May 26, 1954
Issue #2

 

PERSPECTA SOUND DIRECTIONAL SOUND SYSTEM

1. DRAWINGS Distributed 5/25/54
AS-2959 Perspecta Sound System......................Wiring Diagram
AR-2957 Perspecta Sound Control Panel............Wiring Diagram
AQ-2961 Perspecta Sound System......................Block Diagram (Loew's Theatres)
AP-2960 Perspecta Sound Modification...............Rack Layout
AQ-2958 Equalizer
Booklet - - - Perspecta Stereophonic Sound Integrator (Fairchild Recording Equipment Company)
with 3 Drawings - (Limited distribution - full distribution will be made at a later date)

 

2. DESCRIPTION OF PERSPECTA SOUND SYSTEM

Perspecta Sound is a system whereby the program recorded on a single optical track can be routed in the reproducing system to any of three amplifier-speaker channels, or to any combination of them, in any proportion, as determined by three sub-audible control signals recorded on the track. This system is used to give the reproduced sound direction or source localization.

If the action of the picture should require that the sound emanate from an actor on the far left, a 30-cycle control signal is given full amplitude while 35 and 4O-cycle control signals are given lower amplitude; the result is that the recorded program is carried at full level in the left hand amplifier and speaker system and at considerably lower level in the center and right channels. If the source should be slightly left of center, the 30 and the 35-cycle signals are recorded at slightly less than full amplitude and the 40-cycle signal low amplitude. For music the program may be spread over the three channels equally, or one side or the other may be emphasized as various sections of an orchestra may stand out from time to time. The levels of the control signals are controlled by the mixer during the re-recording of the film.

At the present time, three channels are accommodated, the control signals being 30, 35 and 40 cps. for the Left, Center and Right channels respectively. It is planned to add a 25-cps signal to control the Surround channel at a future date.

The Theatre sound system elements required to secure the benefits of Perspecta Sound are as follows:

(1) Standard optical film reproducers
(2) Sound Changeover
(3) Equalization facilities and low-pass filter
(4) Preamplifier and Integrator
(5) Channel balance facilities
(6) Ganged volume control
(7) Three channels of power amplification
(8) Three speaker systems on stage Page 1

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A booth with a standard optical reproducing system and a magnetic 3 or 4-channel stereo system will require the addition of items (3), (4), (5) and (6). Booths with standard optical reproducing facilities and no stereophonic equipment will require the addition of all but items (1) and (2).

The Perspecta Sound sound track adheres to the old standards for location and width, and, for the present, releases will be on the old type film base with wide sprocket holes, therefore, no changes in the film equipment are required to reproduce it. If a theatre is not equipped to utilize the benefits of Perspecta Sound, the track will be reproduced in the normal way and the entire program will be carried by the single speaker. For this reason, prints in this process are referred to as "compatible".

 

3. DESCRIPTION OF INTEGRATOR

The element of the reproducing system which responds to the control signals by delivering the program into various channels at various levels has been called the "Integrator". This equipment as manufactured by Fairchild Recording Equipment Corporation consists of a 17-tube Integrator unit and a two-tube Power Supply unit on a separate chassis.

The total signal voltage from the sound changeover is stepped up in the Integrator input transformer (500:100,000 ohms), controlled by a slotted-shaft potentiometer mounted on the preamplifier sub-assembly, amplified in two stages of twin triode and a cathode follower, and delivered to a 600-ohm bus at a level not exceeding 1 V (-2.2 dbm) for the program and 0.16 V (-13.7 dbm) for the control or "carrier" signal. The program signals and the control signals are then separated by a high-pass filter (-3 db at 63 cps) associated with a program circuit and a complementary low-pass filter associated with a control circuit.

The program signal from the HPF is amplified in a triode amplifier and a phase inverter; it is then fed push-pull to the signal grids of three pairs of 6BE6 pentagrid converters, one pair for each stereo output channel. These tubes pass the program signal at levels depending upon the bias applied to their first grids, the bias being derived from the control signals.

The control signals from the LPF are amplified in the first section of twin diode V2 and fed to the inputs of three band-pass filters each associated with a separate control channel. The control signals are then adjusted by potentiometers accessible at the front of the Integrator Unit. Thereafter they are amplified by pentodes and again filtered. The combination of the two filters in each control channel passes a band 2 cycles wide, attenuates frequencies 2 cycles from the center frequency by 3 db and frequencies 5 cycles from center by 20 db. The outputs of the second filters are push-pull and they are rectified by dual diodes, metered, carried through contacts of a relay, when the latter is energized, smoothed in two-section R-G filters and applied to the first grids of the associated pairs of 6BE6 tubes. Thus if, for example, a 30-cycle control signal is present it passes through the filters of the corresponding control channel, it is rectified and smoothed and applied as a bias to the 6BE6 tubes for the Left Stereo channel, allowing the program signal to pass in that channel at a level determined by the amplitude of the control signal. The smoothing filter has a time constant of about 1/4 second so that fairly rapid changes can be made in the control of the program signal, The potentiometers and the meters provide means of setting the sensitivity of the channels at the correct operating point, the Perspecta Sound Calibration Reel being used as a signal source for these adjustments.

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Several protective features are incorporated in the Integrator, and the relay is provided for this purpose. If all "carriers" drop to a level reading "20" or less, the relay releases within 1 to 2 seconds, biasing the 6BE6 tubes for channels #1 and #3 to cutoff and #2 to 4 to 6 db below full Perspecta output. When any carrier signal reaches "50" or more the relay pulls up in 6 to 12 seconds, reestablishing control of the individual channels. This operation is referred to as a "fail safe" function. A panel switch "OFF - AUT0" is provided so that operation of the relay may be prevented regardless of the control signals, this again producing channel 2 operation.

The relay control circuit derives AC signal from the outputs of the second filter in each control channel. These signals are mixed, passed through a control potentiometer "Auto Switching

Sensitivity the "OFF - AUTO" switch, a cathode follower, a pair of germanium diodes and a delay circuit; thence through a triode and a cathode follower to the relay winding.

