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Alto L-20 Service Manual
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Alto L-20 Service Manual

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Service
MODEL: L-20
www.altoproaudio.com
Version 1.0

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June 13, 2025

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Summary of Contents for Alto L-20

  • Page 1 Service MODEL: L-20 www.altoproaudio.com Version 1.0...

  • Page 2: Table Of Contents

    CONTENTS 1. Specification 2. Block Diagram 3. Schematic Diagram 4. Wiring Diagram 5. PCB Layout 6. Exploded Views &Mechanical Parts List 7. BOM...

  • Page 3: Specification

    1. SPECIFICATION (L-20) 8. TECHNICAL SPECIFICATION Mono input channels Microphone input electronically balanced, discrete input configuration Frequency response 10Hz to 55kHz, + Distortion (THD & N) 0.005% at 4dBu, 1kHz Gain range 0dB to 60dB (MIC) SNR (Signal to Noise Ratio)
  • Page 4 Power supply Main voltage USA/Canada 100 120V~, 60Hz Europe 210 240V~, 50Hz U.K./Australia 240V~, 50Hz Power Consumption 70 watts Fuse 100 120V~ : T800mAL 210 240V~ : T500mAL Standard IEC receptacle Main connection Physical Dimension (W D H) 495mm 630mm 40/117mm (19.48"...

  • Page 5: Block Diagram

    DFX OUT FX OUT L FX OUT R CTRL ROOM DSP BOARD LEVEL DFX SEND PRESETS VARIATIONS MUTE Titel ALTO MIXING CONSOLE DSP FOOTSWITCH Size Model No: Revision L-20 BLOCK DIAGRAM VER030125 Date: 1-Oct-2003 Sheet File: L20MAP.Sch Drawn By: KEVIN LIN.

