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Hello to you all,
After months of hard work, I
finally finished my Aleph 5 mono blocks to accompany my X-BLS. It was
always a dream for me to own an Aleph amplifier and I am very grateful
that, after the production of these amplifiers stopped at Pass Labs,
Nelson made the designs available to the DIY-community. Here are the
specs of the Aleph 5 clones I made.
Power Supply
The transformer (2 * 25 Volt) of
each mono block was sourced from Amplimo and rated at 625 VA. Bridge
rectifiers (one for each secondary winding) are the ordinary high
current (25 A) high voltage (600 V) types. Power supply caps are from
BHC and computer graded. Each cap has 22,000 uF of capacitance and I
used 6 of them in a CRCC-configuration. The 0.39 Ohm resistors used are
rated at 10 Watts each. According to PSU-Designer the ripple should be
something like 50 mV and I can assure you that they are deadly quiet.
The final rail voltages are +/- 31.5 Volt. I "slightly"
overrated the power supply in order to be able to run the amps with
increased bias current. With the standard value of R19 the amps had a
bias current of 1.8 Ampere. At this stage, no power supply hum
whatsoever was audible when one of my ears was in close proximity to the
woofer of my loudspeaker. After the removal of R19, the bias current
increased to 2.1 Ampere and a very slight hum was now audible when I
repeated the ear/loudspeaker-proximity experiment. The hum-level,
however, was nothing to worry about.
PCB and parts
I bought the PCB from a fellow DIY-enthusiast
here in the Netherlands and the beauty of the design is that it can be
used to build various types of Alephs. In addition, it minimizes the
amount of wiring needed because the MOSFETs of the output stage are
soldered directly to it. Apart from the power supply wiring, it is only
necessary to connect a loudspeaker lead (I opted for Van den Hul's
"The Wind MKII") to the Cardas loudspeaker terminals and the
input wiring (Teflon insulated solid core silver) to the Neutrik XLR-connector.
As can be seen in the pictures, the PCB is placed above the power supply
caps and between the heat sinks. Both the IRF9610 and IRFP240 MOSFETs
were matched. The DC-offset due to the mismatching of the IRF9610s is 12
mV for one channel and 4 mV for the other one. Very nice! I bought Black
Gate Standard 220uF electrolytes and after some weeks of running the
Alephs I replaced the cap in the feedback-loop with a Black Gate N-type
(470 uF/16V). This tweak, which I stumbled upon at the Pass Labs Forum
at DIY-Audio, proved to be very worthwhile: it increased the
transparency of the amps without harming their smoothness.
Heatsinks and Casing
The heat sinks used (Junior
Kuhlkörper JK 1170) are 40 mm deep, 300 mm long and 170 mm high. To
finalize the casing 3 mm sheets of black anodized aluminium were used.
The ventilation holes in the bottom and top plate were laser cut. The
amps can be touched for approximately 10 seconds before it becomes to
uncomfortable. I considered this timeframe "Safe to Touch" for
my two infants that wander through the dwellings in search for something
adventurous to do. The front panel was made by Schaeffer/Front Panel
Express and consists of two parts both of which have a thickness of 4
mm. I think the amplifier has a nice clean and understated look.
As to the sound, I can remark that
they sound simply marvelous. It took me some days to get accustomed to
the way they sounded because the sound is so different from the
amplifiers I heard so far. The amps give recordings a nice sense of
unity, which make them real music makers, and time-after-time I find
myself being mesmerized by the music instead of being distracted from
the recording due to your typical HiFi-issues, such as imaging,
spaciousness, air and what have you. The music comes to you in a wholly
organic way that is definitely not upfront. The amps are very detailed
yet very smooth at the same time. If this "sounds"
contradictory than consider it is as an illustration for the fact that I
needed a couple of days to get my ears/brains adapted to the amps. The
differences between recordings are very obvious, which highlights their
potential to appreciate the meaning of the pieces performed. The dynamic
range of the amps is also literally breathtaking: the tiniest nuances of
recordings are audible and more than once I found myself holding my
breath in order to be able to hear them. The bass is not a weak point of
these amps: it goes very deep and is nicely layered. Definitely not of
the blurring one-tone variety. I can go on with compliments like these
for a long time but by now I think you get the sonic message I am trying
to get across. Thanks Nelson for being so generous to the DIY-community
and the participants at diyAudio.com for sharing their expertise.
Jan-Peter Vos The Netherlands
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