TDA1541s studded with crowns. They will work but won't sound any better than the chip I meticulously unsoldered from an '80s junked Magnavox CDP.

1kHz square wave from Stereophile Test CD3
Stock Magnavox CDB560 CD player

Fortunately, I got a chance to sample a genuine single crown S1 graciously donated by Gary B. This select chip made my DAC sound a bit more transparent and cleaner, with a touch more detail and resolution. But I have to reaffirm that not having an S1 isn't a deal breaker. In fact, the darker and warmer sounding regular TDA1541s and TDA1541As can be a blessing in systems that are a bit hot in the top end. 

1 kHz square wave from Stereophile Test CD3
nosTDA1541tube DAC

 Not very relevant to this NOS DAC project, but AFAIK, the only difference between TDA1541A and the non-A is that the A can do 8x oversampling while the non-A is limited to 4x. But let's not go there anymore. Been there, done that...


NOS and Digital Filters


Before I even became aware of NOS DACs, I had been using line transformers as digital sound processors. If you're worried about non-oversampled digital artifacts destroying the irreplaceable diaphragms of your Altec 3000 super tweeters, look for bandwidth limited military surplus transformers. 



But the true analog-sounding line transformers JE Labs uses are those that have a flat response from 30 to 15,000 cycles, like the bokeh'ed pair of Western Electric 111C repeat coils and the UTC A-20s in front. There are so many sleepers out there branded with more letters and numbers, so don't limit yourself to UTC or WE.

My Analog Distortion Generating DAC



I’m happy to report that this repurposed '80s state-of-the-art digital music maker using Mid-Century Modern era devices and sensibilities has been fulfilling my analog-biased musical expectations at the end of this second decade of the 21st century. The DAC bread board doesn't exactly match the LeCorb and Mies aesthetics of my man cave, but I've been enjoying digital encoded music like never before, such that I can't get myself to rebuild it on a nicer chassis.

Many thanks to Gary Bronner and Pete Boser for their contributions to the JE Labs digital audio museum, as well as to the patrons of this blog!


πŸŽ„Happy listening and have a great holiday season!πŸŽ„





2020 Uploads

47 comments:

  1. Yes to NOS DACs! But you knew that already! Happy holidays, Joseph.

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  2. Hello Wonderful DAC. Thank you for sharing. I enjoyed reading your post about this DAC . I like your philosophy behind it and the joy you derive from listening music. I would like to build this. I am relatively new in DIY . Currently I built a Audio Note Kit ANK DAC 4.1 . But I am not happy with the sound of AD1865N. Recently I heard at a friend TDA1541A in Nos mode and I liked the sound. But I like tube output and your post is like a dream come true.
    Is it possible to share the circuit diagram for tube output satge and the rectifier tube?
    Also is it possible to share how you bypassed the SAA7220 oversampling? I see you have connected three wires on the pictures. I will be very thankful if you can help me on this.
    Best Regards
    Vinay

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    Replies
    1. Hi Vinay,

      I've provided detailed information to build this DAC and gave credit to my reference sources. However, if you aren't a seasoned DIYer, I don't recommend that you embark on this project. That's the reason for the WARNING above in BOLD RED LETTERS!

      Thanks for visiting!

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    2. Hi JE,
      Thank you for your answer. Yesterday I was reading again ad again your TDA1541A post. And it answered all my questions regarding the tube stage and many others. You have shared everything and for a DIYer all the details are there. Thank you.
      I am not so new because last year I built WE91 300B Mono blocks based on Joe Roberts article. During this build I was very much helped by Angela Instruments Kit pictures and now I see that you are somehow connected with Angela Instruments. From there also I bought some parts for my 300B project. I live in Bulgaria and it is a joy to read your articles about audio equipment. I will embark on this project but I will keep your warning in my mind.I already found a eBay seller who has this PCB of TDA1541A but now it comes in blue color. Thanks again for sharing.
      Vinay

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    3. If you've successfully built J-Rob's WE91 amp from SP1, you shouldn't have any problems building this DAC. Yes, the DAC PCB is now blue. I recommend buying a pre-stuffed board since the price difference is minimal.

