Yorkville AP4040 pwr sm

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INSTRUCTIONS PERTAINING TO A RISK OF FIRE, ELECTRIC SHOCK, OR INJURY TO PERSONS. CAUTION: TO REDUCE THE RISK OF ELECTRIC SHOCK, DO NOT REMOVE COVER (OR BACK). NO USER SERVICEABLE PARTS INSIDE. REFER SERVICING TO QUALIFIED SERVICE PERSONNEL. Read Instructions: The Owner's Manual should be read and understood before operation of your unit. Please, save these instructions for future reference. Packaging: Keep the box and packaging materials, in case the unit needs to be returned for service. Warning: When using electric products, basic precautions should always be followed, including the following: Power Sources:Your unit should be connected to a power source only of the voltage specified in the owners manual or as marked on the unit. This unit has a polarized plug. Do not use with an extension cord or receptacle unless the plug can be fully inserted. Precautions should be taken so that the grounding scheme on the unit is not defeated. Hazards:Do not place this product on an unstable cart, stand, tripod, bracket or table. The product may fall, causing serious personal injury and serious damage to the product. Use only with cart, stand, tripod, bracket, or table recommended by the manufacturer or sold with the product. Follow the manufacturer's instructions when installing the product and use mounting accessories recommended by the manufacturer. The apparatus should not be exposed to dripping or splashing water; no objects filled with liquids should be placed on the apparatus. Terminals marked with the lightning bolt are hazardous live; the external wiring connected to these terminals require installation by an instructed person or the use of ready made leads or cords. No naked flame sources, such as lighted candles, should be placed on the apparatus. Power Cord:The AC supply cord should be routed so that it is unlikely that it will be damaged. If the AC supply cord is damaged DO NOT OPERATE THE UNIT . Service:The unit should be serviced only by qualified service personnel. INSTRUCTIONS RELATIVES AU RISQUE DE FEU, CHOC ÉLECTRIQUE, OU BLESSURES AUX PERSONNES. AVIS: AFIN DE REDUIRE LES RISQUE DE CHOC ELECTRIQUE, N'ENLEVEZ PAS LE COUVERT (OU LE PANNEAU ARRIERE). NE CONTIENT AUCUNE PIECE REPARABLE PAR L'UTILISATEUR. CONSULTEZ UN TECHNICIEN QUALIFIE POUR L'ENTRETIENT. Veuillez lire le manuel: Il contient des informations qui devraient êtres comprises avant l'opération de votre appareil. Conservez S.V.P. ces instructions pour consultations ultérieures Emballage: Conservez la boite au cas ou l'appareil devait être