Audio Related Things

• My favorite MP3 ripper is a freeware program called AudioGrabber. It does not have the MP3 encoder built in, but that is the good part. It allows your to install what is considered to be the best MP3 encoder, which is Lame. Go to the internet and find lame_enc.dll and copy it into the AudioGrabber directory and you are set to rip MP3s. It is said that ripping them at 192k with Lame gives a copy that cannot be distinguished from the original. I have AudioGrabber set to first rip all tracks of the CD into an intermediate wav file, then normalize the tracks to 98%, and finally delete the wav file. There are numerious options for volume compression that I do not use.
• Here is a link to Defunct Audio Manufacturers that makes for some interesting reading by those who remember these companies.
• Introduction to Electroacoustics and Audio Amplifier Design, Third Edition, ISBN 0-7575-0375-6. A book which I wrote for my Audio Engineering Class.
• Beranek's Law From the book Acoustics by L. L. Beranek.
• The Class-D Amplifier - Basic theory of operation of the class-D amplifier and the filterless class-D amplifier.
• The Klipsch Half-Room Principal An interesting paper on the design of listening rooms.
• An Op Amp Tutorial - Derivation of the op amp open-loop transfer function, the gain-bandwidth product, and the slew rate.
• The Fisher KX-200 (Fisher KX200) vacuum tube amplifier was marketed in kit form in the 1960s. The schematic doesn't seem to exist on the internet. Here are page one and page two. Except for some resistor values, the circuit is almost identical to the amplifier section in The Fisher 500C vacuum tube receiver. The major difference seems to be the use of fixed bias in the 500C while the bias was adjustable in the KX200. The 500C was rated at 75 W IHF total power while the KX200 was rated at 80 W. With an 8 ohm load, the difference in output voltages would be only 0.8 V rms, which is almost an insignificant difference. The IHF (Institute of High Fidelity) power rating was higher than what would be measured with a sine wave. It was supposed to account for the fact that the peak-to-average power ratio for an audio signal is larger than that for a sine wave. The IHF power rating is not used today.
• Closed-Box Loudspeaker Design - Design equations for calculating the internal volume of closed-box loudspeaker systems.
• Closed-Box Loudspeaker Design - What value of Q_TC minimizes the lower cutoff frequency of a closed-box loudspeaker system?
• Vented-Box Loudspeaker Design - Design equations and charts for calculating the internal volume of vented-box loudspeaker systems.
• Zobel Network Design - Design equations for Zobel networks for closed-box drivers. The high-frequency compensation network can be used with vented-box drivers, but not the low-frequency compensation network.
• An Electroacoustic Analysis of Transmission Line Loudspeakers - This is Allen Robinson's 2007 thesis on transmission-line loudspeaker systems.
• Head Amps for Moving-Coil Cartridges - Three pre-preamplifier circuits for moving-coil phono cartridges.
• The Leach Amp Plans - The latest version of the Low TIM amplifier that I published long ago in Audio magazine.
• The Leach SuperAmp Plans - Plans for the Double Barrelled Amplifier that I published long ago in Audio magazine.
• A Three-Way Satellite Loudspeaker System
• Georgia Tech Audio Lab Loudspeaker Plans. - The woofer for this system is no longer available. I know of no substitute. We are working on a new system that uses all Vifa drivers. The following link has a brief description of these.
• Georgia Tech Audio Lab Vifa 3 Way Loudspeaker Plans.
• 2-Way Loudspeaker System Plans - A two-way system using Vifa drivers.
• An FET Audio Peak Limiter - A simple audio peak limiter that uses a JFET as a variable resistor.
• "A Four-Stage FM Broadcast Audio Peak Limiter,"
• Construct a Wide Bandwidth Preamp - An article I wrote for the Feb. '77 issue of Audio magazine that many people have asked me to post. I have learned a lot since then, e.g. not to use ceramic capacitors. Versions of the circuits with FET diff amps are also included. This is a PDF document which might take several minutes to download. I recommend right clicking on the link and saving it to your hard disk.
• Build a Low TIM Amplifier - Parts 1 and 2 - Articles I wrote for the Feb. '76 and '77 issues of Audio magazine that many people have asked me to post. Several following versions are included. The Leach Amp plans linked above are for the latest version of this amplifier. This is a PDF document which might take several minutes to download. I recommend right clicking on the link and saving it to your hard disk. The amp pictured in Fig. 1 has been running over 8 hours a day, 5 days a week, in my office since the article was published.
• Build a Stepped Volume Control - An article I wrote for the Feb. '79 issue of Audio magazine that someone has asked me to post. Some students building preamps at that time had problems getting good volume controls. One student bought a 23 position dual switch and asked me if resistors could be added to it to form a volume control. This article came from that project.
• Operational Amplifier Circuit for Hi-Fi - An article by Bart N. Locanthi that was published in the Jan. '67 issue of Electronics World magazine. Mr. Locanthi was vice-president of engineering at James B. Lansing Sound, Inc., (now JBL) when he wrote this article. It describes the T circuit output stage which I used in my Low TIM amplifier circuit. Electronics World, published by Ziff-Davis, was a great magazine, but it went out of print in the mid '70s. The former British "Wireless World" magazine now uses the name "Electronics World." Mr. Locanthi died in '94.
• Tubes Versus Transistors - Ever wonder why tube amps sound different from transistor amps? This paper explains it. It was published in the digest of the 1981 IEEE ICASSP conference held in Atlanta. Author Stephen Bussey graduated from Georgia Tech.
• If you need an audio signal generator and have a sound card in your pc, download and install WinISD.
• The Perception of Pitch - An interesting article from the 1974 issue of American Scientist published by Sigma Xi. It explains some of the mysteries of why the same note played on different instruments sounds different.
• MP3 File Sizes - A comparison of file sizes for variable bit rate and fixed bit rate sampling.
• Transconductance Doubling - Can "transconductance doubling" (also called "gm-doubling") occur in class-AB output stages? Some audio wizards say that the transconductance increases in the crossover region where both transistors are conducting. You can read why this is an "old wives tale" here.

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