Errata, Corrections, & Updates

Our editorial staff endeavors to publish accurate information in audioXpress magazine, Voice Coil magazine, The Loudspeaker Industry Sourcebook, and The World Tube Directory. When necessary, the staff will post notes pertaining to errata, corrections, and updates on this page. Corrected versions are available online. Please send your comments and suggestions to  

audioXpress May 2020
In the May 2020 Hollow-State Electronics column of audioXpress, the diagrams shown at right and center in Figure 4 are interchanged with respect to the labels: the center diagram is acutally the 8ET and the right-hand one is the 8HY. The correct data is supplied in the digital version of the magazine and is copied below:

Figure 4: The base connection diagrams of the 6L6GC, EL34, and 7027A do not match each other.

​Voice Coil April 2019
Unfortunately, incorrect data for the Klippel testing of the SEAS L26ROY was published in the print edition of the April 2019 issue of Voice Coil. The correct data is supplied in the digital version of the magazine and the article now available online here.

​Voice Coil September 2018
Unfortunately, there was an error during the discussion of the distortion measurements for the Dayton E160CF-8 in the Test Bench column of the September 2018 issue of Voice Coil.​ The sentence should have read: "I set the SPL to 94 dB (4.55 V) at 1 m.​" Already edited in the online article available here.

audioXpress July 2018
In the “Design and Performance of Power Supplies for Hollow-State Amplifiers" by Richard Honeycutt, which ran in the Hollow-State Electronics column in the July 2018 issue of audioXpress, there is a sentence that reads: "The positive half-cycle charges the positive plates of C14, C15a and C16 through diode SR2, and the negative half-cycle charges the negative plates of C15a and C16 through SR1 and the ground connection, and the negative plate of C13 directly. So it is a full-wave doubler rectifier, although it is drawn in a very unique way." It is actually a full-wave voltage doubler.

audioXpress July 2018
Part 1 of “Current Feedback: Fake News or the Real Deal?” article, which ran in the July 2018 issue of audioXpress, contained an incomplete figure. The label “Out_e was left off of Figure 2. It should have been associated with the output of op-amp U1a. Here is the correct Figure 2.

audioXpress June 2018
The Hollow-State Electronics article, "The Evolution of Tone Controls in Tube Amplifiers," contained an incorrect figure, Figure 9, shown on p. 64. The correct Figure 9 is shown here.

Voice Coil April 2017
The Eton 29HD2 tweeter reviewed in the April 2017 issue of Voice Coil contained an incorrect figure, Figure 18, shown on p. 29. The correct Figure 18 is shown here.


audioXpress June 2017
Thomas Perazella’s article “Cherry Bomb—AVFET SET Amplifier (Part 1): The Concept, the Design, and the Plan Modifications,” misidentified an image at the top of p. 53. The caption for the image should read: When we complete the project, our Cherry Bomb VFET SET amplifier should look like this. Here is a front view with the VU meters illuminated.

We regret that some editing errors have crept into Michael Kiwanuka’s article “Current Feedback and Voltage Feedback Fallacies.”
The article original equation 1 - should be:

Also in Michael Kiwanuka’s article “Current Feedback and Voltage Feedback Fallacies” an incorrect image was displayed for Figure 2. The correct image and caption are shown below.
Figure 2: Transadmittance feedback gives rise to a transimpedance amplifier or a current-controlled voltage source (CCVS).

audioXpress July 2016
Oliver Masciarotte's article “The Exciting Sounds of AXPONA 2016” misidentified an image at the top of page 16. The caption for the image should read: Campfire Audio’s new Andromeda featuring five balanced armatures. 

audioXpress May 2016
Gerhard Haas’ article, “Universal Tube Power Amplifier System,” contained errors in two of the schematics in the printed issue. In Figure 3, the capacitor C3 is connected wrong. The negative lead should be connected to the diode.  In Figure 5, the capacitor C6 is connected wrong. The negative lead should be connected to the diode. 
The correct figures are shown below.

Figure 3:


Figure 5:

audioXpress April 2016
David Soffer’s article, “Performance Analysis with FFT Software,” contained an error in the printed issue. The image for Figure 11 was incorrect. The correct image for Figure 11 is shown below:

Voice Coil March 2016
In the ALMA International Symposium & Expo (AISE)2016 article, written by Mike Klasco and Nora Wong, the university for Professor Andrew Barnard and grad students Mahsa Asgarisabet and Troy Bouman was incorrectly identified. The team is actually from the Michigan Technological University.

audioXpress December 2015
James Lin's article, "The SRX Plus Hybrid Amplifier (Part 2): Construct a Modified Tube Amplifier," contained an error in in the power supply for the SRX Plus.  The higher value resistor going to -C should be 100 kΩ rather than 133 kΩ.  The 133 kΩ resistor will "starve" the input tail cathode current sources. The article also contained an error in Figure 1. The common connection point of the three 0.1 µf capacitors of the 100 V Zener diode should be grounded.  

David Mathew’s article "Testing Audio ADC and DACs," contained an equation that was missing a set of parentheses, which changed the formula.The formula should have been 10log(1/(2.63*0.375)). With the corrected formula, the Window Compensation result is correctly calculated to be 0.06 dB.

audioXpress September 2015
In Richard Honeycutt's Hollow-State Electronics article, "Design Hollow-State Amplifiers Using Pentodes," many of the pentode schematics shown in the article have their suppressor grids connected to the control grid. That is incorrect. They should have been connected to ground.

audioXpress May 2015
In Bruce Brown's audioXpress article, "Updating the Bogen MO100A Amplifier," Figure 1 shows the first filter cap in the original power supply with its negative terminal grounded. This is incorrect, the negative terminal should be connected to the positive terminal of the lower filter cap.

audioXpress April 2015
In Ron Tipton's audioXpress article "Playing With Ambisonics," his description for building a small first-order microphone array (on page 17) failed to mention that although the Panasonic WM-61A
is an omnidirectional cartridge, mounting them with sealed rears makes them semi-cardioid. Also, their responses should be matched but they are sufficiently inexpensive to purchase extras.

