Low Capacitance High Impedance Amplifier Circuit Using Transistor

This series-feedback series of compounds give a high input impedance and stable, gain wide-band video amplifier for general purpose applications. This is the figure of the circuit;

 

Circuit source: National Semiconductor Application

Overvoltage Protected Compressor Control Circuit

We can control medium power load, such as AC motors in home appliances, using ACST12 devices. Because of it’s thermal and turn off commutation performances, this device is able to drive an inductive load up to 12 A with no turn if additional snubber. This is the figure of the circuit;

High thermal performances in static and transient modes such as the compressor inrush current or high torque operating conditions of an AC motor also provided by this device. The ACST1210-7 can be driven directly by a MCU through a simple gate resistor as shown in figure below because of it’s low gate triggering current level. [Circuit diagram source: STMicroelectronics Application Note]

LM359 Voltage Controlled Oscillator Circuit

Voltage controlled oscillator (VCO) is similar to a voltage to frequency converter (VFC), an oscillator which its output frequency is determined by a control voltage input. This is the figure of the circuit;

The frequency FO of this VCO is determined by input voltage (VIN), R1, and C as expressed in the following formula:
FO=(VIN-d)/(4hCR1),

Where d is the amplifier input voltage = 0.6V, h=hysteresis of DM1474 (typically = 1V). R2 must be equal to 2R1 for proper operation. Using this circuit, operation up to 5MHz can be achieved.

Hydrophone Pre-Amplifier Circuit

Hydrophone is similar with microphone, except that it is used in underwater environment. Off course a hydrophone can be used to pick up sound in air, but it will be less sensitive since it’s mechanical-acoustical properties is design to match the acoustical impedance of water. This is the figure of the circuit;

The schematic shows the circuit of a low noise hydrophone amplifier with DC-servo.  One half of LT1113 (A)  is used in non-inverting configuration to amplify the voltage signal from hydrophone, and the other half  (B) null the current and voltage offsets error of  amplifier A.  This DC-servo B also nulls out the DC errors of hydrophone output.  The C1 value should match with the hydrophone capacitance, usually between 200 pF and 8000 pF. The servo should have time constant that is larger than the time constant of hydrophone capacitance and the 100M source resistance to prevent canceling the low frequency signal acquired by hydrophone. [Circuit diagram source: Linear Technology Application Notes]

BTL Mono Amplifier With DC Volume Control Circuit

This is BTL (bridged tied load) mono amplifier with DC volume Control circuit. This circuit uses TDA7052A/AT that is suitable not only for monitors and TV but also battery fed portable radios and recorders. The difference between conventional DC volume circuits and TDA7052A/AT the DC volume control is there is no coupling capacitor is needed in TDA7052A/AT the DC volume control to maintain the low offset voltage. 

Besides that, the TDA7052A/AT the DC volume control requires low supply. The advantages of BTL principle are it has the ripple’s frequency on the supply voltage is twice the signal frequency and the supply current peak is lower. This is the figure of the circuit;
 

To save the cost, a smaller capacitor can be used. The BTL principle can be implemented in portable application that will decrease supply voltage but increases the output power. This amplifier has maximum gain of 35.5 dB. The mute mode is when the DC volume control voltage is below 0.3V. This circuit also equipped with thermal protection. The gain will be decreased when temperature reach +150 C. [Circuit diagram source: nxp.com]

Big Muff Distortion Pedal Tone Control Circuit

This is a design circuit for a classic tone stack from the Big Muff distortion pedal. Basically, it’s a pair of filters whose output is combined through the 100k mix pot. The 39k/.01 filter attenuates the highs and only passes low frequency. But, the 3900pF/22k filter does the opposite. This is the figure of the circuit;

This filter passes the high frequency and filters out the lows. The 100k pot blends together the signal from each filter and acts as a tone control. The values of vintage Muff pedal are shown here. Even on that classic box, the values sometimes varied slightly.