Diagram Guide

This is 2X1W audio amplifier circuit with mini-KA2209 IC. It may work well from 3-12V DC and will work from a battery since the quiescent current drain is low. It requires no heat sink for normal use. Input and output are both ground referenced. Maximum output is obtained with a 12V power supply and 8 ohm speaker, however, is especially suitable for driving headphones from a supply as low as 3V.

Amp mini circuit only a few external components, the IC contains most of the necessary circuits. R1, R2 and R3, R4 are the resistances of feedback. C1 provides power supply decoupling. C2 and C3 are the input coupling capacitors, which block any DC that might be present on the inputs. C4, C5 DC block in the feedback loop of the inverting input and C6, C7 are the output coupling capacitors. C8, C9 and R5, R6 act as a Zobel network to provide a high frequency load for stability in the frequencies where the inductive reactance of the loudspeaker can be strong too. The boat provides the attenuation of input level.

C1,C2,C3 : 10 uF/25V ecap
C4,C5 : 100 uF/16V ecap
C6,C7 : 470 uF/16V ecap
C8,C9 : 100 nF poly
R1,R3 : 1k Resistor
R2,R4 : 100R Resistor
R5,R6 : 4R7ohm Resistor
Pot1 : 10k dual gang log pot
IC1 : KA2209 Integrated Circuit

It is a simple and less efficient method to control DC voltage is using a voltage divider and transistor emitter follower configuration. The figure below is illustrated use a 1K potentiometer to set the base voltage of a medium power NPN transistor. The collector of the NPN feeds the base of a larger PNP power transistor which supplies most of the current to the load. The output voltage will be about 0.7 volts below the voltage of the wiper of the 1K pot so the output can be adjusted from 0 to the full supply voltage minus 0.7 volts. Using two transistors provides a current gain of around 1000 or more so that only a couple milliamps of current is drawn from the voltage divider to supply a couple amps of current at the output. The figure is;


Note that this circuit is much less efficient than the 555 timer dimmer circuit using a variable duty cycle switching approach. In the figure below, the 25 watt/ 12 volt lamp draws about 2 amps at 12 volts and 1 amp at 3 volts so that the power lost when the lamp is dim is around (12-3 volts * 1 amp) = 9 watts. A fairly large heat sink is required to prevent the PNP power transistor from overheating. The power consumed by the lamp will be only (3 volts * 1 amp) = 3 watts which gives us an efficiency factor of only 25% when the lamp is dimmed. The advantage of the circuit is simplicity, and also that it doesnt generate any RF interference as a switching regulator does. The circuit can be used as a voltage regulator if the input voltage remains constant, but it will not compensate for changes at the input as the LM317 does.

The Figure shows a linear frequency to voltage converter which works by charging a capacitor up once for every input cycle, the charge to do so being passed by a MOSFET into a summing amplifier.
The component values given are based on an approximate five volt output for the given frequency. The resistor R1 should be made a 100kQ preset if it is required to set a range exactly. The capacitor C2 "smooths" the output and need not be changed from 10pF if fast- response on the upper ranges is not needed. The linearity achieved on the top range will depend on the particular "741" used and if reliable operation is required a higher speed op- amp should be used. 

The tone generator is an astable multivibrator with one of the resistors being variable to change the notes. An amplifier could be used to increase the. volume, but quite a high volume is attained by the astable. Due to the simplicity of the circuit the wave form is rather irregular in shape. (To produce the note. the probe is moved across metal strips wired to points A, B, C etc.)

Simple Musical Organ Circuit


Simple Two-Tone Alarm Circuit Using IC 555

This device gives a two-tone alarm from a digital clock. lt may be used with any CMOS alarm clock chip having an active high alarm output and 1Hz (optional) output. It was built to work with a CT7001 chip and requires no interface components. The 555 operates in normal astable mode when the alarm goes high (ie point (a) approaches VSS). Pin 5 is the normal control voltage input and swings from almost VSS to VDD via the 27K resistor at a 1Hz rate. This causes the audio output to switch between high and low tones, above and below the frequency determined by R1, R2 and C1. To vary the frequency difference, R3 may be altered within wide limits, but it is  inadvisable to keep it below 15K. The basic frequency is best varied by changing C1. Audio output may be varied by changing C3 (depending on  LS impedance). {In the original, a 3552 speaker was used with -12V VDD and was sufficient to rouse an expert heavy sleeper. 

Simple Drum Simulator Circuit

A variety of percussive sounds may be obtained with variations on a simple twin—T oscillator of the type illustrated. The table is given as a guide to the frequency determining and envelope shaping components. 

This article describes the functional and constructional details of a four channel dynamic psychedelic lighting system.  It is capable of driving 24 lamps of 100 watts each in tune with the music fed to the system from a tape recorder, record player or an electronic organ. The system is designed to keep the cost low.  The system drives 24 lamps comprising four channels of music controlled lamps, each of which lights up at a preset input (audio) level, and then continues to flicker along with the music.

