Do It Yourself Electronics

This is another very popular build form mr. Nelsson Pass . It is a 30W A class power amplifier. All output transistors need a huge heatsink and after build it need to be setup. Setup is very easy all what you need is to clamp dmm (which is set to Dc V) at the amp output and to measure dc , which need to be slightly negative, at the same time led diode light will be brightest.  For those who like to tweak their builds mr.Nelsson leaved short tutorial on DIYAudio forum how to do it.





However on these I decided to try my favorite small power Mosfets, the

Toshiba 2SJ313’s. Apart from a different package and pin-out in some

amplifier models, they will drop right in as replacements, and they need to be matched for Vgs at 10 mA.

The Toshiba’s are preferred, but you can make do with other comparable modern Mosfets if you can’t get these parts.

Noting that some units had zener noise with R105 at 4.7K, I dropped that value to 3.3K, and you will note that I optionally deleted Q104, the over-current protection. Also, I moved the chassis ground connection directly to the AC Earth ground.

The addition of the Toshiba Mosfets made for an immediate improvement in power supply noise rejection, dropping it typically by a factor of 4 to 6, to as low as 50 uV unweighted output. This alone justified the effort. Also, as a tweak, you can replace the 220 uF caps with the silk caps from Elna. Listening tests showed a significant improvement over the originals, and I gave copies of these to my business partners for Xmas.


Aleph III Amp – Rev2.0

Aleph3 PDF

Aleph III Amp

2 thoughts on “Aleph 3 30W A class Amplifier

  1. Hi,
    you did a very interesting job. I could be ready to follow you, but first I need to understand a lot of things.
    1. As usual, when dealing with this class of amplifiers, you say that it needs a “huge heatsink”. How much huge? A 0.4 C°/W would be enough (it’s what I have)?
    The service manual says 12 ” W x 12″ D x 6″ H, that is 30,48 W x 30,48 D x 15,24 H.
    Me, I have a 3U depth 400 mm (http://www.hifi2000.it/default.asp?id=104&mnu=104). What do you think?
    2. How much this amplifier can be dangerous to my loudspeakers? that is: a protection circuit is advisable?
    3. How much input is needed to get 30W @ 8Ohm?
    4. Since my DAC has a balanced output do you think that the input can be modified à la ‘Aleph J’ in order to accommodate that?
    Many thanks

    • Hi Teodoro,

      3. 2x20V 300VA transformer
      2. Highly advisible, some solutions I will have as kit on ebay .
      Unfortunately I do not have time to administrate this page so protection kits on site will late.
      4. Im not too familiar with Aleph J however you can try Im sure that you can not damage anything if experiment with the input level signals
      1.sorry, on the link which you gave me can not find 3U enclosure however if your enclosure have same or bigger dimension as it is in service manual it will pass.

      Salute to you and Italy , I will be in Vicenza in Tuesday to buy a bike. 🙂

      kind regards,

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