In Volume 9, Bob Cordell reviewed Gilles Brocart's extensive User Manual for LTspice. Our regular contributor Burkhard Vogel took the opportunity to check out the noise measurement and calculation functions in LTspice and found them wanting in a few places. His comments, together with some recommendations, are here.
Marcel van de gevel commented on Hans Polak's article in Volume 8 'On digital audio formats and the Nyquist-Shannon sampling theorem'. His letter as well as Mr. Polak's reply are here.
Hans Polak commented on Burkhard Vogel's article in Volume 7 'The Poor Man's Measurment Amplifier'. Here are his comments and replies from Burkhard.
Frank Blöhbaum has send me an addendum to his V6 article on Multipled Transconductance Amplifiers.
The addendum addresses some changes to the circuitry to improve reliability in the case of heavy overdrive.
Marcel van de Gevel commented on Daniel Joffe's article in Vol 6 "Practical Electronic Control of Class AB Output Stage Quiescent Current". Here are his comments and Daniel's reply.
Aat Vroegop commented on a circuit issue in Frank Blöhbaum's article on Multiplied Transconductance Amplifiers in Vol 6, specifically on the very large capacitance value for the output stage current source bypassing.
Frank provided an extensive justification and explanation along with some additional performance measurements.
Linear Audio author Ovidiu Popa wrote an extensive letter, commenting on Hans van Maanen's article On the audibily of "high resolution" digital audio formats and how to test this. Dr. van Maanen replies to each section in turn, and the complete exchange can be found here.
Mr. Popa also commented on Bruno Putzeys's article "The G-word, or how to get your audio off the Ground". The comments specifically addressed the 'demo preamp project' and the selection of the volume control potmeter. The comments and Bruno's replies are here.
Then Bruno in turn commented on Richard Burwen's article 'High Frequency Reverberation for finer Sound Reproduction'; the comment and Richards' reply is here.
Another comment to Hans van Maanen's article On the audibily of "high resolution" digital audio formats and how to test this came from Marcel van de Gevel; their lengthy exchange can be found here.
Marcel van de Gevel also commented on Morgan Jones' "Rectifier snubbing - Background and Best practises"; Marcels' comment and Morgans' reply are here.
Finally (for now) Marcel van de Gevel read Gary Galo's article 'An Archival phono preamp' which also lead him to comment on his own "A Tube-based phono preamplifier" article in Volume 4. Their exchange can be found here.
Letter from Walt Jung to Jack Walton on V4 article on power supply measurement and listening tests
Jack's article drew comments from the man who started much of the interest in power supply impact on audio circuits in the 80-ies, Walt Jung. On Walt's request Jack provides some additional information on the transformer and rectifier configurations, and takes some of Walts suggestions for an eventually follow-up test. Their exchange can be downloaded here.
Both Ian Hegglun's article (Towards Reconciliation of Measurements and Listening Tests) and Hans van Maanen's Guest Editorial (The Case for Subjective Listening Tests) in Vol 4 drew comments and some interesting additional information from prolific author Burkhard Vogel. His comments and the replies by both Ian and Hans are here.
The reply from Ian Hegglun also contains several corrections to his Vol 4 article.
(Note: updated 1 Jan 2013)
Brian Lenharth commented on Les Bordelon's article in Vol 4 on DAC design. His comment was specifically aimed at Les' classification of DACs as R-2R or Sigma-Delta. Between them, Brian and Les eventually agreed and added some additional information regarding differences between varies DACs.
Marcel van de Gevel send an addendum to his Volume 4 article A tube based phono preamp. In this preamp, neone lamps are used as overvoltage protection elements. The addendum gives information how to make sure that the neon lamps ignite timely to fullfil their duty.
I received several letters commenting on articles in Volume 3, notably to the articles by Samuel Groner (low noise lab-grade measurement amp), Steven van Raalte (correcting transducer response with inverse filter) and Robert Munnig Schmidt (mechatronics approach to subwoofer design).