  • Page 6: Schematic Diagram

    DIRECT4 100n DIRECT4 DIRECT2 DIR-OUT4 DIRECT2 DIR-OUT2 120R 120R 120R JY-6351G-02-250 DFXOUT-R JY-6351G-02-250 DFXOUT-L FOOTSW 120R JY-6351G-02-250 JY-6351G-02-250 L12PU1 L12PU1-2.SCH Titel DFX OUT FOOTSWITCH PCB# L12PU1.PCB Size Model No: Revision ALTO L12 VER030530 Date: 1-Oct-2003 Sheet File: L12PU1.Sch Drawn By:...
  • Page 7 SW1B LEFT 120R PS-42E85L PS-42E85L JY-5030-030G 120R JY-6351G-02-250 120R 120R JY-6351G-02-250 120R 120R R52 5K1 Titel PCB# L12MN1.PCB SW1C SW1D PS-42E85L PS-42E85L Size Model No: Revision ALTO L12 120R VER030530 120R Date: 11-Jun-2003 Sheet 2 of File: L12PU1-2.Sch Drawn By:...
  • Page 8 JY-6351G-02-250 TRIM2-CH4 U5_1B TRIM1-CH4 R46_1 INSERT 4 C60_1 C46_1 R71_1 NJM4580M INS2-CH4 100P INS1-CH4 R104_3 120R Titel MAIN INPUT STAGE PCB# L12PU2.PCB X2_3 JY-6351G-02-250 Size Model No: Revision ALTO L12 VER030530 Date: 11-Jun-2003 Sheet 1 of File: L12PU2.Sch Drawn By:...
  • Page 9 100n 100n 100n 100n 100n 100n 100n 100n 100n 100n 100n 100n 100n 100n 100n 100n 100n 100n Titel MAIN INPUT STAGE PCB# L12PU2.PCB Size Model No: Revision ALTO L12 VER030530 Date: 11-Jun-2003 Sheet 2 of File: L12PU2-2.Sch Drawn By:...
  • Page 10 U4_2C U4_3C U3_2C U4_1C 47uF 47uF LM393 LM393 4580M LM393 LM393 4580M PGND 47uF 47uF C16_2 -RVCC -VCC 100n 100n Titel PGND PCB# L12MN2.PCB Size Model No: Revision ALTO L12 VER030530 11-Jun-2003 Date: Sheet 1 of File: L12MN2.Sch Drawn By:...
  • Page 11 紅 綠 100K W50K 470P AUX2 AUX-PRE PGND PGND PGND PGND VR10 W50K 100n 100n +VCC 4580M 4580M -VCC 100n 100n Titel PCB# L12MN2.PCB Size Model No: Revision ALTO L12 VER030712 Date: 12-Jul-2003 Sheet 2 of File: CH1.Sch Drawn By:...
  • Page 12 AUX2 R17_1 PGND PGND PGND PGND AUX-PRE VR10_1 W50K C17_1 C19_1 100n 100n +VCC U2_1C U1_1C 4580M 4580M -VCC C18_1 C20_1 100n 100n Titel PCB# L12MN2.PCB Size Model No: Revision ALTO L12 VER030712 Date: 12-Jul-2003 Sheet File: CH2.Sch Drawn By:...
  • Page 13 PGND PGND PGND PGND AUX-PRE VR10_2 W50K C17_2 C19_2 100n 100n +VCC U2_2C U1_2C 4580M 4580M -VCC C18_2 C20_2 100n 100n Titel PCB# L12MN2.PCB Size Model No: Revision ALTO L12 VER030712 Date: 12-Jul-2003 Sheet 4 of File: CH3.Sch Drawn By:...
  • Page 14 AUX-PRE PGND PGND PGND PGND VR10_3 W50K C17_3 C19_3 100n 100n +VCC U2_3C U1_3C 4580M 4580M -VCC C18_3 C20_3 100n 100n Titel PCB# L12MN2.PCB Size Model No: Revision ALTO L12 VER030712 Date: 12-Jul-2003 Sheet 5 of File: CH4.Sch Drawn By:...
  • Page 15 +VCC AUXRTN3-R +VCC CTRMETER.SCH AUXRTN4-L PH PWR -VCC AUXRTN4-R FOOTSW FOOTSW EFXRTN-L MAIN-L-3 EFXRTN-R MAIN-R-3 L12DSP L12DSP.SCH Titel MAIN INPUT STAGE PCB# L12MN1.PCB Size Model No: Revision ALTO L12 VER030531 18-Jun-2003 Date: Sheet 1 of File: L12MN1.Sch Drawn By: BOW.
  • Page 16 100N 100N 100N 100N 100N +VCC 4580M 4580M 4580M 4580M 4580M 4580M -VCC Titel L12STEREO(CH5-CH8) PCB# L12MN1.PCB 100N 100N 100N 100N 100N 100N Size Model No: Revision ALTO L12 VER030710 12-Jul-2003 Date: Sheet 2 of File: L12STEREO.Sch Drawn By: BOW.
  • Page 17 Titel C132 C134 C136 C138 C140 C142 C144 C146 MAIN INPUT STAGE (CH9-CH12) PCB# L12MN1.PCB 100N 100N 100N 100N 100N 100N 100N 100N Size Model No: Revision ALTO L12 VER030710 12-Jul-2003 Date: Sheet 3 of File: L12STEREO2.Sch Drawn By: BOW.
  • Page 18 U45 U46 U47 U48 U49 U50 U51 U52 U53 U54 U55 U56 U57 U58 U59 U60 U61 U62 U63 U64 U65 U66 U67 U68 U69 Titel MAIN INPUT STAGE PCB# L12PU2.PCB Size Model No: Revision ALTO LM12 VER030710 Date: 1-Oct-2003 Sheet File: OTHER.Sch Drawn By: BOW.
  • Page 19 C236 R366 100N 100N 100N 100N 100N 100N 100N 100N VR51 W50K DFX TO MONITOR Titel MAIN INPUT STAGE (AUXRTN) AUX2 PCB# S16MN1.PCB Size Model No: Revision ALTO L12 VER030710 12-Jul-2003 Date: Sheet 5 of File: AUXRTN.Sch Drawn By: BOW.
  • Page 20 AUX4 DFX SEND VR72 W50K C164 R276 R275 47u/25V 47u/25V U24B R260 Titel U24A MAIN INPUT STAGE (AUXSEND) 4580M 510R 4580M PCB# L12MN1.PCB Size Model No: Revision ALTO L12 VER020530 Date: 18-Jun-2003 Sheet 6 of File: AUXSEND.SCH Drawn By: BOW.
  • Page 21 R588 C398 100K 100K R591 C402 47u/25V 47u/25V 47u/25V C400 R593 PGND PGND PGND PGND -VCC 100N R-METER R585 Titel CONTROL ROOM STAGE Size Model No: Revision ALTO L-12 VER030710 12-Jul-2003 Date: Sheet 7 of File: CTRMETER.Sch Drawn By: BOW.
  • Page 22 4580M 4580M LM393 NE555 -VCC C447 C449 C426 C428 C451 C453 100N 100N 100N 100N 100N 100N DGND PGND Titel UDASP IN/OUT SECTION Size Model No: Revision ALTO L-12 VER030424 18-Jun-2003 Date: Sheet 8 of File: L12DSP.Sch Drawn By: BOW.
  • Page 23 +5VD 1N4002 1N4002 7805 1000uF/16V 1000uF/25V PGND PGND PGND PGND 1N4002 1N4002 +15V 1N4002 AC SW 120R AC FUSE T400mAL 16.2V PGND 115 V 3300uF/35V 3300uF/35V 100uF/25V 2P-2.5 AC INPUT 16.2V 10uF/25V PGND 210-240V~ 115 V PGND BRIDGE1 120R 100uF/25V 10uF/25V CON7 3300uF/35V...
  • Page 25 4. Printed Circuit Board...