The operation of the circuit elements in the relay control circuit is not immediately apparent, and a brief description is here given as an aid in possible trouble shooting. The DC potential of cathode of V3-1 is blocked by C21. The series diode passes current only when the cathode of V3_1 swings toward negative, and C19 is therefore charged and this biases the grid of V2-2 negative to cutoff. The plate potential of V2-2 therefore rises to +B value, charging C20 to this voltage and carrying grid of V3-2 with it. V3-2 passes strong current to operate the relay. When no signal is present, grid V2-2 is at cathode potential, current flows in V2-2 through the 5.1 meg. plate resistor causing the potential of the plate and therefore the grid of V3-2 to drop to a small positive value. The current in V3-2 under this condition is insufficient to hold the relay in operation and it drops out. The shunt diode operates on the opposite half cycle and serves to prevent C21 from becoming charged up by the current through the series diode and blocking the action described.

To provide proper operation of the 6BE6 tubes, several positive and negative voltages are provided by the Power Supply. Two voltages may be found from the Fairchild drawings, but for convenience they are listed here as they appear on TB5 of the Integrator:

Terminal.............Voltage


1................+275
2................Ground
3................6.3 V AC
4................6.3 V AC
5................-5
6................variable, approx. -8 V
7................-18.5
8................115 V AC
9................115 V AC
10..............-20 Page 3

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4. AQ-2958 EQUALIZER

This equipment is supplied to provide means for producing a desirable system response characteristic. It consists of L.F. Rise and H.F. Rise R-C networks, connected ahead of the input transformer on the Integrator, and a Low-Pass Filter connected between the output of the Integrator Preamplifier and the Integrator circuit. The R-C networks are varied by replacing elements and the filter characteristic is varied by strapping terminals. The entire unit is housed in a 4" x 4" x 2" box which must be installed on the Integrator chassis.

The AQ-2958 Equalizer mounts flat on the rear of the Integrator chassis in the lower RH corner just below the input transformer.

Remove the 2 screws, nuts and washers which fasten capacitor mounting brackets inside the chassis at this location.

Thread 2 #6 PK screws supplied through these brackets and chassis holes into the holes provided in the equalizer can.

The shielded cable and 3 wire twisted cable from the equalizer should extend out to the right when viewed from the rear and these cables enter the integrator through the large knockout hole in the lower right hand (from rear) side of the integrator.

Connect cables as shown on System Wiring Diagram AS-2959.

Components R1, R2, C1 and C2 are supplied as loose parts. The values selected may be easily mounted by making a right-angle bend in each lead so they may be inserted in the holes in the turret lugs and then soldered. Cut off excess of wires so they do not extend through the panel when inserted in the lugs.

When components are changed in the equalizer section which change the insertion loss, the P-1 calibration reel should be again run and gain of integrator preamplifier reset. A standard response characteristic for Perspecta Sound prints has not yet been established and experience to date has been limited to special demonstration material. It will therefore be necessary to determine the desirable response in the earlier installations from the print to be used for the first showing. It is expected that the new "multi-bilateral" sound track to be used with Perspecta Sound prints will allow a greater high frequency response than has been used with optical prints and possibly some low frequency lift will be desirable. The following will serve as a guide:

CPS	40	70	130	300	500	2000	3000	5000	7000	8000
Note 1	-	0.0	0.0	0.0	0.0	0.0	0.0	-2.5	-7	-12
Note 2	-	+3.5	+2.0	+1.0	0.0	0.0	0.0	-1.5	-6	-10
Note 2	-	0.0	0.0	0.0	0.0	0.0	-0.5	-3.5	-10	-15


Note 1: Suggested curve for first listening test.
Note 2: Recommended range
Reading will not be obtained at 40 cps due to the H-P filter in the Integrator. Page 4

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A test sample of "Gone With The Wind" as released for Perspecta Sound gave very pleasing results in one theatre with the following system curve:

40	70	130	300	500	2000	3000	5000	7000	8000
-	2.0	2.3	0.6	0.1	-0.2	-1.4	-5.6	-12.1	-15.3

We have no information as to whether or not this curve will be suitable for other theatres, and it is believed that in most cases the high frequency response should be better.

You may find that on installations using 7400 reproducers and 7381 preamplifiers that the low pass filter section of the equalizer need not be connected; the normal roll off of these optical systems being sufficient.

5. ADJUSTING THE INTEGRATOR

The booklet Perspecta Stereophonic Sound Integrator, supplied by Fairchild Recording Equipment Company, contains full instructions for setting up the adjustments. A few additional notes are added here.

The circuits can be overloaded if the input signal is excessive. For this reason, the first step in adjustment is to set the 1,000 cps signal level as measured on the 600-ohm bus following the preamplifier sub-assembly. Tip jacks are provided for this purpose in all but a few very early models but it may be more convenient to connect the AS-1800 Meter (AC volts) to terminals 5 and 6 of TB1. (The Fairchild booklet seems to indicate that a 600-ohm load should be shunted across the circuit for this measurement. This is not intended, however, and no load should be added). The instructions state that the level should be adjusted to "0" dbm This is an indication of +0.8 db on the AS-1800 Meter since the correction for 600-ohms is -0.8 db.

Under conditions where the optical changeover switch is preceded by a PEC transformer and fader with no preamplifier this level may not be obtained within the gain limitations of the integrator preamplifier. In these cases the screwdriver gain control on the integrator preamplifier should be set for maximum gain. Successful operation may be obtained at considerably below the "0" DBM point as long as the panel meters can be adjusted to 70 micro-amperes when running the calibration film.

The setting of the front-wall optical fader or volume control used when making adjustment per Par. 2, Page 8 of the instruction booklet must be clearly marked in a permanent way and the operators instructed to use this setting for Perspecta prints. The ganged volume control on the AR-2957 Perspecta Sound Control Panel must be used for volume adjustments when projecting a Perspecta picture.

If the pickup sensitivity of the film reproducers varied from time to time or between machines on changeover, the level of the control signals will also vary. A change of 1 db in the control signal produces a change of approximately 1.5 db in the same direction in the level of the program signal at the output of the integrator.

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Consequently a change, for example, in exciter lamp current which increases the output of the soundheads 1 db will cause the volume to rise about 2.5 db. It is therefore very important to balance machines carefully, avoid darkened exciter lamps, and take any other measures that will aid in stabilizing pickup sensitivity.

