There are two systems or panels that are used to redistribute power or electric current to other equipment or circuits. One is the switchboard and the other is switchgear.
Electric switchboards are a device that directs the electricity from one source to another. It is composed of an assembly of panels. Each panel contains switches to allow electricity to be redirected.
With a switchboard, a technician is protected from possible electrocution. The switches in the board control the amount of current that goes into the switchboard. Such switches are fed from a generator which has AC frequency and load sharing controls. It also has gauges that show the frequency and synchroscope.
It is important that the amount of electric power that goes into the switchboard is equal to the electric power going. When you take a look inside the switchboard, you will see a bank of busbars.
The busbars, which are generally bare and supported by insulators, are wide strips of copper that connect to switchgear. The busbars act to allow passage of large electric current through the switchboard.
Before the switchboard is opened for maintenance, it is important to isolate the power because the busbars are bare. These active busbars are a deadly source of power. When working on live switchboards, precautionary measures are crucial. Be ready with your protective equipment such as thick rubber mats and gloves, when working with an open switchboard.
Switchboards are isolated and protected with other equipment including substations, motors, high or medium voltage distribution networks and transformers.
Switchgear are also essential a type of electrical distribution device that is used to convert incoming electrical power into several smaller voltages. Switchgear can also be used as a circuit breaker.
There are many different types of circuit breaker switchgear. Vacuum circuit switchgear have minimal arcing. The arc quenches when it is stretched to less the 2 to 3 mm. They’re frequently used in modern medium-voltage switchgear of up to 35,000 volts.
If you need to de-energizing equipment, you can use switchgear. It also clears faults downstream and comes in varied parameters, which include number of panels, electrical specifications and mounting style.
The common types of switchgear are vacuum circuit breakers, oil insulated switchgear, gas insulated switchgear, and a simple open air circuit breaker. Oil insulated switchgear depend on an oil vaporization blast through its arc.
The gas insulated switchgear stretches the arc with a magnetic field and also depends on the dielectric strength of the gas to quench the stretched arc. The open air switchgear circuit breakers use compressed air to blow out the arc. The displaced air that tries to escape thus blows out the arc.
Circuit breakers are a unique type of switchboards that interrupts fault currents. Their design is especially made for interruption of fault currents.
The Classifications of switchboards are based on the current rating, the amount of interrupting rating, by voltage class, insulating medium, construction types, operating method, type of current, interrupting type, and application.
Article Source: http://www.articles2use.com - a Rentaccomspain.com company.
- Delay is 5 second
- Speaker- 10W, 4Ω
- Power Supply- 9V
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LED- any color
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Diodes- IN4001 or IN4007
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Input is 230v AC
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R1- for protection of Surge current
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0.22 µF capacitor- for definite charging current
IC- TDA-2822: Max. Output-250 mW, Available in 16 pins and 8 pins (need 8 pins for this ckt)
S1- for call of other intercom
S2- for on-off
It is a class AB stereo audio power amplifier designed for quality hi-fi applications using a TDA2005 module. It is easy to construct and has a minimum of external components. The module has output current protection and thermal protection. This is the data book circuit which produces an excellent sound. The supply voltage required for this kit is 8 - 18V DC at 1 to 2 Amps.
Maximum output power will only be obtained with a power supply of at least 2A at 15V DC, and using 2 ohm speakers (or 2 by 4 ohm speakers in parallel). However approximately 4W per channel can be obtained with only a 15V DC, 1A supply into 4 ohm loads.
The power supply should be well filtered to reduce mains hum, the on board capacitors alone are not adequate for this purpose but are necessary to ensure stability.
Construction
Add the lowest height components to the board first, starting with the resistors. Be careful to get the electrolytic capacitors in the correct way around and all parts in their correct positions. Be careful when soldering the IC not to use excessive heat. Use some heat sink compound between the heat sink & the IC.
Also note if you intend to drive it very hard, it may require a bigger heatsink. Use shielded signal wire for the input connections, and at least 16/0.2 hook up wire for DC input and speaker outputs. Try to keep lead lengths as short as possible.
