Supply is based on TDA4600 (SIEMENS) + BU208A (Telefunken)
- A completely NEW design of power supply was developed By GRUNDIG when designing the CUC720 CHASSIS SERIES.
Based on TDA4600 (SIEMENS) was Universally used for very long time since the design Of the CHASSIS CUC720 is the father of all chassis design from 1981 to the end of GRUNDIG productions, employing a varyiety of versions type of the control IC (TDA460X) except for CHASSIS CUC2201 and CUC3400 and CUC3410 and CUC3510 which they're based on other technology.
Remote control television with external data bus connection,
Remote Control With MOS IC's For TV Sets: THE GRUNDIG AV FEATURE CONNECTOR TECHNOLOGY:
A television receiver is provided for use as a picture display terminal for electronic peripheral equipment, where a control system with a data-bus is built into the television receiver for multitude of commands and in which the television receiver is intended to be used in addition to the normal direct reception of televised pictures for other possible applications. The television receiver can serve as a monitor for a picture tape recorder, which is equipped for recording independently of the television receiver. A complete television receiving set is provided with automatic transmitter seeking mechanism and electronic channel storage.
1. A system for the use of a television receiver for external control of electronic peripheral devices, said television being of the type including a built-in integrated circuit remote control receiver, said remote control receiver being divided into two sections, one section being allocated to the remote control of the receiving and reproduction sections of the television receiver and the other section being allocated to a databus having nothing to do with the television receiver receiving and reproduction sections; an output terminal of said databus comprising an adaptor connector between said television receiver and an external peripheral device; a peripheral device external to the television receiver; cable means connecting the output of said databus with said peripheral device; and a decoder interposed between said databus output terminal and peripheral device for converting data from said databus into a form suitable for controlling functions of said peripheral device.
2. A television receiver as a picture terminal according to claim 1, in which said external coupling includes a connecting cable between the external connections of the television set and the peripheral device forming a unitary unit together with a decoder which transforms the data from the data collector into a code which directly controls the functions of the peripheral device.
3. A television receiver as a picture terminal according to claim 1 or 2, in which the peripheral device is a picture taping device which operates for recording independently from the television set which acts as a monitor.
4. A television receiver as a picture terminal according to claim 1, in which the functions controlled by said first commands include the on-off switching, picture, sound and channel selection of the television receiver and the functions controlled by said second commands include electronic program storage and changeover functions.
Integrated circuits are presently known in the art for the convenient operation of television receivers, whereby the functions of on-off switching, channel selection, picture (video) and sound (audio) can be remotely controlled by the received telecontrol signal. In particular, the following function can be operated by such a system: Switching on and off of the equipment, calling for different program channels, variations and basic adjustments of sound level, brightness and color saturation, silencing of the sound as well as inserting of time references. With a known and presently available operating system up to 16 channels can be installed, so that it is possible, to select directly that number of programs and to tune the receiver to the appropriate channel.
Television receivers available today in many designs provide for up to 30 remotely controlled channels or channels controlled by the received signal (tele-signal) to properly operate. Additionally, infrared control is also becoming popular. These controls provide commands by means of a databus so that the operation of the various functions is possible with the provision of additional commands.
It is further known to equip peripheral equipment such as video tape recorders with a so-called electronic-tap-key rather than keys with a long throw so that all parts which are susceptable to mechanical wear are eliminated and replaced by digital controls.
It has become of interest to connect the peripheral equipment such as the video tape recorder to the television receiver so that both can be conveniently operated. With the development of new concepts simplification of design becomes critical for ease of operation and reduction of expense.
A television receiver as a picture display terminal for electronic peripheral devices wherein a remote control system with a data collector is installed for receiving a plurality of commands and in which only a portion of the commands is used for the remote control functions of the receiving and display portions of the television set, while another portion of the commands is used for adjusting the functions of an electronic peripheral device which may be coupled with a television set, and that the data collector is electrically coupled by means of an external coupling of the television set with the corresponding stages of the peripheral device.
The FIGURE is a diagrammatic showing of a television receiver and electronic periphery device incorporating the invention.