It is also important to balance the machines as to response at the control signal frequencies. The reading of the panel meters on the Integrator when the Calibration Reel is running provides the only direct indication of this response balance, but readings at the output of the Integrator on signals 3, 5 and 7 will also reveal unbalance when it occurs. A change in control signal level of 10 microamperes as indicated on the panel meter produces a change of 2.25 to 2.5 db in the program. Direct readings of the control signals can be made with the AS-1800 meter at the Test Point pin jacks.

In Par. 6, Page 9 instructions are given for setting the "mono-gain" control on the Power Supply to establish the proper relation between gain under Perspecta and single-channel operation.

The objective is to provide the same dialogue level for either operation. However, the carrier level recorded when dialogue is to reproduce predominantly on any single speaker is 50 to 60 microamperes while the test reel is recorded at the maximum signal of 70 microampere9. Thus the test film carrier levels produce a system gain augmented 4 to 6 db over 'hat for normal Perspecta Sound dialogue. It has been found that the required setting of "mono-gain" is with the control close to the extreme ccw position.

In Par. 5, Pages 8 and 9, it is indicated that desired "spatial" effects are sometimes produced by setting the gains of the two outside channels about 2 db above that of the center channel.

Our experience has been that this causes voice volume and apparent quality to change conspicuously and undesirably when the action shifts from center to side screen or the camera angle is shifted.

 

6. FAIRCHILD SCHEMATIC DRAWING G21407 - CORRECTION

The reference drawing shows the relay winding on the incorrect side of the swingers, indicating the released condition for automatic control, The reverse is true. When the relay is energized, the neon lamp lights and the automatic control features of the circuit are effective.

The schematic shows many of the significant socket voltages but does not number the tube terminals. The terminal numbers may be identified from reference to the sketches "Tube Connections" at the left edge of the drawing. For example, R29 is connected to cathode terminal 8 of V3.

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7. CALIBRATION TEST REEL #P1

The above test film which contains recordings of control signals is required for adjusting the Integrator. The films are in short supply for the present but Loew's have arranged to ship "one such test reel to each Loew's Theatre city where one or more Perspecta Stereophonic Sound installations will be made, and those test reels are to remain in the Projection Room of the key Loew's Theatre in that city. They will always be available for Altec inspector use for Perspecta Stereo adjustments in such Loew Theatres".

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-INSERT-

 

New York, N.Y.
September 1954

PERSPECTA PRINTS

(Hum from Control Frequencies when Used On Standard Optical Systems)

C. S. PERKINS-Northwestern Division.

Where Perspecta prints are shown in theatres not equipped with integrators, we have experienced some trouble due to reproduction of the control track at levels sufficient to be disturbing either in direct audibility or through modulation and beating effects on the principal sound. This is particularly true in those systems where the low end response has been raised above that at 1,000 cycles. We have not yet accumulated sufficient data to be able to tell just what the low end response at 30, 35 and 40 cycles must be in order to eliminate this disturbance.

You will undoubtedly receive calls from exhibitors running Perspecta prints but not equipped for Perspecta operation, and it is imperative that such calls be so reported as to give adequate data to the Engineering Department for their analysis and the suggestion of corrections to the Field to meet all such instances. In those cases where you have already experienced this difficulty, we must know what corrective measures were taken and whether or not these measures were completely satisfactory or unsatisfactory. Furthermore, it is highly desirable that we receive information as to the curve of the system when the trouble is experienced and the curve as taken after correction or partial correction.

Some systems are provided with means for the suppression of low frequency response to a more or less satisfactory degree; some are not so provided. In anticipation of more complaints on this subject, I will try to indicate some of the methods which might be used for Field correction or improvement of operation under the conditions.

Obviously, what we would like to do is to be able to produce the response at the control frequencies of 30 to 40 cycles without affecting to any material extent the reproduction at 100 cycles and up. Actually we can tolerate, in some instances at least, a greater response in sound systems below 100 cycles so long as the reproduction of the control signals is kept below a minimum, which has not yet been thoroughly explored. An attempt should be made to keep these control signals at a level which is not disturbing, and yet does not affect response materially from 70 cycles up, with the exception as noted below.

The desired characteristic is that of a high pass filter with nominal cut-off at about 70 cycles. Such a filter is expensive for any one system, and where we service so many types of systems, costs are increased materially due to the varied impedance of the circuits in which it must work, in other words, several filters designed for various conditions. Another characteristic of this filter is that it should affect the pass frequency gain as little as possible.

One effective means of obtaining a desirable characteristic, and which may be applied to various systems is covered in E.B. File 50.22 Loudspeaker Systems, "A" series, Voice of the Theatre, Addendum #6. This consists of tuning the transformer, the input of the 42 amplifier, the intermediate of the 46 amplifier or the intermediate of the 86 amplifier so that it tunes to approximately 70 cycles, with a rapid drop of response below that frequency. As a matter of fact, the peaking frequency for tuning the condenser may be slightly increased without material harm, so long as the response in the frequency range concerned with male speech is not sufficient to become boomy or unpleasant. The values indicated and curves shown in paragraph 4.2 of this bulletin are suggested, and it would appear should be sufficient to completely suppress disturbing influences from the control frequencies. If it is desired to raise this frequency slightly, the values of condensers indicated may be decreased but not, I would think, more than a 25% decrease.

The above method cannot be used at any location where the transformer is loaded. This eliminates output transformers of main amplifiers or output transformers of preamplifiers which are followed by a fader. These conditions would be the equivalent only of a series condenser having a rather slow equalization slope, resulting in considerable loss of speech range quality in order to effect a sufficient reduction of the control frequencies.

Note that in this instance, the frequencies from approximately 50 cycles to 130 or 80 are increased due to the resonant peak of the condenser and the effective inductance of the transformer. This is not harmful as a general thing, since it will only emphasize music bass.

In dealing with the resonating of a transformer of unknown characteristics, in other words other than those specifically mentioned above, the transformer may be tuned to approximately 70 cycles by feeding an oscillator signal into the system and reading the output with variation of capacity until a peak is reached at approximately 70 to 80 cycles. This value then should reduce the control frequencies considerably.