It is recommended that you place a solder lug (supplied) between the heatsink bolt head and front of the IC mounting tab. (NOT between the IC and heatsink) Connect the power supply earth to this lug. This reduces earth currents on the PC board, and lowers the distortion figures by a worthwhile amount. The circuit will, however, perform adequately without it.
OperationThe circuit is straight forward. Most of the circuitry is contained within the amplifier module. C1 & C2 are input coupling capacitors and block DC, as do C10 & C11 which are the output coupling capacitors, and C7 & C9 which block DC from the feed back loop to the differential inputs. R3/R5 (and R4/R6) set the level of feed back. C10/R7 (and C11/R8) provide a high frequency load for stability where loudspeaker inductive reactance may become excessive. C4 and C5 provide power supply decoupling or filtering.
The gain is equal to 1 + (R3/R5) = 37, or 31dB, minus any input attenuation. The gain may be increased by reducing the feedback resistors R5 and R6. A value of 22 ohms would provide a gain of approximately 35 dB. If you need much more than 40 dB gain, it would be better to use a preamplifier.
The maximum supply voltage for this circuit is 18V. Check the power supply voltage and polarity before connecting to the Circuit. If it does not work, first check all external wiring, make sure there are no shorts, then check all the component positions and orientation. Also check all solder joints and make sure there are no dry joints or solder bridges.
Specifications :
D.C. Input : 8 – 18V at 1 – 2 A (15 - 30 VA minimum)
Power output :
> 8 W RMS / channel, 2 ohm load, 16V DC supply.> 6W RMS / channel, 4 ohm load, 16V DC supply.> 4W RMS / channel, 4 ohm load 12V DC supply.
THD : 0.1% @ 1W, 4ohms.
S/N ratio : > 80 dBA.
Frequency response : ~ 15 Hz to 50 kHz, –3 dB
Gain : ~ 30 dB maximum.
Input level : ~ 150 mV for full output
Components
Resistors :
1 ohm, brown black gold -R7, R8 (2 pcs)
33 ohm, orange orange black -R5, R6( 2 pcs)
1k ohm, brown black red- R1, R9 (2 pcs)
1k2 ohm, brown red red -R3, R4 (2 pcs)
120k ohm, brown red yellow -R2( 1 pcs)
Capacitors :
2u2 50V -C1 C2( 2 pcs)
10uF 25V -C3 (1 pcs)
100uF 25V -C5, C6, C8( 3 pcs)
220uF 25V -C7, C9 (2 pcs)
2200uF 16V- C12, C13 (2 pcs)
100 nF monoblock- C4( 1 pcs)
100 nF mylar C10, C11 (2 pcs)
IC-TDA2005
Heat sink
Nut & bolt set for Heat Sink
10 k ohm dual gang log pot
3 pole terminal block
The optimal supply voltage is around 50V, but this amp work from 30 to 60V. The maximal input voltage is around 0.8 - 1V. In this design the components have a big tolerance, so you can build it almost of the components, which you find at home. The and transistors can be any NPN type power transistor, but do not use Darlington types. The output power is around 60W.
Capacitor C1 regulates the low frequencies (bass), as the capacitance grows, the low frequencies are getting louder. Capacitor C2 regulates the higher frequencies (treble), as the capacitance grows, the higher frequencies are getting quieter. This is a class B amplifier, this means, that a current must flow through the end transistors, even if there is no signal on the input. This current can be regulated with the 500ohm; trimmer resistor. As this current increases, the sound of the amplifier gets better, but the end transistors are more heating. But if this current decreases, the transistors are not heating so much, but the sound gets worse.
A battery is a vital element of any battery-backed system. In many cases the battery is more expensive than the system it is backing up. Hence we need to adopt all practical measures to conserve battery life.
As per manufacturer’s data sheets, a 12V rechargeable lead-acid battery should be operated within 10.1V and 13.8V. When the battery charges higher than 13.8V it is said to be overcharged, and when it discharges below 10.1V it can be deeply discharged. A single event of overcharge or deep discharge can bring down the charge-holding capacity of a battery by 15 to 20 percent.