A television receiver and electronic peripheral device incorporating the invention are shown in the FIGURE. The television receiver 10 can be used as a picture display terminal for peripheral device 12. This provides the advantage, that by means of a single tele-control signal, the control of functions of the receiving and displaying sections of the television receiver can be accomplished as well as the control functions of the peripheral equipment 12, which is connected to the receiver. The peripheral device does not require a separate tele-control system since that which is already installed in the television receiver can be used. To accomplish this, portion A of the available commands A, B of the tele-control system 11 are used for the function of the television receiver 10. The remaining portion B of the available commands A, B, which is made available at databus or data collector 14 is used for the control of functions of the peripheral equipment. The databus, which is coordinated with the peripheral equipment, and which is built into the tele-control system of the television receiver, is connected electrically to external terminal 16 of the television receiver. The external terminals at television receivers and peripheral equipment are relatively inexpensive.
The primary expenses result from the necessary cable connections between the external terminals of the television receiver and the peripheral equipment, as well as the auxiliary apparatus, such as decoder 18, which decodes the data from the databus 14 and prepares it for the peripheral equipment. These expenses are reduced by simplified design, in which the connecting cables 20 and 22 together with the auxiliary apparatus or decoder 18 are combined in one component or building block. This building block can be offered as an accessory to the user of television receivers with peripheral equipment.
The invention can be used with especial advantage in connecting a television receiver with a picture tape recorder as a peripheral equipment. The picture tape recorder is equipped preferably for recording independently from the television receiver, so that the latter serves as a monitor only. With such a switching combination it is possible, for example, to accomplish this with a single control system, and by the help of a tele-control system, which is built into the television receiver, to operate the channel selection and drive mechanism control, the control for an electronic switch clock and programming of the switch commands of the picture tape recorder as well as the control of the function of the receiving and displaying unit of the receiver. In this way it is possible to use the tele-control of a television receiver additionally for the tele-control of the picture tape recorder without substantial higher expenses.
Power supply Description based on TDA4601d (SIEMENS)
TDA4601 Operation. * The TDA4601 device is a single in line, 9 pin chip. Its predecessor was the TDA4600 device, the TDA4601 however has improved switching, better protection and cooler running. The (SIEMENS) TDA4601 power supply is a fairly standard parallel chopper switch mode type, which operates on the same basic principle as a line output stage. It is turned on and off by a square wave drive pulse, when switched on energy is stored in the chopper transformer primary winding in the form of a magnetic flux; when the chopper is turned off the magnetic flux collapses, causing a large back emf to be produced. At the secondary side of the chopper transformer this is rectified and smoothed for H.T. supply purposes. The advantage of this type of supply is that the high chopping frequency (20 to 70 KHz according to load) allows the use of relatively small H.T. smoothing capacitors making smoothing easier. Also should the chopper device go short circuit there is no H.T. output. In order to start up the TDA4601 I.C. an initial supply of 9v is required at pin 9, this voltage is sourced via R818 and D805 from the AC side of the bridge rectifier D801, also pin 5 requires a +Ve bias for the internal logic block. (On some sets pin 5 is used for standby switching). Once the power supply is up and running, the voltage on pin 9 is increased to 16v and maintained at this level by D807 and C820 acting as a half wave rectifier and smoothing circuit. PIN DESCRIPTIONS Pin 1 This is a 4v reference produced within the I.C. Pin 2 This pin detects the exact point at which energy stored in the chopper transformer collapses to zero via R824 and R825, and allows Q1 to deliver drive volts to the chopper transistor. It also opens the switch at pin 4 allowing the external capacitor C813 to charge from its external feed resistor R810. Pin 3 H.T. control/feedback via photo coupler D830. The voltage at this pin controls the on time of the chopper transistor and hence the output voltage. Normally it runs at Approximately 2v and regulates H.T. by sensing a proportion of the +4v reference at pin 1, offset by conduction of the photo coupler D830 which acts like a variable resistor. An increase in the conduction of transistor D830 and therefor a reduction of its resistance will cause a corresponding reduction of the positive voltage at Pin 3. A decrease in this voltage will result in a shorter on time for the chopper transistor and therefor a lowering of the output voltage and vice versa, oscillation frequency also varies according to load, the higher the load the lower the frequency etc. should the voltage at pin 3 exceed 2.3v an internal flip flop is triggered causing the chopper drive mark space ratio to extend to 244 (off time) to 1 (on time), the chip is now in over volts trip condition. Pin 4 At this pin a sawtooth waveform is generated which simulates chopper current, it is produced by a time constant network R810 and C813. C813 charges when the chopper is on and is discharged when the chopper is off, by an internal switch strapping pin 4 to the internal +2v reference, see Fig 2. The amplitude of the ramp is proportional to chopper drive. In an overload condition it reaches 4v amplitude at which point chopper drive is reduced to a mark-space ratio of 13 to 1, the chip is then in over current trip. The I.C. can easily withstand a short circuit on the H.T. rail and in such a case the power supply simply squegs quietly. Pin 4 is protected by internal protection components which limit the maximum voltage at this pin to 6.5v. Should a fault occur in either of the time constant components, then the chopper transistor will probably be destroyed. Pin 5 This pin can be used for remote control on/off switching of the power supply, it is normally held at about +7v and will cause the chip to enter standby mode if it falls below 2v. Pin 6 Ground. Pin 7 Chopper switch off pin. This pin clamps the chopper drive voltage to 1.6v in order to switch off the chopper. Pin 8 Chopper base current output drive pin. Pin 9 L.T. pin, approximately 9v under start-up conditions and 16v during normal running, Current consumption of the I.C. is typically 135mA. The voltage at this pin must reach 6.7v in order for the chip to start-up.