In some systems such as Motiograph and Simplex, where there are no transformers prior to the output transformer feeding the stage line, the above method cannot be used. In certain RCA systems it can be used. The selection of adjustments for Simplex and Motiograph systems as a whole, as covered by E.B. File 4.64 Transmission Test Corrections, will permit a reasonable compromise, but will not permit a real bass boost without detrimental control frequency reproduction.

While I am on this subject, I think that the tendency in the past might have been to increase bass response beyond the natural state in order to get what the public might call "pleasing" sound in music. Adherence to Academy curve response would, we believe, result in little or no disturbance from control.

In Western Electric systems, it would seem that there is sufficient control in most cases, coupled with the method given above to produce sound of a very agreeable quality. In wide range systems where the D-49C amplifier carries a considerable bass boost, this should be eliminated and made reasonably flat, and the modification to the tuned transformer made as indicated above. Let me point out that any method of equalization which increases the low end by an RC network will usually continue to rise below any frequencies indicated on the Transmission Correction Chart, File 4.64. Somewhere there must be a limit to this effect.

In extreme conditions the following steps might help:

1. Reduce the value of the grid resistor in the input of the preliminary amplifier in order to arrive at an effective cut-off due to the capacity of the input coupling condenser. It is impossible to give values for all conditions.

2. In amplifiers not having a feed-back loop around the stages involved, reduce the capacity of any plate to grid coupling condensers in order to arrive at the same result. This is not in itself a completely good method. However, if carried out, where possible, in three successive isolated stages (isolated by intervening vacuum tubes), the result can be better than nothing can.

3. A condenser in series with a 500 ohm circlet, terminated at each end in 500 ohms, will provide a low end cut-off if properly proportioned, but at the expense of attenuation of higher frequencies. For example, a 2 mfd condenser will drop 40 cycles about 7 db, 70 cycles about 3 1/2 db, 100 cycles about 2 db and 200 cycles about 7/10 db. This is a rather vicious treatment of voice frequencies unless other equalization in the system tends to increase them without increasing 40. A transmission run will tell you where to go here. A larger condenser will arrive at less 40 cycle attenuation and less attenuation at all other frequencies.

Methods such as juggling the network shelving are completely ineffective. Condensers in low impedance circuits, such as stage lines, are likewise difficult because of the very large condensers necessary.

This memorandum is intended only as a pointer, to possibly assist you in a temporary correction of these difficulties. It does not necessarily mean that the correction must be made this way and remain that way. In connection with RC networks, E.B. File 40.64 "Testing Procedures General, Two-Terminal R-C Equalizer Design" may be helpful. We are happy to assist you by telephone to the Division Office, or your Branch Manager can help with these problems.

In the meantime, the Engineering Department requires information from you in order to assist their study. They are at present designing methods to take care of this trouble, but without adequate information, they are somewhat stymied. Make your reports complete, show the response as found when the complaint is made and as left, with your method of correction or partial correction, and what you did precisely to effect the change. All copies of such reports should be routed in the normal manner to the Division and Headquarters. It is suggested, however, that you mark the report in such a way that it stands out, and may be selected for review and analyses, by indicating in bold letters at the top of the report "TROUBLE DUE TO CONTROL FREQUENCIES".

Inasmuch as this work is the result of a change in the art and the method of recording optical track, we should probably charge for our services at the rate of $6.50 per hour in accordance with Schedule 9B. However, when no material expense is involved, it would probably be detrimental to our interests to ask for the payment of one hour or so for this work. There will be some occasions where, due to unknown characteristics, considerable time may be involved, and in these cases we should obtain an SSA, signed for time and material required. Otherwise, you should submit a memorandum substantiating any reason for not obtaining such an order.

EDITORS NOTE: This memo was sent by Mr. Perkins to all of the Inspectors in his Division. Since it contained a lot of pertinent information, we felt that it would be helpful to inspectors in the other divisions. Consequently, we are releasing it through the EXCHANGE, to be kicked around. Let’s have your comments and reports or your experiences.

-END OF INSERT-

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June 1, 1954

Addendum #1

ALTEC SERVICE CORPORATION

PERSPECTA SOUND DIRECTIONAL SOUND SYSTEM

SIMPLEX 4 STAR SOUND SYSTEMS

The first installation of Perspecta Sound equipment in connection with a Simplex 4 Star Optical System has shown the need for additional steps to be taken to Obtain optimum response and quiet switching.

Referring to Fig. 1, of Wiring Diagram AS-2959 strap the ground side of the 10,000 ohm winding of one transformer to the ground side of the 10,000 ohm winding of the other transformer. Also, shunt the 500 ohm winding of the transformer associated with the AM-1000 Amplifier with a 510 ohm resistor.

It is suggested that Drawing AS-2959 be marked accordingly.

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June 11, 1954

Addendum #2

ALTEC SERVICE CORPORATION

PERSPECTA SOUND DIRECTIONAL SOUND SYSTEM

TRANSMISSION TESTS

When using ED-35 Multi Frequency Test Films to make frequency response runs on Perspecta equipment, it is normally only possible to check the center channel, the left and right channels being biased to cut-off in the integrator,

It is essential that a frequency response run be made on all channels, as is done when CinemaScope equipment is installed.

Until a proposed test reel having recorded the requisite control signals is available, a simple temporary wiring change will activate all channels.

Remove the wire normally connected to Terminal 10 of the power supply and temporarily connect it to Terminal 6 of the power supply together with the wire normally connected to Terminal 6. This puts an operating bias on all channels, allowing quality checks on all, with standard optical prints.

At the conclusion of the measurement, restore the wiring to normal.

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June 11, 1954

Addendum #3

ALTEC SERVICE CORPORATION

PERSPECTA SOUND DIRECTIONAL SOUND SYSTEM

AR-2957 CONTROL PANEL

Some of these panels may be supplied with Peerless S-448-q Transformers instead of Kenyon T6 as indicated on this drawing.

Connections to the two types of transformers are as follows:

T-6	S-448-Q
Primary Term 1	Term 9
Primary Term 6	Term 10
Secondary Term 8	Term 3
Secondary Term 7	Term 4
Terms 6 & 7 strapped	Terms 4 & 10 strapped
Terms 3 & 4 strapped	Terms 1 & 6 strapped
	Terms 7 & 12 strapped

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June 21, 1954

Addendum #4

ALTEC SERVICE CORPORATION

PERSPECTA SOUND DIRECTIONAL SOUND SYSTEM

AQ-2958 EQUALIZER

Response data shown on Drawing AQ-2958 is given as an indication of variations that may be secured by use of the components included in the kit. Other combinations of the components furnished will give intermediate values or a shift in the position of the curve on the frequency scale.

