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Covert
Recorders
Nagra
  
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Nagra SN
Precision miniature tape recorder

Nagra SN is a covert high-precision minature audio tape recorder introduced in 1970 1 by Nagra Kudelski in Cheseaux-sur-Lausanne (Switzerland), and produced for several decades. The device was popular among the law enforment and intelligence community, as it could be concealed on the body. During the Cold War it was used at either side of the Iron Curtain, by agencies like the CIA and the Stasi. The Soviets even made a clone (Yachta), and one SN unit made it to the moon. The Nagra SN was also used as a high-end voice recording device in the motion picture industry.

As the device measures only 147 x 100 x 26 mm, 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/SNN recorder of which the protective cover 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 use in motion pictures. An optional pilot system keeps the audio in-sync with the film.
  
Nagra SNN subminiature audio recorder with tape

The body of the recorder is milled out of a solid block of light metal alloy and all components are created with a fine eye for detail. Because of its stability, its superb audio quality and unrivalled mechanical reliability, the Nagra SN became a desired gadget in the motion picture industry as well as in the law enforcement and intelligence community, in particular for covert recordings.

  1. First prototype in the early 1960s, but not taken into production until 1970.

Storage box for Nagra SN
Inside the storage box
The closed Nagra SN
Nagra SN with protective cover in place
Nagra SN and protective cover
Nagra SNN subminiature audio recorder with tape
Nagra SNN subminiature audio recorder with tape
Nagra SNN subminiature audio recorder with tape, seen from the top
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Storage box for Nagra SN
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Inside the storage box
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The closed Nagra SN
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Nagra SN with protective cover in place
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Nagra SN and protective cover
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Nagra SNN subminiature audio recorder with tape
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Nagra SNN subminiature audio recorder with tape
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Nagra SNN subminiature audio recorder with tape, seen from the top

Features
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 audio 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 side, pressing the operation lever will cause the Nagra SN to start recording. Any previous recording will be erased first.

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The image above shows the Nagra SNN, which was the first model released to the general public in 1970, after the initial prototype of the early 1960s. It uses the full tape width for recording a mono signal at two tape speeds – 9.5 and 4.75 cm/s – selectable with a screwdriver-operated switch under the take-up reel. It is the only model with an ALC threshold adjustment knob.

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Two years later, in 1972, the Nagra SNS was introduced. It was nearly identical to the SNN, but recorded at half-speed (4.75 and 2.38 cm/s) onto one half of the tape width. This reduced the audio quality, but increased the overall recording time significantly. After several reliability improvements, Nagra introduced the SNG in 1973 — a mono half-track version with a HiFi frequency response, followed in 1977 by the SNST — a single-speed (2.38 cm/s) stereo version.

As the latter had a limited frequency response of 170-5000 Hz, Nagra released the SNST-R in 1999. It ran at four times the speed of the SNST (9.5 cm/s) and had a HiFi frequency response of 50-15,000 Hz. It is believed that only a limited quantity of SNST-R units was ever manufactured.

Nagra SNN subminiature audio recorder with tape, seen from the top
Nagra SNS with tape, seen from the top
Green plastic sockets at the left side of the Nagra SN
Close-up of the recording heads
Close-up of the beautiful modulation meter
Pulling-out the lever
Pushing the lever upwards to lock it in place
Close-up of the (red) ALC adjustment
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Nagra SNN subminiature audio recorder with tape, seen from the top
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Nagra SNS with tape, seen from the top
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Green plastic sockets at the left side of the Nagra SN
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Close-up of the recording heads
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Close-up of the beautiful modulation meter
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Pulling-out the lever
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Pushing the lever upwards to lock it in place
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Close-up of the (red) ALC adjustment

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.

Rewinding
Due to the limited size of the device, there is no automatic rewind feature. Instead, the operator has to fold-out a small crank, located to­wards the rear center, and wind it back 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. This uncouples the mechanism. Next, unlock the crank by pushing-in the horizontal grey knob at the top, and erect the small pin. Now rewind by turning the pin clockwise.
  
Rewinding the tape manually

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)
Rewind crank in storage position
Releasing the rewind crank
Raising the pin
Rewind crank release button
Rewinding the tape manually
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Removing the protective ring
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Fixating the reel
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Guiding the tape over the tension arm
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Guiding the tape along the heads
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Guiding the tape between the capstan and the pressure roller
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Guiding the tape onto the take-up reel
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Winding the tape onto the take-up reel
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Start play-back (or recording)
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Rewind crank in storage position
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Releasing the rewind crank
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Raising the pin
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Rewind crank release button
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Rewinding the tape manually

History
The first prototype of the Nagra SN was developed in the early 1960s, possibly after a request from US President John F. Kennedy, 1 who was very keen on making covert recordings [8]. Due to the untimely death of President Kennedy and the fact that miniature components were not widely available at the time, the device was not further developed until ~1970. When the SN/SNN was introduced in late 1970, it was clearly aimed at the motion picture industry as well as the law enforcement and intelligence community, hence the two recordings speeds: 9.5 and 4.75 cm/s.