retourner pour réparation. Warning: Attention: Lors de l'utilisation de produits électrique, assurez-vous d'adhérer à des précautions de bases incluant celle qui suivent: Alimentation:L'appareil ne doit être branché qu'à une source d'alimentation correspondant au voltage spécifié dans le manuel ou tel qu'indiqué sur l'appareil. Cet appareil est équipé d'une prise d'alimentation polarisée. Ne pas utiliser cet appareil avec un cordon de raccordement à moins qu'il soit possible d'insérer complètement les trois lames. Des précautions doivent êtres prises afin d'eviter que le système de mise à la terre de l'appareil ne soit désengagé. Hazard:Ne pas placer cet appareil sur un chariot, un support, un trépied ou une table instables. L'appareil pourrait tomber et blesser quelqu'un ou subir des dommages importants. Utiliser seulement un chariot, un support, un trépied ou une table recommandés par le fabricant ou vendus avec le produit. Suivre les instructions du fabricant pour installer l'appareil et utiliser les accessoires recommandés par le fabricant. Il convient de ne pas placer sur l'appareil de sources de flammes nues, telles que des bougies allumées. L'appeil ne doit pas être exposé à des égouttements d'eau ou des éclaboussures et qu'aucun objet rempli de liquide tel que des vases ne doit être placé sur l'appareil. Les dispositifs marqués d'une symbole d'éclair sont des parties dangereuses au toucher et que les câblages extérieurs connectés à ces dispositifs de connection extérieure doivent être effectivés par un opérateur formé ou en utilisant des cordons déjà préparés. Cordon d'alimentation:Évitez d'endommager le cordon d'alimentation. N'UTILISEZ PASL'APPAREIL si le cordon d'alimentation est endommagé. Service:Consultez un technicien qualifié pour l'entretien de votre appareil. IMPORTANT SAFETY INSTRUCTIONS SAFE_V4.doc Version 4.0 02/11/99 11:54 AM AP4040 Parts List 3/8/99 YS # Description Qty. YS # Description Qty. YS # Description Qty.3570 14 PIN SCKT 641261/3 OR W3114T 1 4520 10K TRIM POT (ENCLOSED) 2 4990 1/4W 8K2 5%MINI T&R RES 2 5906 RED 3MM LED 1V9 20MA .4 SPACER T&R 3 4390 _10K AUDIO DETENT STYLE"P22"16MM 2 4762 1/4W 9K760 0.1% *** T&R RES 8 5908 GRN 3MM LED 1V9 20MA .4 SPACER T&R 3 2448 15.0 AMP CIRCUIT BREAKER 1 4800 1/4W 10K0 1% T&R RES 3 6405 RED 3MM LED 1V7 5MA BRIGHT PACE 3 3410 RED ON LEFT DUAL BINDING POST TPP4 1 4829 1/4W 10K 5% T&R RES 4 6408 GREEN 3MM LED 1V9 5MA FROSTED 3 3415 RED ON RIGHT DUAL BINDING POST TPP4 1 4940 1/4W 10K 5% .2"U T&R RES 1 6419 BRIDGE 35A 400V WIRE LEAD GI3504 2 3918 1/4" SLIM JACK PC MOUNT W/SCREW 2 4983 1/4W 10K 5%MINI T&R RES 8 6425 