https://hermitaudio.github.io/schematics/index.htmlSchematics & Troubleshooting Circuit schematics and troubleshooting guides for the Electrocompaniet amplifiers and preamplifiers, from the original 1973 Otala design through the EC production schematics, the 1982 preamplifier, and the later NRF/Special Version modifications. Ported from Legacy/: evolution of the schematics, original 1973 schematics, the real EC schematics, 1982 preamplifier schematics, transformers, wiring & mechanical assembly, troubleshooting the amplifier, troubleshooting the preamplifier, the NRF modifications, calculations on the 25W amp, and the regulated 25W power amplifier.Hugoen-ushttps://hermitaudio.github.io/schematics/evolution-of-the-schematics/index.htmlMon, 01 Jan 0001 00:00:00 +0000https://hermitaudio.github.io/schematics/evolution-of-the-schematics/index.htmlAlso see the later schematics The first design was taken directly from the paper by Otala and Lohstroh, AES 1973. To it was added a power supply only. The PCB layout and the mechanical design were done at EC. Original Otala — first-series schematics Only 10 amplifiers were made using these schematics. None exist today. The next series was done after early 1976, and incorporated the first changes to the frequency compensation. The changes were made to improve the frequency response and slew rate of the amplifier.https://hermitaudio.github.io/schematics/original-1973-schematics/index.htmlMon, 01 Jan 0001 00:00:00 +0000https://hermitaudio.github.io/schematics/original-1973-schematics/index.htmlNote the hand-drawing on the schematic. First attempts at traditional current limiting can be seen — this was soon discarded. Note also the extra resistors near the output: the loudspeaker was to be coupled between the output terminal and the small 0.1 ohm resistor to ground. This was a later idea (I don’t remember when it was introduced) which would give some current feedback in addition to the traditional voltage feedback. The effect would be to make the loudspeaker “invisible” to the amplifier.https://hermitaudio.github.io/schematics/real-ec-schematics/index.htmlMon, 01 Jan 0001 00:00:00 +0000https://hermitaudio.github.io/schematics/real-ec-schematics/index.htmlThe schematics of the real EC 25W amplifiers, shown below, are taken from a service manual, with full acceptance from Per Abrahamsen of Electrocompaniet. He approved of, and even supported, the idea of making these schematics public through this site, in order to cover the history of Electrocompaniet. Note that the schematic layout is very close to the original, except for the changes to the compensation networks (look at the emitters on the differential voltage-amplification pairs). The major changes can be found by looking at the component lists below, which apply for amplifiers with serial numbers below 275. The component list for serial numbers above 275 is covered in an addendum further down. You’ll need both lists, cross-checked, to get the full picture.https://hermitaudio.github.io/schematics/preamp-1982-schematics/index.htmlMon, 01 Jan 0001 00:00:00 +0000https://hermitaudio.github.io/schematics/preamp-1982-schematics/index.htmlThis is the phono stage, handling both MM (Moving Magnet) and MC (Moving Coil) pickups. The design uses active RIAA compensation, which was untraditional for the EC design — up to this time it used passive high-pass and active low-boost. The gain stages are designed to handle the active feedback, and note (!!!!!), the active RIAA compensation used shunt feedback. A tough job to calculate, but when that was done, it worked wonders!https://hermitaudio.github.io/schematics/transformers-wiring-mechanical/index.htmlMon, 01 Jan 0001 00:00:00 +0000https://hermitaudio.github.io/schematics/transformers-wiring-mechanical/index.htmlThis page is intended to help you if you’re going to service your amplifier. Electrocompaniet still services their old amplifiers, and I still service those I modified between 1979 and 1983 — however, the process may be slow (too much other stuff to do), so if you’re good with a soldering iron and have some instruments to help you along, this page together with the schematics may be what you need.https://hermitaudio.github.io/schematics/troubleshooting-the-amplifier/index.htmlMon, 01 Jan 0001 00:00:00 +0000https://hermitaudio.github.io/schematics/troubleshooting-the-amplifier/index.htmlThis page contains info on troubleshooting the power amplifier. For some info on the preamplifier, see Troubleshooting the Preamplifier. The following are excerpts from the original service manual of the EC 25W amplifier.https://hermitaudio.github.io/schematics/troubleshooting-the-preamplifier/index.htmlMon, 01 Jan 0001 00:00:00 +0000https://hermitaudio.github.io/schematics/troubleshooting-the-preamplifier/index.htmlI will put up schematics and other material on the preamplifier as well. However, first a few tips, based on real cases I’ve had in recent years. “Scraping” in the volume control This is due to DC leakage through the coupling capacitors, out from the RIAA stage and into the line stage. Replace the RIAA output electrolytics with 2.2 µF polyester, and the line-stage input capacitors with 0.68 µF polyester. Remove the 100k loading resistors.https://hermitaudio.github.io/schematics/nrf-modifications/index.htmlMon, 01 Jan 0001 00:00:00 +0000https://hermitaudio.github.io/schematics/nrf-modifications/index.htmlAfter I left Electrocompaniet in 1979, I tried to start up a new audio company in Asker together with two good friends, Paal Rasmussen and Espen Evensberget. We called the company “Norsk Radiofabrikk” (in English, the Norwegian Radio Manufacturing Company). We wanted it to sound old-fashioned, and really had a lot of good fun with this. However, our own original designs never made it into reality. In 1980, or thereabouts, we started to modify EC amplifiers. We modified between 50 and 100 amplifiers, and a somewhat lesser number of preamplifiers. The sound improvement was very good — not too surprising, since I knew these amplifiers in and out. Later we did some 50 amplifiers from the ground up, called the Special Version — the modification taken to its logical end. The components for these amplifiers came partially from Electrocompaniet. I don’t think Per liked it, but I also don’t think he really minded — if he had, he wouldn’t have sold us components, like cabinets and so on.https://hermitaudio.github.io/schematics/calculations/index.htmlMon, 01 Jan 0001 00:00:00 +0000https://hermitaudio.github.io/schematics/calculations/index.htmlThe following image is the first of an analysis done on the 25W amplifier. The date, 4 July 1980, indicates that this was done after I left EC (which was in ‘79, at least on a full-time basis — after a short break in ‘80 or so, I returned on a consultancy basis to do more work for them until sometime in 1982). I will upload the whole analysis. For those technically inclined, it should be interesting — lots of similar analysis was also done earlier. I got the feeling that many people believed we were only some kind of non-serious hippies. Well, in a way we were outside the establishment, but we did our mathematics! Also note the point made at the end of the note, saying that feedback below 20dB is no good idea when it comes to distortion.https://hermitaudio.github.io/schematics/regulated-power-supply/index.htmlMon, 01 Jan 0001 00:00:00 +0000https://hermitaudio.github.io/schematics/regulated-power-supply/index.htmlWe noted early on that the power supply had a significant effect on the sound. We decided to implement regulated power supplies for the amplifier. I’m not quite sure when we did this, but it might have been sometime in ‘76, possibly ‘77. We did it straightforward — no switching, no nonsense, only linear regulators. Hot? Yes, indeed! I’ve had some trouble locating the schematics for the regulators, but I believe I’ve found them. It’s possible that the ones shown here are preliminary schematics — the design never made it into production, so I’m not quite sure if any other version ever existed.