With pride we present the new Marble Lowrider 200, a full tube bass amplifier that really pumps out those low notes with authority. We have designed a modern, powerful amp based on a power section of four KT90s in class AB. Due to the unique power supply, vibration damping and cooling fan, the amp is extremely reliable. Tone shaping is very versatile due to a three band EQ with tone shaping switches. Full flexibility is offered by including a tube-buffered effect loop. The Lowrider Head weighs only 20kG and puts out 240watts R.M.S. at 2, 4 and 8 Ohms without complaint!
The driver stage is constructed around a 12AT7 (phase inverter) and a ECC99 (cathode follower buffer stage). The ECC99 is a power triode that delivers big currents at low impedance, ideal for KT88, KT90 and 6550 tubes. Without the ECC99 it would not be possible for the 12AT7 to produce sufficient current to properly run 4 KT90’s. Great stability and great linearity is ensured across the entire frequency spectrum from as low as 20Hz. This drives the power tubes exactly and absolutely symmetrical from zero to full throttle.
The pre-amp of the Lowrider is based on one of the oldest pre amp designs (originally RCA), an absolute winner for amplifying big bass signals. The signal enters the amp through a set of inputs (one tailored for passive and one for active basses). The input stage is a parallel-wired 12AX7 ideal to amplify and reproduce every detail due to its low gain, low impedance character followed by the input volume control. The second 12AX7 is a so-called cathode follower that operates a classic three band EQ tailored for bass frequencies which are significantly lower than guitar signals. We enhanced this classic EQ with three mini switches to adjust the highs (bright), the mids (shift) and the lows (deep). A master volume adjusts the outcoming signal before it enters the next stage. The 4th mini switch is an effect loop bypass switch to engage or bypass a full tube-buffered effect loop. This effect loop operates with a 12AT7 and enables the player to connect an external graphic EQ or any other effect. For players’ convenience we have located the effect loop controls and send and return sockets on the front of the amp.
Power section and transformers
The KT90 quartet is vibration isolated on a separate dampened chassis to prevent microphonic influence during loud gigs. The Lowrider 200 uses a Multi Voltage Power supply which makes it possible to get maximum output without sacrificing reliability. Furthermore the MVP circuitry enables the lowrider to be switched from 120 – 240 Watts R.M.S. The big advantage of this approach is great reliability coupled with great continuous power.
Output transformers are carefully made with high Mu Grain orientated heat-treated laminations (UK grade). Triple secondary winding pattern is applied for stable operation even at full power and even at 2 Ohms, measured frequency range 20 Hz – 22Khz -3dB. Melanex insulation of primary and secundary windings protects against moisture and extreme temperatures.
Low hum operation is achieved by a special power transformer with Multi Voltage Power taps and double heater leads. Standard British steel lams and vacuum impregnation leads to noise- and vibration-free performance. The power section of the lowrider uses a forced cooling fan for trouble free operation during long stints at full throttle in the most extreme playing environments.