It is therefore necessary for all concerned to monitor the charge level of their batteries continuously. But, in practice, many of the battery users are unable to do so because of non-availability of reasonably-priced monitoring equipment. The circuit idea presented here will fill this void by providing a circuit for monitoring the charge level of lead-acid batteries continuously. The circuit possesses two vital features:
- First, it reduces the requirement of human attention by about 85 per cent.
- Second, it is a highly accurate and sophisticated method.
Input from the battery under test is applied to LM3914 IC. This applied voltage is ranked anywhere between 0 and 10, depending upon its magnitude. The lower reference voltage of 10.1V is ranked ‘0’ and the upper voltage of 13.8V is ranked as ‘10.’ (Outputs 9 and 10 are logically ORed in this circuit.) This calibration of reference voltages is explained later.
IC 74LS147 is a decimal-to-BCD priority encoder which converts the output of LM3914 into its BCD complement. The true BCD is obtained by using the hex inverter 74LS04. This BCD output is displayed as a decimal digit after conversion using IC5 (74LS247), which is a BCD-to-seven-segment decoder/driver. The seven-segment LED display (LTS-542) is used because it is easy to read compared to a bar graph or, for that matter, an analogue meter. The charge status of the battery can be quickly calculated from the display. For instance, if the display shows 4, it means that the battery is charged to 40 per cent of its maximum value of 13.8V.
The use of digital principles enables us to employ a buzzer that sounds whenever there is an overcharge or deep discharge, or there is a need to conserve battery charge. A buzzer is wired in the circuit such that it sounds whenever battery-charge falls to ten per cent. At this point it is recommended that unnecessary load be switched off and the remaining charge be conserved for more important purposes.
Another simple combinational logic circuit can also be designed that will sound the buzzer when the display shows 9. Further charging should be stopped at this point in order to prevent overcharge.
The circuit is powered by the battery under test, via a voltage regulator IC. The circuit takes about 100 mA for its operation.
For calibrating the upper and lower reference levels, a digital multimeter and a variable regulated power supply source are required. For calibrating the lower reference voltage, follow the steps given below:
- Set the output of power supply source to 10.1V.
- Connect the power supply source in place of the battery.
- Now the display will show some reading. At this point vary preset VR2 until the reading on the display just changes from 1 to 0.
The higher reference voltage is calibrated similarly by setting the power supply to 13.8V and varying preset VR1 until reading on the display just changes from 8 to 9.
After the calibration is completed, the circuit may be housed in a suitable enclosure.
Gain of up to 100 can be achieved in this configuration, which is useful for signal conditioning of low output of transducers in millivolt range. The gain selection resistors R3 to R6 can be selected by the user and can be anywhere from 1 kilo-ohm to 1 meg-ohm. Trimpots can be used for obtaining any value of gain required by the user. The resistor values shown in the circuit are for decade gains suitable for an auto ranging DPM. Resistor R1 and capacitor C1 reduce ripple in the input and also snub transients. Zeners Z1 and Z2 limit the input to ±4.7V, while the input current is limited by resistor R1. Capacitors C2 and C3 are the power supply decoupling capacitors. Op-amp IC1 is used to increase the input impedance so that very low in puts are not loaded on measurement. The user can terminate the inputs with resistance of his choice (such as 10 meg ohm or 1 meg-ohm) to avoid floating of the inputs when no measurement is being made. IC5 is used as an inverting buffer to restore polarity of the input while IC4 is used as buffer at the output of CD4052, because loading it by resistance of value less than 1 meg-ohm will cause an error. An alternative is to make R7=R8=1 meg-ohm and do away with IC4, though this may not be an ideal method. Gains greater than 100 may not be practical because even at gain value of 100 itself, a 100μV offset will work out to be around 10 mV at the output (100μV x 100). This can be trimmed using the offset null option in the OP07, connecting a trimpot between pins 1 and 8, and connecting wiper to +5V supply rails. For better performance, use ICL7650 (not pin-compatible) in place of OP07 and use ±7.5V instead of ±5V supply. Eight steps for gain or attenuation can be added by using two CD4051 and pin 6 inhibit on CD4051/52. More steps can be added by cascading many CD4051, or CD4052, or CD4053 ICs, as pin 6 works like a chip select. Some extended applications of this circuit are given below.
