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Pass Laboratories
Aleph L Service Manual
The Aleph L is a simple Mosfet stereo preamplifier having four single-ended inputs and two outputs. Its controls consist of an input selector and a level control. Maximum gain is internally adjustable via a dip switch. The gain stage of the preamp is a single Mosfet operated common source and biased by a Mosfet constant current source. Figure 1 shows the schematic of the preamp, indicating the component designations and values and various voltages. The power supply and the left channel are shown. Power supply and components common to both channels have reference designators less than 100. The left channel is 100 to 199, and the right channel is 200 to 299. The power supply transformer delivers approximately 84 volts (for 120 or 240 VAC operation) unregulated DC into C1, which is then passively filtered and then actively regulated down to about 60 volts at the output of Q1. Q1 is driven by a stack of Zener diodes in parallel with C3 and the regulated output is additionally filtered by C4. The output muting relay is controlled by the circuits of Q2 and Q3. For the relay to activate, both Q2 and Q3 must be conducting. Q3 turns on slowly via the charge on C5, while Q2 will only conduct when there is at least 8 volts difference between regulated and unregulated supplies. Thus Q3 delays relay turn on, and Q2 shuts it off quickly. The audio gain stage consists of Q101. The input goes to the gate, and the output appears at the drain. The circuit is inverting. The circuit of Q102 provides a constant current source of about 40 ma for the gain stage. It is controlled by the circuit of Q103, which works to keep a .7 volt value across R111. The output of the gain stage goes to the level control which is a 23 position stepped attenuator whose wiper is attached to the preamp output. Fig 2 shows the circuit board layout, with the components identified by designators. Fig 3 shows the circuit board layout, with the components identified by values. Fig 4 shows the circuit board layout of the volume control. The maximum gain of the preamp is controlled by the input resistor values in conjunction with the 6 position dip switch on the main board. 0 dB 6 dB 12 dB 18 dB switches 1, 6 = On switches 2, 5 = On switches 3, 4 = On all internal switches = 0n (default)
A
+85V
R1 3.3 3W 4 X 1N4004 C1
+
B
V+ REG V+ DEC V+UNREG
C
D
INPUT 4
C103
15
R2
R111
4.75K
4.75K
1N4004
4V
1000 UF 221 Z8 Z1 R11 IRF9610 9.1V 9.1V 1000 UF R109 221 R110
G S S G
INPUT 3
MPSA92 R4
-
Q103
REGULATOR
.7V
4.7K 3W
1
D
680 UF
R10
R5
D5
C2
CURRENT SOURCE
Q1 IRF610 D1-4
1
+65V
TH1
D
S1 C4 C3 9.1V C104 1000 UF 680 PF LED1 1000 UF C102 10UF R6 9.1V 2.21K Z3 100 R112
SELECT
OUTPUT
Z2
THERMISTOR
INPUT 2
4.75K
C 1
C 2
C 3
C 4
221 Q102
+60V
AVEL 4007
A B C D
R108
10K
R106
S 1
R101
R102
22.1K
R103
47.5K
INPUT 1
10K
2
47.5K
2
1 1 5 A 0 A 1 1 5 B 0 B
+30V
R7
G
C 2
C 2
C 2
IRF9610
S
Z4
S2 Q101 R105 R8
G D
0 DB
+12 DB
+6 DB
NEGATIVE RELAY
Q3
D 100-120V
Z101
9.1V
C 1
C 1
C 1
C101 221K 221 IRF610
S
D6
9.1V R3 Z5
INPUT GAIN
Q2 221
G D
10UF 6.81K
9.1V
+4V
2.21K
1N4004
R104
221K
Z102
9.1V
R107
GAIN TRANSISTOR
+25V
+4V
R9 C5 220UF
1N4004
Z7
LEVEL CONTROL
RELAY NC 100 124 150 182 221 274 331 392 475 562 47.5 56.2 68.1 82.5 750
10
15
18.2
22.1
27.4
33.1
L 2
RV22
RV21
RV20
RV19
RV18
RV17
RV16
RV15
RV14
RV13
RV12
RV11
RV10
RV9
RV8
RV7
RV6
RV5
RV4
RV3
RV2
RV1
4
39.2
C 2
POSITIVE RELAY
OUTPUT 2
9.1V
.25A SLO Z6 IRF610
S
OUTPUT 1
D7
9.1V
F1
3
6.8K 3W
200-240V
3
C 1
L 1
Title Size
ALEPH L PREAMP
Number
4
B
Date Filename
PL20
Drawn by Sheet
Rev
PASS
of
2/1/96 PL20.S01
A B
C
D
SPECIFICATIONS Gain 17 dB (all internal switches = 0n) 12 dB (switches 3, 4 = On) 6 dB (switches 2, 5 = On) 0 dB (switches 1, 6 = On) Freq. Response Distortion Maximum Output Output Impedance Input Impedance +0, -3 dB @ 10 Hz and 100 kHz < .2 % THD typically .02% @ 1 volt @ 1KHZ 10 volts rms. 0 - 750 ohms 20 Kohm, 6.5 dB gain setting (default) 10 Kohm, 13.4 dB gain setting Output Noise Power Consumption Dimensions Shipping Weight less than 10 microvolts, unweighted 20-20khz 15 watts 12 " W x 11.5 " D x 4" H 22 lb.