The entire system (excluding 1 lamps) can be built at a nominal cost of Rs 200. Working The control circuit, as shown in Fig. 1, consists of two sections an input signal comparator and a multichannel lamp driver. The input signal comparator uses an IC LM239, which contains four independent comparators, each of which has one inverting input, one non- inverting input and an output. VR1 to VR6 along with Rl to R3 provide a reference voltage at the non inverting input of each comparator. An audio signal is fed at the inverting input of each comparator, through R4 and VR7.

 Now each comparator compares the input signal voltage with its reference voltage. If the input voltage is less than the reference voltage, the output of the comparator remains high. If the input level exceeds the reference voltage level, the output of the  corresponding comparator goes low. This output voltage is fed to the lamp driver circuitry. Each lamp driver consists of a CMOS inverting buffer. The output of the buffer goes high when the output of the corresponding comparator goes low. When the output of the comparator goes high, a moderately filtered voltage V2 is fed at the gate of the corresponding triac.

Thus, the triac conducts and lights up the parallel lamp combination connected to it. Since outputs of the comparators  and the buffers change state (high/low) 1 rapidly, the lamps seem to flicker. The four outputs of lCl go low in succession. Hence, the four lamp channels light up in succession according to the input level. VR2 to VR5 can be used to {adjust the reference voltage of corresponding comparator. VR7 is used to attenuate the input signal.

Power supply

The control Circuit requires a well regulated 9V DC power supply for ICl, a moderately filtered lOV power supply for driving the triacs and a 230V y AC mains supply for driving the lamps. The power supply circuit shown in Fig. 2 can be used for this purpose. It con- sists of stepdown transformer Xl, a full—wave rectifier (D1, D4), filter .capacitor C2 and 9V regulator IC3. An- other full-wave rectifier (D2, D3) connected to the same transformer provides a 10V output which is moderately filtered by C1. The 230V AC supply is taken directly from the mains. Thus, the outputs of 9V DC, 10V DC and l 230V AC are available at V1, V2, V3 respectively. The LED indicates the presence of the mains supply. A safety indicator, built around the neon lamp and R18, has been incorporated to in- dicate proper earthing of the device.

Construction

The PCB and corresponding com- ponents layout are shown me Figs 3 and 4 respectively. Many components are kept out of the PCB. Wiring between the PCB and the components mounted on the heatsink should be done with ut- most care. Thick copper wires must be used for carrying mains while the re- maining connections may be done through a colour—coded multiway rib- bon cable. ICI, IC2 and their associ- ated circuitry may be wired onto the PCB as shown in Fig. 5. Care should be taken while soldering IC1 and IC2 as excessive heat can lead to their destruc- tion. Use of an IC socket is recom- mended for IC2. As triacs will dissipate a lot of heat during continuous operation, they should y be provided with an adequate heatsink. I The triacs and IC3 should be mounted as shown in Fig. 5 using mica washers . for insulation. The wires may be sol- dered to the pins of the triacs and IC3 as shown in Fig. 5 . Ribbon cables should be used for connecting triac gates and lC2, and insulated copper wires for the remaining connections. After assembling the circuit, recheck it for any dry soldering or shortcircuits. Using a multimeter or continuity tester, it should be ensured that there is no electric connection between the triac, IC tabs and the heatsink§ After assembly, the circuits may be housed in a suitable cabinet. The heatsinks are fixed inside the cabinet using plastic washers and screws. Points ‘a’ and ‘b’ should be connected to any two points on the (metallic) cabinet. Finally, using a continuity tester it should be ensured that the heatsink and the live wire (mains) are not touching the cabinet anywhere.
adjustments and application

After the circuit has been success- fully assembled, the parallel lamp com - bination should be connected to the output terminals of the circuit using thick 2-way cables of suitable length. Now the unit can be connected to the mains. ` Once the safety indicator (neon lamp, indicating that the unit is grounded) lights up, an audio signal can be fed from any tape recorder, record player or musical organ. Keeping all other controls in their maximum resistance position, adjust the overall input sensitivity using VR7. Adjust VR2 so that the lamps of the first channel glow and adjust VRl and VR6 to make the lamps flicker with the music. Now increase the input signal level slightly and adj ust VR3 so that the lamps of the second channel (L7—Ll2) start glowing and flickering in unison with music. The sensitivity of the other two channels is i also set in a similar manner, after ad- justing VR4 and VR5. Now VR, VR6 and VR7 are readjusted so that the lamps of the four channels light up in e succession along with the increasing audio input signal level.

seful hints

The system can drive lamps of higher wattage hy directly replacing the 4A, 40OV triacs with higher watt- age triacs. No change in the circuitry is required. Only the size of the heatsink needs to be increased. . 2. The system in its present form is sensitive to the input level. But it can be made sensitive to the audio frequency level by connecting suitable active or passive filters at the input of each comparator. 3. Lamps of each channel can be covered with a coloured celluloid pa- per, to make the effects more sensational. 4. For maximum sensitivity, the unit » should be directly connected to the preamplificr’s output.