- 1. Error correction in transducer amplifiers by correcting gain.
- Auto ranging in DMM.
- Sensor selection or input type selection in process control.
- Digitally preset power supplies or electronic loads.
- Programmable precision mV or mA sources.
- PC or micro controller or microprocessor based instruments.
- Data loggers and scanners.
| Truth Table | (Control | Input vs | Gain) |
| X,Y (On-switch Pair) | (2) B | (1) A | Gain (Av.) |
| X0,Y0 | 0 | 0 | 1/10 |
| X1,Y1 | 0 | 1 | 1 |
| X2,Y2 | 1 | 0 | 10 |
| X3,Y3 | 1 | 1 | 100 |
Here is a low-cost circuit of an FM booster that can be used to listen to programmes from distant FM stations clearly. The circuit comprises a common-emitter tuned RF preamplifier wired around VHF/UHF transistor 2SC2570. (Only C2570 is annotated on the transistor body.) Assemble the circuit on a good-quality PCB (preferably, glass-epoxy). Adjust input/ output trimmers (VC1/VC2) for maximum gain. Input coil L1 consists of four turns of 20SWG enamelled copper wire (slightly space wound) over 5mm diameter former. It is tapped at the first turn from ground lead side. Coil L2 is similar to L1, but has only three turns. Pin configuration of transistor 2SC2570 is shown in the figure.
The USB serial bus can be configured for connecting several peripheral devices to a single PC. It is more complex than RS232, but faster and simpler for PC expansion.
Since a PC can supply only a limited power to the external devices connected through its USB port, when too many devices are connected simultaneously, there is a possibility of power shortage. Therefore an external power source has to be added to power the external devices.
In USB, two different types of connectors are used: type A and type B. The circuit presented here is an addon unit, designed to add more power to a USB supply line (type-A). When power signal from the PC (+5V) is received through socket A, LED1 glows, opto-diac IC1 conducts and TRIAC1 is triggered, resulting in availability of mains supply from the primary of transformer X1. Now transformer X1 delivers 12V at its secondary, which is rectified by a bridge rectifier comprising diodes D1 through D4 and filtered by capacitor C2.
Regulator 7805 is used to stabilise the rectified DC. Capacitor C3 at the output of the regulator bypasses the ripples present in the rectified DC output. LED1 indicates the status of the USB power booster circuit.
Assemble the circuit on a generalpurpose PCB and enclose in a suitable cabinet. Bring out the +5V, ground and data points in the type-A socket. Connect the data cables as assigned in the circuit and the USB power booster is r e a d y t o function.
This charger for series-connected 4-cell AA batteries automatically disconnects from mains to stop charging when the batteries are fully charged. It can be used to charge partially discharged cells as well.
The circuit is simple and can be divided into AC-to-DC converter, relay driver and charging sections.
In the AC-to-DC converter section, transformer X1 steps down mains 230V AC to 9V AC at 750 mA, which is rectified by a full-wave rectifier comprising diodes D1 through D4 and filtered by capacitor C1. Regulator IC LM317 (IC1) provides the required 12V DC charging voltage. When you press switch S1 momentarily, the charger starts operating and the power-on LED1 glows to indicate that the charger is ‘on.’
The relay driver section uses pnp transistors T1, T2 and T3 (each BC558) to energize electromagnetic relay RL1. Relay RL1 is connected to the collector of transistor T1. Transistor T1 is driven by pnp transistor T2, which, in turn, is driven by pnp transistor T3. Resistor R4 (10-ohm, 0.5W) is connected between the emitter and base of transistor T3.
When a current of over 65 mA flows through the 12V line, it causes a voltage drop of about 650 mV across resistor R4 to drive transistor T3 and cut off transistor T2. This, in turn, turns transistor T1 ‘on’ to energize relay RL1. Now even if the pushbutton is released, mains is still available to the primary of the transformer through its normally open (N/O) contacts.
