Unison Research P70 White Paper - VMAX Services

All the operations of the amplifier, included the safety functions, are
controlled by a microprocessor to ensure maximum reliability and intuitive
user interface.
The amplifier itself is constituted by an input stage featuring two double
triodes ECC83 and one double triode ECC82, and a power stage with two
KT88 per channel.
The output transformer has been custom designed by Unison Research and
ensure a bandwidth of more than 30kHz at full power.
The design
During the development of the first prototype, we had the possibility to
observe and analyse how the push-pull power stage requires a driving current
significantly higher and differently shaped than that of a single ended power
stage. Thus we concentrated our efforts in redesigning the circuit so to keep
the output impedance as low as possible.
Another point that has required special care is the polarization of the whole
output stage, which had to be stable enough to sustain the large signal
excursions required to properly drive the stage under the most critical
operating conditions.
The preamplifier is constituted by a double differential pair in an original
configuration. The two differential stages are DC coupled and allow to reach
the needed gain. They are followed by a couple of cathode followers, again
DC coupled, which guarantee the low output impedance required.
The power supply for the whole preamplifier stage has a very high voltage,
around 600V.