https://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)Hugoen-ushttps://hermitaudio.github.io/technical-reference/post-ec-nrf/nrf-modifications/index.htmlMon, 01 Jan 0001 00:00:00 +0000https://hermitaudio.github.io/technical-reference/post-ec-nrf/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/technical-reference/post-ec-nrf/preamp-1982-schematics/index.htmlMon, 01 Jan 0001 00:00:00 +0000https://hermitaudio.github.io/technical-reference/post-ec-nrf/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/technical-reference/post-ec-nrf/calculations/index.htmlMon, 01 Jan 0001 00:00:00 +0000https://hermitaudio.github.io/technical-reference/post-ec-nrf/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.