## Harmonic Generator With Single Opamp

Quartz crystals have the
property that their amplitude/phase characteristic repeats itself at
frequencies that are an uneven multiple of the fundamental frequency.
There are so-called overtone crystals that are cut in such a manner that
they possess this property to a greater extent. However, in principle,
any crystal may be used on one or more of its harmonic frequencies.
Harmonic generators based on transistors may operate satisfactorily on
the 3rd harmonic, but if the 5th or 7th harmonic are wanted, the circuit

This circuit is based on a single, fast opamp and oscillates readily
at the 3rd, 5th or 7th harmonic. The opamp is set up as a non-inverting
amplifier with the quartz crystal connected between its output and the
non-inverting input. The circuit amplification, which in principle must
be unity to ensure oscillation, is determined by the network formed by
R4, R5 and trimmer capacitor C3. This network is frequency-dependent
such that the amplification increases as the frequency rises. The

The setting of the capacitor must be such that the gain is too small
for oscillation at the fundamental frequency, but sufficient for, say,
the 5th or 7th harmonic. The author uses a standard computer crystal of
10 MHz. Depending on the setting of C3, the circuit provides a stable
output at frequencies between 50 and 70 MHz. It should be noted that
these frequencies are multiples of the series fundamental frequency of
the crystal. Tuning is carried out simply with a frequency counter

#### Harmonic Generator Circuit Diagram With Single Opamp

The output frequency is varied with C3. When the capacitor is
roughly at the correct setting, the frequency ‘locks’ as it were at the
harmonic. The area where locking occurs is not well-defined, however, so
that the setting of C3 is not critical. When tuning is completed, the
output frequency is crystal-stable. In principle, the circuit may be
used for frequencies of up to 100 MHz, when the values of R4 and R5 may
need to be reduced.

When a crystal with a higher fundamental frequency, say, 15 MHz, is
used, the circuit may be tuned to the 3rd harmonic, that is, 45 MHz. The
circuit should be tested with a supply voltage of 5–9 V (the maximum
supply voltage for the IC is 12 V). The peak to peak output voltage has a
value of about that of the supply voltage less a few volts. The output
can provide a current sufficient to drive relatively low-impedance

author: gert baars – copyright: elektor electronics

## an Op Amp with Discrete Components

You can use three
discrete transistors to build an operational amplifier with an open-loop
gain greater than 1 million (Figure 1). You bias the output at
approximately one-half the supply voltage using the combined voltage
drops across zener diode D1, the emitter-base voltage of input

Build an op amp with three discrete transistors figure 1Resistor R3
and capacitor C1 form a compensation network that prevents the circuit
from oscillating. The values in the figure still provide a good
square-wave response. The ratio of R2 to R1 determines the inverting
gain, which is −10 in this example.You can configure this op amp as an

It drives a load of 1 kΩ. The square-wave response is good at 10
kHz, and the output reduces by 3 dB at 50 kHz. Set the 50-Hz
low-frequency response with the values of the input and the output
capacitors. You can raise the high-frequency response by using faster
transistors and doing careful layout.

## Subwoofer Lowpass Filter using uA741 Single Op-Amp Ic

This is the simplest Sub
woofer Low Pass filter Circuit using uA741 single op amp ic. The
circuit is very low cost with respect to their work. The cut off
frequency of this circuit is 25Hz to 80Hz maximum. Using this circuit ,
you can easily design a 2.1 Sub-woofer Speaker System at your own Home.
The circuit contains very few components.In Pakistan, the cost of this
circuit with PCB红包扫雷苹果下载地址 is Rs:45 The same circuit is working in my own hand made sub-woofer system. So Try this Link:

#### Circuit diagram

Parts List:

R1,R3,R4 = 10K 1/4W
R2=100K 1/4W
CY1,CY2 = 0.22uF Polyester
C1,C2 = 10uF/25V Electrolytic
IC1 = uA741A Single Op-Amp Ic + 8 Pin Ic Socket
3 Pin Male & Female Connector x 2
2 Pin Male & Female Connector x 1
PCB红包扫雷苹果下载地址 as in required size 4.5 cm x 3.4 cm

## Zero Gain Mod For Non-Inverting Opamp

Electronics textbooks
will tell you that a non-inverting opamp normally cannot be regulated
down to 0 dB gain. If zero output is needed then it is usual to employ
an inverting amplifier and a buffer amp in front of it, the buffer
acting as an impedance step-up device. The circuit shown here is a trick
to make a non-inverting amplifier go down all the way to zero output.
The secret is a linear-law stereo potentiometer connected such that when
the spindle is turned clockwise the resistance in P1a increases (gain
goes up), while the wiper of P1b moves towards the opamp output (more
signal). When the wiper is turned anti-clockwise, the resistance of P1a
drops, lowering the gain, while P1b also supplies a smaller signal to

Circuit diagram:

## Opamp With Hysteresis

At first glance, the
circuit in the diagram does not look out of the ordinary, and yet, it
is. This is because it combines two characteristics that are usually
assumed to be incompatible: hysteresis and a high input impedance. In a
standard op amp circuit, this is, indeed, true, because the creation of
hysteresis is normally achieved by positive feedback to the +ve input of
the op amp. Unfortunately, the requisite resistance network causes a
drastic deterioration of the original high input impedance of the op
amp. So, when a high input impedance and hysteresis are wanted, the
solution is to obtain the needed positive feedback by coupling the

Circuit diagram:

#### Operational amplifier With Hysteresis Circuit Diagram

When this done, the hysteresis so obtained is calculated from Uh =
1.2/R4Uo, where Uh is the hysteresis voltage and Uo is the output
voltage of the op amp, both in volts The value of R4 must be in kΩ. The
level of Uo depends, of course, on the load.

## Low Cost Bass-Treble Controller Using Op-Amp 741

This is simple but
powerful bass, treble, volume control is made by General Op-Amp IC
LM741. The input voltage is 12V, but it will also work with 9V and 6V.
This has inbuilt pre-amplifier also. Left channel is shown. Right
channel is same.

Parts List:

IC LM741 ×1
T/C 10k,22k,100k All x1
Triansistor BC148/548 = 1
220uF/25V = 2
4.7uF/25V = 2
2.2uF/10V = 1
10uF/25V = 1
Small resistors x12p

## Dual Opamp Buffered Power Supply

There will be instances where the currents
from each supply will be unequal. Where this is the case, the resistor
divider is not sufficient, and the +ve and -ve voltages will be unequal.
By using a cheap opamp (such as a uA741), a DC imbalance between
supplies of up to about 15mA will not cause a problem. However, we can
do better with a dual opamp (which will cost the same or less anyway),
and increase the capability for up to about 30mA of difference between

source:

## Regulator power supply with op-amp

Power supply circuit has a first amplifier using op-amp is IC uA741. Op amp circuit that is used only one, but it also features an adjustable voltage, which is steered by a trimpot resistors. Rtrim will set the input to the IC input on pin 2, so that if the detainee on Rtrim which will be channeled into ic enlarges the output voltage will be small, and otherwise. After the voltage is boosted and filtered and then the voltage will be regulated and boosted again by a NPN transistor. Output voltage 0.5V – 35V

Part List :
Resistor
R1____1K5
R2____1K trim
R3____10K
R4____330R
R5____1K
R6____47R
R7____68R
R8____820R
R9____47K
R10___22K
R11___1K5

Capacitor

Transistor
Q1____2N3565
Q2____2N3565
Q3____S9013
Q4____S9013

Diode
D1____1N4007
D2____1N4007
LED1_Red Led

IC
U1____uA741 (op-amp ic)

## What is the difference between op amps and comparators?

i well remember the first time that i saw an operational amplifier; it was 1965 at cambridge electron accelerator –it was a mysterious box containing numerous transistors that could be connected in various ways for various functions. both analog and digital integrated circuits (rtl –resistor transistor logic) would soon be introduced, but i never could have guessed what the future would hold. now some 50years later having used both op amps and comparators, i have good understanding of these devices and wish to pass some practical information along.

Popular devices

Schematics a cursory glance may suggest that the two schematics are very similar with both having identical differential inputs, but observe the differences in the output structure. the lm324 has a complementary output while the lm339 is open collector. in the complementary output, current can flow in either direction as required (either source or sink) while the open collector output can only sink current. this basic difference is typical of all op amps and comparators (although a few comparators have complementary outputs).

Application issues

Power supplies (or rails)

the ground rail is generally logic common. in a single supply comparator, it is also generally the negative rail or the most negative voltage in the circuit. some comparators like the lm311 cannot compare voltages at ground potential due to limitations in the common mode input voltage range so they require a negative rail to power the analog section. these devices offer a separate logic ground pin that is tied to logic common. so in the lm311 class of comparators there are (3) rails: common, analog positive and analog negative. a possible 4th rail would be the logic positive rail that is equal or lower in voltage than the analog positive power supply rail –this is what powers the output pull-up resistor. the analog positive and negative rails are often ±12v, but can actually be whatever is desired or required such as ±5v –also, they need not be equal in voltage.

note that some comparators (perhaps 10%) have a complementary rather than open collector output –with such, the analog positive rail must be equal in voltage to the logic positive rail.

Open collector output

the open collector output is the usual means of interfacing the comparator output to the logic input. such requires an external pull-up resistor. it allows the logic positive rail to be lower in voltage than the analog positive rail. open collector outputs also provide the means of a “wired or” connection where multiple open collector outputs are tied together –all open collector outputs must be high (off) in order for the output to go high. Op amps as comparators

Comparators as op amps

very, very seldom are comparators used as op amps, but never say never. here is an application note that shows how to make it work. the addition of the output capacitor slows the device so that it can operate without oscillation in the linear output voltage range. the only time this might be practical is when a low performance op amp function is required, but the only device available is one section of an lm339 quad comparator. now, i have never done this, but it would make a great experiment. Use the LP311 instead of the LM311

Datasheets

For the future

applying a comparator as an op amp, an experiment