The 2 Channel Audio Amplifier
Now, here’s an amp combo that Finns can be proud about: The 2 Channel Audio Pre- and Power Amplifier.
It’s based on research by Matti Otala (Finn), inspired by the work of Tapio Köykkä (Finn), on TIM (Transient Intermodulation Distortion), and on how to get rid of it in a transistor amp thereby making it sound much better than if only low THD (achieved with loads of negative feedback) was under focus.
Otala together with Jan Lohstroh presented a paper on the subject titled “An Audio Amplifier For Ultimate Quality Requirements” at the 44th Audio Engineering Society Convention in Rotterdam in 1973. The paper also describes (schematics) how to build an amp that takes the research results fully into account. The presentation included a sound demonstration as well.
Svein Erik Borja, a Norwegian broadcast and record producer heard the presentation and was impressed. So much so that when back in Norway he approached Per Abrahamsen at Electrocompaniet with the idea of building such an amp. Two prototypes were built: one is now in Norway, and the other in Finland. The amps sounded so promising that Borja and Abrahamsen decided to build ten units more. Later Terje Sandstrom joined the company, and was deeply involved in the development of the amplifier.
However, Lohstroh and Otala did not want Electrocompaniet to use their names in these later amps because the design had not been authorised by them for all parts. So as of December 1975, the name was changed to: The 2 Channel Audio Power Amplifier.
The amp had only 20dB of negative feedback, which was a little as compared to the conventional amps of the time, but for many, sounded better than the more linear amps - linear in terms of THD figures.
So were things back then but The 2 Channel Audio Amplifier still sounded great when I got the chance to (quickly) audition them together with sensitive widebandwidth loudspeakers. Very crisp and clean sound without being tiring, fast sounding too. No complaints in the bass department either. The units (pics) were numbered as 80 and 81. The caps in the preamp's power supply had been replaced with fresh ones, and some of the circuit boards were better supported. The power amp was partly rewired. All mods and pics by Veikko Luukkanen.