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Making my version of the Aleph P 1.7 I had a lot
of discussions how to make everything as optimal as possible. The clue is that even trying to make it
extreme, one has to make compromises.
To make it as good as possible I made the
following steps:
Paying extreme attention to the layout. (Especially GND and +60V power wiring)
Keeping faithful to the original diagrams.
Use of 70u copper layer on the PCB instead of the normal 35u.
Use of slivered led for all soldering on the Pre. PCB.
Using SMD components to make wiring shorter, the design more compact and to minimize the number of
solder joints.
Having curved angels for all signal-carrying traces.
The signal wires are soldered directly on leaded resistors on the Pre. pcb to reduce the number of
solder joints.
Using an Elma 2 deck switch as input selector - all GNDīs not used are disconnected.
Using an Elma 4 deck/ 2K ohm/ 24 step switch as output attenuator, designed with steps suiting my set
up and demands.
The Pre PCB is tinned using solder tin, making no use of lacquer on the PCB.
I designed my own output delay circuit for
short-circuit of the outputs during start up. Cooling the IRFR9220/ 110 transistors is done via the
bottom plate, because I felt that the "fins" on the PCB weren't enough.
The P 1.7 clone has 4 RCA/ 1 XLR inputs and 1 XLR/RCA output. The XLS input has additionally an
inverted position.
The cabinet is made of 2,5mm aluminum, the 10mm
front plate is polished and anodized black. The bronze knobs are turned, glass blown and lacquered.
"Densen" products inspired the design. (http://www.densen.dk/)
Previously I have built 2 revisions of "The
Balanced Line Stage". (picture 9 - 10) One having current sources to source pins of the Fetīs. I
tried to use a Balanced ladder attenuator like on picture 11 on the input side. This however caused
the preamp to oscillate when the volume was turned down. I now understand the advantage of attenuating
on the output.
Furthermore I had hum problems so I changed the
power supply from one 317/337 regulator-based +60V/-25V to 2 pcs of the original Pass +60V design
including ac coupling of in/output and introduced 2 common mode coils (it actually helped).
The "sound"
On a show I once heard the What/puppy on Krell Class A equipment - it did not impress me before I
heard all the other set upīs. The P 1.7 is very neutral too, it really reveals details not herd
before along with all the problems you have in a listening room and mixing faults on the CDīs. For me
it was definitely worth the effort to build. I would recommend building the P1.7 over the balanced
line stage and use it fully balanced in your set up.
I would like to thank:
The Pass Lab crew for sharing their knowledge. I hope you one day will publicize the diagrams for the
Supersymmetry based Preamplifiers. Reading the reviews and articles is really thrilling.
My wife Helle for all the Beyschlag resistors,
Arcotroninc capacitors and the patience she brought up during my design and build of this. (She is
importing these components to DK, OY, SE - so it is important and cheap to use them - actually they
are some of the best obtainable). My company for sponsoring, PCB & Moss feet's and help of making
the mechanics (Vagn). My college Henning Skourup, for all the discussions of how to make it optimal to
the extreme.
Having this script on the Passdiy home page is
an honor for me.
It is a great pleasure for me to read and be inspired by all the other nerds.
With kindly regards Marcus Gram - Smoerum /
Denmark - Marcus.gram@get2net.dk |
