Hammond Instrument Co. J. Solovox Schematic

Hammond Instrument Co. J. Solovox

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Product Information:
Model:J. Solovox
Manufacturer:Hammond Instrument Co.

Schematics Content

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These readings are taken with a 1000 ohms-per-volt meter, having three scales of 15,150 and 600 volts. All voltages are taken with a line voltage of 117 and deviations of as much as 20 % may be caused by tine voltage variations. All controls are off, the volume control is in its softest position, and no key is depressed unless specified. The negative lead of the voltmeter is connected to chassis ground.

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The Solovox remains in tune indefinitely. However, because of the variation in pitch of the piano or other instrument with which the Solovoz is to be played, a tuning adjustment knob has been provided (The runing knob, about the size of the end of a pencil, projects through the curved surface of the woodwork near one corner of the tone cabinet)
Tuning the Solovox is a very simple matter as all of the tones are simultaneously tuned by making this single adjustment. Clockwise turning of the knob lowers the pitch and counter-clockwise turning raises it. For greatest accuracy, only the " CONTRALTO " VIBRATO OFF * and " DEEP TONE control tablets should be "in" and the middle octave F, F # or G keys of the Solovox tuned to the corresponding piano notes. (A control tablet is "in" when the top of the tablet is pushed in.)
Some favor tuning the Solovox a little sharper than the piano. We do not recommend too much of this, but in no case should it be at all flat to the piano.
There is another so-called " ine tuning adjustment " in the form of a control on the back of the tone cabinet. We suggest that you leave this alone, unless you want to get into something considerably more complicated, which is described further on in the technical section of this leaflet.

Limit of Tuning Whereas the turning of the single tuning knob tunes all botes of the Solovox, there is of course a limit which cannot be exceeded before some thing starts to go wrong with the notes in some octaves. (Notes " GARGLE, " or play exactly one octave up, or an exact musical fifth down.)
A second very simple adjustment will then fix these notes as well, and you will find it easy to make this adjustment if the occasion should arise, by following the procedure given below, called " Adjustment of Oscillators. "
Of course you need not bother with these adjustments unless you hear the " GARGLE " or the wrong octave effect.

Adjustment of Oscillators If some notes are noisy or play the wrong pitch, adjust the oscillators as follows: Push in the " SOPRANO, " and " DEEP TONE " controls, with all others off. Tune highest F # to corresponding F # on piano with tuning knob, paying no attention to what other notes do. Notes in the highest octave of the Solovox will now have the same pitch as the top Octave of the piano.

Holding down the F # key in the middle octave of the Solovox, place a screwdriver in the second oscillator adjustment " slot (See Figure 4 on backside of this leaflec) and turn it, first one way and then the other. The instrument will play higher than the right pitch in one direction, and tower in the other, while in the range between it will play an F # note of the same pitch as the second highest F # key on the piano. The pitch can be checked by making sure that there is no sudden jump in pitch between the Solovox middle octave B and the highest octave C, When the proper pitch is determined, find the farthest point in each direction where it will play this note, and place the slot exactly midway between these limits.
Holding down the lowest octave Solovox F # key, repeat this procedure with the " third oscillator adjustment. " As before, there should be a smooth transition in pitch between the B note of the octave being adjusted, and the C more of the next octave above, which has already been adjusted.
To adjust the fourth oscillator, hold down the lowest octave F # key with only the " CONTRALTO, " and DEEP TONE " controls in. For the fifth oscillator use " TENOR " and " DEEP TONE, " and for the sixth oscillator adjustment, use " BASS, " and " DEEP TONE, " holding the lowest F # key in each case. Adjustment of Maximum Volume Control Knob The maximum volume obtainable is controlled by a knob located under the keyboard to the left of the volume control, and regulates the maximum loudness when the knee-operated lever is all the way to the right. With the lever in this position the knob may be turned by the player to suit himself.
To determine where to set this knob, first set the controls to some useful setting such as " TENOR " and " DEEP TONE. " Now move the knee-operated volume control as far as it will go to the right hold down some key such as middle C, and turn the maximum volume control knob to the right until the volume becomes as loud as is useful. Do not turn the knob to the right any farther as to do so will only mean that the knee. operated volume control will become unnecessarily sensitive which is particularly undesirable for the novice and beginner.
When playing in large halls, or with other instruments, it may be found advantageous to increase this maximum volume very materially. Under these conditions, when a very loud tone is played, the quality will become very bright. This increase in brilliance produces many novel tent qualities which are useful under conditions where a loud piercing tone is desirable.