Pass Laboratories Foresthill CA 95631 tel fax (530) 367 3690 (530) 367 2193
Pass Laboratories
Aleph L Service Manual
Rev 1.2
9/26/96
The Aleph L is a simple Mosfet stereo preamplifier having four single-ended inputs and two outputs. Its controls consist of an input selector and a level control. The volume control is passive up to the 3:00 o'clock position where the gain is unity. At 3:00 o'clock, the connection from input to output is direct, with no components in the signal path, and past the 3:00 o'clock position the unit becomes an active preamp. The gain stage of the preamp is a single Mosfet operated common source and biased by a Mosfet constant current source. Figure 1 shows the schematic of the preamp, indicating the component designations and values and various voltages. The power supply and the left channel are shown. Power supply and components common to both channels have reference designators less than 100. The left channel is 100 to 199, and the right channel is 200 to 299. The power supply transformer delivers approximately 84 volts (for 120 or 240 VAC operation) unregulated DC into C1, which is then passively filtered and then actively regulated down to about 60 volts at the output of Q1. Q1 is driven by a stack of Zener diodes and the regulated output is additionally filtered by C3 and C4 to form the left and right supplies. The output muting relay is controlled by the circuits of Q2 and Q3. For the relay to activate, both Q2 and Q3 must be conducting. Q3 turns on slowly via the charge on C5, while Q2 will only conduct when there is at least 8 volts difference between regulated and unregulated supplies. Thus Q3 delays relay turn on, and Q2 shuts it off quickly. The audio gain stage consists of Q101. The input goes to the gate, and the output appears at the drain. Q102 inverts the signal, so the circuit as a whole is non inverting. The output of the gain stage goes to the level control which is a 23 position stepped attenuator whose wiper is attached to the preamp output. Fig 2 shows the circuit board layout, with the components identified by designators. Fig 3 shows the circuit board layout, with the components identified by values. Fig 4 shows the circuit board layout of the volume control. Fig 5 shows the Aleph L upgrade.
4
OUTPUT 2 OUTPUT 1
C 1 C 2 L 2
2
3
INPUT 1 Z102 Z101
1
INPUT 2
C 1
INPUT 3
INPUT 4
RELAY NC
A
L 1
A
C 2
9.1V R107 221K
9.1V
S 1
C 3 C 4
S1
SELECT
RV22
10
RV21
15
RV20
18.2
RV19
22.1
RV18
27.4
R120 6.81K R109 221K 220uF C104
C101
10UF
LEVEL CONTROL
RV17
33.1
RV16
+4V
39.2
R110 22.1K
R104
RV15
221
47.5
B C
Size Date
B
RV14
56.2
G
R113 1K R111
S G
Q102
+30V
IRF610
Q101
RV13
68.1 R106 221
S
D
D
RV12
82.5
10pF R114 221 221 R112 C104
10
IRF9610
RV11
100
R115 470
C102
10UF
RV10
V+ REG
124
+60V
RV9
150
+4V
R8 221K 2.21K
L
RV8
182 220UF C5
RV7
221
D6 1N4004 221 R9
4.75K LED1 R11
4.75K R10
R7
RV6
274
REGULATOR
S D
L
RV5
331
1000 UF C4
R21
G
Q1
10
C
G
IRF610
+85V
RV4
392
R
NEGATIVE RELAY
IRF610
1000 UF C3
R22 R4 221 10
Q2
RV3
S
475
D
+65V
RV2
562
R5 4.75K
RV1
750
D7 1N4004
Z2 R6 9.1V
Z1 9.1V
+25V
Q3 R3
D
2.21K
V+ DEC
IRF9610
S
G
POSITIVE RELAY
6.8K 3W
1000 UF C2
Z7 9.1V
Z6 9.1V
Z5 9.1V
Z4 9.1V
Z3 9.1V TH1 THERMISTOR
Title
R1
3.3 3W
B
Filename
1000 UF C1
Number
9/24/96
V+UNREG
1 1 5 A
A
ALEPH L PREAMP
D
Sheet of Drawn by
D
-
0 A
B
+
AVEL 4007
200-240V
D1-4
100-120V
1 1 5 B
C
PL20MB12
Rev
F1
0 B D
4 X 1N4004
.25A SLO
PASS
4
3
2
1
ALEPH L Update Rev 1.0 to 1.1 The kit contains one new main board with the correct value for R212, but please verify before doing the conversion. To update the Aleph L from rev 1.0 to either rev 1.1 is a simple matter of replacing the main board, with two minor exceptions. 1. R212 must be 562 ( see attached drawing for location). 2. When keeping the old volume control board the white wire must be attached as shown in the drawing of the old volume board.
SPECIFICATIONS Gain Freq. Response Distortion Maximum Output Output Impedance Input Impedance Output Noise Power Consumption Dimensions Shipping Weight 17 dB +0, -3 dB @ 10 Hz and 100 kHz < .2 % THD typically .02% @ 1 volt @ 1KHZ 10 volts rms. 0 - 750 ohms 20 Kohm less than 10 microvolts, unweighted 20-20khz 15 watts 12 " W x 11.5 " D x 4" H 22 lb.
Pass Laboratories 24449 Foresthill Rd. Foresthill CA 95631 tel fax (530) 367 3690 (530) 367 2193