Links/PDFs:
(click on highlighted link to load)

The article(s) listed below fall into the category of material which has enjoyed continued interest over
the years since original publication.
  • 1977: As a preface to the 1977 The Audio Amateur series 'Slewing Induced Distortion in
    Audio Amplifiers', Walt authored a guest editorial for issue 1/1977, pp. 3, titled 'The
    Impossible Void'. This was a hopeful expression towards bridging the gap between
    measurements and listening tests, with SID/TIM measurements as a case in point. Looking
    back after nearly 30 years of time, there may be some question if this void has been
    narrowed. SID/TIM Guest Editorial
  • 1977: The 1977 The Audio Amateur series 'Slewing Induced Distortion in Audio Amplifiers',
    was co-authored in part with Mark  L. Stephens and Craig C. Todd. This long series featured
    five parts in the four 1977 issues of the magazine, and goes into great detail on
    measurements and testing of IC op amps for distortion characteristics. It was later to give
    rise to two major spin offs, described just below. Although many of the ICs discussed have
    since disappeared, the basics are just as true today as they were back in the 70s.
  • 1977: The paper 'Slewing Induced Distortion and Its Effect on Audio Amplifier Performance
    -- With Correlated Measurement/Listening Results' was co-authored along with
    Mark  L. Stephens and Craig C. Todd. It was presented at the May 1977 AES convention, and
    published as AES preprint 1252.

  • 1979: The 'An Overview of SID and TIM' article series was co-authored with
    Mark  L. Stephens and Craig C. Todd. It appeared in Audio in three parts, in June - August of
    1979. This series of articles had prior roots in the above 1977 AES presentation as well as
    the earlier 1977 series within The Audio Amateur.


    There is an ironic footnote here. Although the 1977 AES paper was rejected for inclusion in
    the Journal, yours truly received an AES fellowship in November of 1979, cited as: "for his
    publications on the subjects of audio applications of integrated circuit operational amplifiers
    and the analysis of distortion". Walt Jung AES Fellowship
 
  • 1980: 'Picking Capacitors, Part 1',  co-authored with Dick Marsh, was published in Audio, in
    February of 1980. This two part article examined a number of capacitor types for
    performance characteristics relevant within audio applications. Picking Capacitors, Part 1
  • 1985: 'A Real-Time Signal Test for Capacitor Quality', authored by John Curl and Walt Jung,
    was published in The Audio Amateur, in issue 4 of 1985. This article illustrated a simple
    differential comparison test between a sample capacitor and a like-value high quality
    reference capacitor.   A Real-Time Signal Test for Capacitor Quality
  • April, 2006: 'A Collection of Composite Line Driver/Amplifier Articles for Audio Uses'
    In response to numerous requests from readers over the last few years, this archive set
    describes various design approaches to audio line driver stages. While some of the articles
    have been stand-alone pieces, others have been in the context of a larger work, such as the
    ADI seminar notes of 1992, 1993 and 2002.

    This archival set is a series of individual articles, each focused on using op amps optimally
    as audio line driver stages. This article series is evolutionary, beginning with the first from
    1992 and progressing with the most recent, from 2002. The basic topology used is a
    combination of two op amps, each optimized for either the input or output stage function.
    Thus, it can be referred to as a composite amplifier, since the two amplifier combination
    serves functionally as a single driver amplifier.

    The intent of the combination is to employ the best of their individual specs, to form a unique
    resultant. In this case, the target goal is a low distortion audio line driver, with ample output
    power to drive either long lines or headphones, for example. At the input side, a low
    distortion FET input device is typically used, to offer minimal loading to the source (and thus
    lowest distortion).

    The articles and their original publication are briefly summarized below.

    1.  Walt Jung, ‘A High Performance Audio Composite Line Driver Stage’, from
    "Applications for Amplifiers in Audio," Ch. 5 within Walt Kester, Editor, 1992 Amplifier
    Applications Guide, Analog Devices, Inc., Norwood, MA, 1992, ISBN 0-916550-10-9,
    pp. 18 – 22. A High Performance Audio Composite Line Driver Stage

    Although not cited as an author here, it should be noted that AD744 op amp designer
    Scott Wurcer provided the original inspiration for the two amplifier concept in use,
    which employed the AD744 and the AD811 as a composite driver.