HOW THE SOLOVOX WORKS All of the notes of the Solovox are controlled by a single radio vacuum tube master oscillator operating at the audio frequencies of the highest octave of the instrument (2093-3951 c.p.s.). Each time a key is depressed, a switch under it tunes this master oscillator to the pitch associated with the key in this highest octave range. Thus, whenever a "C" key is depressed (the tuning key contacts for all the " C's " are in parallel), this oscillator is tuned to 2093 c.p.s., which is its lowest frequency. If a "B" note is depressed the frequency will be 3951 c.p.s., which is its highest frequency.
The output of this master oscillator controls the frequency of a first con trolled oscillator (called the " buffer oscillator ") which is adjusted to operate at the same frequency as the master oscillator. The output of this buffer oscillator, in tum, controls the frequency of the second controlled oscillator so adjusted to oscillate at one-half the frequency of the first oscillator. This new frequency corresponds to a note of pitch one octave lower than the buffer oscillator.
Similar cascaded oscillators provide pitches of two, three, four and five octaves below that of the buffer oscillator. In this way, each time the master oscillator is tuned to some given note, each of these six controlled oscillators produces a note which is in exact octave relation to the master, chus forming a series of six notes in exact octave relationships. The particular oscillator selected for sounding through an amplifier and speaker depends upon the particular playing key depressed, and also upon which of the BASS, TENOR, CONTRALTO OF SOPRANO controls are used. A vecond contact under each key operates an electrical relay, having contacts to select the desired oscillator.
There arc three relays one for each of the three octaves of keys. A further function of the second key contact is to transmit the signal to the speaker with a controlled rate of attack so as not to be musically abrupt. Tuned electrical circuits and tone controls similar to radio tone controls alter the quality of tone over a wide range

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The Oscillators All the tones of the Solovox are controlled by a single vacuum tube oscillator called the "MASTER OSCILLATOR " (Vi, Figure 1). This oscillator operates at any one of the twelve audio frequencies comprising the twelve notes of the highest octave range of the instrument (2093 cycles to 3951 cycles). Each time a key is depressed, a contact under it close to tune this oscillator to the pitch associated with that key. For instance, whenever any G key is depressed (there are three C keys on the key board), this master oscillator is tuned to 2093 cycles, its lowest frequency. If, on the other hand, any one of the three B keys is depressed, the master oscillator will operate at 3951 cycles, its highest frequency. If, on the other hand, any one of the three B keys is depressed, the master oscillator will operate at 3951 cycles, its highest frequency.
The condensers which tune the master oscillator are shown at the left of Figure I, and are located in the vibrato box fastened to the Solovox keyboard.
The output of this master oscillator controls the frequency of the first controlled oscillator, called the " BUFFER OSCILLATOR " (V2. Figure 1), which operates at the same frequency as the master oscillator.
Following this buffer oscillator is the SECOND CONTROLLED OSCILLATOR, whose frequency is tuned to approximately one-balf that of the frequency of the buffer Oscillator. Furthermore, its frequency is stabilized to be exactly one-half that of the buffer oscillator by applying a " locking " signal from the buffer oscillator to its grid circuit. The amount of this locking signal is regulated by a potentiometer. Thus, the output frequency of the second controlled oscillator is an outave lower in pitch than the master oscillator.
Similarly, the third, fourth, fifth and sixth CONTROLLED OSCILLATORS provide respective outputs of exactly two, three, four and five octaves lower in pitch than that of the master oscillator. A poten tiometer associated with each provides the correct amount of locking signal. It is to be noted that these controlled oscillators (being of the relaxation type), are readily tuned by altering their grid bias. It is the function of the tuning resistors in parallel with the tuning condensers to apply the appropriate grid bias to tune all of the controlled oscillators simultaneously to their approximate sub-octave frequencies. The amount of bias varies, depending upon which tuning contact is connected by a playing key, and the frequencies of the controlled oscillators shift correspondingly.
When no key is depressed, all the oscillators operate at their highest pitches ("B" notes). Thus, whenever a key other than "B" is depressed all oscillators shift simultaneously from their "B" frequencies to the frequencies corresponding to the key depressed. The tuning condensers accurately tune the master oscillator, and the tuning resistors tune the controlled oscillators. By interconnecting the controlled oscillators in Register Controls and Relays From the above, we see that whenever any one of the three G # keys, for instance, is depressed, the oscillators are tuned to provide a series of G # sotes in exact octave relations. The selection of the particular oscillator output to sound through the speaker is determined by a second contact uuder each of the playing keys. This second contact is called the CONTROL CONTACT. There are three relays connected to the control contacts one relay is operated any time a key in the lowest octave of playing keys is depressed, another relay for the middle octave of playing keys, and a third relay for the highest octave of playing keys.
Also, whenever a control contact is closed, a cutoff bias is removed from push-pull control tubes Vli and V12, causing them to transmit the signal with a smooth rate of tonal attack to the power output tube and speaker. This function of the control tubes will be explained subsequently,
Each of the three relays has a contact to connect the grid of the preamplifier tube V9 to the desired oscillator through the register controls (" BASS - TENOR - CONTRALTO SOPRANO "). For example, if we push in the " SOPRANO " control and depress the G key in the middle of the keyboard, the tuning contact will tune all the oscillators to the G notes of the respective octaves, and the control contact will operate the middle octave relay. This relay completes a circuit from the output of the second controlled oscillator, whose wire is numbered 25, through a 50,000 ohm register control resistor to the middle octave relay contact, and then to the preamplifier tube V9. Thus, the register controls function to shift the pitch range of the Solovox keyboard as a whole to four different positions. By simultaneously depressing two or more of these controls, a composite tone will be heard, consisting of the outputs of several oscillators simultaneously sounding in their octave relations to each other,
Other contacts associated with each of the relays serve to prevent undesirable tones from occurring when two keys are simultaneously depressed in adjoining octave groups through a legato style of playing on the part of the musician. If two keys are depressed within one of the three occa e groups. the lowest pitched of the two will be automatically selected for sounding through the speaker.