These comments (some extend to several exchanges) can be downloaded here.
The comments were in some cases accompanied by the following LTspice files, referenced in the text: jm-1.txt; jm-2.txt; rms-1.txt; rms-2.txt and finally jm-3.pdf (in French).
Be sure to rename the .txt to .asc.
Letter from Burkhard Vogel to the review of his book by Ovidiu Popa
Burkhard Vogel, the author of The Sound of Silence, commented on the review of his book by Ovidiu Popa in Vol 3. Mr. Vogel offers some additional information about applying very-low-noise BJTs in phono preamps.
Samuel Groner from Zurich, Switzerland, commented on Ed Simon's article in Vol 1 "Resistor non-linearity - there's more to Ohm than meets the eye". The comments, along with Ed's reply, can be found here.
Brad Wood from Canoga Park, CA, USA, commented to the article by Ovidiu Popa in Vol 1 "On the Noise performance of Low Noise Input Stages". Ovidiu replied to each comment here.
Cyril Bateman commented on Ed Simon's article on resistor non-linearity in Vol 1. Cyril recalled some vintage testequipment documentation and application notes for measuring passive device non-linearities. He has graciously provided PDF copies of these documents. The document links are in his comment.
Dr. Ramkumar Ramaswamy wrote a nice article for Linear Audio "A universal Continuous-Time active filter", Vol 1, pp 77. I had an intersting discussion with Ramkumar about the meaning of the "Characteristic Frequency" of a filter. As a follow-up, Ramkumar has written On the Characteristic Frequency of a Filter . This article is available online.
Another comment to Bruno Putzeys' article in Vol 1 "The F-word - or, why there is no such thing as too much feedback", this time from Marcel van de Gevel. Marcel adds a few pieces to the puzzle on where the 'feedback is bad' story originated. His comments and Bruno's reply is here.
Burkhard Vogel from Stuttgart, Germany commented to Ovidiu Popa's article in Vol 1 "On the Noise performance of Low Noise Input Stages", and to Brad Wood's letter to the same article. Vogel's letter contains a complete MathCad noise analysis and the MathCad worksheet is also available for download from within the letter. The full document including Ovidiu's reply can be found here. This is the MathCad worksheet referred to.
Menno van der Veen commented to Bruno Putzeys' article in Vol 1 "The F-word - or, why there is no such thing as too much feedback". In replying to Menno, Bruno en passant comes up with a conclusion in which way feedback really decreases distortion. Read it here.
Peter van Willenswaard from Bergschenhoek, The Netherlands, commented on Stuart Yanigers article in Vol 0: "Split the Difference: The Truth about the Humble Cathodyne". Their views can be read here.
Burkhard Vogel from Stuttgard, Germany wrote a letter with comments to Joachim Gerhard's article in Vol 0: "Down the Rabbit Hole - Adventures in the Land of Phonostages". Joachim replied here.
Both Burkhard Vogel, from Stuttgart, Germany, and Dave Kimber from London, UK commented on Frank Blohbaums article in Vol 0 "A New Low-Noise Circuit Approach for Pentodes". Their comments and Frank's replies are here.
Another reaction to Stuart Yaniger's article in Vol 0 about the Cathodyne (aka Concertina) phase splitter, this time by frequent contributor Burkhard Vogel from Stuttgart, Germany. Burkhard has analysed this circuit in a more formal way and comes to the conclusion that Stuart had it right. Vogel even added the complete MathCad derivation in the appendix which you can download. For those who donot have MathCad on their system, here's the PDF version.
The never-ending saga on the cathodyne output impedances: Chris Paul wrote me a letter, commenting on both Burkhard Vogel's LTE and Stuart Yaniger's article in Volume 0. Here is Chris' latest letter.
Christopher Paul from Bayport, NY, USA commented on Stuart Yanigers article in Vol 0: "Split the Difference: The Truth about the Humble Cathodyne". Here are his views and Stuart's reply.