    2.  Walt Jung, 'High Performance Audio Stages Using Transimpedance Amplifiers',
    within Gary Galo, "POOGE-5: Rite of Passage for the DAC960," The Audio Amateur,
    issue 2, 1992, pp. 15-18. High Performance Audio Stages Using Transimpedance
    Amplifiers

    This article appeared as a sidebar to Gary Galo’s modification piece on the Philips
    DAC-960. It illustrated the basic composite line driver using the AD744 and the
    AD811 op amps. It also had some measurement discussions on DAC output levels,
    and showed a method of using a transimpedance (current feedback) type amplifier
    as an integrator in a DAC I/V stage.

    3. Walt Jung, Adolfo Garcia, "Op Amps in Line-Driver and Receiver Circuits, Part 2,"
    Analog Dialogue, 27-1, 1993, pp. 14 - 17. Op Amps in Line-Driver and Receiver
    Circuits, Pt 2

    This article expanded upon the basic two amplifier concept, showed alternate line
    drivers, and discussed topics related to high performance line drivers.

    4. Walt Jung, ‘Audio Line Drivers’, from "Audio Applications," Ch. 8 within Walt Kester,
    Editor, 1993 System Applications Guide, Analog Devices, Inc., Norwood, MA, 1992,
    ISBN 0-916550-10-9, pp. 8-63 – 8-100.  Audio Line Drivers

    This work expanded substantially on numbers 1 and 3 above. Also discussed are
    housekeeping details such as driving capacitive loads and bypassing. A special note
    here for page 8-64—the non-inductive bypasses should be film, not ceramic
    capacitor types, i.e., polyester or PPS would be examples. Other application
    examples are both single-ended and differential drivers, as well as transformer
    drivers with and without feedback. A useful measurement technique shown includes
    a non-inverting test to examine input stage non-linearity with regard to amplifier
    sensitivity to source impedance.

    5. Walt Jung, "Composite Line Driver with Low Distortion", Electronic Design Analog
    Special Issue, June 24, 1996, pp. 78-80. Composite Line Driver with Low Distortion

    This article is a focused application of the two-amplifier line driver concept, suitable
    for headphone use or very high current line driving. It added impedance
    compensation to the input stage op amp for lowest distortion for a given source
    impedance. Interestingly, it also showed how thermal distortion can be generated by
    high current outputs, a phenomenon that is intrinsically addressed by use of the
    composite connection.

    6. Walt Jung, "Walt’s Tools & Tips:  ‘Op Amp Audio – Minimizing Input Errors (Part 4)’”,
    Electronic Design, December 14, 1998, pp. 80-82.  Op Amp Audio - Minimizing Input
    Errors

    This article, the final installment of Walt’s Tools and Tips in Electronic Design (also the
    fourth in the Op Amp Audio series), showed a complete composite amplifier
    optimized for audio use. It employs the basic two-stage amplifier, but with stage one
    modified to operate with lower open loop bandwidth via the use local feedback.

    7. Walt Jung, ‘Audio Buffers and Line Drivers’, from section 6-1, "Audio Amplifiers"’,
    within Walt Jung, Editor, Op Amp Applications, Analog Devices, Inc. 2002, ISBN 0-
    916550-26-5, pp. 6-48 – 6-78.  Audio Buffers and Line Drivers   

    This, the most recent work on this topic, expanded considerably on numbers 1, 3,
    and 4 above. Again discussed are housekeeping details such as driving capacitive
    loads and bypassing. Application examples are both single-ended and differential
    drivers, as well as new distortion canceling transformer drivers using feedback. The
    measurement technique using a non-inverting test to examine input stage non-
    linearity with regard to amplifier sensitivity to source impedance is expanded/
    updated with the performance of current devices.

    The link following is the entire (210 page) chapter from Op Amp Applications which  
    contains this work. It is also recommended  as a broad resource on amplifier
    techniques. Chapter 6 from Op Amp Applications



Classic Audio Articles