It is often suggested that the letters 'SN' stand for Série Noir (Black Series), but there appears to be no eveidence for that. It seems more likely that it simply means Small Nagra, which is what it was called internally at Nagra [7]. According Nagra, the SN/SNN was taken to the moon on one of the Apollo missions in the early 1970s [1].

In 1972, the SN/SNN was followed by the Nagra SNS, which featured half-track and slow-speed, making it more suitable for covert recording of long conversations. Because of this, the SNS became a standard tool for many law enforcement agencies and intelligence services worldwide. Later models were suitable for HiFi, stereo and HiFi-stereo recording.  Overview of models

For many years, the SN was Nagra's flagship for the law enforcement community, but also for the motion picture industry (film) as it was small enough to be hidden on the actor's body. The Nagra SN was succeeded in 1984 by the much smaller Nagra JBR, but was kept in production until after 2000. Over the years, more than 15,000 units were sold [5]. Furthermore, existing Nagra SN and other models are still being serviced by authorised Nagra service centers to this day (2019) [5].

  1. John F. Kennedy was the 35th President of the United States. He was inaugurated on 20 January 1961 and was assasinated 22 November 1963.

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Russian clone   Yachta
The success of the Nagra SN recorder did not go unnoticed. Around 1987, the design was copied by the Soviet Union (USSR) for use by Cold War intelligence services like the GRU, the KGB and the Ministry of Internal Affairs (MVD). The device was made by the Special Machinery Factory in Kiev (Ukraine) and its exterior is a near-exact copy of the Nagra SN, except for the audio level meter.

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The image above shows an original Nagra SN (right) next to Yachta — the Soviet clone of the Nagra SNST (left). On Yachta, the meter is replaced by an LED that indicates a low battery level. The rest is virtually identical, as shown in the image above. Internally, the device is completely different however, as it was made with special integrated circuits from Soviet production.

 More about Yachta



Accessories
Storage case
Operating Instructions
Spare audio tapes
Microphone
Mic
Remote control unit
Pilot tone generator
Leather storage case
DSP-1 audio amplifier
Pilot transfer unit
Storage case
The Nagra SN was originally supplied in a black rectangular storage cassette that measures approx. xx x xxx x xxx cm. Inside the case is a padded area for the recorder, the microphone, the remote control unit and spare batteries.

The operator's manual is usually stored behind a panel in the top lid of the case.
  
Storage box for Nagra SN

Operating instructions
...   

Spare audio tapes
...   

Microphone
A range of microphones was available for the Nagr SN, such as the omni-directional lavalier version shown in the image on the right. It has a metal clip at the rear that allows it to be fitted to the clothing.

It should be connected to the Mike/Line socket at the left side of the recorder. Note that the recorder will automatically switch to recording mode as soon as the microphone is connected.
  
The special microphone

Remote control unit
When the Nagra SN is hidden under the clothing, it will be difficult to start or stop a recording. To overcome this, the wired remote control unit shown in the image on the right was available.

The remote unit consists of a slide switch in a grey plastic enclosure, fitted to a 1 metre long grey cable with a custom Nagra 5-pin plug at the end. It should be connected to the 5-pin socket (generally green) at the left side of the recorder.
  
Remote control unit

Leather storage case
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Leather carrying bag for Nagra SN

Pilot tone generator
...   
Nagra SGXS crystal pilot generator

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

Pilot transfer unit
...

 More information
  
Nagra Pilot Transfer Unit

Storage box for Nagra SN
Inside the storage box
Nagra SGXS crystal pilot generator
Left side view with locking screw
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
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Storage box for Nagra SN
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Inside the storage box
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Nagra SGXS crystal pilot generator
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Left side view with locking screw
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Close-up of the case contents
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The special microphone
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Remote control unit
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Close-up of the microphone front
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Clip at the rear of the microphone
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Remote control unit
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Separate remote control unit
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Box with two tape reels

Interior
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
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One of the three large bolts that hold the rear cover
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Nagra SN interior
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Bottom view (solder side of the PCBs)
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Close-up of the PCBs
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Rear view of the meter
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The slim-line motor
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View of the components on one of the PCBs
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Block diagram in the case shell

