Welcome! Body only. Power-on confirmation has been obtained, but detailed information is unconfirmed as I do not have the connecting equipment. According to the previous owner, it works without problems. Please purchase with the understanding. Therefore, it is slightly cheaper than the market price. There are small scratches and dirt, but it is generally in a clean condition! ● Stereo power amplifier equipped with newly developed Ro (output impedance) control. ● The basic circuit configuration of the B-4 is a DC power amplifier configuration that employs a low-noise dual FET cascode bootstrap differential amplification circuit in the first stage, a cascode-connected current mirror push-pull differential amplification in the pre-drive stage, and a 3-stage Darlington connection pure complementary parallel push-pull OCL using High-fT transistors in the output stage. The B-4 is equipped with Ro control, which can change the output impedance in the range of +1Ω to -1Ω. ● The first stage assembles a bootstrap circuit in a balanced sending differential amplification circuit with a source follower using low-noise, high-gm dual FETs and dual transistors connected in cascode. The second stage employs a push-pull differential amplification circuit using a cascode-connected current mirror circuit. In this stage, the use of a cascode bootstrap circuit minimizes the increase in distortion due to changes in the signal source impedance. The current mirror circuit adopted in the pre-drive stage provides sufficient gain as a voltage amplification stage, and the two transistors function as a kind of push-pull circuit, canceling out even-order harmonic distortion. #Yamaha #Amplifier #Audio