2 - Knob Compressor Pedal
Created: Aug 11, 2016
No description available.
Signal compression is considered to be a valuable signal shaping effect used in the audio industry. This compression effect functions by reducing the dynamic range of the input signal. It basically attenuates the louder signals while boosting the weak ones. Compression helps your signal to be more tightly sounding and volume-consistent. This effect is also known to add sustain to your sound. Many kinds of compressor with different designs have existed having their own characteristics and edge to one another others.
This circuit is a compressor circuit in a pedal or stomp box setup that can be used by guitar players for their recording and live performances. It has two knobs that can be used to set the compression level and the volume of the output. A 9V DC adapter supplies the circuit. The circuit has an LT3463 chip, a dual DC-DC converter, which converts the 9V supply to a +15V and -15V, to supply the op amps used. The circuit uses a 2SK246 JFET for gain control, together with the LM4562 op amp. The JFET is used to function as a voltage-controlled resistor. As the input in the JFET increases negatively, the resistance presented by the JFET will also increase varying the gain of the op amp U2A. A control circuit is also included to provide the control signal for the JFET. This is comprised of op amps U3 and U4. The op amp U4 gets a signal from the input, which is then processed to provide a signal at the inverting input of U3. The op amp U3 acts as a comparator, which compares the input signal at its inverting pin to the reference signal present in its non-inverting pin coming from the op amp U2A. When the input signal is lower than the reference signal, the comparator outputs a high signal approaching +Vcc. This creates a less negative voltage to be inputted to the JFET. When the input signal is higher than the reference signal, the comparator outputs a low signal approaching –Vcc. This output reversely biases the diode D3 and makes the -15V supply in the voltage divider as the only source of gate input of the JFET, which produces a more negative signal to the JFET.
The compression knob is a potentiometer dual ganged with the gain control of the U2B op amp (LM4562). The circuit has also a true bypass feature. When the effect is not ON, the guitar signal would flow to the bypass going to the amplifier. An LED indicator is included to point out to the user that the effect is engaged.