Models
Year Model Description Speed 2 Qty 3
~1960 SN Prototype ? none
1970 SNN Mono full-track, ALC 9.5 + 4.75 cm/s 3972
· SNN-2 Thicker chassis (1.5 mm instead of 1 mm) · ·
· SNN-3 Improved control and reliability · ·
1972 SNS Mono half-track, half-speed 4.75 + 2.38 cm/s 6031
· SNS-2 Thicker chassis (1.5 mm instead of 1 mm) · ·
· SNS-3 Improved control and reliability · ·
1973 SNG Mono half-track HiFi 1 4.75 + 2.38 cm/s 42
1977 SNST Stereo 170-5000 Hz 2.38 cm/s 3844
1999 SNST-R Stereo HiFi 50-15000 kHz 9.5 cm/s 15
      Total 15,000+
  1. Version with full frequency response.
  2. Specifications supplied by Günter Hütter [4].
  3. The numbers in the rightmost column show the production quantity by the year 2000 [3]. Please note that according to Nagra these numbers are inaccurate and incomplete [5]. The total production quantity of the SN was more than 15,000 units.

Specifications
SN/SNN
  • Model
    SN
  • Year
    1970
  • Type
    SNN
  • Year
    1970
  • Channels
    1 (mono)
  • Track width
    Full
  • Tape speed
    9.5 and 4.75 cm/s
  • Input
    ≥200Ω, 3-80µA
  • Response
    60-15.000 Hz ±2dB
  • Automatic with adjustable theshold
  • Recording time
    18µ tape: 26 min, 12.5µ tape: 38 min
  • Power
    2 x 1.5V AA-size battery
  • Consumption
    125 mA
  • Dimensions
    147 x 100 x 26 mm
  • Weight
    574 g
SN/SNS
  • Model
    SN
  • Type
    SNS
  • Year
    1971
  • Channels
    1 (mono)
  • Track width
    Half
  • Tape speed
    4.75 and 2.38 cm/s
  • Input
    ≥200Ω, 1.7-45µA
  • Response
    50-6.000 Hz ±3dB
  • Automatic
  • Recording time
    18µ tape: 1h 40m per track, 12.5µ: 2h 30m per track
  • Power
    2 x 1.5V AA-size battery
  • Consumption
    125 mA
  • Dimensions
    147 x 100 x 26 mm
  • Weight
    574 g
SNST
  • Model
    SN
  • Type
    SNST
  • Year
    1977
  • Channels
    2 (stereo)
  • Tape speed
    2.38 cm/s
  • Response
    170-5.000 Hz
  • Automatic
  • Recording time
    3.5 hours (max.)
  • Dimensions
    147 x 100 x 26 mm
SNST-R
  • Model
    SN
  • Type
    SNST-R
  • Year
    1977
  • Channels
    2 (stereo)
  • Tape speed
    9.5 cm/s
  • Response
    50-15.000 Hz
  • Automatic
  • Recording time
    30 min.
  • Dimensions
    147 x 100 x 26 mm
Glossary
ALC   Automatic Level Adjustment
When recording, this adjustment controls the compression level threshold. It is located between the erase head and the tape tension arm, and has a red knob. Note that ALC is only available on the SNN model. Other models have a white plastic cap in this position.
TTA   Tape Tension Adjustment
This is a mechanical adjustment that controls the tension of the movable tape guide (tape tension arm) at the front left corner. It is present on all models.
Documentation
  1. Nagra SN, Operating Instructions. Mode d'emploi 1
    User Manual (English/French). Code No 20.20.002.153.
    Nagra Kudelski SA. Date unknown.

  2. Nagra SN leaflet
    Nagra Kudelski SA. Date unknown. 4 pages.

  3. Nagra SN brochure
    Nagra Kudelski SA. Date unknown. 8 pages.

  4. Preisliste für Miniatur-Tonbandgerät SN und Zubehör
    Price list of Nagra SN recorder and accessories (German).
    Austerlitz Electronic GmbH. 12 December 1970.

  5. Nagra SN, Set of Schematics 1
    Nagra Kudelski SA. 12 May 1971.

  6. Nagra SN, Spare Parts 1
    Nagra Kudelski SA. 1 October 1975.

  7. Nagra SN, Service Manual 1
    Nagra Kudelski SA. October 1983.
  1. This manual is available from Nagra Audio [1][5].

References
  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, Production overview and quantities
    Internal Nagra document. Date unknown, est. 2000.

  4. Günter Hütter, Overview of models and specifications
    Personaly correspondence, May 2018.

  5. Nagra Audio, Personal correspondence
    January 2019.

  6. JBond (username), Nagra Stories Sound-men won't ever tell
    JWSound Group forum, 29 January 2015.

  7. JBond (username), The Mystery of the Nagra 'Serie Noir'
    JWSound Group forum, 5 August 2016, updated February 2018.

  8. Wikipedia, John F. Kennedy
    Visited 1 May 2021.
Further information
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Crypto Museum. Created: Sunday 25 March 2012. Last changed: Monday, 02 May 2022 - 16:07 CET.
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