"...I have always found the Aleph 2 to be the most neutral of the [Aleph] bunch."

I guess the above comment from a master explained it all!  The other reason is that with the enjoyment I have with my current Aleph 5 also gave me confidence!  I am sure pretty sure Aleph 2 would provide me with a better sound, while provide me more power I would like to have.  I just hope that I don't need change the wire in my house due to the extra power than my Aleph 5!

At this moment, I have the materials I need for the Aleph 2.  I also have 4 PCBs from hifizen's Aleph X project.  I am not sure if I should use the parts I have to make high-power Aleph X or Aleph 2.  No matter what, I would still draft up this journal, so that I can jump on this Aleph 2 wagon anytime I would like and hopefully, I can share it with all who are interested in making one of their own!

To study Aleph 2, you can find the Owner's and Service manual in Pass Labs web site.

The commercial Aleph-2 has bi-wire output post.  My DIY version, as many others, is using just one pair of output post for each mono-block.

The main board is the same as my previous Aleph-5 and is supported also by a group purchase from PRBS, a dedicated DIYer who made Aleph-2 and Aleph-1.2 and many more!  This board has been modified from Brian Bell's original layout.  The same board actually can be used for all Aleph series amp.  Refer to the above parts difference, if you plan to make any different Aleph amp.  One main board is for one channel.  You need 2 main boards for every Aleph project.  The output board details is discussed below.

The most important tasks in this project is to match the MOSFET.  There is an article about how to do the matching from Nelson here.  Another discussion forum for matching the device in diyaudio.com is here.  When matching, make sure to test it until the digits stabilized!  I tested each one for about 20 - 30 minutes each.   All Input MOSFET IRF9610 (Q1 & Q2) should matched to 0.01V.  Q3 does not need to be matched, but it doesn't hurt if you do so.  For the Power and Bias output MOSFET, IRFP240, I matched them down to 0.01V.  This is the photo when I am doing the match.

The number of MOSFET for each Aleph amp is (refer to output board below):

Aleph 1.2 needs 8 output boards, total of 48 mosfets.
Aleph 2 needs 4 output boards, total of 24 mosfets.
Aleph 4 needs 4 output boards, total of 24 mosfets.
Aleph 5 needs 2 output boards (each need to cut in half), total of 12 mosfets. 

I replaced the R19 with a Vishay 100K variable resistor.  This will later make adjusting bias voltage much easier!  If you prefer a fix value resistor for better sound, you can use the pin socket.  Use the VR to adjust the bias first and then pull out the VR and measure its value and put back with a fix value resistor.

Aleph series Transformer spec.

For my own project, I am still deciding whether to pick the 750VA version or the 1000VA transformer.  Nelson Pass suggested the 1.5KVA transformer if you can, but that really is too big for my house's wiring.  For the VDC output, some DIYer use the 35V or 37V for their Aleph 2.  If you are not sure, simply buy the 37V.  If the transformer you pick has high efficiency and your PSU is not very sophisticate in causing big voltage drop, then 33V should be fine!

The potted toroidal should have a better result, but the high cost may not be a good choice for many of us!  The main reason for our DIY is the cost and performance, right?

For the coupling capacitors on the PSU, you can start with a 4.7 uF MKP and then adjust it by either using a Oscilloscope or use the PSU software by PSU Designer II to simulate yours before installation.  

If you like to use a better rectifier, some of other DIYer used are:  Ixys DSEI30-06A Diodes (30A 600Volt, FRED Diodes, TO247 package, Digi-key#: DSEI30-06A-ND, $1.95), IR MUR3020WT, which lists for $2.68 each at Digi-Key.  Nelson Pass uses ST Micro BYW99W-200, which is a dual "high efficiency, fast recovery" 35 A, 200V diode on their amps.  There is also this reference for High current ultra fast bridge rectifier project on diyaudio.com.

The AC inlet ground is connect to earth via the ground connection to chassis.  Theoretically, if you wired earth ground and chassis ground together, it is very easily that you will induce the ground loop noise!  For this reason, the AC inlet has a Thermistor in it before connecting to the chassis is for reducing the possible noise!  In my case in Aleph 5, I bring the AC ground and ground out of filtering capacitors together and the result is dead silence!  The choice is yours, as long as you know the difference of these two grounds.  If not, this is a good reference article you can read during your tea break!

The following is the power wiring illustration that I used on my Aleph 5 (and I will use the same for my Aleph 2).  Do this part with care, as they are live electricity here and it can hurt you!  (Click to see in lager size).

This is the output board.  I use one for Bias board and one for Output board on each channel.

There are two ways to connect the +V and -V to the main board.  The external board I use can be used for both Bias board and Output board.  I am not very good in using P2P method, as many preferred!  I prefer a more easy and organized way to put the power transistors!

One way is from the output of filtering capacitor (+ side) --> Bias board -> (from Drain of output board) main board.  For the (-) side, the connection is from the output of filtering capacitor (- side) --> Output board -> (from Source of output board) main board.  Do not connect both + and - to any of the Bias or Output board.  They have to be distributed from both side of main board to complete the circuit.

The other way is connect the +V to the +VCC on the main board, which will go through the Drain down to the Bias board.  Connect the other -V to +VCC on the main board.  This will complete the circuit via the Source of the Output board.  Either way works well and the choice is yours.

The connection of Aleph 2 is illustrated below.  This is for your reference only!  (Click the image for bigger size)

When soldering the 3W (main board) and the 5W (output board) resistors, remember to leave a space between the resistor and the board, as they tend to get pretty hot!

From many reading for other DIYer's article, I found out that the most common mistake is that they finish the first pretty quickly and many goes wrong when making the second mono block.  Therefore, always do it carefully and slowly is the most important key in the success of one's DIY project!

