Tunable bandpass filters variable resistors

Tunable bandpass filters variable resistors

One of the difficulties in the design of higher-order tunable bandpass filters is achieving correct tracking of the variable resistors in the RC networks. The use of switched capacitor networks can obviate that difficulty, as is shown in this filter. The filter can be divided roughly into two stages: an oscillator that controls the electronic switches arid the four phase-shift networks that provide the filtering proper. The oscillator, based on a 555, generates a pulsating signal whose frequency is adjustable over a wide range: the duty factor varies from 1:10 to 100:1. Electronic switches ESI through ES4 form the variable resistors whose value is dependent on the frequency of the digital signal. The operation of these switches is fairly simple. When they are closed, their resistance is about 60 ; when they are open, it is virtually infinitely high. a switch is closed for, say, 25% of the time, its average resistance is therefore 240 . `Varying the open:closed ratio of each switch varies the equivalent average resistance. The switching rate of the switches must be much greater than the highest audio frequency to prevent audible interference between the audio and the clock signals. The input signal causes a given direct voltage across CI, so the op amp can be operated in a quasisym-metric manner, in spite of the single supply voltage. The direct voltage is removed from the output signal by capacitor C10. The fourth-order filter in the diagram can be used over the entire audio range and it has an amplification of about 40, although this depends to some extent on the clock frequency. The bandwidth depends mainly on the set frequency. The circuit draws a current of not more than 15 mA.

Tunable bandpass filters variable resistors

Stereo Amplifier Circuit TDA2007A 12W Bridge

Stereo Amplifier Circuit TDA2007A 12W Bridge general description

The following schematic shows 12 W Bridge Amplifier circuit diagram as an application of the TDA2007A a class AB dual audio power amplifier which is designed for stereo application in music centers, TV receivers and portable radios. According to the datasheet, this TDA2007A has features such high output power, high current capability, AC short circuit protection, and thermal overload protection.

For description about stereo test circuit, PCB components layout of the circuit, the recommended values of the components of Stereo 12W Bridge Amplifier Circuit Diagram using TDA2007A can be seen.

 Stereo Amplifier Circuit TDA2007A 12W Bridge circuit diagram

 Stereo Amplifier Circuit TDA2007A 12W Bridge

Peamp circuit extra-deep bass change capacitor

Peamp circuit extra-deep bass change capacitor

The input impedance is the value of potentiometer Rl. If your instrument has extra-deep bass, change capacitor Cl to 0.5 mF. What appears to be an extra part in the feedback loop is a brightening tone control. The basic feedback from the op amp's output (pin 6) to the inverting input (pin 2) consists of resistor R7, and the series connection of resistor R4 and capacitor C3, which produce a voltage gain of almost 5 (almost 14 dB). That should be more extra oomph than usually needed.

Peamp circuit extra-deep bass change capacitor

Stereo amplifier uses a National LM3871C

Stereo amplifier uses a National LM3871C

Stereo amplifier uses a National LM3871C. The pin numbers in parentheses are for one channel, and those not in parentheses are for the other channel. The supply voltage can be +9 to +30 Vdc at about 10 mA. The output voltage swing is about Vee-2 V pk-pk.

Stereo amplifier uses a National LM3871C

60W Bass Control Audio Power Amplifier Circuit diagram

Audio Power 60W Bass Control  Amplifier Circuit diagram 

60W Bass Control Audio Power Amplifier Circuit diagram

Audio Power 60W Bass Control  Amplifier Circuit description
This design adopts a well established circuit topology for the power amplifier, using a single-rail supply of about 60V and capacitor-coupling for the speaker(s). The advantages for a guitar amplifier are the very simple circuitry, even for comparatively high power outputs, and a certain built-in degree of loudspeaker protection, due to capacitor C8, preventing the voltage supply to be conveyed into loudspeakers in case of output transistors' failure.
The preamp is powered by the same 60V rails as the power amplifier, allowing to implement a two-transistors gain-block capable of delivering about 20V RMS output. This provides a very high input overload capability.

