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Nagra SN
Precision miniature tape recorder

The Nagra SN was a high-precision minature audio tape recorder built by Nagra-Kudelski in Cheseaux-sur-Lausanne (Switzerland) from 1970 onwards. It was based on a prototype from the early 1960s and was built to the highest possible Swiss standards. During the Cold War, the Nagra SN was popular at either side of the Iron Curtain: both the CIA and the Stasi loved it.
As the device measures only 14.5 x 10 x 2.6 cm, it could easily be hidden under a person's clothing, making it the ideal companion for inconspicuous (covert) recordings. The image on the right shows a typical Nagra SN recorder of which the protective lid has been romoved.

The audio quality of the SN, that records onto narrow 3.81 mm wide tape, is unparalleled. Furthermore, the quartz driven capstan drive motor is so stable, that the recorder is suitable for the film-making business. A special pilot system keeps the audio in-sync with the film.
The Nagra SN recorder ready for use

The body of the recorder is milled out of a solid block of light metal alloy and all components are created with the finest eye for detail. Because of its extreme stability, its superb audio quality and unrivalled mechanical reliability, the Nagra SN became the preferred recording machine for many law enforcement agencies around the world and for the intelligence community at large. It was used numerous times in the motion picture business, both on-screen and as a production tool.

The letters 'SN' stand for Série Noir (Black Series) as the recorder was originally ordered by US President John F. Kennedy for use by the American secret services [2]. According to the Nagra website, the SN was even taken to the moon on one of the Apollo missions in the early 1970s [2].
In 1972, the SN was followed by the Nagra SNS, which featured half-track and slow-speed, making it more suitable for covert recording of a conversation. Because of the extended recording time, it became a standard tool for many law enforcement agencies and intelligence services.

Due to the limited size of the device, there was no mechanism to rewind the tape automatically as with later recorders. Instead, the operator had to fold-out a small crank that is located at the top center, and wind the tape back manually. The image on the right shows how it was done.
Rewinding the tape manually

First, the recorder has to be placed in REWIND mode, by pulling-out the operation lever at the bottom left and pushing it up a little, so that it is locked in place. This uncouples the mechanism. Next, unlock the rewind crank by pushing-in the horizontal grey knob at the top and erect the small pin at the center of the crank. You may now rewind the tape by moving the crank clockwise.

For many years, the Nagra SN was the most propular professional body wearable audio recorder in the law enforcement scene, but also in the motion picture industry (film) were it was used for recording the actor's voice when shooting a movie. In total, nearly 14,000 units were built by the early 1980s. Eventually the Nagra SN was succeeded in 1984 by the even more sophisticated and smaller Nagra JBR: a body wearable recorder without controls and with a separate playback unit.
Storage box for Nagra SN Inside the storage box Nagra SN with protective cover in place Nagra SN and protective cover The closed Nagra SN The Nagra SN recorder ready for use Close-up of the recording heads Close-up of the beautiful modulation meter
Close-up of the case contents The special microphone Remote control unit Close-up of the microphone front Clip at the rear of the microphone Remote control unit Separate remote control unit Box with two tape reels
Rewind crank in storage position Releasing the rewind crank Raising the pin Pulling-out the lever Pushing the lever upwards to lock it in place Pushing the lever in to start recording or play-back Rewind crank release button Rewinding the tape manually

The image below shows a top view of the Nagra SN. The leftmost reel is the so-called supply reel. The tape is fed from the supply reel, over the tape guide and the tension arm, along the three heads: first the (black) erase head, then the recording head and finally the play-back head.

When no microphone or line input is connected, the Nagra SN acts as a play-back device. Turning the recorder ON by pushing-in the operation lever, will start play-back. If a suitable microphone or line input is connected to the rightmost green socket at the left, pressing the operation lever will cause the Nagra SN to start recording. Any previous recording will be erased first.
Tape loading
Loading a fresh tape onto the Nagra SN is pretty straightforward and is similar to loading tape on a domestic tape recorder. Place an empty reel on the axle at the right. It will be used as the take-up reel. The reel should be locked by rotating the knob at the centre about 90 degrees clockwise.
Place a loaded reel on the left axle, in such a way that the tape comes down at the left, and lock the reel. Put the mechanism in LOAD mode by pulling out the operation lever at the left and locking it in place. The device is now unlocked and the tape can be moved freely. Ensure that the plastic tape protection clip is removed.

Guide the tape, following the black arrow, over the first tape guide and then under the tape tension arm at the bottom left. From there, guide the tape along the three heads and then between the capstan and the pinch roller.
Winding the tape onto the take-up reel

Now load the tape onto the take-up reel as shown in the images below. Ensure that the tape does not 'slip' so that the take-up reel can pull the tape through the machine. Now start play-back by pushing-in the operation lever at the bottom left. For recording: connect a microphone first.
Removing the protective ring Fixating the reel Guiding the tape over the tension arm Guiding the tape along the heads Guiding the tape between the capstan and the pressure roller Guiding the tape onto the take-up reel Winding the tape onto the take-up reel Start play-back (or recording)

DSP-1 Audio amplifier
Althoug the Nagra SN was primarily intended for covertly recording conversations, the unit was also capable of playing back a recorded session. Normally, when playing back, the a pair of headphones had to be connected to the 3 mm jack sockets at the rear left.

In order to play back the sound in, say, a room, Nagra developed the special DSP-1 amplifier in the late 1970s. It was battery-powered and was connected to the phones socket of the Nagra SN.

 More information
Click for more information about the DSP-1 amplifier

The interior of the Nagra SN can be accessed by loosing the three large bolts at the sides of the device and pulling away the rear shell of the case. The interior of the recorder will now be visible. It consists of seven small high-quality PCBs, that all have their solder side facing upwards.
The image on the right shows a bottom view of the Nagra SN after the case shell has been removed. At the bottom right at the two 1.5V penlight batteries that power the machine. At the top right is the rear of the modulation meter. The large circular metal unit to the left of the meter is the slim-line motor that drives the unit.

Further details in the images below. The block diagram, that is printed inside the bottom case shell, should explain how the unit works.
Nagra SN interior
One of the three large bolts that hold the rear cover Nagra SN interior Bottom view (solder side of the PCBs) Close-up of the PCBs Rear view of the meter The slim-line motor View of the components on one of the PCBs Block diagram in the case shell

  • 1960: Nagra SN - Serie Noir (prototype)
  • 1970: Nagra SNN - Mono full-track recording (9.5 and 4.75 cm/s) (3972)
  • 1972: Nagra SNS - Mono half-track recording (4.75 and 2.38 cm/s) (6031)
  • 1973: Nagra SNG - Version of the SNS with full frequency response (42)
  • 1977: Nagra SNST - Stereo version (3844)
  • 1999: Nagra SNST-R - HiFi version of the SNST (15)
  1. The numbers in red indicate the production quantity by the year 2000 [4].

  1. Nagra - Audio Technology Switzerland, The Nagra SN
    Nagra website. Retrieved March 2012.

  2. Nagra - Audio Technology Switzerland, The Nagra SNST-R (special version)
    Nagra website. Retrieved March 2012.

  3. Nagra, Nagra SN Operating Instructions. Mode d'emploi
    User Manual (English/French). Code No Date unknown.

  4. Nagra, Production overview and quantities
    Internal Nagra document. Date unknown, but probably 2000.

Further information

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Crypto Museum. Created: Sunday 25 March 2012. Last changed: Friday, 02 December 2016 - 07:25 CET.
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