The following are the important key points and steps in making the project successful:

1. When your Toroidal transformer arrived, first check the secondary AC voltage is to the spec.
2. Then connect the transformer secondary out to [ bridge ] rectifiers.   I use the dual bridge rectifiers (see part number in parts list).  Of course, if you like to use more exotic rectifier (as mentioned above), you are free to do so.  Hey!  That's the fun of a DIY, right?  There is nothing to measure to at this connection. 
3. One thing important is remember to add the Bleeder resistor to the rectifier capacitors.  This is for safety reason and not to damage your system later on.  I use 2-10K, 3W resisters.  
   
   To calculate the resistor value, you can use this formula (in a steady-state):

   Time constant (sec) = R * C (R in ohms and C in Farads)

   (Notes:  The actual formula should be: t = -ln (Vc / Vo) * RC ).

   So if you have a 25,000 uF of cap and you would like 15 seconds of discharge time, your R = t / C = 600 ohms.   The power (P) dissipation of the resistor will be P=V^2/R. V is the unreg supply voltage.  I recommend double P value of the resistor...as this will get hot.   You can use this resistor before working the innards of your amp so you can bleed off stored energy and avoid a nasty spark or shock.  (some quoted from diyaudio)

   Now, connect the rectifiers' output to the filtering capacitor group.  Before connecting, it is better to wear a protective eye-glass and stand a feet away before powering up, if you do not have a Variac power supply!  (See picture below.  I don't have one; therefore, I am fully armed!)  After a few seconds, if all looks well, measure the VDC from the capacitor.  It should be about +90V across the capacitor (or +45V for capacitor + side to ground and - side should be -45V).  (Optional is to measure the AC ripple to see it match your simulation!)
   

4. Shutdown the power and let the capacitor bleed off before connecting to the main board.  Now connect the power and all wires, except the Inputs and Output, carefully!  (Compare your connection with the illustration above).  Beware not to mess up the wires.  (Clearly mark the cable is a good practice!).  Connect the LED, as this will tell you if the power is running in OK or not! 
5. Critical moment is now!  Turn on the power and stand back.  If everything looks fine (no smoke, no fumes...), then measure these few spots:

 

Item	Measurement
R11	This should be 4 - 5V
Z5	about 9.1V
Q1	Source pin to GND should be +4V
R14	This should be 4 - 5V
Q5	Pin C & E should be 4 - 5V
Output Resistor	Across the resistor should be 0.5V



6. It is better to measure each output resistor (1R).  Now adjust the R19 VR, so that they are about 0.5V.  (If you want to use higher bias, you need to make sure you have enough heat sink to dissipate the extra heat!)
7. Now connect the Input lines (as in the illustration).  I use a toggle switch to switch between Unbalanced RCA input or Balanced XLR input.  If you don't use the switch to toggle it, the difference is the loss of 6 dB.
8. Now connect the Speaker output wires.  Nelson Pass did not use speaker protector and I don't plan to do so, even I make one of my own.
9. Check the DC offset by measuring from the binding post.  The spec. is < 100mV.  The lower the better and the number will stabilize after about 1 hour.  I recommend do an initial check up and then do the final measurement when both mono blocks are done!  Ideally, the difference between the two is also as smaller as possible!
10. Repeat the steps to make the second mono block.  Remember, this is the easiest one to go wrong, as you thought the first is done easily, I definitely can do the second one "fast"!  Be careful, go slowly!
11. One other thing to be careful is that the Aleph 2 will draw a constant source of power.  Make sure your home electric wire can withstand the extra amperage you add up to it.  One quick way is always consult your local expert.  You don't want your wife shouting at you, because the circuit breaker is activated all the time!
12. Now, hook up your preamp, FM radio, CD player, etc.  Prepare a coffee or tea.  Pop in a nice Beethoven CD and start enjoying!  However, for the first 20 hours, you need to watch it to make sure there is no any abnormal situation occurs (by measuring the bias voltages again).  The sound should open it up, according to Nelson, after about 100 hours of burn-in time.  Enjoy!

I don't really believe the ultra high cost of the interconnect cable [ or power cable ] will make any [ big ] difference; however, a pair of nice and decent XLR interconnect cable would make sure to pass the good sound between the preamp and Aleph 2 amp.

The finished Aleph 2 should be like this one.  This is the brain child of a DIYer "Bear", who did it in the previous case GP.   I choose to join this case GP, because I believe with the heat sink fins on all 4 sides, like the original Aleph 2, makes more sense than only on 2 sides, left and right!

I will put my completed Aleph 2 when mine is done.

Speaker: Triangle Celius 202
Preamp: Pass Balanced Zen LS  (hoping to make Aleph P 1.7 in the future!)
CD Player: Sony DVP-NC650V
FM Stereo Tuner: Sansui TU-717
DAC: Audio Alchemy DTI Pro 32 + Perpetual P-3A (I also I like MSB DAC II with upsampling)

• Nelson Pass:  Many thanks for your wonderful design and generosity to share your intelligence!
• Brian Bell's PCB layout and PRBS in supplying the modified boards.  
• Case are designed by Vincent Chang and was a group purchase from Taiwan by Michael Chen & Mr. Jeng.  Many thanks for their time spent just to let us enjoy the Aleph 2 DIY!
• XLR part of the illustration is made from Yang's article (diyzone.net).  Thanks!
• Russell Sun:  My friend who taught me all things about Audio and he is the person who persuaded me to buy my first amp and speaker!
• My family's support in DIY hobby!  They don't know about the meaning of "PASS", but they can surely tell the difference between my Aleph 5 and my previous Sansui integrated amp.