      Thank you for the kind remarks about the blog. It's all about the music!

      Happy listening!

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  3. Thank you for your recommendation of buying a pre-stuffed board.

    I was studying the DAC breadboard and I see the ground scheme is similar to Angela kits on solder Tags. I used this scheme on WE91 and is very successful.
    One small question,if you don't mind I see a green resistor/capacitor? after 33uF 450V capacitor.
    Is it bleeder resistor?

    I have marked it with red green arrow in this pic.
    https://i.imgur.com/Eg5gT2W.jpg
    Thank you.

    Have a nice day.

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    Replies
    1. That R/C combination was part of a voltage divider to lift the filament supply about 40V above ground for the 2C51/WE396A circuit. It's disconnected and is acting as a bleeder as you surmised.

      A bleeder resistor to discharge the HT caps is always a good idea for safety: 100K-200K/2W MO or WW.

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  4. Hi JE,
    One more question, about the filament power supply , In the circuit diagram posted above , the 6CG7 filament supply is from main Heath 54-34, but in your description of the power supply you write " The 6 volt DC supply, which lights up the 6CG7 filaments, is provided by a separate filament transformer." Can you please help me here? I am starting to build this DAC and I ordered the PCB and today I ordered power transformers and chokes.
    Thanking you.
    Best Regards
    Vinay

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    Replies
    1. The Heath 54-34 6.3V filament taps light up the 6X4 rectifier. I used a separate 6.3V @ 2A filament transformer for the DC filaments. That way both transformers are running cool.

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    2. Btw, thanks for the donation, much appreciated!πŸ™πŸ»

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  5. Hi JE,
    You are welcome.
    I was studying the both circuits and I redrew the power supply , is this correct because in your diagram you show the 6CG7 filament supply from Heath Transformer?
    Here is link to my drawing
    https://i.imgur.com/E2AggKz.png

    I have started ordering all the parts and I have some questions if you don't mind.
    1. Does the 90 Ohm 1/2 watts resistor needs to be special like Audio Note Tantalum or Caddok? I am not able to find exact 90 , is 90R1 Ok?
    2. I see the 1/2 6CG7 has 2 V at cathode and then it becomes 82V and that is fed to grid 2 of other 1/2 6CG7. Then it is amplified to 88V. Am I right? What is the output voltage at the final output RCA?
    3. In 6CG7 pin out where the 9th Pin( shield ) is connected? Another question when I started to buy 6CG7 , another tube 6FQ7 is shown as similar, is this tube direct substitute? I read that it has no screen. Which 6CG/ do you recommend or your favorite?
    I am getting here some Westinghouse black plates and Sylvania silver plates.
    Another synchronicity happened , you mention that you bought a NOS mod board for SAA7220 from Bulgaria, I live in Bulgaria and I bought a DAC from the same guy and he offred me such a mod for $25. But I will use your simpler mod with 3 wires.
    Hope you don't mind my so many questions.
    Thanking you
    Have a musical day.
    Best Regards
    Vinay

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  6. Hi Vinay,

    Resistors - I prefer Allen-Bradley or Riken carbon composition in audio circuits. If I can't find the values in carbon comp, I settle for carbon film.

    Coupling Caps - since the 90s, I've only used paper in oil caps - Vitamin Qs and Russian K40y/42y or US military surplus I can get my hands on at radio shows/hamfests. Jensen copper foil in oil sounded great but they get leaky over time, that's why I stopped using them.

    Basically I summarized what I wrote 20 years ago: http://jelabsarch.blogspot.com/2012/06/je-labs-shop-talk.html

    The under chassis and bread board pics of my projects for the past 10-20 years will show how the parts I use have become less tweaky. ;)

    I'm also not the person to talk to about tube rolling because I've learned that operating points make more difference than tubes from different manufacturers. Truth be told, I don't have any NOS 6CG7/6FQ7s at all! I used/test good tubes I acquired at radio swap meets for this particular project.