  • Page 44: Wiring Diagram

    AUX2 AUX4 AUX3 LOGIC +VCC PH PWR AC115V AC210V PHANTOM POWER (TO L12PU1) 2.0-18P-B24A (TO L12PU1) 2.0-18P-B24A Titel ALTO MIXING CONSOLE Size Model No: Revision A2(C) L-8 WIRE CONFIGATION VER030628 24-Aug-2004 Date: Sheet 1 of File: L20PIN.Sch Drawn By: SAMBOW...
  • Page 45 8. Exploded Views...

  • Page 48: Bom

    7. BOM L-20 parts list No. Parts No. Description Specification Remarks MA03900 panel MA03899 panel MA03898 panel L-20_V1.2 MJ01186 hot gradual zinc 1.0t*2135*1220mm MB03654 rear board L-20MKII ALTO_V1.0 MB03533 rear board L-20MKⅡ MB03534 bottom board L-20MKⅡ_V1.0 MJ00058 iron board 1*2135*1220 20.45kg...
  • Page 49 Parts No. Description Specification Remarks NI02386 konb φ14*13mm NI01166 slide key 6*7*8 COOL GRAY 8U NI02309 knob 24*11.5*11 NI02352 knob 24*11.5*11 NI02353 knob 24*11.5*11 NI01863 φ5.5*W10*7.5 NI01862 5.5*5.5*14.5 NI02377 knob φ5.5*7.5mm(內3.3*3.3mm) MG00041 screw M3*6 NI02548 handle 401*31*25mm NI02547 handle 401*31*25mm MG00027 screw M3*12...
  • Page 50 8P-8P 360mm UL1007 20AWG HA00861 power cord Europe 3P LT-312+LT-501 NI00218 cable tie-black ALT-102SB NI02519 knob φ15.9*8.0mm(RF-006) NF00061 assurance card ALTO NF01494 instruction L-20 ALTO_V1.3 NH00149 paper 889*640mm NB02230 colour box L-20 ALTO NB02469 L-20 HJ00006 desiccant NA00136 PE bag 0.05t*820*540mm NE05004...
  • Page 51 Parts No. Description Specification Remarks HC00321 row-wire header(male) 14P 2.0mm 180° CN1,CN2,CN4 HC00524 row-wire header(male) 15P 2.0mm 180° C9,C9-1,C9-2,C9-3,C10-1,C10, CB00029 electrolytic capacitor 22uF/35V φ5*11mm C10-2,C10-3 C107,C108,C109,C110,C7, CB00175 electrolytic capacitor 47uF/25V SLL φ5*11mm C7-1,C7-2, C7-3,C8,C8-1,C8-2, CB00042 electrolytic capacitor C12,C12-1,C12-2,C12-3, 47uF/63V 105℃ LZ φ8*11mm C13,C13-1,C13-2, C13-3,C36,C36-1, R1,R1-1,R1-2,R1-3,R2,R2-1,R2-2,...
  • Page 52 Parts No. Description Specification Remarks P-L12MN2-DIP HK03991 PC board R52,R53 RA00174 fixed resistor 1/4W 47Ω M type C21,C21-1,C21-2,C21-3,C22,C22-1,C22-2,C22-3 CB00009 electrolytic capacitor 1uF/50V φ4*7mm C2,C2-1,C2-2,C2-3,C3,C3-1,C3-2,C3-3, CB00175 electrolytic capacitor 47uF/25V SLL φ5*11mm C4,C4-1,C4-2,C4-3, CF00023 metal-film capacitor MSC 0.033uF/63V 5% CASE01 C11,C11-1,C11-2,C11-3,C12,C12-1,C12-2,C12-3 0.0015uF/100V 5% CASE01 C10,C10-1,C10-2,C10-3 CF00003 metal-film capacitor MSC...