The use of a higher value capacitor with any given resistor will shift the curve downward and less capacity upward without affecting the insertion loss. Curves "C" and "D" illustrate this affect. An increase in the value of resistor with any given capacitor will increase the insertion loss and, therefore, the overall rise.

The need has been shown, based on reports from the first few installations completed, for an HF Rise curve that has a greater effect than that shown for Curve "E".

An example of this is in systems using the TA-7400 Reproducer and TA-7381 Amplifier, as shown below:-

		2KC	3KC	5KC	8KC
Normal response		-1.6	-3.0	-6.4	-12.5
Suggested	Min.	0	-0.5	-3.5	-15
Response	Max.	0	0	-1.5	-10
Equalization	Min.	+1.6	+2.5	+2.9	-2.5
Required	Max.	+1.6	+3	+4.9	+2.5

Equalization Suggested	2KC	3KC	5KC	8KC
Min.-HF – 1000 ohm/.068MF	+1.5	+2.6	+4	+5.0	Curve L
LPF-.05MF/.05 MF	0	-0.2	-1.0	-10.4	Curve G
Total	+1.5	+2.4	+3.0	-5.4
Max.-HF – 2200 ohm/.03MF	+1.9	+3.2	+5.5	+7.4	Curve K
LPF- 0.3MF/ 0.3MF	-0.2	-0.5	-1.7	-5.4	Curve I
Total	+1.7	+2.7	+3.8	+2.0

It is intended to add a 2200 ohm resistor and .03 MF capacitor to the kit on future shipments of the equalizer. In the meantime and until this change can be put into effect, components should be purchased locally, to obtain optimum response

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July 22, 1954

ALTEC SERVICE CORPORATION

STEREOPHONIC SOUND SYSTEMS

SIMPLEX XL PERSPECTA STEREOPHONIC SOUND SYSTEMS

The Simplex G-2461 Plug-In Warping Assembly is supplied for mounting in the integrator cabinet and is intended to be connected into the preamplifier circuit. This equipment should not be connected between the preamplifier and the integrator nor between the transformer and the preamplifier. The proper point of connection is between the input terminal strip TB-3 on the top of the chassis and terminals 1 and 2 of the terminal strip TB-l on the under side of the chassis, which places the equalizer in series with the primary of the input transformer. To accomplish this it will be necessary to remove the plugs from the Warping Assembly leads and it may be necessary to extend the shielded cable. The leads found connected to the male connector should be connected to the input strip TB-3 and the leads to the female connector should be connected to the strap TB-1 under the chassis.

The integrator currently furnished by National Theatre Supply Company is of a form that is not readily serviced. To make service possible, the wiring to the equipment at the time of installation must be made long enough to permit the equipment to be removed from the cabinet without disconnecting the wiring and stood on end on a table or shelf located next to the cabinet. The theatre should be instructed to provide this table, Without such a table trouble shooting will be virtually impossible.

The following extract from a field report contains useful suggestions:

"The cabinet supplied by N.T.S. is drilled and tapped for mounting the Integrator in the bottom area, above which is a 2" blank panel, then the Power Supply is supposed to be mounted and a ten inch blank panel at the top. The G-2461 equalizer is mounted inside the left side of the cabinet directly behind the Power Supply. This arrangement is very bad. To reach the gain control pot of the Integrator pre-amp for adjustment it would be necessary to lay the arm across the AC terminals of the P.U.; the equalizer is inaccessible; and it would be impossible to change tubes in the Integrator.

I had the electrician drill and tap the cabinet so as to mount the P.U. at the top and the blank panels in the center. Thus with the blanks removed the equalizer, Pre-amp, and the integrator are accessible.

The Integrator is mounted on a pan. If relay contacts need adjustment it is necessary to remove the Integrator entirely from the cabinet, turn it upside down, remove bottom cover and make adjustments. This is very inconvenient and makes it necessary that all cables and wiring be sufficiently long that Integrator may be removed without disconnection. To facilitate removal of the Integrator I had the electrician provide two pieces of wood 1" high by 2" wide which were placed in the bottom of the cabinet and acted as runners, or a support for the Integrator as it is moved in or out."

Page 12

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Page 13 Missing

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File in Perspecta
Sound booklet
After Page 13


ALTEC SERVICE CORPORATION

PERSPECTA DIRECTIONAL SOUND SYSTEM

PROCEDURE FOR ADJUSTING PERSPECTA SOUND INTEGRATOR

1. Check d-c voltages on terminal strip TB5, See Page 3 for nominal values.

2. Connect oscillator between test jacks. Set level to +0.8 db (actually 0.0 dbm in 600 ohms) as indicated on red scale of oscillator panel meter with oscillator output attenuator set to C and frequency set to 35 cps.

3. Connect DC voltmeter between terminal 3 of 12AU7 V3 and ground or chassis (neg.). This connects the meter across the relay coil.

4. Set center channel control so that panel meter reads 50 microamperes. Turn Auto Switching Sensitivity to zero to insure that relay is not operated, then advance it slowly until relay clicks in, lighting the indicator lamp. The first time this operation is carried out it may require several minutes for the operate current to build up while the 4 mf - 450 volt electrolytic capacitor C20 forms through 3.3 megohm resistor R25. (Note that the value for R25 of 5.1 megohms as shown on the schematic has been reduced to 3.3 megohms to reduce the operate time).

Readjust Auto Switching Sensitivity as necessary to secure relay operation at 50 microamperes and release at 20 microamperes assuming that the relay itself is in correct adjustment. (See Step 5).

5. The relay should operate when the voltage across its coil is approximately 100 to 105 volts, and it should fall out at approximately 50 volts. If it does not meet these requirements adjustment should be made. However, an application of glyptol to the brass armature adjusting screw is evidence that the relay itself was carefully adjusted at the factory for proper sensitivity, and for simultaneous engagement and release of all contacts. The setting should not be disturbed except as a last resort.

