INTRODUCTION
After the good
experience made using
the
Excicon mosfet
ECW20N20
on
DC
Circlotron I immediately thought about their use in this project.
Using
ECW20N20 is possible to reduce the output impedance for a good
damping factor and we have lower distortion and more output power.
The
DC
Circlotron is very complex and I found low interest from DIY but I
can understand them.
In any case this new Amplifier End sound much
better than
DC
Circlotron and it is more simple.
This new version of the
Amplifier
End uses easy-to-find pre-assembled modules for the protection, soft
start and filaments power supply.
It was also possible to reduce
weight and costs with some changes on power supply section but always
without output noise.
In the driver section you can decide to use the Siemens
D3a (expensive pentode to use in triode connection) or the Russian
6Z51P
/ 6Ж51П (cheap pentode tested on
Bartola®
article).
I have used these russian pentode also in
the my last
Power Folllower
and in the
Inpol/Mofo and these
vacuum tubes sounded better than the NOS Mullard and Siemens.
Like all my amplifiers also this can be driven directly by a CD, DAC or
Phono pre-ampl.
The main benefit
of a Circlotron design is an high power amplifier with no switching output stage like a pure
class A but higher efficiency, with only 1A bias current still
1mA
with 2.3A on 8 load.
Specifications:
Pout = 60w on 8ohm with 1.5% thd
Pout = 105W
on 4ohm with 1.6% thd
Pout = 21W on 8ohm no-switching with 1A bias
Pd = output stage 2 x 1A x 38V = 76W each channel with 1A bias
Zout = 0.4ohm to have a damping factor of 20.
Ft(-3dB) = 20Hz-56KHz at 0dB
and
10Hz-65KHz at -3dB
NOTE
Please do not touch with multimeter probe the mosfet gate after the power on because this
operation will destroy the mosfets.
Before to solder the mosfets set the trimmer to have 0.2VDC on all trimmer
outputs, then turn off the amp., unload the capacitors of the
power stage, solder the mosfets, screw them on the heatsink with a
silicon pad isolator and after the power on increase both trimmers, any time one turn
for each, until you get the correct bias and turn only one trimmer to get zero DC voltage on output terminals (after check again the
current to get 1A).
