Technical Info about SAM

I transcribed the following text from an original document typed by Edward Ihnatowicz. The scans of the document are at the included at the side of the page. I have transcribed the document as closely as possible, including formatting and typos. I have added photos of SAM as it looks today (2004).



SAM is basically a electro-hydraulically operated sound-seeker.
It consists of:

1) The head - a Fibreglass shape compound of four parabolic reflec-
tors and carrying four microphones and their associated pre-ampli-
2) The Spine - a stack of eight articulated alluminium castings
each with a pair of antagonistically acting hydraulic pistons. Four
segments provide the horizontal movement and four the vertical.

3) The base - the wooden box containing two hydraulic servo-valves
and their associated manifolds ( the four segments of each set are
connected in parallel), the shut-off valve and a hydraulic accumulator

[Editor: it also contains the electronic circuit boards]


There are two completely independent channels, one vertical, one
horizontal, each actuated by its own microphones and operating its
own set of "vertebrae".
The principle of operation is that of phase shift discrimination.
The sound is picked up by two microphones separated by about 8" and
amplified independently by two cascaded operational amplifiers
( Motorola's MC1437 integrated circuits - dual 709) to give a gain
of about 1000000. The first stages are mounted directly behind the
microphones in the back of the head and have their power supply iso-
lated by a separate regulating circuit. The second stages saturate
giving a square wave with a phase difference proportional to the
angle of incidence of the dominant sound. After going through phase
delaying networks which slope the leading edges the waves are cross-
chopped by transistors 1 & 2, the resultant voltages being summed at
the summing junction of the following integrator. The output of the
integrator is thus proportional to the angle of the detected sound
and its polarity indicates its direction.
This output is further amplified by an output amplifier which
drives the hydraulic servo-valve which causes the movement of the
sculpture in the direction of the sound, thus closing the loop.


  1. A hydraulic power supply.
    Pressure : 200 lbs/sq. inch.
    Capacity : 15 gallons/hour
    Filtration : 5 microns
  2. A well regulated electronic power supply
    Voltage : positive and negative 16 V.
    Current : 300 mA.


  1. Connect the hydraulic supply (Do not mount the head yet).
    The nylon hose (3/8" O.D.) connected to the accumulator is
    the supply line.
  2. Bleed the system.
    This is done best by laying the base on the ground with a large
    bowl under the spine.
    Partly unscrew the bleeding nipples, one at a time - the nipples
    are in the centre of the blanking-off plugs - and undo with one
    of the Allan keys provided - and rock he related servo-valve's
    rocker manually fairly fast a number of times until no air bubbles
    are visible in the pipe. This works best if the bleeding nipple
    can be held uppermost.
    A small amount of air will not noticeably affect the performance
    of the sculpture.
  3. Test the electronic "Breadboard".
    Apologies are offered for the experimental state of the electro-
    nics - this is due to the lack of time.
    See separate instruction sheet.
  4. Mount the head.
    Thread the five wires through the centre of the spine into the
    box. Secure the head in position on the spine with the socket-head
    screw provided, leaving the separating waser (Recessed side down)
    between the head and the spine.
    Before tightening check that the head is free to move by equal
    amount to right and left of the central line of the base. (The so-
    cket screw engages with an actuating flange which can rotate over
    about 45 degrees.)
  5. Place the electronics board in the box and connect the leads from
    the head. There are four leads numbered 1 through 4 and a fifth
    which is the supply line. Solder the four leads to the four pins
    marked on the diagram II and connect the screens to earth. Solder
    the red lead of the supply line to pin No 17 (positive) and the
    yellow line to pin No. 18. Earth the screen.
  6. Connect the servo-valves.
    There are two leads connected to the output meters. These must be
    connected to the valve terminal blocks - left one to the left block
    and the right one to the right one. Also the blue lead connects
    with the blue valve lead and yellow one with yellow. The other
    two leads are earthed.
  7. Connect the electronic power supply.
    Positive lead to pin No. 15, negative to No. 16, earth to the centre


Connect a loudspeaker with a flexible lead to a audio signal gene-
rator set a 1K Hz to produce a low to medium level sound source.
Switch on the electronic power only and observe the movement of
the output meters. With thee loudspeaker held about 3 feet away
centrally in front of the head the needles should remain at zero.
Moving the loudspeaker to left or right should make the left meter
deflect to half full scale; moving it up and down should make the
right one do the same.
Switch off the speaker and turn on the oil pressure. The head
should remain stationary. If it drifts to one side, set the VR3
to zero (anticlockwise) and check that the output meter (left)
reads zero. Adjust with VR6. Return the VR3 to half full value.
If the meter remains noticeably off zero with no noise present
adjust the integrator offset with VR2.
Turn on the speaker and see if the head follows it. Turn it off
and see if it remains stationary. If it lifts or drops down, repeat
the adjustments on the vertical integrator and amplifier.


The pistons and the PTFE seals were newly made prior
to the dispatch to US and are therefore stiffer than they
will be after a week or so of operation. This means that if the
hydraulic pressure is adjustable it can be increased to about
350-400 psi for the first few days. It also means that
after some time the movement of the sculpture may become too
free & violent. The pressure can then be reduced but this will
work up to a point only since the vertical movement requires much
more power than the horizontal one.
Output of the horizontal integrator should then be reduced
by means of VR3. It may also help to increase the value of the
integrating capacitor to 5 mF.
In general do not expect a very accurate following of sound
by the sculpture. The frequency response of the microphones is
unequal and consequently certain sounds will produce turning
even when coming from dead ahead. The best that can be achieved
is a pleasant movement which is recognisably affected by ambient
Due to the unsophisticated materials and methods of construction
wear and consequent oil leakage will occur in time and must be
tolerated until it becomes excessive when rehoning of cylinders
and making of new pistons and/or seals must be undertaken.
I can supply special instructions if this is to be done
in the US.
Should it become necessary to dismantle any part of the spine
please bear in mind that the clearances of the pistons are very
small (less that 0.0001" in some cases) so that the work must
be carried out under extremely clean conditions.


  1. Connect the ends of the two output leads (blue & yellow)
    via two 1K resistors to earth to replace the torque motor's
    impedances. Connect the inputs of the two pairs of amplifiers
    (pin Nos. 1&2 and 3&4) together. Testing the two channels separat-
    ly, apply a sine wave of 0.5V at 1K Hz to the inputs of the two
    ouptut amplifiers in turn (pins 13&14) making sure that the
    two preceeding pots are not turned to zero, and check the wave-
    forms on an oscilloscope. Adjust for best shape with VR5-7.
    Adjust the VR6-8 to make the output meters read 0.
  2. Turn the signal down to 0 and adjust VR6-8 again to optimise
    the two readings.
  3. Return the signal strength to 0.5V and reduce the frequency to
    0.5 Hz and see that the meters reach half scale on each swing
    (The meters do not show correct values).
  4. Set the signal generator to give 0.2V at 1K Hz. Connect to the
    inputs of the two main amplifiers, one strapped pair at a time,
    (pins 1&2 and 3&4) and check the waveforms. They should be square
    and in phase. (pins 5&5 and 7&8).
  5. Check thee waveforms at the output of the fase discriminators
    (pins9&10 and 11&12).These should look as below.

  1. Check the readings of the output meters. Adjust the offset of
    the integrators with VRs 1&2 to obtain 0.
  2. Adjust the outputs of the front-end supply isolator with VRs 9 & 10
    to be plus and minus 15 V.





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