Semiconductor circuit for supplying power to electrical equipment, comprising a transformer having a primary winding connected, via a parallel connection of a collector-emitter path of a transistor with a first capacitor, to both outputs of a rectifier circuit supplied, in turn, by a line a-c voltage; said transistor having a base controlled via a second capacitor by an output of a control circuit acted upon, in turn by the rectified a-c line voltage as actual value and by a reference voltage; said transformer having a first secondary winding to which the electrical equipment to be supplied is connected; said transformer having a second secondary winding with one terminal thereof connected to the emitter of said transistor and the other terminal thereof connected to an anode of a first diode leading to said control circuit; said transformer having a third secondary winding with one terminal thereof connected, on the one hand, via a series connection of a third capacitor with a first resistance, to the other terminal of said third secondary winding and connected, on the other hand, to the emitter of said transistor, the collector of which is connected to said primary winding; a point between said third capacitor and said first resistance being connected to the cathode of a second diode; said control circuit having nine terminals including a first terminal delivering a reference voltage and connected, via a voltage divider formed of a third and fourth series-connected resistances, to the anode of said second diode; a second terminal of said control circuit serving for zero-crossing identification being connected via a fifth resistance to said cathode of said second diode; a third terminal of said control-circuit serving as actual value input being directly connected to a divider point of said voltage divider forming said connection of said first terminal of said control circuit to said anode of said second diode; a fourth terminal of said control circuit delivering a sawtooth voltage being connected via a sixth resistance to a terminal of said primary winding of said transformer facing away from said transistor; a fifth terminal of said control circuit serving as a protective input being connected, via a seventh resistance to the cathode of said first diode and, through the intermediary of said seventh resistance and an eighth resistance, to the cathode of a third diode having an anode connected to an input of said rectifier circuit; a sixth terminal of said control circuit carrying said reference potential and being connected via a fourth capacitor to said fourth terminal of said control circuit and via a fifth capacitor to the anode of said second diode; a seventh terminal of said control circuit establishing a potential for pulses controlling said transistor being connected directly and an eighth terminal of said control circuit effecting pulse control of the base of said transistor being connected through the intermediary of a ninth resistance to said first capacitor leading to the base of said transistor; and a ninth terminal of said control circuit serving as a power supply input of said control circuit being connected both to the cathode of said first diode as well as via the intermediary of a sixth capacitor to a terminal of said second secondary winding as well as to a terminal of said third secondary winding.
Such a blocking oscillator switching power supply is described in the German periodical, "Funkschau" (1975) No. 5, pages 40 to 44. It is well known that the purpose of such a circuit is to supply electronic equipment, for example, a television set, with stabilized and controlled supply voltages. Essential for such switching power supply is a power switching transistor i.e. a bipolar transistor with high switching speed and high reverse voltage. This transistor therefore constitutes an important component of the control element of the control circuit. Furthermore, a high operating frequency and a transformer intended for a high operating frequency are provided, because generally, a thorough separation of the equipment to be supplied from the supply naturally is desired. Such switching power supplies may be constructed either for synchronized or externally controlled operation or for non-synchronized or free-running operation. A blocking converter is understood to be a switching power supply in which power is delivered to the equipment to be supplied only if the switching transistor establishing the connection between the primary coil of the transformer and the rectified a-c voltage is cut off. The power delivered by the line rectifier to the primary coil of the transformer while the switching transistor is open, is interim-stored in the transformer and then delivered to the consumer on the secondary side of the transformer with the switching transistor cut off.