    Tweaking operating points and circuits is what I indulge in nowadays. Once I'm happy with the sound, I listen and enjoy LOTs of music!

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  7. Hi Vinay,

    I had a long day yesterday and missed your two other questions. Sorry!

    1. 90 ohm = 2 x 180 ohm in parallel, those are 1/4W carbon film resistors I bought in bulk from Radio Shack RIP :( This can be tweaked to your ears delight if you read the Lampizator. I've used 50-100 ohm in this position. When I drew the schematic 90 ohm was installed. Find out what your ears like best!

    2. I checked your schematic yesterday and was puzzled why you redrew it since my schematic was clearly drawn/marked. Then I realized that in my schematic, the 6.3V filament from the Heath 54-34 light the 6CG7 DC filaments while the outboard transformer heats up the 6X4 rectifier and in the breadboard it's the reverse. Good eye! But in the real world, as long as the filament lines have sufficient current ability, it doesn't matter. (BTW, your schematic shows 350V output, it should be 305V ;)

    3. More important is my buddy Roscoe Primrose's comment in my latest upload (PSE6SN7 amp) wherein I'm running the output of the 6X5 (octal based 6X4) to a 22uf cap or in this case 33uf cap when the tube data specifies 10uf MAX! I will rectify this in the schematics ASAP!

    I admire your enthusiasm in DIY audio but I'm hoping that as you complete more projects you'll refrain from overthinking. Instead, keep your soldering iron heated and focus on building so that you'll gain more practical experience how circuits operate. That's the best answer to all your questions!

    I've said this a few times before, I blog about my audio adventures to encourage others to venture on their own without having to follow an audio guru or the latest trends in internet forums. People may or may not like what I upload but as long as their ears decided in service to music, that's all that matters to me.🍻


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  8. Hi Thank you for the link to " Shop Talk" I thoroughly enjoyed reading it. Now I understand your simple and unique circuits very well. I am inspired to build and listen LOTs of music.

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    Replies
    1. I'm glad you found some inspiration there, happy soldering and listening!

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  9. Hi
    I my DAC PCB and transformers ( Hand wound in Greece ) Have arrived. One question which 5A bridge rectifier do I need? Do you have a part number please?
    You mention about 1:1 line transformers as digital sound processors, do I need one? I see Audio Note uses Mu-metal can type transformers. Are these same as the WE NOS you mention?
    Can I ask my transformer maker to make one for me? Do you know the specifications so I cn ask the transformer company to make for me?
    Audio Note also uses output transformers to step down in their ECC82 and 6463 tube stage. Do you have any experience about that? Or is it too much transformers.
    Thanks again I wish you a nice day. Vinay

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    Replies
    1. Hi Vinay,

      Please google "5 amp bridge rectifier," it's a generic part. The URL will fill up the reply box if I copy and paste.

      I don't know how Audio Note configures the transformers in their DACs.

      I uploaded a hi-res picture of the UTC A20 above so readers can see all the specs if it's right clicked.

      Anyway, the line transformer is optional. Since the oversampling filter is disabled in this DAC, the natural roll off of any audio line transformer acts like a passive filter for digital artifacts. But the DAC will work without a line transformer.

      You can read more about why I started using them many years ago in this link - https://jelabs.blogspot.com/2017/12/line-transformers-redux-art-dudley-aq.html

      For alternatives to the UTC A20, google is your friend.

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  10. Hi JE,
    Thank you for the very interesting read on transformers. It could be futre upgrade but as you explained it is not needed.
    I found a oil filled 50 uF capacitor , can I use it instead of 47 uF electrolyte? I have many of these in my WE91 and I like the sound. Your blog is very interesting and everyday I read it with joy. Thank you

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  11. Only the 10uf cap value at the rectifier output is critical. Use your favorite capacitors. No need to consult, it's your DAC project, not mine.πŸ˜‰

    BTW, I just realized that the line transformer article was already linked above + all the info you needed in your previous inquiry were already there.

