https://hermitaudio.github.io/audio-design/index.htmlAudio Design Miscellaneous audio-design work not tied directly to the Electrocompaniet history: the school amplifier project, cooling-fin calculations, the AES paper on AB distortion, later prototypes, and other designs. Ported from Legacy/: the School Amplifier, the ultimate cooling fins, the AES paper on AB distortion, the May ‘78 preamplifier, later designs (the 1982 preamplifier and power amplifier prototypes), other designs (including the “Krinken” preamplifier for NRK), and the Perfect 25W Amplifier design notes.Hugoen-ushttps://hermitaudio.github.io/audio-design/school-amplifier/index.htmlMon, 01 Jan 0001 00:00:00 +0000https://hermitaudio.github.io/audio-design/school-amplifier/index.htmlØistein Klevhus, now at FHI (the Norwegian Institute of Public Health), and myself did a project together at the end of our engineering school. I am greatly in debt to Øistein, because he was the one who made it possible for me to go through with that school — I was far too busy with EC, and had far too little time for school. Øistein came over to me at EC with schoolwork tasks and other stuff I had to do, and in that way it was possible for me to get through the school without nearly being present. I am forever grateful for that!https://hermitaudio.github.io/audio-design/cooling-fins/index.htmlMon, 01 Jan 0001 00:00:00 +0000https://hermitaudio.github.io/audio-design/cooling-fins/index.htmlThese cooling fins may be the best-engineered fins ever made for an audio amplifier. They are the result of a strong interest in thermodynamics I had at the time. The fins are much thicker at the base than ordinary fins, and are gradually made thinner outwards. This was done to improve heat transfer through the fins, while at the same time ensuring a well-defined air flow and an even surface temperature — thus the lowest overall heat-transfer resistance.https://hermitaudio.github.io/audio-design/ab-distortion/index.htmlMon, 01 Jan 0001 00:00:00 +0000https://hermitaudio.github.io/audio-design/ab-distortion/index.htmlMy Audio Engineering Society journal article on class AB distortion in power amplifier output stages, 1983 — referenced throughout the Schematics and Theory sections. “Distortion in Class AB Power Amplifiers”, Terje Sandstrøm (Institute of Physics, University of Oslo). Presented first as an AES convention paper, then published in the Journal: AES Convention 71, Paper Number 1870, presented 6 March 1982 — AES E-Library entry Journal of the Audio Engineering Society, Vol. 31, Issue 11, pp. 858–861, November 1983 — AES Journal Forum entry This was one of two papers I presented at AES conventions in the early ’80s; this is the one that made it into the Journal. I haven’t been able to identify the other one — if you know its title, let me know via the about page.https://hermitaudio.github.io/audio-design/may-78-preamplifier/index.htmlMon, 01 Jan 0001 00:00:00 +0000https://hermitaudio.github.io/audio-design/may-78-preamplifier/index.htmlDetails on this preamplifier will be added over time. First, the line stage — the specifications achieved are shown below: The design was made very similar to the “Otala” designs. It was a single-power-supply design — note the input and output capacitors. It was designed to replace our old, completely single-ended preamplifier, which was never a big hit.https://hermitaudio.github.io/audio-design/later-designs/index.htmlMon, 01 Jan 0001 00:00:00 +0000https://hermitaudio.github.io/audio-design/later-designs/index.htmlPreamplifier of 1982 This preamplifier was designed in 1982, and a prototype made in 1983. Only one unit exists, and it sounds wonderful — by far the best-sounding preamplifier I have ever made. Still today I’m rather pleased with the design. It is divided into several gain blocks. In the accompanying schematics section I’ve shown the block schematics and one of the gain stages, which is used in two places. More details on this design will follow later.https://hermitaudio.github.io/audio-design/other-designs/index.htmlMon, 01 Jan 0001 00:00:00 +0000https://hermitaudio.github.io/audio-design/other-designs/index.htmlThere were several EC designs made between ‘75 and ‘80, in that first period. Several of these never made it into production. On the pages in this section, details of these designs are given, as far as we have been able to recover them: some schematic details, some of the story behind them and the reasons for their development, and some technical goodies — and possibly a hint or two.https://hermitaudio.github.io/audio-design/the-perfect-25w-amplifier/index.htmlMon, 01 Jan 0001 00:00:00 +0000https://hermitaudio.github.io/audio-design/the-perfect-25w-amplifier/index.htmlHow should it be done? Base it on the Special Version schematic. That should be the starting point. Don’t attempt to modify an existing amp — it should be built from scratch! Then follow the points below: Change the power supply as follows: Increase the pre-stage voltage from 30 to 35V. Place regulators on the pre-stage voltage supply, allowing 5 more volts to drop here, taking the unregulated DC voltage up to 40V. Add a cascode stage on the 3rd amplifier stage. Replace the output transistors with modern Japanese types, e.g. the … (never specified — my notes don’t give a part number). Refine the other stages, as shown in the suggested schematics. Design a new PCB layout, following the PCB rules detailed below. Use heavy-gauge wire on all supply lines and loudspeaker outlets. If possible, use steel/copper bars between the electrolytics. Keep all wires close to the chassis, glue them onto the metal. Place emitter followers before the 3rd stage. Use shielded wires from the input signal jacks to the board. Use two signal wires, one for ground and one for active, with the shield connected only at one end. PCB layout rules: