Improved 3 Transistor Audio Amp (80 milliwatt)

This circuit is similar to the one above but uses positive feedback to
get a little more amplitude to the speaker. I copied it from a small
5 transistor radio that uses a 25 ohm speaker. In the circuit above,
the load resistor for the driver transistor is tied directly to the
+ supply. This has a disadvantage in that as the output moves positive,
the drop across the 470 ohm resistor decreases which reduces the
base current to the top NPN transistor. Thus the output cannot
move all the way to the + supply because there wouldn't be any
voltage across the 470 resistor and no base current to the NPN transistor.


This circuit corrects the problem somewhat and allows a larger
voltage swing and probably more output power, but I don't know
how much without doing a lot of testing. The output still won't
move more than a couple volts using small transistors since the
peak current won't be more than 100mA or so into a 25 ohm load.
But it's an improvement over the other circuit above.




In this circuit, the 1K load resistor is tied to the speaker so
that as the output moves negative, the voltage on the 1K
resistor is reduced, which aids in turning off the top NPN transistor.
When the output moves positive, the charge on the 470uF capacitor
aids in turning on the top NPN transistor.



The original circuit in the radio used a 300 ohm resistor where
the 2 diodes are shown but I changed the resistor to 2 diodes so
the amp would operate on lower voltages with less distortion.
The transistors shown 2n3053 and 2n2905 are just parts I used
for the other circuit above and could be smaller types.
Most any small transistors can be used, but they should be
capable of 100mA or more current. A 2N3904 or 2N3906 are probably
a little small, but would work at low volume.




The 2 diodes generate a fairly constant bias voltage as the battery
drains and reduces crossover distortion. But you should take care
to insure the idle current is around 10 to 20 milliamps with
no signal and the output transistors do not get hot under load.



The circuit should work with a regular 8 ohm speaker, but the
output power may be somewhat less.
To optimize the operation, select a resistor where the 100K is shown
to set the output voltage at 1/2 the supply voltage (4.5 volts).
This resistor might be anything from 50K to 700K depending on
the gain of the transistor used where the 3904 is shown.

Audio from a telephone line can be obtained using a transformer and capacitorto isolate the line from external equipment. A non-polarized capacitor isplaced in series with the transformer line connection to prevent DC currentfrom flowing in the transformer winding which may prevent the line fromreturning to the on-hook state. The capacitor should have a voltage ratingabove the peak ring voltage of 90 volts plus the on-hook voltage of 48 volts,or 138 volts total. This was measured locally and may vary with location,a 400 volt or more rating is recommended. Audio level from the transformer isabout 100 millivolts which can be connected to a high impedance amplifier ortape recorder input. The 3 transistor amplifier shown above can also be used.For overvoltage protection, two diodes are connected across the transformersecondary to limit the audio signal to 700 millivolts peak during the ringingsignal. The diodes can be most any silicon type (1N400X / 1N4148 / 1N914or other). The 620 ohm resistor serves to reduce loading of the line if theoutput is connected to a very low impedance.

LED Photo Sensor

Here's a circuit that takes advantage of the photo-voltaic voltage of an ordinary
LED. The LED voltage is buffered by a junction FET transistor and then applied
to the inverting input of an op-amp with a gain of about 20. This produces a
change of about 5 volts at the output from darkness to bright light. The 100K
potentiometer can be set so that the output is around 7 volts in darkness and
falls to about 2 volts in bright light.

Triangle and Squarewave Generator

Here is a simple triangle/squarewave generator using a common 1458 dual
op-amp that can be used from very low frequencies to about 10 Khz.

The
time interval for one half cycle is about R*C and the outputs will
supply about 10 milliamps of current. Triangle amplitude can be altered
by adjusting the 47K resistor, and waveform offset can be removed by
adding a capacitor in series with the output.

Low Frequency Sinewave Generators

The two circuits below illustrate generating low frequency sinewavesby shifting the phase of the signal through an RC network so thatoscillation occurs where the total phase shift is 360 degrees. The transistorcircuit on the right produces a reasonable sinewave at the collectorof the 3904 which is buffered by the JFET to yield a low impedanceoutput. The circuit gain is critical for low distortion and you may needto adjust the 500 ohm resistor to achieve a stable waveform with minimumdistortion. The transistor circuit is not recommended for practicalapplications due to the critical adjustments needed.

The op-amp based phase shift oscillator is much more stable than thesingle transistor version since the gain can be set higher thanneeded to sustain oscillation and the output is taken from theRC network which filters out most of the harmonic distortion.The sinewave output from the RC network is buffered and the amplituderestored by the second (top) op-amp which has gain of around 28dB. Frequencyis around 600 Hz for RC values shown (7.5K and 0.1uF) and canbe reduced by proportionally increasing the network resistors (7.5K).The 7.5K value at pin 2 of the op-amp controls the oscillator circuit gainand is selected so that the output at pin 1 is slightly clipped at thepositive and negative peaks. The sinewave output at pin 7 is about 5 voltsp-p using a 12 volt supply and appears very clean on a scope since theRC network filters out most all distortion occurring at pin 1.

Touch Activated Light

The circuits below light a 20 watt lamp when the contacts aretouched and the skin resistance is about 2 Megs or less.The circuit on the left uses a power MOSFET which turnson when the voltage between the source and gate is around6 volts. The gate of the MOSFET draws no current so thevoltage on the gate will be half the supply voltage or6 volts when the resistance across the touch contacts isequal to the fixed resistance (2 Megs) between the source and gate.
The circuit on the right uses three bipolar transistors toaccomplish the same result with the touch contact referencedto the negative or ground end of the supply. Since the baseof a bipolar transistor draws current and the current gain isusually less than 200, three transistors are needed to raisethe microamp current level through the touch contacts to a coupleamps needed by the light. For additional current, the lamp could bereplaced with a 12 volt relay and diode across the coil.

AC Line Current Detector

This circuit will detect AC line currents of about 250 mA or more without
making any electrical connections to the line. Current is detected by passing
one of the AC lines through an inductive pickup (L1) made with a 1 inch
diameter U-bolt wound with 800 turns of #30 - #35 magnet wire. The pickup
could be made from other iron type rings or transformer cores that allows
enough space to pass one of the AC lines through the center. Only one of the
current carrying lines, either the line or the neutral should be put through
the center of the pickup to avoid the fields cancelling. I tested the circuit
using a 2 wire extension cord which I had separated the twin wires a small
distance with an exacto knife to allow the U-bolt to encircle only one wire.


The magnetic pickup (U-bolt) produces about 4 millivolts peak for a AC line
current of 250 mA, or AC load of around 30 watts. The signal from the pickup
is raised about 200 times at the output of the op-amp pin 1 which is then
peak detected by the capacitor and diode connected to pin 1. The second
op-amp is used as a comparator which detects a voltage rise greater than the
diode drop. The minimum signal needed to cause the comparator stage output
to switch positive is around 800 mV peak which corresponds to about a 30 watt
load on the AC line. The output 1458 op-amp will only swing within a couple
volts of ground so a voltage divider (1K/470) is used to reduce the no-signal
voltage to about 0.7 volts. An additional diode is added in series with the
transistor base to ensure it turns off when the op-amp voltage is 2 volts.
You may get a little bit of relay chatter if the AC load is close to the
switching point so a larger load of 50 watts or more is recommended. The
sensitivity could be increased by adding more turns to the pickup.

The circuit below responds to sound pressure levels from about 60 to 70 dB.
The sound is picked up by an 8 ohm speaker, amplified by a transistor stage
and one LM324 op-amp section. You can also use a dynamic microphone but I
found the speaker was more sensitive. The remaining 3 sections of the LM324
quad op-amp are used as voltage comparators and drive 3 indicator LEDs or
incandescents which are spaced about 3dB apart. An additional transistor is
needed for incandescent lights as shown with the lower lamp. I used 12
volt, 50mA lamps. Each light represents about a 3dB change in sound level
so that when all 3 lights are on, the sound level is about 4 times greater
than the level needed to light one lamp. The sensitivity can be adjusted
with the 500K pot so that one lamp comes on with a reference sound level.
The other two lamps will then indicate about a 2X and 4X increase in volume.



In operation, with no input, the DC voltage at pins 1,2 and 3 of the op-amp
will be about 4 volts, and the voltage on the (+) inputs to the 3 comparators
(pins 5,10,12) will be about a half volt less due to the 1N914 diode drop.
The voltage on the (-) comparator inputs will be around 5.1 and 6.5 which
is set by the 560 and 750 ohm resistors.




When an audio signal is present, the 10uF capacitor connected to the diode
will charge toward the peak audio level at the op-amp output at pin 1.
As the volume increases, the DC voltage on the capacitor and also (+)
comparator inputs will increase and the lamp will turn on when the (+)
input goes above the (-) input. As the volume decreases, the capacitor
discharges through the parallel 100K resistor and the lamps go out.
You can change the response time with a larger or smaller capacitor.



This circuit requires a well filtered power source, it will respond
to very small changes in supply voltage, so you probably will need
a large filter capacitor connected directly to the 330 ohm resistor.
I managed to get it to work with an unregulated wall transformer
power source, but I had to use 4700uF. It worked well on a regulated
supply with only 1000uF.

Alternating ON-OFF Switch, #1

ERROR FIX: The PCB contained several errors and prevented the circuit from working. A new printed circuit board and lay-out is listed below

.

Please note that neither PCB or Layout is drawn to scale!
PCB measures approximately 3-3/4 x 1-1/2 inches (70 x 39mm or 207 x 123 pixels).

Parts List


Resistors are 1/4 Watt, 5%


R1,R3 = 10K (brown-black-orange)

R2 = 100K (brown-black-yellow)

R4 = 220 Ohm (optional) (red-red-brown)

C1 = 0.1uF, (100nF any type) C2 = 0.01, (10nF any type)

D1 = 1N4001 (see text)

Led1 = Led, 3mm, red (optional)

Q1 = PN100, NTE123AP, 2N4401, 2N2222, 2N3904 etc. (see text)

IC1 = 4069, CMOS, Hex Inverter (MC14069UB), or equivalent

S1 = Momentary 'on' switch

Ry1 = Relay, 8 or 9 volt

A complete KIT (now with pcb and relay) for this circuit is available. >> Click Here <<

Use this circuit instead of a standard on-off switch. Switching is very gentle. If you don't use the Printed Circuit
Board, connect unused input pins to an appropriate logic level ('+' or '-'). Unused output pins *MUST* be left open!
On the pcb this is already done. First 'push' activates the relay, another 'push' de-activates the relay.




IC1, the MC14069 (or 4069) is a regular Hex-inverter type and is constructed with MOS P-channel and N-channel
enhancement mode devices in a single monolithic structure. It will operate on voltages from 3 to 18 volts, but most
applications are in the 5 to 15 volts. Although the 4069 contains protection circuitry against damage from ESD
(Electro Static Discharge), use common sense when handling this device. Depending on your application you may want to
use an IC-socket with IC1. It makes replacement easy if the IC ever fails. The IC is CMOS so watch for static
discharge!




You can use any type of 1/4 watt resistors including the metal-film type.




The type for D1 in not critical, even a 1N4148 will work. But, depending on your application I would suggest a 1N4001
(or similar) as a minimum if your relay type is 0.5A or more. Any one in the 1N400x series diodes will work.




Any proper replacement for Q1 will work, including the european TUN's. Since Q1 is just a driver to switch the relay
coil, almost any type for the transistor will do. PN100, NTE123AP, BC547, 2N3904, 2N2222, 2N4013, etc. will all work.




For C2, if you find the relay acts not fast enough, you can change it to a lower value. It is there as a spark-arrestor
together with diode D1.




For the relay I used an 8 volt type with the above circuit and a 9 volt battery. Depending on your application, if the
current-draw is little, you can use a cheap 5V reed-relay type. Use a 8V or 9V relay type if your supply voltage is
12V. Or re-calculate resistor R3 for a higher value.

The circuit and 9V will work fine and will pull the relay between 7 and 9 volt, the only thing to watch for is the
working voltage of C2; increase that to 50V if you use a 12V supply.

The pcb was designed for an Aromat/Omron relay, 9V/5A, #HB1-DC9V. You can easily re-design the relay pads on the
PCB for the relay of your choice. If you wish to use something you already have, and you don't want to re-design the
PCB, you can glue the relay up-side-down on the pcb and wire the relay contacts manually to the pcb-holes or directly
to your application.