In Richard Honeycutt’s Hollow-State Electronics column, "Classic Tube Power Amplifier Circuits," there were a few errors. First, the phase splitters in the Heathkit and Fisher amplifiers are of the split-load variety, not long-tailed pairs. 
In both cases, the phase splitter is the second stage, and it is followed by a balanced (Class-A push-pull) driver stage. Second, the cathode circuit of the Fisher has cathode feedback provide by a tapped winding of the output transformer, not a tapped inductor. Third, the transformer winding feeding the screens of the McIntosh actually provides positive feedback to bootstrap the final driver and output screens.

audioXpress October 2014

An article in the audioXpress October Hollow-State Electronics column, “Controlled-Source Theory in Hollow-State Design,” in correctly identified the developer of the Mu Follower. Chris Paul developed the circuit and gave it its name. References to Chris Paul’s work with this circuit include:

The Audio Amateur, Letters to The Audio Amateur (TAA), February 1985, page 51.
The Audio Amateur, March 1991, page 43.
AudioAsylum Trader, Tube DIY Asylum, “Need 6gw8 or similar mu stage design,” Feburary 2006,
“John Broskie’s Guide to Tube Circuit Analysis & Design, SRPP+ (Part 3),” Tube Cad Journal, October 2009,

Voice Coil January 2014

Celestion was incorrectly identified in the January issue of Voice Coil. Celestion is a UK-based company.  

Voice Coil August 2013

The directory of OEM Voice Coil suppliers Voice Coil’s August issue (p.14) included incorrect information. Chen Hong Industrial does not supply voice coils to Italian pro sound driver manufacturer RCF. RCF has never done business with Chen Hong Industrial. Our apologies to RCF!  

audioXpress July 2013

Figure 2 and Figure 3 published on p. 37 of Vance Dickason's Test Bench column (audioXpress July 2013) were incorrect. The two figures, part of his review of the Beston Technology RT004A ribbon tweeter, appear correctly below.

Beston RT004A on-axis frequency response


Figure 3: Beston RT004A on- and off-axis horizontal frequency response (0° = solid black; 15° = dot blue; 30° = dash green; 45° = dash/dot purple)


audioXpress June 2013

An incorrect biography for audioXpress contributor Ron Tipton was published on p. 44 of the June 2013 issue. His correct biography appears here: Ron Tipton has degrees in electrical engineering from New Mexico State University and is retired from an engineering position at White Sands Missile Range. In 1957 he started Testronic Development Laboratory (now TDL Technology, Inc.) to develop audio electronics. During the 1960s and 70s, TDL built active filters and pseudo-random noise generators for well known companies such as Bose Corp. and Acoustic Research. He also designed several audio products for GMS, Inc., a contractor to the Baldwin Piano and Organ Co. He is still the TDL president and principal designer.  

Voice Coil March 2013

In Voice Coil’s Test Bench section (p. 20), the review on Tang Band’s T1-1942S incorrectly listed the company’s website. The correct website is  

audioXpress May 2013

In Bruce Heran's article titled "Poddwatt Series II Stereo Integrated Valve Amplifier," published in the May 2013 issue of audioXpress, an error appears in the main schematic on Page 18. Here is the corrected schematic.

Loudspeaker Industry Sourcebook 2012

  • Applications Acoustiques de Composites (AAC) was inadvertently not included in the 2012 Loudspeaker Industry Sourcebook’s “Loudspeaker Cone Vendor Survey 2012” article. AAC is a major cone manufacturer. Created in 1989 from the NEOS Company founded in 1935, AAC has become a major manufacturer of loudspeaker components.

In addition to manufacturing membranes in cellulose fiber (paper), AAC has become more diversified through the development of new technologies and the use of materials such as glass fiber, aramid fiber (Kevlar), carbon fiber, titanium, aluminum, ceramics, plastic materials and, more recently, magnesium or sandwich composite.

With customers worldwide, AAC produces cones and membranes, domes, dust caps and dust barriers, surrounds, and spiders. AAC also manufactures domes for tweeters, notably the automobile industry. To contact AAC, visit; AAC, ZI Chemin de la Poterie, 72340 La Chartre Sur Le Loir, France; call +33 (0)2 43 79 03 60; or e-mail

  • The 2012 Loudspeaker Industry Sourcebook also incorrectly identified Audax, which is a drivers manufacturer. To contact Audax visit; ZI Chemin de la Poterie, 72340 La Chartre Sur Le Loir, France; call +33 (0)2 43 79 03 60; or e-mail

  audioXpress February 2013

  • A review of the Motus UH25CTi dome tweeter, from Motus Audio, starts on page 38 of the February 2013 edition of audioXpress. The table of contents on page 4 includes an incorrect reference to the page number.

Voice Coil April 2012

  • On page 8 in the Driver Awards section, the captions for Photo 4 and Photo 5 are reversed. In Photo 4, Peter Larsen, president of LOUDSOFT, Ltd., accepts the Titanium Driver Award. In Photo 5, Alex Voishville, manager of Transducer Engineering & Acoustic Research at JBL Professional, receives a Titanium Driver Award.

Voice Coil October 2012
  • On page 5 in the Supporting Companies section, the correct URL for Eckel Industries, Inc. is
  • For NTi Audio on page 28 in the Measurement Microphone Sourcebook Directory section, Tom Mintner is the sales contact for NTi Americas. The other listed name was an error.