Audio Power 60W Bass Control  Amplifier Circuit Technical data:
Sensitivity:
70mV input for 40W 8 Ohm output
63mV input for 60W 4 Ohm output
Frequency response:
50Hz to 20KHz -0.5dB; -1.5dB @ 40Hz; -3.5dB @ 30Hz
Total harmonic distortion @ 1KHz and 8 Ohm load:
Below 0.1% up to 10W; 0.2% @ 30W
Total harmonic distortion @ 10KHz and 8 Ohm load:
Below 0.15% up to 10W; 0.3% @ 30W
Total harmonic distortion @ 1KHz and 4 Ohm load:
Below 0.18% up to 10W; 0.4% @ 60W
Total harmonic distortion @ 10KHz and 4 Ohm load:
Below 0.3% up to 10W; 0.6% @ 60W
Bass control:
Fully clockwise = +13.7dB @ 100Hz; -23dB @ 10KHz
Center position = -4.5dB @ 100Hz
Fully counterclockwise = -12.5dB @ 100Hz; +0.7dB @ 1KHz and 10KHz
Low-cut switch:
-1.5dB @ 300Hz; -2.5dB @ 200Hz; -4.4dB @ 100Hz; -10dB @ 50Hz

Notes:
The value listed for C8 is the minimum suggested value. A 3300µF capacitor or two 2200µF capacitors wired in parallel would be a better choice.
The Darlington transistor types listed could be too oversized for such a design. You can substitute them with MJ11014 (Q3) and MJ11013 (Q4) or TIP142 (Q3) and TIP147 (Q4).
T1 transformer can be also a 24 + 24V or 25 + 25V type (i.e. 48V or 50V center tapped). Obviously, the center-tap must be left unconnected.
SW1 switch inserts the Low-cut feature when open.
In all cases where Darlington transistors are used as the output devices it is essential that the sensing transistor (Q2) should be in as close thermal contact with the output transistors as possible. Therefore a TO126-case transistor type was chosen for easy bolting on the heatsink, very close to the output pair.
R9 must be trimmed in order to measure about half the voltage supply from the positive lead of C7 and ground. A better setting can be done using an oscilloscope, in order to obtain a symmetrical clipping of the output waveform at maximum output power.
To set quiescent current, remove temporarily the Fuse F1 and insert the probes of an Avo-meter in the two leads of the fuse holder.
Set the volume control to the minimum and Trimmer R3 to its minimum resistance.
Power-on the circuit and adjust R3 to read a current drawing of about 30 to 35mA.
Wait about 15 minutes, watch if the current is varying and readjust if necessary.

Power Amplifier 60 Watt supply voltage 30 - 60 Volts

Power Amplifier 60 Watt supply voltage 30 - 60 Volts

This is a simple and low cost 60W power amplifier. The optimal supply voltage is around 50V, but this amp can work from 30 to 60V. The maximum input voltage is around 0.8 - 1V. As you can see, in this design the components have a big tolerance, so you can build it with almost any components that you can find at home. The output power transistors can be any NPN types, but do not use Darlington types.

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 500 Ohm trimmer resistor. As this current increases, the sound of the amplifier is better, but output transistors are dispatching more heat. If the current is decreased, the transistors are dispatching less heat, but the sound quality is decreased.

Wireless am microphone

Wireless am microphone

Transistor Ql and its associated components comprise a tuneable rf oscillator. The rf signal is fed to transistor Q2, the modulator. Operational amplifier ICl increases the audio signal and applies it through resistor R4 to the base of Q2. Tune an Wireless am microphone AM radio to an unused frequency between 800 to 1600 kHz. Tune Ll for a change in the audio level coming from the radio. Peak the output by adjusting L2 If Ll is disturbed, it may be necessary to readjust L2 for peak performance. Depending on the impedance of the microphone audio sensitivity can be increased by decreasing the value of RIO and vice versa. Wireless am microphone.

Wireless am microphone