In the blocking converter described in the aforementioned reference in the literature, "Funkschau" (1975), No. 5, Pages 40 to 44, the power switching transistor is connected in the manner defined in the introduction to this application. In addition, a so-called starting circuit is provided. Because several diodes are generally provided in the overall circuit of a blocking oscillator according to the definition provided in the introduction hereto, it is necessary, in order not to damage these diodes, that due to the collector peak current in the case of a short circuit, no excessive stress of these diodes and possibly existing further sensitive circuit parts can occur.
Considering the operation of a blocking oscillator, this means that, in the event of a short circuit, the number of collector current pulses per unit time must be reduced. For this purpose, a control and regulating circuit is provided. Simultaneously, a starting circuit must bring the blocking converter back to normal operation when the equipment is switched on, and after disturbances, for example, in the event of a short circuit. The starting circuit shown in the literature reference "Funkschau" on Page 42 thereof, differs to some extent already from the conventional d-c starting circuits. It is commonly known for all heretofore known blocking oscillator circuits, however, that a thyristor or an equivalent circuit replacing the thyristor is essential for the operation of the control circuit.
It is accordingly an object of the invention to provide another starting circuit. It is a further object of the invention to provide a possible circuit for the control circuit which is particularly well suited for this purpose. It is yet another object of the invention to provide such a power supply which is assured of operation over the entire range of line voltages from 90 to 270 V a-c, while the secondary voltages and secondary load variations between no-load and short circuit are largely constant.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a blocking oscillator-type switching power supply for supplying power to electrical equipment wherein a primary winding of a transformer, in series with an emitter-collector path of a first bipolar transistor, is connected to a d-c voltage obtained by rectification of a line a-c voltage fed-in via two external supply terminals, a secondary winding of the transformer being connectible to the electrical equipment for supplying power thereto, the first bipolar transistor having a base controlled by the output of a control circuit acted upon, in turn, by the rectified a-c line voltage as actual value and by a set-point transmitter, and including a starting circuit for further control of the base of the first bipolar transistor, including a first diode in the starting circuit having an anode directly connected to one of the supply terminals supplied by the a-c line voltage and a cathode connected via a resistor to an input serving to supply power to the control circuit, the input being directly connected to a cathode of a second diode, the second diode having an anode connected to one terminal of another secondary winding of the transformer, the other secondary winding having another terminal connected to the emitter of the first bipolar transmitter.
In accordance with another feature of the invention, there is provided a second bipolar transistor having the same conduction type as that of the first bipolar transistor and connected in the starting circuit with the base thereof connected to a cathode of a semiconductor diode, the semiconductor diode having an anode connected to the emitter of the first bipolar transistor, the second bipolar transistor having a collector connected via a resistor to a cathode of the first diode in the starting circuit, and having an emitter connected to the input serving to supply power to the control circuit and also connected to the cathode of the second diode which is connected to the other secondary winding of the transformer.
In accordance with a further feature of the invention, the base of the second bipolar transistor is connected to a resistor and via the latter to one pole of a first capacitor, the anode of the first diode being connected to the other pole of the first capacitor.
In accordance with an added feature of the invention, the input serving to supply power to the control circuit is connected via a second capacitor to an output of a line rectifier, the output of the line rectifier being directly connected to the emitter of the first bipolar transistor.
In accordance with an additional feature of the invention, the other secondary winding is connected at one end to the emitter of the first bipolar transistor and to a pole of a third capacitor, the third capacitor having another pole connected, on the one hand, via a resistor, to the other end of the other secondary winding and, on the other hand, to a cathode of a third diode, the third diode having an anode connected via a potentiometer to an actual value input of the control circuit and, via a fourth capacitor, to the emitter of the first bipolar transistor.
In accordance with yet another feature of the invention, the control circuit has a control output connected via a fifth capacitor to the base of the first bipolar transistor for conducting to the latter control pulses generated in the control circuit.
In accordance with a concomitant feature of the invention, there is provided a sixth capacitor shunting the emitter-collector path of the first transistor.
Other features which are considered as characteristic for the invention are set forth in the appended claim.
