https://hermitaudio.github.io/technical-reference/index.htmlTechnical Reference Schematics, troubleshooting guides, and calculations for the Electrocompaniet amplifiers — the true EC factory designs, plus what came after: my own NRF-era (Norsk Radiofabrikk) modifications and personal work, kept clearly separate below. Electrocompaniet Evolution of the schematics Original 1973 schematics The real EC schematics Transformers, wiring & mechanical assembly Troubleshooting the amplifier Troubleshooting the preamplifier The regulated 25W power amplifier See Post-EC / NRF for what came after — not EC factory work, my own modifications and designs from the NRF era (1979 onward), kept separate in the menu on the left.Hugoen-ushttps://hermitaudio.github.io/technical-reference/evolution-of-the-schematics/index.htmlMon, 01 Jan 0001 00:00:00 +0000https://hermitaudio.github.io/technical-reference/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/technical-reference/original-1973-schematics/index.htmlMon, 01 Jan 0001 00:00:00 +0000https://hermitaudio.github.io/technical-reference/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/technical-reference/real-ec-schematics/index.htmlMon, 01 Jan 0001 00:00:00 +0000https://hermitaudio.github.io/technical-reference/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/technical-reference/transformers-wiring-mechanical/index.htmlMon, 01 Jan 0001 00:00:00 +0000https://hermitaudio.github.io/technical-reference/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/technical-reference/troubleshooting-the-amplifier/index.htmlMon, 01 Jan 0001 00:00:00 +0000https://hermitaudio.github.io/technical-reference/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/technical-reference/troubleshooting-the-preamplifier/index.htmlMon, 01 Jan 0001 00:00:00 +0000https://hermitaudio.github.io/technical-reference/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/technical-reference/regulated-power-supply/index.htmlMon, 01 Jan 0001 00:00:00 +0000https://hermitaudio.github.io/technical-reference/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.https://hermitaudio.github.io/technical-reference/post-ec-nrf/index.htmlMon, 01 Jan 0001 00:00:00 +0000https://hermitaudio.github.io/technical-reference/post-ec-nrf/index.htmlPost-EC / NRF (Norsk Radiofabrikk) Not EC factory work — my own modifications and designs from the NRF era (1979 onward), after leaving Electrocompaniet. The NRF modifications (including the Special Version) 1982 preamplifier schematics Calculations on the 25W amp (1980, done on a consultancy basis)