Not ported: photo.htm (a generic FrontPage sample-photo placeholder with no
real content) and news.htm (a changelog of the old website itself, not
Electrocompaniet history).
Subsections of History
The Story of the "Otala" Amplifier
A story of the legendary 25W “Otala” amplifier as seen by Terje Sandstrøm, one
of the original designers.
Also see “The People Involved”, for other designers and
people who contributed.
Introduction — the birth of the Otala amplifier
At an AES conference in 1973, Dr. Matti Otala
presented a paper describing the design of a TIM-free audio amplifier. Present
at this conference was Svein Erik Børja, a Norwegian record and broadcasting
producer, and a great audio enthusiast. Svein Erik Børja was also one of the
greatest Golden Ears of his time — he was able to hear even the slightest
imperfection in an audio component. Having been dissatisfied with the sound of
the transistorized audio amplifiers of that day, he saw an opportunity here for
an audio amplifier of a new generation. Dr. Otala’s talk about TIM also
explained the imperfections Svein Erik himself had noted in audio amplifiers.
He brought the paper to a friend of his who was running his own audio company
in Norway, Per Abrahamsen of Electrocompaniet. Per decided to give the
amplifier a try, to see what it might bring. They got the help of Nils Jørgen
Kjærnet at Nera in Oslo, who did the circuit board design and also, to my
knowledge, helped with the mechanical design of the amplifier.
They first made just a couple of amplifiers, but the sound was so good,
fulfilling all their expectations, that they decided to manufacture a series of
these amplifiers.
I started showing up at Electrocompaniet in the autumn of ‘74, and started to
work for Per in the spring of ‘75. One of my first jobs was to assemble the
first production series of the Otala amplifiers — a series of 10 amplifiers,
based on the same PCBs as the original two prototypes. During the summer I
started to look at the design, having been an electronics hobbyist since my
early teens. At that time neither Per nor I knew too much about high-end audio
design. That may well have been the factor behind the amplifier’s success, as
it evolved over the next 5 years — we didn’t know how it should be done, so we
worked it out from the framework given by the Otala design. We may well have
been the first audio amplifier designers of the new school — the TIM-free
designers, so to speak.
The first Otala amplifier in “production”
The first amplifier series used the same printed circuit boards as the first
two prototypes. The PCB was a two-layer design — we called it a T-board, due to
its shape. The power transistors were mounted onto the cooling fin from both
sides of the stem of the “T”. One layer of the board was a ground plane (Nera
being an RF company, that wasn’t so strange). The ground plane caused us a lot
of mounting problems, because the component legs often got stripped when they
were squeezed through the holes in the PCB, causing small metal pieces from the
legs to curl up and make sweet, nearly invisible, shorts to the ground plane.
We did see smoke …
In the autumn of ‘75 we started to get some attention, and a visit to Matti
Otala at the VTT (Valtion Teknillinen Tutkimuskeskus — the Technical Research
Centre of Finland), where he worked as a professor, became necessary. There
were several reasons:
We had named the amplifier “Otala-Lohstroh” after its inventors, and Otala
wanted to see the amplifier before he and Lohstroh could possibly allow us to
use his name.
At the same time, we started to experience problems with the amplifier — it
didn’t quite meet the specifications stated in the AES paper. We needed his
help.
As it turned out, the amplifier was renamed to “The 2-channel audio power
amplifier”, which was the name used for the rest of the amplifier’s lifetime.
The relationship with Otala was established, and he visited the company on
several occasions. There is still good contact between Otala and
Electrocompaniet.
Period of confusion, start of revision
It was early 1976. We started to invest in measuring equipment. The company
slowly turned into an audio amplifier company. It lost several of its old
customers; the loudspeakers it sold became more neglected. We worked from
early morning into the late nights. That would be the standard for the next
4 years. An amplifier brought to the US by Svein Erik blew
up at the first listening test — embarrassing. We used the night to invent a
new type of short-circuit protection. We didn’t want
anything that could affect the sound, so we simply used a high-impedance
circuit to sense the current through the output transistors, and then used a
relay to switch off the voltage to the output transistors. It worked!
We now understood that we had to start changing the amplifier. Svein Erik’s
golden ears became even more important than ever before. We were in uncharted
territory; the old measurement methods could not be trusted. We had to rely on
our own methods, our own interpretations of the measurement results. Now began
an active period of theory, practice, and reading articles (Svein Erik provided
us with articles en masse, on all aspects of audio design and electronics
design in general).