Although the invention is illustrated and described herein as embodied in a blocking oscillator type switching power supply, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
npn transistors,pnp transistors,transistors
Category: NPN Transistor, Transistor
MHz: <1 MHz
HIGH VOLTAGE CAPABILITY
JEDEC TO-3 METAL CASE.
The BU208A, BU508A and BU508AFI are
manufactured using Multiepitaxial Mesa
technology for cost-effective high performance
and use a Hollow Emitter structure to enhance
* HORIZONTAL DEFLECTION FOR COLOUR TV With 110° or even 90° degree of deflection angle.
ABSOLUTE MAXIMUM RATINGS
Symbol Parameter Value Unit
VCES Collector-Emit ter Voltage (VBE = 0) 1500 V
VCEO Collector-Emit ter Voltage (IB = 0) 700 V
VEBO Emitter-Base Voltage (IC = 0) 10 V
IC Collector Current 8 A
ICM Collector Peak Current (tp < 5 ms) 15 A
TO - 3 TO - 218 ISOWATT218
Ptot Total Dissipation at Tc = 25 oC 150 125 50 W
Tstg Storage Temperature -65 to 175 -65 to 150 -65 to 150 oC
Tj Max. Operating Junction Temperature 175 150 150 °C
GRUNDIG Simplified horizontal / line deflection circuit.
This GRUNDIG CHASSIS Series was featuring a BU208A based Simplified horizontal deflection section replacing all Thyristor horizontal timebase based circuits.
A horizontal deflection circuit makes a sawtooth
current flow through a deflection coil. The current
will have equal amounts of positive and negative
current. The horizontal switch transistor conducts
for the right hand side of the picture. The damper
diode conducts for the left side of the picture.
Current only flows through the fly back capacitor
during retrace time.
For time 1 the transistor is turned on. Current
ramps up in the yoke. The beam is moved from the
center of the picture to the right edge. Energy is
stored on the inductance of the yoke.
For time 2 the transistor is turned off. Energy
transfers from the yoke to the flyback capacitor. At
the end of time two all the energy from the yoke is
placed on the flyback capacitor. There is zero
current in the yoke and a large voltage on the
capacitor. The beam is quickly moved from the
right edge back to the middle of the picture.
During time 3 the energy on the capacitor flows
back into the yoke. The voltage on the flyback
capacitor decreases while the current in the yoke
builds until there is no voltage on the capacitor. By
the end of time 3 the yoke current is at it's
maximum amount but in the negative direction.
The beam is quickly deflected form the center to the
Time 4 represents the left hand half of the picture.
Yoke current is negative and ramping down. The
beam moves from the left to the center of the
The current that flows when the horizontal switch is
closed is approximately:
Ipk ≅ Vcc T / Ldy
Ipk = collector current
T = 1/2 trace time
Ldy = total inductance (yoke + lin coil + size coil)
note:The lin coil inductance varies with current.
Tr ≅ 3.14 √ L C
The current that flows during retrace is produced by
the C and L oscillation. The retrace time is 1/2 the
oscillation frequency of the L and C.
I2L /2 ≅ V2C /2 or I2L = V2C As stated earlier the energy in the yoke moves to the
flyback capacitor during time 2.
V= the amount of the flyback pulse that is above the
D.C. annualizes is inductors are considered
shores, capacitors are open and generally
semiconductors are removed. The voltage at the
point “B+” is the supply voltage. The collector
voltage of Q1 is also at the supply voltage. The
voltage across C2 is equal to the supply voltage.
When we A.C. annualize this circuit we will find
that the collector of Q1 has a voltage that ranges
from slightly negative to 1000 volts positive. The
average voltage must remain the same as the D.C.
In the A.C. annualizes of the circuit, the
inductance of the yoke (DY) and the inductance of
the flyback transformer are in parallel. The
inductance of T2 is much larger than that if the
DY. This results is a total system inductance of
about 10% to 20% less than that of the DY it’s
The voltage across the Q1 is a half sinusoid pulse during the flyback or retrace period and close to zero at
all other times. It is not possible or safe to observe this point on an oscilloscope without a proper high
frequency high voltage probe. Normally use a 100:1 probe suitable for 2,000V peak. The probe must have
been high frequency calibrated recently.
HORIZONTAL SIZE / E/W AMPLITUDE - CORRECTION CIRCUIT:
There are several different methods of adjusting horizontal size.