6. Reset carrier to 70 and check the timing of the auto switching circuit by means of the manual switch. When the switch is thrown to Auto, the relay should pull up in 6 to 10 seconds.

7. Repeat Step 6 with 30 and 40 cps.

8. By means of a transmission test, insure that the optical systems are in correct adjustment and in good condition. Replace any questionable lamps, set guide rollers, inspect optics for deterioration, etc.

9. Connect the oscillator to the photo-cell through 10 megohms and measure the response at 30, 35 and 40 cps relative to 1000 cps. Repeat for each machine. The response must be alike within about 1/2 db for each machine at the carrier frequencies. The actual response itself is not critical so long as 30 cps is not down more than about 6 or 8 db. If response at carrier frequencies is not balanced between machines equalization will be necessary. Facilities are available in the TA-7381 Amplifier. For other systems it may be most convenient to shunt the PEC resistor with a resistor in series with a condenser. If there is a .5 meg resistor in the d-c circuit shunted by another .5 meg resistor in the preamplifier, open the second and add a condenser in series with it of .001 mf for 1/2 db rise at 30 cps, .00075 mf for 1 db, .0005 for 2 db and .00035 mf for 3 db rise at .30 cps. The values may be confirmed or others selected with the aid of the oscillator - 10 meg. connection. In the case of the MI-1040 Sound Head it is suggested that .5 meg in series with an appropriate capacitor be connected between +90 and the PEC anode or across the high side of the PEC transformer as dictated by the physical problem. It may be noted that special equalization for balancing response has not been necessary in many cases.

Page 14

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10. Using a 1000 cps loop, balance machines carefully.

11. Now proceed with adjustment of the Integrator using the special test film as described on Page 5 of bulletin Perspecta Sound Directional Sound System and in the Fairchild instruction booklet.

Steps 1 to 7 can be completed during a show and even before the equipment is wired into the system. The possibility of time delays occasioned by operating troubles and equipment defects provides a strong argument for testing the Perspecta equipment as soon as possible. It is also practicable to set up the equalizer during the show, using the oscillator to confirm the curves and

basing the selection of equalization on the known response of optical systems of the type employed, In this case the output of the Integrator can be strapped through to a stereo amplifier at the switching panel and the tests made without disturbing the show.

Page 15

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File in Perspecta
Sound Booklet after
Page 15.

PERSPECTA DIRECTIONAL SOUND SYSTEM

RCA STEREOPHONIC SYSTEMS

August 25, 1954

Low system gain has been reported on some early installations of Perspecta Equipment including the Fairchild Integrator and Altec AR-2957 Panel in connection with RCA Stereophonic Systems. This is primarily due to the lower gain of RCA Power Amplifiers which are usually rated 50 DB from 500 ohm input. It is possible in the PG-301 Series and PG-300 Systems to connect the AR-2957 Panel ahead of intermediate amplifiers instead of just ahead of the power amplifiers and thus obtain additional gain for Perspecta operation. This cannot be done in the PG-300-A System as no intermediate amplifiers are used.

The recommended procedure is as follows:

PG-300 System (MI-10266 and MI-10261 Pre-Amplifiers)

1. Remove Red and Black wires in MI-10288 Pre-Amplifier Assembly which connect Terminals 3 and 4 of 10 pin Jones female plugs J4, J6 and J8 to Terminals 11 and 12 respectively of 10 pin Jones female plugs J5, J7 and J9.

2. Connect TS - 3 of AR-2957 Panel to Terminals 3 and 4 of J4 (MI-10266-#1), J6 (MI-10266-#2) and J8 (MI-102661-#3).

3. Connect TS-4 of AR-2957 Panel to Terminals 11 and 12 of J5 (MI-10261-#1), J7 (MI-10261-#2) and J9 (MI-10261-#3).

4. Disconnect and splice leads connected to Terminals 1 and 8 of T-l, T-2 and T-3 on AR-2957 Panel.

NOTE 1 - This method provides an additional 31 DB of system gain for Perspecta operation.

NOTE 2 - The RCA Stereo volume control is used for both magnetic and Perspecta reproduction. The volume control on the AR-2957 Panel should be strapped out or used only as a system gain fixed setting control.

PG-301 Series Systems (MI-9268 and MI-9362 Pre-Amplifiers)

1. Disconnect the RG-62U cables found connected to the input terminal board, Terminals 1 and 2, 3 and 4, and 5 and 6, of the MI-9269 chassis in the MI-9374 Rack.

2. Splice additional lengths of RG-62U cable to those disconnected and connect the other ends to TS-3 of the AR-2957 Panel.

3. Using RG-62U cable connect input terminals 1 and 2, 3 and 4, and 5 and 6 of the MI-9269 chassis to TS-4 of the AR-2957 Panel.

NOTE 3 - This method provides an additional 34 DB of system gain for Perspecta operation. It is believed that this increase will be more than can be tolerated and therefore it might be advisable to disconnect the transformers on the AR-2957 panel. Under this condition the increase in system gain will be of the order of 20 DB.

Page 16

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File in Perspecta
Sound Booklet
after Page 16

ALTEC SERVICE CORPORATION

PERSPECTA DIRECTIONAL SOUND SYSTEM

AP-2993 THREE CHANNEL ATTENUATOR STRIP

LOEW THEATRES

October 1, 1954

When magnetic stereo sound systems using the 150 and 1500 Type Amplifiers were installed, it was found desirable, in a number of instances, to reduce the gain of the 1500 Type Amplifiers in order to operate with the gain control of the 150 Type Amplifier at approximately mid-position.

Later when Perspecta Sound Systems were installed it was found necessary, due to the lower gain settings of the 1500 Type Amplifiers, to operate near or at the top of the Perspecta master gain control.

To correct this condition an assembly coded AP-2993 has been ordered for each Loew Theatre, where 1500 Type amplifiers are installed, and it is to be installed behind the AR-2957 Perspecta Panel on a convenient routine call when the magnetic and Perspecta circuits are not in use.

It consists of 3 - 15 db attenuator pads assembled on a terminal strip which, by the method of mounting, are inserted in the lines from channels 1, 2 and 3 of the 150 type amplifier.