The " Mure "
The signal from the plate of the preamplifier tube V9 is ted to the grid of the " MUTE " tube. This tube operates nonlinearly to suppress the sharp curvature of the input signal wave form, and thus renders the tone more mellow. When this ruted effect is not desired, the mute switch is used to by-pass this portion of the circuit. " Deep Tone, " " Full Tone, " " First Voice, " " Second Voice " and " Brilliance " Controls Following the " mute " is a series of tone controlling circuits arranged to alter the frequency characteristic of the amplifier in a manner similar to radio tone controls. For instance, with " DEEP TONE " the signal develops across a condenser which emphasizes the low frequencies; with " FULL TONE " the signal develops across a resistor with a small condenser in shunt, which leaves the frequency characteristic essentially flat except for the very high frequencies: " FIRST VOICE " puts a resonance in the 500 cycle zone; " SECOND VOICE " puts a resonance near 1000 cycles; and with " BRILLIANT " the signal develops across an inductance, LIO, emphasizing the higher frequencies. It is to be noted that these tone control circuits are connected in series,
and may be used singly or in groups. Control Tubes Vor and V 12 As mentioned before, the control contacts under the playing keys serve to remove the cutoff bias from control tubes V11 and V12, as well as to operate one of the three relays. This is explained by considering that the cathodes of tubes Vll and V12 are connected to the mid-point of the voltage divider shown to the left of the control tubes in Figure
1. When no playing key is down, this voltage is about 165 volts positive with respect to ground, and, therefore, ulcs: tubes are cut off, When any playing key control contact is closed, the resistance of the relay coil is put in parallel with the 6000 ohm resistor and this causes the cathode voltage to drop to 50 volts. This removes the cutoff bias from tubes VII and V12, which are of the remote cutoff type. The 16 mid. condenser across the 6000 ohm resistor serves to make the tonal attack and decay rate smooth. Al mfd. condenser connected between the control tube cathodes and the center tap of transformer is produces a slow rate of attack but can be disconnected if desired by operating the " fast attack " switch.

Volume Control The volume of the Solovox is controlled by a knee-operated rheostat. This rheostat is actually a switch connected to seven fixed resistors, and is, therefore, not subject to wear as is the usual type of volume control. This theostat forma part of a voltage divider circuit which varies the grid bias to the remote cutoff control tubes Vil and V12, and, therefore, changes the gain of these tubes to produce a corresponding change of volume in sound from the speaker. The grid potential varies from approximately + 45 volt at the maximum volume position (depending on set ting of maximum volume control), to ground potential at the minimum position.