  • Page 53 Parts No. Description Specification Remarks C23,C23-1,C23-2,C23-3 CI00063 SMD ceramic capacitor 0603 470PF/50V NPO ±5﹪ C14,C14-1,C14-2,C14-3,C15,C15-2,C16, CI00075 SMD ceramic capacitor 0603 0.1uF/50V Y5V +80,-20% C16-2,C17,C17-1, U4,U4-1,U4-2,U4-3 SG00306 SMD integrated circuit LM393DR(TI)/(MEXICO) D2,D2-1,D2-2,D2-3,D3,D3-1,D3-2,D3-3, SE00011 SMD rectifier diode RLS4148 0.5A (LL-34) D4,D4-1,D4-2,D4-3 U1,U1-1,U1-2,U1-3,U2,U2-1,U2-2, SG00122 SMD integrated circuit NJM4580M-TE3...
  • Page 54 Parts No. Description Specification Remarks LEDS-11 11mm NI01782 LED spacer support 2.54 180°2*8P 6/11.6mm HC00499 row pin (single)#2200 8P 2.5mm 90° HC00072 row-wire header(male) 14P(male)-14P(female) 60mm UL1007 HA02446 wire 28AWG 15P(male)-15P(female) 60mm UL1007 HA02445 wire 28AWG HA02444 wire 18P(male)-18P(female) 640mm UL1007 CN2,CN3 28AWG HC00154...
  • Page 55 Parts No. Description Specification Remarks R582,R609 RD00087 SMD fixed resistor 1/10W 2.0KΩ ±5% 0603 R67,R68,R233,R234,R375,R635 RD00088 SMD fixed resistor 1/10W 2.2KΩ ±5% 0603 R69,R70,R199,R200,R626,R627 RD00091 SMD fixed resistor 1/10W 3.3KΩ ±5% 0603 RD00352 SMD fixed resistor 1/10W R329,R330,R335,R336,R338,R339 3.6KΩ ±5% 0603 R210,R211,R212,R213,R217,R218 RD00093 SMD fixed resistor 1/10W...
  • Page 56 Parts No. Description Specification Remarks U62,U63,U64,U65,U66,U67 SG00032 SMD integrated circuit LM339DR/(TI) U75,U5,U9,U18,U19 SG00306 SMD integrated circuit LM393DR(TI)/(MEXICO) SG00094 SMD integrated circuit NE555DT/(ST) SE00007 SMD rectifier diode RB400D(D3A) SG00122 SMD integrated circuit NJM4580M-TE3 U1,U2,U3,U4,U6,U7,U10,U8,U11,U12,U13, U14,U15,U16,U17, D21,D30,D31,D32,D33 SE00011 SMD rectifier diode RLS4148 0.5A (LL-34) SE00008 SMD rectifier diode DA204K/T-146...
  • Page 57 SMD rectifier diode RLS4148 0.5A (LL-34) SG00068 SMD integrated circuit 74HC14DT(SO-14)/(PHI) SG00138 SMD integrated circuit AS4LC256K16EO-60JC SG00166 SMD integrated circuit TY-2 ALTO(GMCODE:105022) SG00147 SMD integrated circuit CHEF DSP(GMCODE:105022) SG00037 SMD integrated circuit LD1117DT33C(TO-252) HC00233 IC socket (SMD) PLCC32 (D03-32T.A.4) SG00016...
  • Page 58 PC board P-L12PU4-SMD HB00961 L12PU4(1*6)_VER030530 R1,R2,R3,R4,R5,R6,R7,R8 RD00007 SMD fixed resistor 1/8W 120Ω ±5% 0805 MJ01235 side board L-12 left MJ01236 side board L-20 left 1.0t*400*115 MJ00058 iron board 1*2135*1220 20.45kg NE02717 label MADE IN CHINA NH00038 paper 0.115*1M NI00028 membrane 0.110*1M...
  • Page 59 Parts No. Description Specification Remarks MI01843 fixed bracket L-16 MI01844 fixed bracket L-16 2.0t*15*50*100 MJ01154 iron board 2.0t*1850*950mm 27.6kg NB02473 cushion L-12;16;20series contrary NB02474 cushion L-12;16;20series right MG00322 copper pillar φ3.5*φ6*10 MG00363 copper pillar M3*14*0.5PH NI02833 caushion 0.5t*15.5*72.5 L-16 NI00375 film 45*60.5*0.5mm NI01825...