TECHNICAL INFORMATION
The first stage of the GBE-600 preamp uses a low noise bi-fet linear scaling amplifier with a 2 pole low cut point at 23 Hz to prevent excessive speaker cone excursion and intermodulation distortion. Addi- tional bandwidth roll-off is provided at 20 kHz for RFI suppression. The variable gain stages are a feed- back-divider type control, one of which is all solid state and the other utilizing a cathode follower (tube), each providing a maximum gain of about 30 dB. On the tube stage, variable non-linear loading creates a smooth and natural sounding overdrive rich in harmonics. These foot-switchable and blendable gain stages feed 3 foot-switchable, user adjustable signal shaping filters and the 5 band active equalizer. These EQ filters provide over 12dB of boost and cut, with center position flat. The output amplifier feeds the master volume control and fully protected power amplifier. A low noise differential drive output ampli- fier is provided for the direct output (switchable pre/post eq and ground lift) and is phantom power pro- tected.
The power section consists of a low distortion bipolar power amplifier with integrated limiter which allows gradual overload without sudden loss of feedback control of the speakers. The output is rated at 275 watts RMS at 8 ohms, 425 watts RMS at 4 ohms and 625 watts RMS at 2 ohms. The amplifier topology is low feedback class A-B with servo control of bias and DC offset.
Also provided is on board output limiting, dual slope integrated VI limiting, solid state thermal protection, short circuit load protection, dc fault protection and RFI suppression. All amplifier status points are indi- cated on a dual color led array. This amplifier uses heavy duty copper based bi-polar power transistors directly mounted to a 2 speed fan cooled extruded aluminum heatsink tunnel. The output section sports a combined rating of 1600 watts and 128 amps to insure a conservative and reliable design.
An important and not commonly discussed specification is the power amplifier’s ability to deliver rated power into a reactive load. All speakers present a reactive load to the amplifier, reducing real world driv- ing ability. The power section of the GBE-600 amplifier is rated to deliver full power into a reactive load with a 45 degree (leading or lagging) power factor phase angle. This is one important reason Genz Benz amplifiers sound so big.
FEATURES
The following feature set is included on the GBE-600 Bass Amplifier. These features were developed based on usability and are the result of input from veteran players from around the country. It is impor- tant for an amplifier to reflect the real needs of the players using them. We feel that this amplifier does just that.
Input — The ¼” input has switchable sensitivity. With the switch in the passive position, the preamp pre- sents a higher gain and input impedance which is tailored to the characteristics of passive pickups. Two distinct types of passive pickup exist (there are some exceptions which aren’t important for this discus- sion). A passive magnetic pickup consists basically of a permanent magnet (or one for each string), called a pole piece, with a wound wire coil around it. As the string interrupts the magnetic field, the coil picks up the changes, or disturbances, in the magnetic field and translates these changes into a small electrical signal. (This is the same principal as the large electrical generator used by your utility company to power your rig on stage!) In order to develop a strong enough signal to drive an amplifier, the number of windings on the coil(s) must be very large. Additionally, in order to keep the efficiency of the pickup high, the dimensions of the wire coil must be small and the magnet flux density kept very high, thus, a small diameter wire is used. The end result is a signal that has significant output impedance due to the size and length of the wire used in the pickup’s windings. A passive piezo-ceramic or piezo-film pickup is made of a piezo-ceramic crystal (or distorted Kynar film). When this material is moved by the vibration of instrument’s body, the resulting strain on the crystal or film is converted to voltage via the “piezo-electric effect”. The output impedance of a piezo type pickup is typically higher than the magnetic pickup. The input impedance of the amplifier’s passive input is set high enough to prevent interaction with the high output impedance of all commonly used passive pickups, including magnetic, piezo-ceramic and piezo film types.
