My Library

On feedback and related subjects Small-Signal Distortion in Feedback Amplifiers for Audio, James Boyk and Gerald J Sussman, April 2003 Combining positive and negative feedback - John M. Miller, Electronics, March 1950. First commercial successful design using a combination of positive and negative feedback to lower distortion that I know of. Tubes, of course. Feedback Amplifier Analysis Tools by TI's Ron Mancini. Clear expose on amp stability issues and how to avoid them. Audio design leaps forward? Giovanni Stochino, EW&WW, Oct 1994. Generalized op-amp model simplifies analysis of complex feedback schemes - Jerald Graeme, Burr-Brown Corporation. EDN, April 1993 Negative feedback and non-linearity - Exploring the fallacy that nfb reduces all harmonics equally - Cathode Ray, Wireless World Oct 1978. (Cathode Ray was a nom de plume of M. G. Scroggie). Amplifier design for low Transient Intermodulation Distortion - Matti Otala's Low Tim Amplifier from AES preprint H-6(R) from Feb 1973 On perception and (subjective or objective) testing - Audio - Science in the service of Art, by Floyd E Toole, PhD, at the time Vice President Acoustical Engineering, Harman International Industries, Inc. Very balanced paper about issues connected to subjective listening tests and bias. My own tests: On 9 April 2012 a few members of the NL AES section met at the residence of Hans van Maanen, 'mister Temporal Coherence'. We listened to 15kHz brick-wall filtered (and heavily phase-shifted) music and tried to hear a difference with the same music unprocessed. Yes we did hear a difference! Read my little report! Between Amplifier and Speaker - Ivor Brown, Electronics & Wireless World, Feb 1995 Un ingénieux dispositif réducteurde distortion pour amplificateurs de puissances, Revue du Son, No 242, Juin 1973. This is an early realization that in my opinion is identical in concept to Hawksford's error correction scheme. In French, but it refers to an article in Wireless World. Miscellaneous subjects: Making the Best of an Audio Transformer - Norman H. Crowhurst, Audio Engineering, 1953 A new distortion mechanism in class B amplifiers - Edward M. Cherry, AES Engineering Report, May 1981 Inaudible High-Frequency Sounds Affect Brain Activity: On the perception (or not) of frequencies above 20kHz A great little utility called ResCalc - that calculates series/parallel resistor values for you to get that non-standard value. Written by Mark Lovell and Morgan Jones. Everything about RFI, ground loops, pin 1 problems etc for audio. An extensive library well worth perusing! Generated and/or collected by Jim Brown at Audio Systems Group A very old paper on Transient response, ringing and the role of feedback, from a Mr. Roddam from 1952! The oldest I have ever seen related to audio amplifiers. Courtesy of Leo Sahlsten from Finland. Dr. Hirata et al Engineering Report for the AES from April 1981, on a distortion measurement method that gives insight into the TYPE of non-linearity rather than a single distortion number: Non-linear Distortion Measurement Using Composite Pulse Waveform. A separate distortion study by Hirata appeared in the Sept JAES in 1981 A different, but related type of transient testing by Southworth, from 1966. One of the best I/V stage design I ever saw is from Michael Smeedegaard, presented in his # 4326 AES preprint: "Low Input Impedance Current to Voltage conversion circuit for Current-Output DACs" John Linsley Hoods' Linear AC amplifier Liniac - simple but high performance. Several vintage documents on thermal distortion in power stages, resulting from signal-related die temperature changes. Also called 'memory distortion': 'La distorsion thermique' Part I, Part II, by Héphaütos (from L'Audiophile, 1984), and 'Amplifier transient crossover distortion resulting from temperature change of output power transistors', AES preprint 1896 (October 1982) "Class B in a new class" by Mike Renardson, Electronics World April 1998. An 'ideal diode' - from Linear technology Errata sheet for CS8420 SRC/receiver A vintage (1963) AES paper by Langevin about IM in tape recorders. A classical amplifier in the mid-70-ies was the 'Barney amplifier'. Designed by Barney Oliver at HP, and manufactured, tested and documented as a regular HP piece of equipment. The Tech- & User Manual is here. A gem! Edward Cherry's Nested Differential Feedback Concept and the NDFL Amp from ETI (1983). Contribution by John Curl related to the LT1166 bias chip. The measurements are here and here. In Nov 2011 we gathered with a group of audiophiles in Stuart Yaniger's residence in Austin TX to enjoy a live concert by Southpaw Jones. Scott Wurcer brought his mic preamps which he described in his articles in Linear Audio Vol 1 and Vol 3. We were so impressed with the quality and realism of his recordings that we asked the artist for permission to post a song here, which he agreed to. Listen to An Army of Kittens and a section of the subsequent applause By popular request: here is Barrie Gilberts (in)famous paper Are Opamps really Linear? My interview with Malcolm Hawksford has been published in two parts in audioXpress, Part I in September and Part II in October, 2009. Golden Ear Special: For those that have exceptional acute hearing, I have a nice set of six music fragments. Some of these are unprocessed, some have been processed. It is your task to divide the files into the two groups, the processed and the non-processed ones. If you think you cracked it, please contact me on pm so as not to take away the fun for others ;-). The files have random number names that have no specific meaning other than to identify them. (You may want to download before playing; these are large files). Courtesy Professor Malcolm Hawksford. 7; 61; 88; 232; 522; 923 (cheat sheet: if you can't really hear a difference, here's the effect increased 1000 times. Knowing what to listen for may help). Another psycho-acoustic riddle: listen to this track on headphones. Decide at which side you hear which tone. Then turn the headphone around and swap L with R and vice versa. Now decide again at which side you hear each tone. Astonishing, isn't it? Thanks to Jürg Jecklin from Jecklin Float fame for bringing this to my attention. (Note: this ONLY works with headphones!). Forces in Capacitors: A study on the acoustic emissions due to mechanical vibrations in capacitors caused by magneto- and electrostriction. Even if one million astronomers believe something, that doesn't make it true - a remarkable story about the human condition. An excerpt from Carl Sagan's "The varieties of scientific experience". Notch filter Auto-tunes for audio applications - John R Ambrose (EDN July 2010) HP 3577A application note for using the 3577 to do loop gain measurements of a feedback loop: HP PRODUCT NOTE 3577A-2 Extensive treatise by Kendall Castor-Perry about decoupling and bypassing. This is very detailed, covering a lot of angles and well-documented. A gem: Part 1; Part 2; Part 3; Part 4; Part 5; Part 6 The 'Otala-Lohstroh' low-tim amplifier design (AES preprint H-6(R), AES convention 1973, Rotterdam, The Netherlands) "Possible methods for the measurement of transient intermodulation distortion", Matti Otala and Eero Leinonen, Technical Research Center of Finland, 1976. A great article by Bruno Putzeys from Linear Audio Vol 1 - The F-word, or, why there is no such thing as too much feedback. No nonsense, factual, and technical, but also giving some historical perspectives to the often-heard notion that 'feedback sucks the life out of music'.