Abstract: Apparatus operable without need for an external power source for conveniently interconnecting data communication equipment (DCE), such as a modem, and multiple data terminal equipments (DTE), such as terminals and/or printers, which each have an interface conforming to a serial data communications standard, for permitting access to the DCE of any of the DTEs that may be connected to the apparatus. In the preferred embodiment, intended for the interconnection of interfaces conforming to the E.I.A. RS-232-C standard, a circuit interconnecting the data leads of a multiplicity of pluggable cable connectors supported on a chassis includes a transistor connected to be powered by input data signals from the DTEs and to operate as a switch under certain signal conditions and to be effectively removed from the circuit under other signal conditions.

Abstract: An amplifier having a gain control terminal amplifies an input signal to produce an output signal of a desired magnitude. A gain control circuit coupled between the input and output signals and to the control terminal includes detectors of the input and output signal amplitudes. The control circuit further includes a first impedance network connected to the control terminal and a feedback circuit connected in series therewith, the feedback circuit including a second impedance network complementary to the first impedance network. A feedback signal of the feedback circuit is multiplied by the amplitude of the input signal and combined with the amplitude of the output signal and a reference signal at a summing point of the feedback circuit to maintain a response time of the control circuit which is essentially invariant with respect to the amplitude of the input signal.

Abstract: A tone control circuit using only one potentiometer to provide bass or treble control is described. An integrator and a differentiator are connected to the input of the circuit and their outputs to the two ends of the potentiometer. Electrical connection between the potentiometer and the input is also made to provide a flat frequency characteristic component in the output signal.

Abstract: An electric guitar is described which provides signals from each of its electrically conducting strings by the cutting of magnetic field lines. The magnetic fields are produced by removably mounted permanent magnets which produce concentrated fields. The return wire or wires of the strings are near the surface of the neck. Various circuit configurations are used to minimize noise pickup, to combine the signals from each signal and to modify the sound produced by each string.