INSTALLATION PROCEDURE

1. Remove fanning strip with wiring attached from TS-3 on AR-2957 Panel

2. Remove nut from top mounting screw in TS-3 on AR-2957 Panel.

3. Connect black, white and gray wires to TS-3 as shown on Drawing AP-2993 packed with the assembly.

4. Mount the AP-2993 Strip directly in back of TS-3 on AR-2957 Panel by means of the threaded spacers provided, using the top mounting screw in TS-30

5. Reconnect fanning strip to AP-2993 terminals.

6. Raise gain of 1500 Type Amplifiers approximately 15 db. (To obtain same gain control setting for magnetic reproduction and a setting approximately 7 steps lower on Perspecta).

Page 17

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File in Perspecta
Sound Booklet
after Page 17


ALTEC SERVICE CORPORATION

PERSPECTA DIRECTIONAL SOUND SYSTEM

ED-50 TEST REEL

October 1, 1954

GENERAL

The ED-50 Test Reel is made by the Research Council to Altec’s specifications for the purpose of adjusting Perspecta Sound equipment. It replaces any further use of Test Reel P-1 referred to in the Fairchild Instruction Booklet. Its use in accordance with these instructions will result in a changed calibration or adjustment of the integrator which will then be in accordance with the so-called "new standard".

DESCRIPTION

The film contains two sound tracks, one on each edge of the film printed head to tail. One track is used (a) to indicate the balance of output from the several machines at mid-frequency and at the frequencies of the carriers, and (b) to adjust the integrator. The other track permits measurements of frequency response and level at the system output of each channel. Leaders are supplied similar to those described in equipment bulletin ED-35, File Reference 4.20, except that the titles are appropriate to the present film. The frequencies and footages are as follows:

 

INTEGRATOR	ALIGNMENT
Frequency	Footage
Leader	17
1000	45
None	10
30	15
None	3
35	15
None	3
40	15
30 + 800	42
30	5
35 + 1000	42
35	5
40 + 1200	42
None	5
1000	43
Leader	17

FREQUENCY	FILM
Frequency	Footage
Leader	17
30 + 1000	35
30	3
30 + 70	15
30	3
30 + 5000	15
30	3
30 + 8000	15
30	14
35 + 1000	35
35	3
35 + 70	15
35	3
35 + 5000	15
35	3
35 + 8000	15
35	14
40 + 1000	35
40	3
40 + 70	15
40	3
40 + 5000	15
40	3
40 + 8000	15
Leader	17
TOTAL	329


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The levels recorded on this test reel are as follows: 800, 1000 and 1200 cycles 6 db below 100% of 76 mil variable area modulation; 30, 35 and 40 cycles 26 db below 100% of 76 mil variable area modulation. These levels have been adopted by the Research Council as a motion picture industry practice.

USE

1. Thread up the test film from leader labeled "Start Integrator Adjustment" and connect the AS-1800 meter to the output of the Perspecta Sound preamplifier. Record the response at 1000, 30, 35 and 40 cycles.

2. Stop the machine after the 40 cps section, rewind and repeat the same operation in the other machine or machines.

3. Take the necessary steps to balance machines at mid-frequency and carrier frequencies. Substitute the oscillator for the test film where this speeds the procedure.

4. Repeat the running of the same track of the test reel on one of the machines, set the preamplifier gain control to produce an indication of –2.2 db (0.55 V) on the meter on the initial 1000 cycle section. Adjustments are not made on the sections containing 30, 35 and 40 cycles alone, and while these are being reproduced reconnect the meter at the system output, center channel.

5. Adjust the carrier channel sensitivity control on Section 30 + 800, 35 + 1000 and 40 + 1200 to secure meter indications of 50 microamperes. Additionally, on the section containing 35 + 1000, observe and record the reading of the meter at the system output (center channel).

6. On the conclusion of the 40 + 1200 cycle section, the relay should drop out any the indicator light go out placing the Fairchild integrator in the "mon-aural" condition. The system output level should be observed on the final 1000 cycle section or center channel and the Mono-Gain control adjusted to provide the same output level as was recorded during the 35 + 1000 section.

7. Rethread the test reel in the same machine without rewinding, calling the operator’s attention to the necessity for keeping the emulsion toward the light. The position of the titles will guide the operator.

8. Record all readings at the system output with the meter connected first to the left channel, then to the center and finally to the right channel. When 35 + l000 is reproduced, the center channel balance control should be adjusted so that the level is the same as observed for 30 + 1000, left channel, and when the section containing 40 + 1000 is reproduced, the right channel balance control should be adjusted to produce the same reading.

9. Complete transmission test should be made using ED-35 and with the meter connected at the output of the center channel.

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NOTES

SENSITIVITY OF RELAY OPERATING CIRCUIT

Section 4 of bulletin "Perspecta Directional Sound System", page 14, states that the Auto Switching Sensitivity is to be adjusted to operate at 50 microamperes in 6 to 10 seconds and release at 20 microamperes.

This instruction is amended. The relay should operate at 40 microamperes in 6 to 10 seconds. Care must be taken to avoid a final setting permitting operation much below this figure since the release level will correspondingly be lower and trouble in operation from commercial releases may result.

DISCUSSION

The system set up in accordance with the new standard as detailed above will have approximately 4 db more gain when running a given feature than it had when set up according to P-l Test Reel due to the readjustment of the carrier controls. This is a highly approximate figure and should not be used as a basis for a short-cut adjustment. Theoretically, no readjustment of the preamplifier gain control will be required but it frequently will be found that a small correction is indicated.

The revised adjustment of the relay will avoid mal-functioning in the case of prints in which the carrier is somewhat low in level.

All Perspecta Sound installations adjusted after receiving this instruction shall be in accordance with these instructions and all past installations on service shall be readjusted as soon as practicable in accordance herewith.

DISTRIBUTION OF ED-50 TEST REEL

A number of copies have been assigned to the Division offices for allocation as the circumstances require.

ED-50 Test Form Omitted - MBH

Pages 20 & 21

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File in Perspecta
Sound Booklet
after Page 21


ALTEC SERVICE CORPORATION

PERSPECTA DIRECTIONAL SOUND SYSTEM

FAIRCHILD INTEGRATOR

November 3, 1954

In some theatres, when the Fairchild Integrator is installed, it may be found impossible to calibrate at 50 microamperes when using the ED-50 film.