In the charging section, regulator IC1 is biased to give about 7.35V. Preset VR1 is used for adjusting the bias voltage. Diode D6 connected between the output of IC1 and battery limits the output voltage to about 6.7V, which is used for charging the battery.
Pushing switch S1 latches relay RL1 and the battery cells start charging. As the voltage per cell increases beyond 1.3V, the voltage drop across resistor R4 starts decreasing. When it falls below 650 mV, transistor T3 cuts off to drive transistor T2 and, in turn, cuts off transistor T3. As a result, relay RL1 de-energizes to cut off the charger and red LED1 turns off.
You may determine the charging voltage depending on the NiCd cell specifications by the manufacturer. Here, we’ve set the charging voltage at 7.35V for four 1.5V cells. Nowadays, 700mAH cells are available in the market, which can be charged at 70 mA for 10 hours. The open-circuit voltage is about 1.3V.
The shut-off voltage point is determined by charging the four cells fully (at 70 mA for 14 hours). After measuring the output voltage, add the diode drop (about 0.65V) and bias LM317 accordingly.
The 22 watt amp is easy to build, and very inexpensive. The circuit can be used as a booster in a car audio system, an amp for satellite speakers in a surround sound or home theater system, or as an amp for computer speakers. The circuit is quite compact and uses only about 60 watts.
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The circuit works best with 4 ohm speakers, but 8 ohm units will do.
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The circuit dissipates roughly 28 watts of heat, so a good heatsink is necessary. The chip should run cool enough to touch with the proper heatsink installed.
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The circuit operates at 12 Volts at about 5 Amps at full volume. Lower volumes use less current, and therefore produce less heat.
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Printed circuit board is preferred, but universal solder or perf board will do. Keep lead length short.
| Part | Total Qty. | Description |
| R1 | 1 | 39K 1/4 Watt Resistor |
| C1,C2 | 2 | 10uf 25V Electrolytic Capacitor |
| C3 | 1 | 100uf 25V Electrolytic Capacitor |
| C4 | 1 | 47uf 25V Electrolytic Capacitor |
| C5 | 1 | 0.1uf 25V Ceramic Capacitor |
| C6 | 1 | 2200uf 25V Electrolytic Capacitor |
| U1 | 1 | TDA1554 Two Channel Audio Amp Chip |
| MISC | 1 | Heatsink For U1, Binding Posts (For Output), RCA Jacks (For Input), Wire, Board |
This is a simple Laser communication system. It can transmit and receive signal from any audio device.Communication distance is few meters. All components are not critical.
This is a simple communication system that transmits data using laser beam. Transmitter output is a laser diode which transmits a signal to a photo transistor in the receiver. Laser diode is best taken from a laser pointer costing around 20kn.
Transistors Q6 and Q7 signal amplifier consists of photo transistor. The transistor Q6 is necessary to put a small refrigerator. Components are not critical.
This is a four channel amplifier ideally suited for use with quadraphonic equipment such as a Sound Blaster Live card. There is no volume control,audio levels being directly controlled from the sound card itself.
Parts List:
D1-D4: 1N4001 (4)
C1,C20: 1000u CAP (2)
C2,C11: 47u CAP (2)
C3,C5,C7,C8,C12,C14,C16,C17,C21,C22: 0.1u CAP (10)
C4,C6,C13,C15: 10u CAP (4)
C9,C10,C18,C19: 2200u CAP (4)
R1,R4,R9,R12: 1M RESISTOR (4)
R2,R6,R10,R14: 100k RESISTOR (4)
R3,R5,R11,R13: 1k RESISTOR (4)
R7,R8,R15,R16: 2R7 RESISTOR (4)
IC1: 7812 (1)
IC2,IC3: LM1778N (2)
SPK1,SPK2,SPK3,SPK4: 8R 2 Watt speakers (4)
Notes:
Construction is straight forward and is suitable for Verobaord. Overall gain is controlled by the ratio R14/R13 and R6/R5. Used with small hifi speakers the volume was too loud for my room so I reduced R14 and R6 to 33k. The zobel network formed by R7,C7,R8,C8,R15,C16,R16,C17 prevents instability which can happen with long speaker wires. The input impedance is high, 1M and if very long input cables are present could pick up noise. Screened cable should be used, in my case I used 10k resistors between points A & C, B & C, D & F, E & F. This provides a DC path to ground and higher noise immunity. If instability does occur, then you will notice sound distortion and the LM1877N will become hot to touch.
