File name Pass-Labs_Aleph-ONO_Rev.0,1,2,3_sm.pdf
ALEPH ONO SERVICE MANUAL
REV 0, 1, 2, 3 9/30/1997
The Aleph Ono starts off with a low noise power supply using a
custom designed, shielded, low noise 60 Watt toroid transformer.
This gives plus and minus 42-volt DC primary supplies. These are
passively filtered with resistors and capacitors. The rails are then
actively regulated down to plus and minus 32 volts with zero
feedback Mosfets, Q9 for the positive rail and Q23 for the negative.
The Mosfets references are filtered zener stacks of four 9.1 volt
zeners. These supplies are then passively filtered again for each
channel. The moving coil stage has it's own separate capacitance
multiplier Q24 that regulates down to 26 Volts for Q14 the MC amp
The moving coil stage uses 4 matched very low noise Jfets
(Q 10 - Q13) operated in parallel giving a noise floor of 475 picovolts.
These are operated at about 15 volts on the drain. These devices
operate feedback free and feed a cascode stage (Q14) whose output
is buffered by Q15 unity gain inverter. This signal is then feed to the
main gain and equalization stage.
The main gain stage provides its gain with a dual monolithic JFET
(Q5) biased with a low noise current source (Q16). This differential
pair is cascoded into Q1 and Q2 and feeds a P channel Mosfet and
then Transistor Q6 . Q3 and Q6 are feed to current source Q17. The
reference for Q17 and Q18 is red Led D5 witch sets the voltage
across R53 and R67 at 1 volt after the base emitter drops. This
reading across these two resistors is important for this stage to work
The equalization is performed using 1-% tolerance metal film
resistors and polypropylene capacitors. C4, C5 and C6 along with R8
and R9 provide the Riaa equalization curve in the feedback loop. R28
and C8 provide the high frequency EQ and roll off.
Balanced negative out is provided by a unity gain inverter. Q21 and
Q22 differential pair feed Q8 and Q19 N channel Mosfets.
Q25 and Q26 are used to power the mute relays. The front panel
LED must function for Q25 to turn on and pull the mute relays off.
The differences between revisions are generally minor in nature. In
rev 1 muting relays were added to the output. More gain settings
were added in rev 2, along with a physical layout change. An extra
loading resistor was added to the moving magnet input in rev 3.
ALEPH ONO SPECIFICATIONS
Gain 40 dB @ 1 KHz (MM)
71 dB @ 1 KHz (MC)
76 dB @ 1 KHz (MC)
RIAA response plus/minus .1 dB 20-20 KHz
Distortion < .05 % THD @ 20 volts
balanced @ 1 KHz
Maximum Output 20 volts rms.
Output Impedance 150/150 ohms
Input Impedance 47 Kohm 0-650 pF (MM)
5 ohm - 47 Kohm (MC)
Unweighted Noise -90 dB ref. 10 mV input (MM)
-81 dB ref. 1 mV input (MC)
Power consumption 20 watts
Dimensions 19 " W x 11.5 " D x 4 " H