A modification of the Fairchild Integrator will correct this condition. It should be attempted only if the above condition exists.

MODIFICATION PROCEDURE

(a) Replace R-24 - 2000 ohm resistor with a 1000 ohm resistor.

(b) Remove green wire from Terminal 9 on Transformer T2 and connect it to Terminal 10.

(c) Strap Terminals 8 and 9 on Transformer T2.

Serial number 576 and above will not require this modification.

Recalibrate the integrator after modification is completed.

Page 22

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File in Perspecta
Sound Booklet
after Page 22


ALTEC SERVICE CORPORATION

PERSPECTA DIRECTIONAL SOUND SYSTEM

SIMPLEX XL600 SOUND SYSTEM

AM-1151 CABINET KIT

December 9, 1954

(Refer to Drawing W-1199 AM-1151 Cabinet Kit, Schematic)

A. Capacitor C6 (.1 mf, 400V) attenuates the control tones excessively when the AM-101 Volume Control Amplifiers in Four Star Sound Systems are matched to the XL600 System.

B. In such instances, it is recommended that a capacitor of not less than .25 mf, 400V be substituted at installation until the change is incorporated in kits shipped from the factory.

Page 23

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File in Perspecta
Sound Booklet
after Page 23

ALTEC SERVICE CORPORATION

PERSPECTA DIRECTIONAL SOUND SYSTEM

SIMPLEX XL600 SOUND SYSTEM

CALIBRATION OF AM-1150 CONTROL UNIT

December 9, 1954

A. The Motion Picture Research Council Test Film ODS-1(ED-50) has two sound tracks; one on each edge of the film printed head to tail. One track is for calibration of the Control Unit and the other to check and adjust the electrical characteristics of the individual channels.

B. Calibration Procedures Using ODS-1 (ED-50) Test Film.

1. Remove the AM-1034 Cabinet Cover and, before starting the film, set the controls as follows.

2. AM-1151 Cabinet Kit Selector Switch - Set on FOR PERSPECTA SOUND FILM.

3. AM-1150 Control Unit - Set controls as follows:-

a. Power Switch ON.

b. Function Switch S1 on NORM.

c. Meter Switch S3 on position "1".

d, Tone Gain Control R1 (on chassis) approximately 3/4 clockwise.

4. AM-207 System Selector Box (when Single Film Stereophonic is installed) - Depress the FOR PERSPECTA SOUND FILM button.

NOTE:- Apply a label (supplied with the Am-1151 Cabinet Kit) marked FOR PERSPECTA SOUND FILM over the designation DOUBLE FILM STEREO.

5. Set each front wall volume control for normal operating level.

NOTE:- Apply a label (supplied with the Am-1151 Cabinet Kit) marked "FOR PERSPECTA SOUND FILM SET TO _______" in a prominent location on the front of each cabinet and record the normal volume setting in the blank space. Do not change the setting of these volume controls during the running of Perspecta Sound Film. The AM-1151 Cabinet Kit Volume Control must be used to regulate volume.

6. Calibrate per Table 1. R27, R45 and R63 are adjusted so that M1 reads 25.

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TABLE 1

CALIBRATION OF AM-1150 CONTROL WITH ODS-1 (ED-50) TEST FILM

Step	Frequency	Time Sec.	Setting Meter Switch S3	Adjust Control	Meter Reading M1
1	Leader	10	-	-	-	-
2	1000	30	-	-	-	R1 setting 3/4 clockwise. Record output level of channel 2 with VTVM.
3	None	6	-	-	-	-
4	30	10	1	R27	25	Readjust R1, if necessary to obtain reading of 25 on M1 (See note: 1).
5	None	2	-	-	-	-
6	35	10	2	R45	25	R1 setting same as in step 4.
7	None	2	-	-	-	-
8	40	10	3	R63	25	R1 setting same as in step 4.
9	30 + 800	30	-	-	-	Retain R1 and R27 settings. Adjust AM-1151 Cabinet Kit Volume Control to obtain the same output level in channel 1 as recorded in step 2 (See Note: 2)
10	30	3	1	-	25	-
11	35+ 1000	30	-	-	-	Retain R1, R45 and volume control settings. Check channel 2 output level. It should be within +/- 1 db of level recorded in step 2 (See Note: 2)
12	35	3	2	-	25	-
13	40 + 1200	30	-	-	-	Retain R1, R63 and volume control settings. Check channel 3 output level. It should be within +/- 1 db of level recorded in step 2 (See Note: 2).
14	None	3	-	-	-	-
15	1000	30	-	-	-	Check output level of channel 2. It should be within +/- 1 db of level recorded in step 2.
16	Leader	10	-	-	-	-

Page 25

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NOTES

1. If meter reading of 25 cannot be obtained, change R7 to 100K and readjust R1 and R27.

2. Each AM-1150 Control Unit output channel has an adjustable attenuator (terminals marked "0",

"-2" and "-4" db) for equalizing the output levels. Connected to -2 db terminal hen shipped. Adjust, if required, so that the output levels of the channels are within +/-l db of each other,

 

Page 26

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File in Perspecta
Sound Booklet
after Page 26
12-16-54

ALTEC SERVICE CORPORATION

PERSPECTA DIRECTIONAL SOUND SYSTEM

PERSPECTA SOUND REPRODUCTION

Troubles with volume of Perspecta Sound reproduction have been experienced with certain prints, In these cases the volume range is unnaturally exaggerated so that low levels may be too low and high levels too loud. Distortion may be observed in the same prints.

The exaggerated dynamic range may not be noticed when these prints are reproduced on a conventional optical sound system. If the system includes a Perspecta Sound integrator, however, the variation of the reproduced level of carriers as well as of program signals may produce a result that is sometimes rather extreme.

It has been established that these troubles exist in certain color prints and are not found in the sound negative. Trouble may appear only with one or two reels of a feature and may not be found in the same reels of a different print.

We are advised that the cause of the imperfections in the prints has been determined and that steps have been taken to insure that no prints will be released in the future with a defect of this kind. In the meantime, if trouble of the kind described is reported by a theatre, it should be suggested that the picture be reproduced over the "regular" optical system or through the integrator with the latter set for monaural reproduction.

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