Connections: The back of a sound blaster live card has colour coded 3.5mm stereo jacks. The image below shows a close up of the rear of my Sound Blaster Live card. As well as colour coding, each connector has an appropriate marking, for easy connectivity.
The normal output connector is green and the rear speaker connector is black. Creative provide utilities and sound mixer for use with Windows. Under Linux the utility Gamix can be used, which allows independent volume control for all channels.
Here is the schematic for an 8 watt audio amp. This amp can be used as a simple booster, the heart of a more complicated amplifier or used as a guitar amp.
Parts:
C1 - 10uf Electrolytic Capacitor
C2 - 470uf Electrolytic Capacitor
C3 - 0.1uF Disc Capacitor
C4 - 2000uf Electrolytic Capacitor 2200uF
R1 - 2.2 Ohm Resistor Anything Within 10%
R2 - 220 Ohm Resistor Anything Within 10%
IC1 - LM383 8 Watt Amp IC ECG1232
Notes:
- IC1 MUST be installed on a heat sink.
- C3 is for filtering and to prevent oscillation and should not be omitted.
- The circuit can be built on a perf board, universal solder board or PC board, the PC board is preferred. I built the circuit on a perf board and had to add extra inductors, capacitors and resistors to prevent oscillation.
- The circuit draws about 880 ma at 12 V.
- By swapping the values of R1 and R3, you can turn this amplifier into a guitar amp with no preamp required.
- If you can't find 2000uF, then replace C4 with a 2200uF unit.
- If you add a 0.2uF capaciitor in series with a 1 ohm resistor to the output you can prevent oscillation of the circuit under certain conditions.
This amplifier was designed to be self-contained in a small loudspeaker box. It can be feed by Walkman, Mini-Disc and CD players, computers and similar devices having line or headphone output. Of course, in most cases you'll have to make two boxes to obtain stereo. The circuit was deliberately designed using no ICs and in a rather old-fashioned manner in order to obtain good harmonic distortion behavior and to avoid hard to find components. The amplifier(s) can be conveniently supplied by a 12V wall plug-in transformer. Closing SW1 a bass-boost is provided but, at the same time, volume control must be increased to compensate for power loss at higher frequencies. In use, R9 should be carefully adjusted to provide minimal audible signal cross-over distortion consistent with minimal measured quiescent current consumption; a good compromise is to set the quiescent current at about 10-15 mA. To measure this current, wire a DC current meter temporarily in series with the collector of Q3.
Technical data:
Output power: 1.5 Watt RMS @ 8 Ohm, 2.5 Watt @ 4 Ohm, 3.5 Watt @ 2 Ohm (1KHz sinewave)
Sensitivity: 100mV input for 1.5W output @ 8 Ohm
Frequency response: 30Hz to 20KHz –1dB
Output power: 1.5 Watt RMS @ 8 Ohm, 2.5 Watt @ 4 Ohm, 3.5 Watt @ 2 Ohm (1KHz sinewave)
Sensitivity: 100mV input for 1.5W output @ 8 Ohm
Frequency response: 30Hz to 20KHz –1dB
Parts:
P1 = 10K Log.Potentiometer
R1,R2 = 33K 1/4W Resistors
R3 = 33R 1/4W Resistor
R4 = 15K 1/4W Resistor
R5,R6 = 1K 1/4W Resistors
R7 = 680R 1/4W Resistor
R8 = 120R 1/2W Resistor
R9 = 100R 1/2W Trimmer Cermet
C1,C2 = 10΅F 63V Electrolytic Capacitors
C3 = 100΅F 25V Electrolytic Capacitor
C4,C7 = 470΅F 25V Electrolytic Capacitors
C5 = 47pF 63V Ceramic Capacitor
C6 = 220nF 63V Polyester Capacitor
C8 = 1000΅F 25V Electrolytic Capacitor
D1 = 1N4148 75V 150mA Diode
Q1 = BC560C 45V 100mA PNP Low noise High gain Transistor
Q2 = BC337 45V 800mA NPN Transistor
Q3 = TIP31A 60V 4A NPN Transistor
Q4 = TIP32A 60V 4A PNP Transistor
SW1 SPST switch
SPKR 3-5 Watt Loudspeaker, 8, 4 or 2 Ohm impedance.
