|
The project was started after I had experienced the very good sound
quality of the Aleph5 amplifiers build by a friend. I was simply impressed.
I used for the amplifier boards available from Kristijan
Kljucarcic. The quality of the boards is very good and solid. The board for the power supply including
an 'active' filtering I have developed by myself. For the housing of the mono amplifiers I used a
straight forward approach, all components with the exception of the XLR inputs, the speaker output
posts and the AC connector are mounted on the heat sink.
The head sink profile is a SEIFERT K240/200 with a rated thermal
impedance of 0.2 K/W. This is sufficient as the temperature at the case of the power transistors is
measured at 48 Deg.C after about 30 min. The power transistors are sandwiched between the PC board and
the heat sink and placed as close to the center of the heat sink profile as other design constrains
allowed. The power transistors are matched / selected to groups of 3 out of a batch of about 50
devices. This gave very well matching of Vgs under rated operating current.
The transformer is a 500VA +/-25V molded type. A NTC device is
used to limit the inrush current of the transformer. The protective ground is connected also via an
NTC to the chassis GND. Due to the straight forward design approach there is only very little wiring
necessary, preventing all sorts of noise and coupling problems. Star ground center is the GND post at
the power supply. The ripple voltage at the amplifier supply is less than 5mV and hence the amplifier
is extremely quiet. DC offset is less than 20mV.
Both mono amplifiers worked right first pass after powering up.
All operating voltages were well within the expected limits. After several hours of 'burn in' I
connected the amplifiers to my stereo system. The system consist now of a TRANSTOTOR ROTERY turntable
with an AT OC09 MC pick up system, a home made ONO MC-preamp and Aleph 1.7 pre amp. The speakers are
AUDIO PHYSIC Avanti I.
How does it sound? To make it simple, I will not switch back to
my old gear! It sounds clean, open with solid bass, just correct.
I'd like to thank Nelson Pass for his willingness to share his
designs with the DIY community. Thanks also to the contributors of the 'DIYaudio' forum for the
interesting discussions.
Best Regards from Good Old Germany,
Werner e-mail: dw-elmer@t-online.de
|