    As the blog has grown (and me getting older + busier), I added a search function on the top left hand corner as a convenience. Please try and use it before posting a comment/inquiry. Much appreciated!🍻

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  12. Hi Thank you and yes you are perfectly right. The more I read the more I see. Sorry for asking too many questions. I am thankful. Best regards Vinay

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  13. Hi JE,

    A small question about your JE's DIY NOS module for SAA7220. Do I remove the shaded pins from the IC holder? The Binatch site you referred for the mod says " remove shaded pins from holder". In your photo I cannot see the bottom of the nod. So do I remove all the 6 connected pins or the 3 pins on the left? Taank you for your answer. I know you are busy but I could not find the answer on google. Mostly it is about CD players and not stand alone DACs.
    best Regards
    Vinay

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  14. Hi JE,
    Followed your lead and got rid of analog section on my DAC board, same one you have. Great tip on where to tap into the right and left channels out of the TDA1541! Used a 12.5 ohm Mills non-inductive resistor for I/V, a 1nf cap to ground filter, and out through some poly caps for coupling. Have plenty of gain, feeding my Superphon preamp that goes into the amp. The 12.5 ohm resistor sounds cleaner than the 47 ohm I had previously used. I like the sound better than my Arcam Blackbox 2, which sounds too homogeneous in comparison. Great listening, couldn't wish for more :)
    Thanks,
    Den

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  15. Hi Joseph,
    Many thanks for this project that I built for a friend: beautiful sounding with GREAT tones and very large image. I think I'll build another one for me :)
    Cheers,
    Vinz

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    Replies
    1. Glad to hear that, Vinz!🍻

      JE

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    2. Hi again Joseph. Can I use this circuit (without I/V resistor) as line preamp or I have to change the working point of the first section. Thanks

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  16. Hi JE,

    Thanks for sharing your design and steps to build this tube DAC. I'm looking to build this DAC and I have a question/clarification.

    I have the exact same board as you including the USB module. Is the USB signal also processed by the TDA1541 or does it have its own DAC? I see some chips on the USB module and googling it it shows to be some sort of DAC. Is the TDA bypassed when USB is being used and only coax and optical passes through the TDA?

    Thanks again.

    ReplyDelete
    Replies
    1. I understand your concern since the PCM2704 chip can also function as a DAC - https://www.amazon.com/Signstek-Coaxial-Converter-Convert-Analogue/dp/B00FEDHHKE

      But in this particular application, it's configured merely as a USB input. Otherwise, I won't hear music out of the tube analog stage, which is tapped directly from the analog output of the TDA1541 chip, when the USB module is fed with a digital data stream from a music streamer source like a Raspberry Pi.

      Study the traces in the TDA1541 DAC PC board, that shows it all!

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  17. Hello, thank you for sharing information.
    I'm trying to do this edit. Is the schematic up to date?

    Thank you

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    Replies
    1. I'm still using the DAC as featured above. No updates.

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  18. Good evening, 1 year later I built your lampizator mod. The sound is very good. but I have a mass problem. I have 100hz on the speakers. Are the grounds of the dac connected to the preamp input? qualitatively it is better than the OP amp. THANKS

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    Replies
    1. Yes, the DAC board and the tube output ground are connected.

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  19. Thank you so much.
    Do you have an idea for the 100hz raw in the speakers?
    thank you

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    Replies
    1. It's probably a ground path/wiring issue. However, it's impossible for me to troubleshoot unless the unit is in front of me.

      Good luck!

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  20. Hi, C1 ( power supply ) max 10uf 450v
    or 20uf ou 33uf its ok ? Thanks.

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    Replies
    1. I used 10uf at the 6X4 rectifier output because that's the recommended value in the tube manual. Using higher capacitance in that position might shorten the lifespan of the rectifier.

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  21. Can we increase the 47uf to 470uf or 1000uf? Thank you for your attention.

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    Replies
    1. The uploaded PS schematic works well for me. I haven't experimented further than 100uf.

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