PartTimeProjects Aleph X Amplifier

IN PROGRESS *

The Aleph X amplifier is a do-it-yourself amplifier designed by "Grey." Generally, its intended to be an improvement to the classic Pass Labs Aleph 3 amplifier. It adds differential circuitry and supersymmetry concepts (also pioneered by Pass Labs).

Reference Materials

Aleph X Build Thread (a very long read)
Aleph X Build "Wiki".
Aleph X Parts and Schematic, latest version will be on the "Wiki."
Aleph X Spreadsheet, latest version will be on the "Wiki."

One useful link I found was Eric's web site- "Eric's" High Power Aleph X.
There is a lot of information at this site. You might want to look it over if you are building an Aleph X.

About the Aleph X and My Implementation

The amplifier operates class "A" and is fully balanced. Unlike the Krell Clone, it has trouble driving very low impedances due to the nature of its design. Since it does not increase its output current as the load decreases (beyond a certain limit) it is safe to accidently drive this amplifier into a short circuit. The Krell would blow up at this point, since I have not installed any current limiting. The Aleph X is known for its smooth almost tubelike sound. The basic circuit uses 4 output transistors for about 30 watts per channel. My version is scaled up to 12 transistors per channel and should put out about 60 watts per channel into an 8 ohm speaker. It consumes over 350 watts at idle (with no input). The additional output devices necessitated some design changes from the original circuit.

Key parameters of my version are as follows.

Key Parameter	My Implementation
Power Supply	Dual mono CRC= 60,000 uF, 0.20 ohms (25W metal clad), 60,000 uF
Power transformers	Two Victoria Magnetics 18V CT/ 700 VA Toroids
Bridge Rectifiers	IXYS 400V, 50 amp modules, fast recovery
Power supply snubbers	510 ohms in series with .01uF Wima MKT
Power supply bleed resistors	5K (1/2W) across the terminals of each Electrolytic to discharge caps when turned off
Voltage after CRC/ripple	22 VDC/ ??mV ripple
Softstart method	CL-60 thermisters in-line with each transformer primary, bypassed after 3 seconds
Output devices	12 each of IRFP0244 per channel, matched

For the design phase I did a number of simulations and calculations, using the Duncan Amp PSU simulation and the Aleph X Spreadsheet (see link in "reference materials," above).

Duncan Amp PSU Simulation	Power Output Graph	Operating Conditions

A lot of people wonder how to connect multiple output transistors to this board to make a higher power version of the amplifier. The board only has room for 4 power MOSFETs.

Here are some options to add transistors, in my example there are 12 rather than the original 4 power MOSFETs.

The schematic is only of half of the board, the other half is symmetrical (the same) so its easily duplicated for those components. I used "Option 3" because it was easy to but screw-headers in the spots where the transistors originally went, and to connect the power supply directly to the output boards.