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Ben Duncan's 'Supertuning CD' and 'Improved CD Electronics'

Discussion in 'd.i.y.' started by DoctorRad, Jun 1, 2020.

  1. DoctorRad

    DoctorRad pfm Member

    I've 'digitally remastered' Ben Duncan's related 'Supertuning CD' and 'Improved CD Electronics' articles from the late 80s. These are concerned with re-engineering the output stages of TDA1541(A) 16-bit, 4x-oversampling players using Philips' standard chipset. In particular, it explains why simple parts substitution will only get you so far, and outlines a circuit which needs no DC blocking capacitor, instead offering a user-tweakable DC offset control.

    I hope to re-draw the schematics for my own use, as I am musing over hot-rodding the output stage of the Rotel RCD-855 which should be arriving soon. I also hope to come up with a single set of schematics with equivalent parts correctly referenced from both texts. It's worth reading both articles as the style could hardly be different, and the content does not completely overlap. The Google document is open for comments, and if anyone else can make sense of the obvious typos, I'd be grateful.

    My growing archive of Ben Duncan articles can be found here, including photos of the complete AMP-02 text.

    Revisions to original document:
    1. 1st June 2020: Added 'Supertuning CD - A Refresher' - One year after ‘Supertuning CD', Ben Duncan returns to the subject of DIY improvements to the electronics of CD players. Includes notes on some (then) latest op-amp developments and a handy guide to swapping a TDA1541 for a TDA1541A.
    2. 2nd June 2020: Redrawn Hifi News main schematic.
     
    Last edited: Jun 2, 2020
    iant likes this.
  2. Darren

    Darren All Business

    Years ago Ben Duncan hot rodded some amps for me - it has to be said that he's the real deal, though the service wasn't cheap and he's quite a pushy salesman to boot!
     
  3. DoctorRad

    DoctorRad pfm Member

    My personal viewpoint is that he takes and talks no bullshit - he does engineering properly in a way that makes sense to me but which I don't have the training or experience to emulate - only appreciate. His takedown of the standard Philips / Marantz TDA1541 output stage makes it obvious why these players are so heavily compromised.
     
  4. DoctorRad

    DoctorRad pfm Member

    Redrawn main schematic - removed NE5534 designations to avoid confusion - see below and article for opamp recommendations.

    [​IMG]
     
    Last edited: Jun 3, 2020
  5. Dan K

    Dan K pfm Member

    Very interesting :), thanks for sharing. I'm now wondering if this will work on my Sony 337.

    I'm sure that it would. +/-15V in the Sony and 2 off duel OPA604 Op-Amps.
     
  6. martin clark

    martin clark pinko bodger

    Ben Duncan;s approach was good at the time; today it's not the best you can do for this dac, I'd say by a fair chalk.

    I'd not lash this into a Sony 337 and think it better, for a start: The BD solution very context -sensitive to the original player it is based on; for a start, a bipolar opamp like the 5534 isn't the best choice for the I/V conversion, just about the best at the time.
     
    narabdela and Dan K like this.
  7. DoctorRad

    DoctorRad pfm Member

    If you take a glance at the article itself, it goes into a lot of detail as to why the 5534 is the bare minimum you should use (i.e.: don't). He says that 'the performance of these chips is execrable in many areas, particularly the DC parameters', and goes on to describe its DC behaviour as 'disgraceful'.

    I've used it as a placeholder in the schematic for various project-based reasons. At the time, the OP42 was the favoured op-amp, for the I/V conversion at least... that's what (the article says) it was designed for.
     
    Last edited: Jun 3, 2020
    martin clark likes this.
  8. awkwardbydesign

    awkwardbydesign Officially Awesome

    But I had to invoke consumer legislation to get what I had actually paid him for!
     
  9. DoctorRad

    DoctorRad pfm Member

    Ouch!
     
  10. awkwardbydesign

    awkwardbydesign Officially Awesome

    But the active crossover he designed is still in operation! Since 1983, with numerous upgrades.
     
  11. DoctorRad

    DoctorRad pfm Member

    Funny you should mention that, the 'epilogue' Revisited article specifically mentions that 'even up-market players like Sony‘s 337-ESD can benefit'... but as Martin suggests, don't go with 5534s. You can do a whole lot better, especially these days.
     
  12. DoctorRad

    DoctorRad pfm Member

    When the central library reopens, I will be grabbing this and various other articles for the archive.

    I hadn't realised until last week that in autumn 1990, Hifi News published a BD bitstream output stage project. I'd just arrived at university and had other fish to fry...
     
  13. martin clark

    martin clark pinko bodger

    The OP42 was indeed excellent for such uses (incidentally, what Naim used in their CD players for a decade or more)

    One thing that the article doesnt give is why such a part works well -it is a FET-input opamp, and therefore handles the rf noise on the input more gracefully- less likely to suffer rectification effects, quite apart from the other figures of merit discussed in the articles.


    Iirc Naim used the opa604s later eg in cd3 & cd3.5 /cd5; again, solid choice- and FET input
     
    DoctorRad likes this.
  14. Mike P

    Mike P pfm Member

    I fitted OPA2604 into Dan's 337.
     
    Dan K and martin clark like this.
  15. DoctorRad

    DoctorRad pfm Member

    The companion Improved CD Electronics article does mention that "Current-to-voltage conversion is best handled by a fast-settling op-amp with a (low trans-conductance) Bi-fet or degenerated bipolar input". This article, written later, mentions the following chips as being suitable for the I/V conversion stage: OP44 / 42, AD845 / 744, or Harris HA 2525 and HA 5137.
     
  16. Mike P

    Mike P pfm Member

    In my old Arcam Alpha 5 project I had OPA627 on I/V duties which were great.

    I did try 2x OPA627AU on Brown Dog adaptors in the 337 but I wasn't convinced by the sound.
     
  17. Dan K

    Dan K pfm Member

    The 2604's are very decent. Nice analog flow to them. I've actually just swapped them back in after trying an 825/604 module. The 825 did give a bit more detail, but was too pushy for my tastes. I also tried it with local 0.1uF across the power pins, even more forceful.
     
  18. Dan K

    Dan K pfm Member

    If there is a way to directly couple the output from my 337 (or any Sony CDP) then please shout!
     
  19. Mike P

    Mike P pfm Member

    Well first measure the DC offset it has.

    Does the input of your preamp have coupling capacitors?
     
    Dan K likes this.
  20. DoctorRad

    DoctorRad pfm Member

    One of this circuit's explicit goals is to do away with an output coupling capacitor by using a precision DC current source to compensate for the DAC current offset, and also allowing for opamp DC offset adjustment if you want it.
     

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