The Vibrato The vibrato effect is produced by means of a magnetically driven reed having a small piece of powdered iron attached to it in such a way ag to vibrate in and out of a coil placed beside the seed. Thus, the inductance of the coil varies periodically as the powdered iron core swings in and out of it. This coil is connected to a tap on the master oscillator tuning coil, and causes the oscillator frequency to vary, producing a vibrato effect. This reed is caused to swing when the volume control lever is pulled forward in starting the instrument. After the reed is once started, the magnetic drive keeps it in motion as long as the instrument is on.

The Solovoa, as a whole, is tuned by adjusting the frequency of the master oscillator. The tuning knob accomplishes this moving a powdered iron core in and out of inductance LI.

Power Outpul Tubes V13 and V14 are power output pentodes connected in the usual push-pull manner to drive the loud speaker. The speaker field functions as a choke coil in the power supply system.

Power Supply The power supply of the Solovox uses a single rectifier tube V8.
Note that control tubes Vil and V12 have a separate heater winding on power transformer T8. This prevents an appreciable difference in potential from arising between the heaters and cathodes of control tubes Vil and V12.

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PRACTICAL SERVICE SUGGESTIONS The materials and electrical parts in the Hammond Solovox are of the finest quality available. Aside from occasional replacement of a vacuum tube, no service problems need be expected to arise. A few conditions which might possibly be encountered are listed below with information which will enable a radio service technician to correct them without difficulty. Some additional in formation useful to the service, technician is in the first section entitled * TUNING AND SIMPLE ADJUSTMENTS. "
If any of the following conditions appear, first make sure that the three cable connectors in the left end of the keyboard under the piano are secure. The faces of the plugs and their receptacles should be together. If the Solovox does not play properly, this is the most likely cause.

1. Changing tubes - There are fourteen tubes in the Solovox: Six type 7A4, four type 7A7, two type 7B5, one type 7B6, and one type 5Y3G. These are all standard radio tubes, and can be tested and replaced, if necessary, by any radio dealer. All tubes can be reached from the back of the tone cabinet. A metal guard covering the lower row of tubes is easily removed by taking out two screws see Fig.
4. Be sure to replace all tubes in the exact sockets from which they came.
If any of the 7A4 tubes are replaced, the oscillators should be readjusted as described under " Adjustment of Oscillators, " Page
The two type 7A7 control tubes (V11.and V12, located in the amplifier channel, Fig. 4) should be matched to avoid undesirable thumps when keying. It is therefore recommended that both be replaced at the same time with new tubes of the same make.

2. Some notes are noisy or play the trong pitch. If a note is noisy, it may be due to (A) a faulty oscillator adjustment, (B) a tauley relay contact, or (C) a faulty key contact. To ascertain which of these is the cause, follow this procedure: (A) If the trouble lies in a faulty oscillator adjustment, the corresponding note one octave lower in pitch will also be noisy because it is controlled by the higher oscillator. If, on the other hand, the lower note is not noisy, it indicates that the oscillator adjustment is satisfactory. In the event that readjustment is necessary, check as described in " TUNING AND SIMPLE ADJUSTMENTS. "
1. any notes still do not play correctly, replace the 7A4 tube associated with the highest pitched oscillator that fails to operate properly on any note. The following chart will be helpful in finding the oscillator associated with notes of any particular x tave.
Highest Octave of Octave of Octave oi Playing Keys Playing Keys Playing Key " BASS " Control Connects to 6th Osc. 5th Osc. 4th Osc. " TENOR " Control Connects to 5th Osc. 4th Osc. " CONTRALTO " Control Connects to 4th Osc. 3rd Osc. 2nd Osc. " SOPRANO " Control Connects to 3rd Osc. 2nd Osc. Master Osc.
After the tube has been replaced, reset the oscillator adjustment potentiometers see page 2, Adjustment of Oscillators. " (B) If the trouble lies in a faulty relay contact, it will be present on all 12 keys of one of the octave groups and will persist on these 12 keys regardless of the combination of playing controls used, All contacts used are of precious material so that in all probability a particle of lint has lodged between the contacts which may be easily cleared by lifting and wiping the contact. Note that the relays are accessible without disconnecting any wires, it merely being necessary to first remove the two large nuts which hold the relay assembly to the tone cabinet frame work. After removing these two mits, turn over the assembly and remove the four screws which hold the cover plate. After removing the cover plate, all contacts will be readily accessible. (C) If the trouble lies in a faulty key contact, trouble will be present, of course, only on one note. In this case, move the bus bar shifters as described in the following suggestions numbered "6" and "7".