BAV21 200V 0A25 DIODE T&R 4 3628 PC-MOUNT 250TAB SPEAKON #4SCREW GRY 3 6116 1/4W 10K0 1%MINI MF T&R RES 12 6438 1N4004 400V 1A0 DIODE T&R 17 3657 FEMALE XLR PC MOUNT HORIZONTAL 2 4856 1/4W 12K 5% T&R RES 4 6825 1N4148 75V 0A45 DIODE T&R 48 3860 FAN 80MM X 80MM 40CFM 12VDC 1 4630 1/2W 15K 5% T&R RES 2 6934 MR854 400V 3A0 DIODE FAST RECOV 20 3821 HEYCO #1200 STRAIN RELIEF 1 4830 1/4W 15K 5% T&R RES 4 6439 1N5225B 3V0 0W5 ZENER 5% T&R 2 8701 4-40 KEPS NUT ZINC 20 4771 1/4W 17K8 1% T&R RES 2 6440 1N750ARL 4V7 0W5 ZENER 5% T&R 9 8793 4-40 HEX NUT ZINC 3 6125 1/4W 18K 5%MINI T&R RES 2 6461 1N5240BRL 10V0 0W5 ZENER 5% T&R 1 8760 6-32 KEPS NUT TIN PLATED 64 4885 1/4W 20K 5% T&R RES 4 6450 1N5242B 12V0 0W5 ZENER 5% T&R 4 8800 6-32 KEPS NUT ZINC 3 6123 1/4W 20K0 1%MINI MF T&R RES 6 6822 1N4745A 16V0 1W0 ZENER 5% T&R 4 8720 #8 SPRING NUT 2 4777 1/4W 21K5 1% T&R RES 2 6824 1N5246B 16V0 0W5 ZENER 5% T&R 2 8797 5/16-18 KEPS NUT JS500 1 4632 1/2W 22K 5% T&R RES 8 6432 1N5248B 18V0 0W5 ZENER 5% T&R 2 3797 TO-247 THERMO CONDUCTIVE PAD 4 4832 1/4W 22K 5% T&R RES 2 6429 1N4747A 20V0 1W0 ZENER 5% T&R 1 3815 TO3 PREGREASED MICA 56-03-2AP 32 6118 1/4W 22K 5%MINI T&R RES 1 6465 1N5250B 20V0 0W5 ZENER 5% T&R 1 3846 TO220 THERMO PAD LARGE HOLE 56359B 8 4833 1/4W 27K 5% T&R RES 8 6463 1N5251BRL 22V0 0W5 ZENER 5% T&R 1 3580 12 CIR WAFER W/LCK VT 0.1" 1 4840 1/4W 33K 5% T&R RES 3 6433 1N5257B 33V0 0W5 ZENER 5% T&R 4 3583 8 CIR WAFER W/LCK 0.1" 2 6122 1/4W 33K 5%MINI T&R RES 1 5101 BC550C TO92 NPN TRANS. T&R 14 4597 22AWG STRAN TC WIR 25 4834 1/4W 47K 5% T&R RES 1 5102 BC560C TO92 PNP TRANS. T&R 14 4599 22AWG SOLID SC WIR T&R 114 6119 1/4W 47K 5%MINI T&R RES 4 5103 MPSA06 TO92 NPN TRANS. T&R 3 5299 24AWG SOLID SC WIR RAD 40 4835 1/4W 56K 5% T&R RES 8 5108 2N5401 TO92 PNP TRANS. T&R 2 4745 5.0W 0R1 5% BLK RES 12 4898 1/4W 91K 5% T&R RES 4 5113 MPSA42 TO92 NPN TRANS T&R 2 4749 5.0W 0R15 5% BLK RES 4 4838 1/4W 100K 5% T&R RES 2 5114 MPSA92 TO92 PNP TRANS T&R 2 4974 1.0W 0R47 5%FLAME PROOF T&R RES 2 6120 1/4W 100K 5%MINI T&R RES 2 6854 2N6517 TO92 NPN TRANS. 3 4677 1/2W 1R 5% T&R RES 4 4851 1/4W 120K 5% T&R RES 2 5105 MPSA13 TO92 NPN DARLINGTONT&R 2 4973 1.0W 1R 5%FLAME PROOF T&R RES 4 4886 1/4W 200K 5% T&R RES 1 5106 MPSA63 TO92 PNP DARLINGTONT&R 1 4688 1/2W 2R2 5% T&R RES 3 4641 1/2W 220K 5% T&R RES 2 6814 MJF6668 221D- PNP DARLINGTON 1 4911 1/4W 2R2 5% T&R RES 8 4668 2.0W 220K 5%10MM BODY T&R RES 2 6815 MJF6388 221D- NPN DARLINGTON 2 4748 2.0W 3R9 5% BLK RES 2 4841 1/4W 220K 5% T&R RES 2 6873 MJE340 TO126 NPN TRANS 6 4733 5.0W 5R6 5% BLK RES 2 6126 1/4W 220K 5%MINI T&R RES 6 6874 MJE350 TO126 PNP TRANS. 