Use a 2N2222 transistor for Q1 if your supply voltage is higher than 9V and/or your relay is heavy duty, or doesn't want
to pull-in for any other reason.




Again, the pcb drawing is not to scale. Use 'page-setup' to put the scale to 103% for a single pcb, vertically, and
your scale should be correct. I use a laser printer and so I don't know if this scale of 103% is for all printers. To
check, print a copy onto regular paper and see if the IC pins fit the print. If so, your copy is correct. If not,
change the scale up of down until a hardcopy fits the IC perfectly.




The Led is nice for a visual circuit indication of being 'on'. For use with 12V supply try making make R4 about 330
ohms. The LED and R4 are of course optional and can be omitted. Your application may already have some sort of
indicator and so the LED and R4 are not needed.

Labels: All, Other

Alternating ON-OFF Switch, #2

Alternating ON-OFF Switch, #2
Parts List

Resistors are 1/4 Watt, 5%



R3,R5,R6 = 1K (brown-black-red) R1,R7 = 2K7 (red-violet-red) R4 = 100K (brown-black-yellow) R2 = 180K (brown-gray-yellow) C1 = 10uF/16V, electrolytic C2 = 220uF/16V, electrolytic C3 = 1uF/16V, electrolytic D1 = 1N4148 Led1 = Led, red Q1,Q2 = BC557B (or 2N3906) Q3 = BC337-40 (or 2N3904) S1 = Momentary on-switch Ry1 = Relay (see text)





Description:

This circuit is the transistor version of the 4069 cmos type. Every press of the push-button will activate or
de-activate the relay.



On power-up, the voltage on the base of Q1 and Q2 is equal with the supply voltage. The base of Q3 is at ground
potential. So, all three transistors are blocking. Relay Ry1 not energized and the Led is off.

Pressing momentary switch S1, Q2 is biased. After a small delay, caused by capacitor C1, Q3 is also biased. The
collector of Q3 is now put to ground potential, which causes relay Ry1 to energize and light the led at the same time.
At this time Q1 is biased and the circuit stabilized, because the base of Q2 is now connected to ground potential via R1.
This keeps Q2 biased when S1 is released (like a latch). C1 is recharged via R3, close to the supply voltage.

If S1 is pressed again, Q2's base gets biased with a positive voltage instead of being put to ground potential. Q2 will
block and the whole sequence will repeat itself. This circuit works like a thyristor. In fact, Q2 and Q3 are together
a discrete thyristor.



This circuit can be used in many applications by selecting different relays.


The coil of Ry1 should be capable of handling 5 to 12V at 250mA maximum or Q3 will go up in smoke!

The prototype used 70mA and less than 0.1uA when idle.



Labels: All, Other

50W Power Amplifier OCL Mosfet (K1058 + J162)

Circuit 50W Power Amplifie OCL Mosfet (K1058 + J162)
162)
The 50W Power Amplifier OCL Mosfet (K1058 + J162) is easy to build,
and very inexpensive. To use Power Supply +35V -35V >2A.
Mosfet (K1058 + J162) must be mounted on heatsink.
Can be directly connected to CD players, tuners and tape recorders

PCB 50W Power Amplifie OCL Mosfet (K1058 + J162)

Circuit - 50W Power Amplifier Mosfet

This Circuit 50W rms Power Amplifier.
by Power Mofet IRF530 and IRF9530.
For supply +35V and -35V >3A

This IC chip was designed specifically for use in power boosting applications in automobiles. It is self protecting against short circuits and thermal problems. In the bridge configuration shown it will deliver 20 watts of power into a 2 ohm speaker operating at 14.4 volts.
Labels: All, Audio

4-WATT AF AMPLIFER

The circuit is very simple and incorporates darlington output transistors that will provide more than enough output current than is needed to drive a 3-ohm speaker. The gain may be pre-set for a variety of input levels, making it suitable for amplifying computer and cassette-deck Line-output levels. The input level is also suitable for use with the TDA7000 receiver. All components are easily available and I will shortly be making this project available as a kit. Naturally, the project will be built on a PCB which will also be available separately. Here is the first PCB, assembled and working.

Labels: All, Audio