P1 = 10K Log.Potentiometer
R1,R2 = 33K 1/4W Resistors
R3 = 33R 1/4W Resistor
R4 = 15K 1/4W Resistor
R5,R6 = 1K 1/4W Resistors
R7 = 680R 1/4W Resistor
R8 = 120R 1/2W Resistor
R9 = 100R 1/2W Trimmer Cermet
C1,C2 = 10΅F 63V Electrolytic Capacitors
C3 = 100΅F 25V Electrolytic Capacitor
C4,C7 = 470΅F 25V Electrolytic Capacitors
C5 = 47pF 63V Ceramic Capacitor
C6 = 220nF 63V Polyester Capacitor
C8 = 1000΅F 25V Electrolytic Capacitor
D1 = 1N4148 75V 150mA Diode
Q1 = BC560C 45V 100mA PNP Low noise High gain Transistor
Q2 = BC337 45V 800mA NPN Transistor
Q3 = TIP31A 60V 4A NPN Transistor
Q4 = TIP32A 60V 4A PNP Transistor
SW1 SPST switch
SPKR 3-5 Watt Loudspeaker, 8, 4 or 2 Ohm impedance.
This is a 100 watt basic power amp that was designed to be (relatively) easy to build at a reasonable cost. It has better performance than the standard STK module amps that are used in practically every mass market stereo receiver manufactured today.
The input stage is an LF351 op amp which provides most of the open loop gain as well as stabilizes the quiescent dc voltage. This feeds a level shift stage which references the voltage swing to the (-) rail. The transconductance stage is a darlington, to improve high-frerqency linearity. The 2SC2344 by itself has a rather large collector-base capacitance which is voltage dependent. The MPSA42 presents this with a low-z and has a C(ob) of only a few pf that is effectively swamped by the 33pF pole-splitting cap. The stage is supplied by the 2SA1011 active load (current source) which is about 20 ma. The current to the stage is limited by the 2N3094 to about 70 ma under worst case.
The output is a full complementary darlington with paralleled outputs. Although you could "get away with" only one if only 8 ohm easy-to-drive loads are used, this is not recommended. The use of parallel devices increases the ability to drive reactive loads (which can pull a significant current while the voltage waveform crosses zero and puts a high voltage and a high curent across the transistor simultaneously), gives the amp a higher damping factor, and reduces the maximum current each transistor has to supply to peaks (remember, the gain of a power transistor drops as the current increases).
Compensation is two-pole and one zero. The op-amp's pole and the pole generated by the 33pf cap and the 470 ohm bias resistor of the MPSA42 dominate. (the 33pF gets multiplied by the stage gain.) The 22 pf feedback capacitor provides lead compensation, and is taken from the output of the tranconductance stage rather than the output itself. In this way, the phase lag introduced by the output transistors is not seen by the high-frequency feedback. This intorduces a closed-loop pole which limits the high-frequency response. The two compensation capacitors must be type 1 creamic (NPO) or silver mica - with ZERO voltage coefficient.
The amp was designed to run 2 channels off a +/- 55 volt unregulated supply, reducing to +/- 48 volts under full load. It used a 40-0-40 volt, 5 amp toroid transformer, a bridge rectifier, and 10,000 uf of filter cap per side. If a standard EI transformer is used, a 6-amp rated unit should be used. With this power supply, it produces 100 watts continuous, both channels driven into 8 ohms resistive with no clipping. Dynamic headroom is about a db and a half. For more headroom, unloaded voltages to +/- 62 volts can be used with no circuit modification.
By the way, the schematic is in Postscript.