We found that the compensation scheme used in the amplifier did not work
correctly. As we measured the bandwidth to be far less than specified, we
needed to redesign these filters. The amplifier used shunt feedback — one of
its really strong points — with an input lag compensation; at each of the
three amplifying stages, a lead-lag compensation was introduced. These did not
match the actual poles we measured. One of the reasons for this, we assumed,
was that the original design used “fresh,” newly developed Philips
transistors. As both Otala and Lohstroh were working at the Philips labs in
Eindhoven at the time of the design, we assumed they had access to better
transistors. (I don’t remember if Otala ever confirmed this to be the case.)
In any case, a period followed where we changed the compensation back and
forth with little or no effect. We did achieve something, but no significant
improvement.
We had also now measured the distortion (having just bought our first
distortion measurement set and spectrum analyzer). It wasn’t pretty — the
distortion was far worse than specified, and performance was far below even
our own expectations. Again we didn’t manage to do anything significant at
first.
A major change came first when we started to change the quiescent current of
the transistors. The design was in fact done as a mix between the old way and
the new way. Older design books teach that you should use low current in the
first stage due to noise. This was also done here (see “Noise Optimisation”
for an explanation of why that’s not actually the case). We knew this theory
was wrong, so we increased the quiescent currents, which decreased the
resistance and again dramatically increased the bandwidth of the amplifier.
The distortion also went down — not dramatically, but enough to make a
significant change for the better in the sound (see “Transistors, Resistors,
Current and Distortion” — not yet written).
The Audio Critic
At this time we started to hear rumours about a test in
the US on our amplifier. One day our mail started to overflow, and a few days
later we got hold of the test ourselves. It was in a magazine named The Audio
Critic, and the test was fabulous. It started:
Audio freaks - Eat your hearts out: This is the worlds best sounding
amplifier, and One: You can’t buy one in this country (The USA!), and Two:
(not surprisingly - the only slightly negative in the whole test) It is too
low powered to be counted.
Suddenly we had more requests for amplifiers than we could hope to handle.
Sales boomed. It was mid-‘76.
We worked all summer, mornings, days, evenings, and into the night — Monday to
Friday, Saturday and Sunday. Per’s wife, Anne, was not always too happy about
this. Per had two small boys, and she had to take care of them a lot by
herself. Anyway — her “sacrifice” made building these amplifiers possible, and
the nice thing about it all is that both Per’s and Anne’s sons now work at
Electrocompaniet! So in the end it turned out to be an investment in their own
future as well!
The great change
Dr. Otala’s theorems on TIM very often came out as an attack on high-feedback
amplifiers. Although it is correct that high-feedback amplifiers are more
prone to TIM than low-feedback amplifiers, there is no magic here. The main
goal of any amplifier is to reproduce the incoming music as perfectly as
possible, neither adding nor subtracting anything. TIM is just one type of
distortion; swapping one type for another doesn’t help. It is true that some
types of distortion are harsher to the ear than others, but there still is a
balance to be struck. If 0.1% of TIM equals 1% of THD in audibility, then an
amplifier with 2% THD and 0.07% TIM will sound worse than an amplifier with 1%
THD and 0.1% TIM.
So, we realised that the balance of distortions was the essential factor to
consider. Not only do you have to balance THD against TIM, but also
low-frequency distortion against high-frequency distortion, frequency and
phase response against non-linear distortion in general, and so on.
This insight triggered the Great Change:
One night (it always happened at night!) we increased the feedback by 10 dB,
for a total of 30 dB of feedback. The sound improvement was staggering — and
contrary to common belief in our own community!
After this we only adjusted the amplifier slightly. It had found the form it
should have for its remaining life at Electrocompaniet. And the amplifier was
a success!
On marketing
We did brochures! The first one was rather
technical. The second one was more
professional. The rest of the marketing was done by word-of-mouth. The fact
that the amplifier and the company were both hard to get hold of stimulated
the market. Here was a mysterious company with a killer amplifier. Audio
people love such stuff!
Several people were involved in the development of the 25W amplifier. This
chapter takes the history from the perspective of the people involved, in
chronological order.
A Finnish professor named Matti Otala
(also here). On sabbatical at Philips in Eindhoven,
together with Jan Lohstroh he designed a TIM-free amplifier. It was one
step in Otala’s quest against the new distortion called TIM, and later DIM.
Svein Erik Børja, a Norwegian broadcast and record producer, heard the
presentation given by Dr. Matti Otala at an AES conference in Copenhagen in
1973. Together with Nils Jørgen Kjærnet at Nera he built two units based on
the Otala/Lohstroh schematics.
Per Abrahamsen was contacted by Svein Erik, who knew him from his Mojo
Blues days, and also knew that Per had an audio/electronics company. Per was
mostly working with PA equipment, but the arrival of the Otala amp turned his
company, Electrocompaniet, into an audio company.
