The gate will become negatively biased with regards to the source, negative values of V GS will start to shut Q 15 off. As the current increases, a voltage drop will develop across the Zener, until the diode will be reversed biased. With zero V GS the transistor enters in saturation region allowing a large current to flow through the JFET, so the current will increase. Then the voltage drop across the Zener diode D2 and V GS will be zero. When the +Vcc voltage source is turned on, no current is yet flowing through the JFET Q 15.The start-up of this part of the circuit is simple: The JFET Q 15 is a self-biased current source, it will provide a constant current source independent from the voltage supply. This stage highlighted in green color is formed by Q 1, Q 7, Q 13, Q 14, Q 15, R 1, R 9 and D 2:

A stable current source is important in order to improve linearity and noise rejection. The Active Current Supply it is a utility stage which provides a constant flow of current to the different blocks.

Find below the simplified circuit provided by JRC, broken down into blocks: Current Supply, Input Stage, Voltage Amplifier Stage (VAS), Output Stage (OPS) and Feedback Path. 'Jimmy' Lin an RCA researcher) following the classic 741 type opamp structure with some modifications. The JRC4558 internal schematic is based on the Lin Topology (named after Hung C. Table of Contents:ġ.2.1 Long Tailed Pair Differential Amplifier. Despite its questionable audio performance, it seems to be well suited to duty in overdrive circuits. As such, it was used in huge volumes of Japanese audio equipment. This IC was undoubtedly chosen in the beginning by Japanese design engineers because it was one of the cheapest dual opamps on the market with acceptable audio performance. Many designers included this part in some of the most successful effects like the Orange Squeezer, DOD YJM 30, Boss OD1, Tube Screamer or Peavey equipment. The 4558 dual amp is linked with the history of the guitar pedals development. The first RC4558 monolithic dual opamp was developed by Raytheon Semiconductors in 1974. This chip has industry standard pinout, meaning that there are several different suppliers manufacturing pin compatible 4558 devices and also it can replace other standard dual op-amps like the TL072, NE5532 or the OPA2134. The high voltage gain (100 dB typ.), good input impedance (5 MΩ typ.) and versatile power supply (± 4 to 18 Volts) make it perfect to fit in pedal circuit designs. The JRC4558 integrated circuit by Japan Radio Company is a dual operational amplifier internally compensated and constructed with bipolar transistors on a single silicon chip.

Persamaan ic 4558d