Q: How is the wideband balanced amplifying topology being used in this line stage 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 stage 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 global negative feedback. Hence, the purity of the musical signals can be faithfully preserved.
Q: Is the line amplifier VL19 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 new VL19?
A: The VL10 has been gone through a mild break-in at the factory. When you power it up the first time, it should sound reasonably well. But 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 one hour after it is operated for 3 to 4 hours.
Q: Can I use VL19 in bi-amp configuration driving two pairs of power amplifiers?
A: Yes, you can use the two sets of balanced outputs to drive two pairs of power amplifiers.
Q: Do I need to bias the tubes of the VL19?
A: Unlike most power amplifiers, line amplifiers such as VL10 do not require to manually bias the tubes.
Q: Can I swap the tubes within the line amplifier VL19?
A: It is not recommended to swap any 6H30. The three 6H30s in each channel have been tested so 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 or pressing the push buttons of VL19?
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 VL19 inside a Hi-fi cabinet?
A: It is recommended not to place the VL19 inside a Hi-fi cabinet. Otherwise, it will cause the temperature of the VL10 getting too high. This will shorten the life of VL19. If the VL19 must be placed inside a Hi-fi cabinet, measures should be taken to ensure the ventilation openings of the VL19 are not obstructed and the distance between the VL19 and enclosure is at least greater than 80mm. The cabinet doors should be opened. And the lid of the vacuum tubes compartment must be removed.