Nagra IV-S: interior
I suppose one of the most obvious things that separate the professional instrument from the amateur
'wanabee machine', is how much thought has been given to access, adjustment and ease of
servicing. I am reminded here of my old Ferrograph 5AN tape recorder that needed only two
knurled screws to be undone to get into it's works. It was perhaps rather too easily for un-trained
and inquisitive fingers to risk damaging (themselves or the recorder) that distinguished machine.
The Nagra III here though is a little more difficult, requiring the use of at least a screwdriver to get
into it's guts, though like the Ferrograph it does have a deck mechanism that hinges upwards away
from the electronics and main casing. Once inside one can easily appreciate the care and skill used
in this machine's manufacture, it was remarkably expensive but also remarkably well put together.
Indeed one might conclude that this machine was built to near military standards of construction.
The Nagra III is a single motor transport with belt drive of the supply an take-up reels. The motor
has servo speed regulation and its velocity is sensed by (I believe) capacitive means. Using servo
feedback control of a fairly low inertia low voltage DC motor was very advanced for the time,
certainly amongst the first, or perhaps the very first application of this type of technology to an
audio tape recorder. Though as with most innovations once the technology becomes available them
then it is not long before a number of people also get on the bandwagon. A good low voltage DC
servo motor system is of course ideal for a portable tape machine, as a heavy capstan flywheel is
not needed, and the motor should be able to better cope with random machine movements and
varying power supply voltages. Accurate speed control is also vital in film sound recording
applications to maintain 'lip sync', as (in those days) the film camera and the sound recorder would
both free run as independent machines after the clapper board was used.
Most of the electronics are built into the seven screened enclosures. The motor servo system and
the R.F. bias electronics are the un-screened mass of circuitry towards the rear of the machine in
the above photo (the batteries live under this area). This machine was built in the days of
Germanium transistors and because these devices were both physically and electrically rather
delicate they have quite long 'legs' to minimize the possibility of the junctions being damaged by
the heat of the soldering iron. Some of these transistors are also retained on thin metal plates to
(presumably) also help with heat sinking. The electronics of this machine are and interesting
combination of the old and the (then) very new, as they seem to be a transition between the earlier
construction techniques of point to point wiring and the newer ways of the printed circuit. One
may notice that while high quality un-masked glass fiber printed circuit boards are used (printed
solder masks having not yet been invented), many of the components are also wired onto turret
lugs riveted to these PCBs. This indicates that this is a completely hand wired machine, with the
circuit boards 'populated' and soldered manually. Solder masked, reflow soldered circuit board
techniques were yet to be developed, and it was only much later that printed circuits would be
stuffed, soldered and cropped by machine. But not until the very robust, both thermally and
electrically, silicon transistors had been introduced first. The type of electronics used in this
machine very much relied upon largely unsung human (mostly female) dexterity and skill in its
production. Now long gone and replaced by computer controlled robots of course.