Q: How is the wideband balanced amplifying topology being used in this line amplifier different from the conventional design?
A: A fully balanced amplifier will cancel out the noises and distortions picked up by the audio cables caused by electromagnetic interferences. The wideband balanced amplifying topology allows a vacuum tube line amplifier to be operated in a fully balanced condition, from the input to the output in one single stage. This single-gain stage wideband balanced amplifier contains no load resistors, no buffers, no followers and no global negative feedback. Hence, the purity of the musical signals can be faithfully preserved.
Q: Is this line amplifier phase non-inverting?
A: Yes. The output signals are in phase with respect to the input signals at the XLR receptacle. The pin configuration of the XLR receptacle is given as follows: pin-1 is ground; pin-2 is +VE and pin-3 is –VE signals.
Q: What is the break-in time for a VL20?
A: The amplifier has been gone through a mild break-in at the factory. When you power it up the first time, it should sound reasonably well. It may take about 50 to 100 hours before it completely breaks in. However, it is not advised to turn on the amplifier continuously all day. It is recommended to turn it off for a while after it is operated for 3 to 4 hours.
Q: Do I need to bias the tubes of VL20?
A: Unlike most power amplifiers, it is not required to bias the tubes in line amplifiers such as VL20.
Q: Can I swap the tubes within the amplifier?
A: It is not recommended to swap any 6H30. The two 6H30 in each channel have been tested such that they work best in the current positions in terms of noise level and operating voltages.
Q: Why can some noises be heard from loudspeakers when tapping the chassis of VL20?
A: This is so called microphonic effect due to vibration of the grid winding. The 6H30 is frame grid twin triodes with large frame structure so as to increase transconductance, voltage gain and to reduce plate impedance. The 6H30 exhibits a little more microphonics compared with non-frame grid audio tubes such as 12AX7, 12AU7 and 6SN7, etc. But the microphonics do not affect the sound in normal operation.
Q: Can I place the VL20 inside a Hi-fi cabinet?
A: It is recommended not to place the VL20 inside a Hi-fi cabinet. If the VL20 must be placed inside a Hi-fi cabinet, measures should be taken to ensure the ventilation openings of the VL20 are not obstructed. The cabinet doors should be opened.