At this time several others were involved with the company, but I don’t
remember all of them, mostly because they were before my time, and also
because they slowly disappeared as the company changed from a PA company to an
audio company. Among these were Petter Hjerpseth and Klaus Væthe Jr.
The latter later became a good friend of mine, and we tried to make an audio
company together in 1983, with the help of Paal Rasmussen, my former
partner at NRF — more on that later. Petter
disappeared during 1975; Klaus stuck with the company on and off until
sometime in 1977/78.
I (Terje Sandstrøm) first turned up in late 1974, and started to visit EC
on a monthly basis. After half a year of this, Per told me we were both better
off if I started to work for him, instead of just spending his time. In the
beginning I mostly did assembly work, but during 1975 I worked myself up the
ladder, and later I did more and more of the theoretical work on the
amplifier, calculations and so forth. I stayed until 1979, but did some part
time work and consulting for EC until 1982.
It is important to note that Svein Erik stayed with the company as its Golden
Ear for a very long time. In a way this was his hobby!
Peik Borud entered the company in 1976. He was an M.Sc. engineer in
electronics, and an audio freak. He stayed throughout 1978, and was, together
with Per and me, one of the basic designers of the 25W amplifier in this
period. Peik did a lot during his time at EC.
Paal Rasmussen entered the company in 1977 and stayed on and off for
slightly less than a year. He came from Seas AS, a loudspeaker company, and
before that he had worked in England with several of the famous designers
there. He and I were two of the three who started The Norwegian Radio
Manufacturing Company in 1979 — more on this later.
Kjell Winther was our record provider, and got amplifiers in return. He
was also a hi-fi nut, working in a record store, and provided us with the
latest and best-sounding records for our sound tests.
Nils Kvam was a record producer who also worked with listening tests and
also provided opportunities for the company sales-wise. He is still working
with EC.
Øistein Klevhus helped me with the Engineering High School (I was rarely
present …), and I got him a part-time job at EC from early ‘78 (or late ‘77)
until spring ‘79. We did the School Amplifier together,
spring ‘79.
Two of the people in production who really stayed for a while were Knut Arne
Jacobsen and his then-girlfriend Aud. There were also a couple of girls
who came from Tandberg to work in production — (their names are not
remembered). These also stayed for quite a while.
There were also some sales and managing people (Helge …, Jan
Richter, among others) involved from period to period. I’m working on
re-remembering their names. Any help from others is appreciated.
Others who contributed included, for example, Svein Erik’s brother, Bjørn
Børja, from Seas AS, who designed a cute little moving-coil amplifier that EC
manufactured for some time.
During 1979 the company moved, I started my way out, other people came in, and
I don’t recall their names, sorry. However, the first era of the Otala
amplifier ended sometime in 1979-1980, and the new Electrocompaniet appeared.
It moved to Skårer, where it is still located.
This text was originally written some time in the late 1990’s, and minor
updated around 2005.
Protection Networks
Protection networks, power supplies, and other stuff not so interesting, but
still needed.
You’ve read the section on how this came about? If not,
go back and do so! Otherwise, take a look
at the world’s first protection network that did not affect the sound AT ALL.
Yes — it is the first one!
The design is very simple: passive sensing of current, then triggering a relay
which removes the supply voltage from the output stage. As you probably know,
the EC design uses one power supply for the voltage-amplifying stages and one
for the power output, where all the large currents go. This separation made
this protection scheme work. If not, big bangs would be heard …
The power supply also needed some care.
However, we did not make it difficult. The major point here was the use of
small capacitors instead of the sluggish big ones everybody else used at that
time. We understood that small capacitors in parallel were a better choice
than single big ones.
The cabling was another issue — more on that later.
The Audio Critic Test
The Audio Critic test, from 1976, that triggered the flood
of orders for the amplifier:
Marketing Brochures
We did brochures! See the Otala story for the
context.
Our first brochure
It was rather technical.
The two remaining pages are still waiting to be scanned.
Our second brochure
More professional this time :-)
Norsk Radiofabrikk
Norsk Radiofabrikk — The Norwegian Radio Manufacturing Company
The company was founded in 1979 by Espen Evensberget, Paal Rasmussen and
myself. More info on this will follow later, but for now, see what the press
said at the time below.
The company also put out its own press release, “Tre Faser i en Utvikling”
(“Three Phases in a Development”), about the story of the Otala power
amplifier including the NRF modifications, written in 1979 — that document
hasn’t survived, or hasn’t been found again yet.
