A project that challenge myself (ALEPH-1.2)

by:biru  translate:ackcheng

First of all, I would like to thank NELSON PASS for his kindness in making the schematic available. Aleph 1.2 is indeed a very special amp. I would also like to thank a owner of a web site in Taiwan - PRBS for his help along the way. Before this Aleph 1.2, I have also made an Aleph 2 and the chassis is also my DIY product. When I finished the Aleph2, I found the sonic character a very pleasing one. The kind that I have cherished for a long time! But the problem of Aleph 2 is that it is not able to dive my pre-owned B&W802 well?K.. Therefore, I have the idea of Aleph 1.2. It has been at least 15 months from the time I started gathering information.
 

As every DIYer knows, the hardest part of any project is chassis. Luckily, I do have some knowledge in this very area. I also have friends working for living in this field! When I completed the Aleph 2 using the chassis shown above, the chassis was amazingly hot. So this time, I decided to use a heat sink with a width of 280mm and a height of 600mm. The final size of the chassis will be 660 x 340 x 620mm. The size of the final chassis will be HUGH ?V I call it ??The Beast?? 

 
The picture below shows the partially completed chassis before polishing and anodizing.
 
The transformer was a group buy from Taiwan. Rating of the transformer is 2500W!
 

What about filtering caps? Because we have a few other friends building the same amp, we arranged a group buy from the factory with the help of Ben from diyrealaudio.com. We ordered 44 pcs of BHC 47000uF in total. I use 6 pcs for each channel!

 

For the MOSFET, I ordered 650 pcs of IRF240 for matching. The matching process was very tiring but worth every bit of time!

 

The following pictures should the 3.9mH choke for my CLCC filtering.

 

Matching IRF240 needs a lot of time

 

The bridge is formed buy MUR3040PT

 
In order to save space, the transformer is placed vertically. I have also specially made a 2mm stainless steel case for it. The connections for the caps are made of 2mm thick copper.
The resistors we used were RA

On the main board C5 C9 C10 were BLACK GATE. After all the components were ready, I started to put them together

The main board and the output board

When I did the Aleph2 last time, I accidentally cut my fingers and needed 5 stitches. This time, I have created a cart to bring the whole thing in and out of the working table!

Indeed, this is my first heavy weight DIY project. It is estimated that each channel will weigh 100 Kg!!

 

After completed the power supply, I have double check the circuit many many times, if I had made a mistake here, it will be a disaster!

 

In order to prevent the current surge during setup, I have also created a softstart circuit as shown below

After repeated checking and checking, it is time to turn on the power. This moment has put me on a lot of pressure!

You can see on the picture that I put the MOSFETs in the lower half of the heatsink. This is deliberate as the heat will move up and I can make use of the whole heatsink!

Before I switched on the amp, I used 3 multimeters, the first one was connected to the Z5 to measure the voltage across the zener. The second one was connected to R11 and  the last one to the output to measure the output DC. Counting 1..2..3 and then switched on?K. Superb! All readings were close and the DC output was 120mV and slowly came down to 55mV. Very happy! So I just let it run and I copied the reading down every 15min. One hour later?K. I could not wait anymore and connected the amp to a small speaker. Using an electric pen to touch the input?K. Yes, I could hear the current noise!

I have tested it for 2 consecutive days and each day about 3-4 hours. The first channel eventually settled down. Now, my confidence built up and I am ready for the second channel. Without much problem, the second channel was also completed in a very short time. And the DC output was only 12mV!!! That is very good indeed, but I am a perfectionist so I decided to change the 9610 (Q1 & Q2 ) from the first channel (DC output 55mW)?K?K.. this decision ended up in disaster! While I was removing the 9610, I forgot the capacitors were not fully discharged and I have sorted the circuit?K?K. In split second, I heard some noise with flashing lights?K.. Oh shit! Burnt the Q2 and 18 pcs of MOSFETs?K?K Oh my!!!!!!

 

Luckily, I have 24 spared matched MOSFETs originally prepared for another Aleph 2. Put them on and luckily, this time is OK!! And the DC output is now 11mV! Now after 2 days of testing, I finally connect it to my ATC-20 speaker 

 

Testing equiptment:

This is my DIY BZLS preamp. Yes?K.. the case is DIY as well and no?K. they are not for sale.

 
 Speaker ATC-20

It was really touching the moment I connect it up! It has been 15 months, you know?K?K.. After listening for awhile, I turned it up to 12 o??clock but I have noticed that the mid range is a little bit distorted. Two days later, I rewired all the connection and it is still the same?K.. After some help from my friend Mr. Tai, I changed the bias to 0.5V. Because the R19 on the circuit board was originally fixed at 56.2K, I changed it to a 100K pot and change the bias to 540mV. After waited 1 hour for it to be stable, I could not wait any longer but to connect it up to the amp again. That was 5:00am! And the human voice was so loud when the volume was only at 9o??clock position. I immediately turned down and the voice was really seductive! I have never thought that bias has such an important effect. On the following afternoon, I turn the volume way up and using a drum CD to try out. Wow! I have never seen my speaker??s woofer moves like this! As many of you may know, ATC-20 is very difficult to drive, using this DIY Aleph 1.2, I can finally say that my speaker is satisfied! I couldn??t stop the machine until 4 hours later when I have to pick up my wife/boss!

 

 

 

My current equiptment

 

Preamp:  MARKLEVINSON 26S

Power amp : DIY ALEPH1.2

CDP:  TEAC VRDS-25X

 

I will try to compare my BZLS and the 26S later

This is my reference!