Limitations:
With no modifications the amp will drive 4-ohm speaker systems with no current limiting. The short-circuit current limit is set to about 4.5 amps peak, which will handle conventional speaker loads.(It will, of course, produce higher peak currents as the output voltage swing approaches the rail.) If you are going to be running some of those high-end speakers with impedance minima of half an ohm, or that stay reactive throughout most of the audio band ( ie, 0.5 +j3.2 ohms) you will probably already own a better amp than this. If the higher-power Motorola power transistors are used, it will drive a 2-ohm resistive load without problems (except heat).
I have never heard any slew-induced distortion on this amp with a CD player's band-limited (22KHz) signal. I suppose that real high-end freaks could pick it to pieces by hitting it with a TTL square wave mixed with a 19KHz stereo pilot tone and crank it up. I guarantee that there will be spurs all over the spectrum, but who listens to that?
Possible Modifications:
The Toshiba output transistors (2SD424/2SB554 pair) shoud not be used with supply voltages above +/-60 volts. If you plan on cranking it up, use more in parallel or use the 250 watt Motorola pairs (MJ15024/MJ15025). If very low impedances are expected, raise the bias in the transconductance stage to give more base drive to the output darlingtons or add another current gain stage. Higher-Beta (and faster) power transistors can't handle reactive loads worth a crap. Don't substitute high-fT parts unless you are sure they have adequate second-breakdown capability.
The NE5532 op-amp can be used in the input stage. If more than one are used off the +/-15 volt shunt regulators (balanced ins, anti-slew Bessel filters, etc.) the 2.7K dropping resistors may need to be reduced to say, 1.8K ohm to maintain regulation. The 2.7K resistors will allow up to 4 LF351 type op amps off the regulator (I used a quad 347 for balanced inputs to avoid hum in a DJ setup).
Construction tips:
The output transistors and thermal compensator (2SC1567) will need to be mounted on a common heat sink - a finned unit measuring 5 in. high by 8 in. wide with 1.25 in fins should do nicely for one channel. (They look nice if you make the sides of the case out of them). Most normal applications won't require more cooling than this. The reason the 2SC1567 was chosen for the output bias regulator is because it is fully insulated - the ECG version will require additional mounting hardware. TO-3 hardware for the outputs is cheap and easy to get.
The driver transistors and voltage amps (2SC3344/2SA1011 pairs) will all require heatsinking as well. Individual TO-220 heat sinks on the circuit board will suffice - the voltage amps dissipate about 1.4 watts each. A common piece of 1/8 in. thick 1 in. wide X 4in. long angle aluminum will suffice for all 4 on each channel, but bear in mind that it must be oriented to take advantage of natural convection, and the transistors must be insualted.
Keep the imput grounds separate from everything else, and return them at ONE point. Failure to do so WILL result in high distortion (5% or so), or even oscillation.
The output stage bias should be set to about 25 milliamps in the output transistors. This value takes a while to stabilize, and you may have to monitor it over an hour or so during initial setup. To measure it, measure the voltage across the emitter resistor and use Ohm's law. This way, you can check the current sharing in the parallel output transistors at the same time and change them if there is a serious discrepancy. With parts of the same date code, they should not be off by more than 10% after it has warmed up. Higher output stage biases can be used, but it takes more care in setting it. If you want an idle current of more than 50 milliamps per side, increase the value of the emitter resistors.
Initial Checkout:
DO NOT just plug something like this in! A seemingly insignificant error can set your house on fire! (As well as blow out $30 worth of transistors in a microsecond.) A variac will work in theory, but the amp may latch to the rail if the supply drops too low. I suggest the use of a ballast resistor - a 60 to 100 watt light bulb in series with the AC mains. You get a bright flash when the caps charge, and then it goes (almost) out as the idling supply current reaches its nominal low value. The amplifier will then work normally at low volumes. If the amp draws too much current for whatever reason, the lightbulb will glow brightly, increase resistance, and limit the power to the circuit. Usually, there will either be a mis-wire (use your DMM) or oscillation (will show up on a scope or RF power measuring device). If the bulb goes dim-bright-dim-bright... then the amp is marginally stable and the grounding layout should be checked. Compensation capacitor values may need to be adjusted if any significant changes were made. Mine is stable the way it is.