3. Instrument fails to play. Ordinarily the first thing to do in this case is to test all the tubes. If the tubes are lighted, the cable plugs are making proper connection, and the controls are in playing position, the most likely source of trouble is in the amplifier circuit. In most respects this is a conventional amplifier circuit, and the voltage measurements given on page 13 will enable a radio service technician to locate the trouble.

4. Key thumps or clicks. If a transient effect in the form of an annoying thump appears each time a key is released, the two type 7A7 control tubes (V11 and V12) are probably not matched properly. In this case, install two new tubes of the same make. A loud click each time a key is released indicates that the control fube cathode condenser is probably open, or partially open.

5. Hum. An excessive 120 cycle hum in the speaker indicates that the filter choke (19) is defective, or one of the filter condensers is open.

6. One key does not sound. If a certain key fails to play on any of the register controls, ic probably has a dirty control contact which can be cleared easily by shifting the control contact bus-bar whose adjustment is at the right end of the keyboard. To reach the bus-bar shifters, first remove the two molded bakelite end pieces. A drawing accompanying the keyboard (Figure 5), shows how the contact shifters are arranged. Loosen the clamping screw and shift the bus-bar about 1/32 ". Be sure to tighten the clamping screw carefully.

7. One key plays note "B" instead of its correct pitch (neith adjacent keys playing correctly). If this occurs, the key under question has a dirty tuning-contact which can be cleared easily by shifting the tuning contact bus-bar having adjustment at the left end of the keyboard. This is reached as described in the preceding paragraph.

8. One octave oj nores fails to play. If a single octave of the Solovox keybwart fails to play for any combination of the register controls, the trouble is probably in the relay associated with that octave or a wire leading to it. Check voltage at the relay coil and the control tube cathodes (V10 and Vii).

9. Adjustment al Master Oscillator Fine Tuning Condenser. An additional tuning adjustment is provided in the form of a screw driver operated trimming condenser at the back of the tone cabinet, upper left hand corner (See Fig. 4). After several years of use under very adverse conditions of humidity, or if an exceedingly accurate tuning is required, this adjustment may need to be made. First, however, always tune as described on page
1. If, after runing F, F = or G. it is found that other notes (most likely Cor Bl are out of tune, the tuning breadth of the octave may be readjusted as follows: (a) Depress the middle "C" key with the " VIBRATO OFF, " " CONTRALTO, " and " DEEP TONE " controls pushed in. Tune to zero beat, prefer ably with a Hammond Organ, or piano which has just been tuned. In tuning this "C" use the tuning knob of the tone cabinet. If it is found impossible to tune the "C" with the tuning knob, the two wood screws at the top of the tuner may be loosened, and the black bakelite tube moved to a position in the tuning coil such that the range of the tuning knob does cover the correct "C" pitch. Before making this adjustment, be sure the " VIBRATO " switch tablet is not set midway between its on and off positions. For tuning purposes, the "VIBRATO " tablet should be pushed in at the top of the tablet. (b) After tuning the "C" key with the tuning knob, depress a "B" key and tune to zero beat with the screw driver operated trimming condenser located in back of the tone cabinet, see Fig.
4. The instrument will now be exceedingly accurately tuned DIRECTIONS FOR CONNECTING ADDITIONAL AMPLIFIERS TO SOLOVOX When the Solovox is used in large auditoriums or with a large orchestra, additional amplifiers may be connected across the Solovox voice coil terminals which are accessible for this purpose on the speaker framework, Standard Hammond Organ Tone Cabinets are recommended as they may be connected with no changes necessary other than securing a push-pull ground with two 200 ohm resistors connected to the Solovox voice coil terminals and their junction point used as a ground for the Hammond Organ Tone Cabinet. By locating the resistors in the Hammond Organ Tone Cabinet, it is only necessary to run two wires (they need not be shielded and may be as long as 200 feet) to the extra tone cabinet