Add a variable coil to the yoke current path
causes the total inductance to vary with the coils
The yoke current is related to supply voltage,
trace time and total inductance. This method
has a limited range!
The horizontal section uses a PWM to set the
horizontal size. One DAC sets the horizontal
size and another DAC sets the pincushion and
The Raster Centering (D.C. centering) is
controlled by a DAC.
On small monitors the retrace time is fixed. On
large monitors or wide frequency range monitors
two different retrace times are available. The flyback time is set by the micro computer by selecting two
different flyback capacitors. At slow frequencies the longer retrace time is selected.
Different S corrector capacitor values are selected by the micro computer. At the highest frequency the
smallest capacitor is selected.
SPLIT DIODE MODULATOR
This horizontal circuit consists of two parts. D1, C1, C2 and DY are the components as described above.
D2, C3, C4 and L1 are a second “dummy” horizontal section that does not cause deflection current. By the
D.C. analyzing this circuit the voltage across C2 + C4 must equal the supply voltage (B+). Deflection
current in the DY is related to the supply voltage minus the voltage across C4. For a maximum horizontal
size the control point must be held at ground. This causes the dummy section to not operate and the DY
section will get full supply voltage. If the control point is at 1/3 supply then the DY section will be
operating at 2/3 supply.
Note: The impedance of (D1,C1,C2 and DY) and (D2,C3,C4 and L1) makes a voltage divider. If the
control point is not connected then there is some natural voltage on C4. Most split diode monitors are built
to pull power from the dummy section through L2 to ground. A single power transistor shunts from the
control point to ground. It is true that power can be supplied from some other supply through L2 to rise the voltage on C4. For maximum range a bi-directional power amplifier can drive the control point.
The most exciting feature if the split diode modulator is that the flyback pulse, as seen by the flyback
transformer, is the same size at all horizontal size settings.
HORIZONTAL SWITCH/DAMPER DIODE
On the right hand side of the screen, the H. switch transistor conducts current through the deflection yoke.
This current comes from the S correction capacitors, which have a charge equal to the effective supply
voltage. The damper diode allows current for the left hand side of the screen to flow back through the
deflection yoke to the S capacitors.
The flyback capacitor connects the hot side of the yoke to ground. This component determines the size and
length of the flyback pulse. ‘Tuning the flyback capacitor’ is done to match the timing of the flyback pulse
to the video blanking time of the video signal. The peak flyback voltage on the horizontal switch must be
set to less that 80% if the Vces specification. The two conditions of time and voltage can be set by three
variables (supply voltage, retrace capacitor and yoke inductance) .
The S capacitors corrects outside versus center linearity in the horizontal scan. The voltage on the S cap
has a parabola plus the DC horizontal supply. Reducing the value of S cap increases this parabola thus
reducing the size of the outside characters and increasing the size of the center characters.
S Capacitor value: Too low: picture will be squashed towards edges.
Too high: picture will be stretched towards edges.
By simply putting a capacitor in series with each coil, the sawtooth waveform is
modified into a slightly sine-wave shape. This reduces the scanning speed near the
edges where the yoke is more sensitive. Generally the deflection angle of the electron
beam and the yoke current are closely related. The problem is the deflection angle
verses the distance of movement on the CRT screen does not have a linear effect.
BASE DRIVE CURRENT
The base drive resistor determines the amount of
base drive. If the transistor is over driven the Vsat
looks very good, but the current fall time is poor.
If the base current is too small the current fall time is very fast. The problem is that the transistor will have many volts across C-E when closed.
The best condition is found by placing the transistor in the heaviest load condition. Adjust the base resistor for the least power consumption then increase the base drive a small amount. This will slightly over drive the base.
Note on the bottom right cabinet the Ensemble / Stereo bandwidth enhancer unit.
This version Incorporates a Stereo band expansion Unit fitted on the right bottom side of the cabinet.
It combines circuits to feature the Stereo sound expansion:29502.006.01
A system and method for enhancing the stereo sound effect produced by speaker systems having two or more speakers fed by two or more channels or audio, respectively. Second-order high pass filtering is applied to first and second audio signals of a stereo signal. A phase shift of approximately 180 degrees is applied to the resulting signals. A mixer mixes the processed first audio signal with the original second audio signal and mixes the processed second audio signal with the original first audio signal, whereby an expanded stereo sound field effect is created.