6 4594 1/8W 10R0 2%FLAME PROOF T&R RES 2 4843 1/4W 470K 5% T&R RES 2 6752 MTP10N15L TO220 N CHAN MOSFET 2 4605 1/8W 10R 5% T&R RES 1 4844 1/4W 1M 5% T&R RES 1 6925 MTP8P20 T220 P CHAN MOSFETT 2 4610 1/4W 10R 2%FLAME PROOF T&R RES 10 4948 1/4W 1M 5% .2"U T&R RES 1 6900 YS6900 (22) TO3 NPN TRANS. 16 4930 1/4W 10R 5% .2"U T&R RES 1 4951 1/4W 4M7 5% .2"U T&R RES 2 6989 MJL1302A T03P PNP TRANS PWR 2 4591 1/8W 22R1 1%FLAME PROOF T&R RES 2 6132 1/4W 8M2 5%MINI T&R RES 2 6990 MJL3281A T03P NPN TRANS PWR 2 4589 1/8W 33R 2%FLAME PROOF T&R RES 4 3699 RELAY 2C 01AMP DC48 ???MA PC-S 1 6927 YS6927 (23) TO3 PNP TRANS. 16 4607 1/8W 39R 2%FLAME PROOF T&R RES 10 3735 RELAY 1A 16AMP DC48 011MA PC-C 1 6840 MC33078P IC DUAL OP AMP 5 4899 1/4W 39R 5% T&R RES 6 3604 21" 14C-28AWG DIP HDR CABLE .050" 1 5190 MBS4992 TO92 8V5 DIAC T&R 2 6134 1/4W 47R 5%MINI T&R RES 2 3706 13" 8C-26AWG RIB 1 W/LCK HDR 0.1" 2 6444 MAC224-4 TO220 40A TRIAC 200V 2 6200 1/4W 47R5 1%FLAME PROOF T&R RES 2 3740 15" 12C-26AWG RIB 1 W/LCK HDR 0.1" 1 6859 NSL-28AA OPTO-COUPLER 2 4811 1/4W 68R 5% T&R RES 2 8865 4-40 X 5/16 PAN PH MS SJ500 2 6880 4N35 OPTO-COUPLER 4 4593 1/8W 150R 2%FLAME PROOF T&R RES 4 8742 4-40 X 3/8 PAN PH TAPTITE JS500 2 6478 AS35FN-TO92 TEMPERATURE SENSOR 2 4859 1/4W 150R 5% T&R RES 2 8861 4-40 X 3/8 PAN PH MS SJ500 8 6489 5R0 20% NTC THERMISTOR 2 4984 1/4W 150R 5%MINI T&R RES 2 8741 4-40 X 1/2 PAN PH MS JS500 11 5401 _10P 500V 5%CAP T&R RAD CER.2"NPO 4 4909 1/4W 200R 5% T&R RES 6 8827 4-40 X 1/2 FLAT PH TAPTITE SJ500 6 5410 100P 100V 10%CAP T&R BEAD NPO 2 6201 1/4W 200R 1%FLAME PROOF T&R RES 6 8871 4-40 X 5/8 PAN PH MS SJ500 8 5197 220P 100V 2%CAP T&R RAD CER.2"NPO 1 4645 1/8W 220R0 1%FLAME PROOF T&R RES 4 8799 #6 X 1/4 PAN PH TYPE B JS500 2 5412 220P 100V 10%CAP T&R BEAD NPO 13 4857 1/4W 220R 5% T&R RES 6 8832 6-32 X 1/4 PAN PH TAPTITE SJ500 1 5417 330P 50V 10%CAP T&R BEAD NPO 2 4977 1/4W 220R 5%MINI T&R RES 5 8801 6-32 X 3/8 PAN PH TAPTITE SJ500 4 5201 470P 100V 5%CAP T&R RAD CER.2"NPO 2 4606 1/8W 249R 2%FLAME PROOF T&R RES 8 8829 6-32 X 3/8 FLAT PH TAPTITE BO#4 HEA 18 5416 470P 50V 10%CAP T&R BEAD NPO 2 4867 1/4W 270R 5% T&R RES 2 8761 6-32 X 1/2 PAN PHIL MS ZINC CLEAR 64 5273 __1N5 200V 5%CAP T&R RAD CER.2"NPO 2 4986 1/4W 270R 5%MINI T&R RES 2 8806 6-32 X 1/2 PAN PH TAPTITE SJ500 2 5427 __2N2 500V 10%CAP T&R RAD CER.2" YB 6 4855 1/4W 330R 5% T&R RES 2 8837 6-32 X 1/2 ROUND PH MS SJ500 1 5209 __4N7 250V 5%CAP T&R RADIAL.2"FILM 2 4821 1/4W 470R 5% T&R RES 6 8824 8-32 X 5/16 PAN QUAD TAPTITE SJ500 3 6451 __4N7 250V 20%CAP AC Y ONLY RAD10MM 1 4980 1/4W 470R 5%MINI T&R RES 3 8869 8-18 X 1/2 THRD CUTTING FOR PLASTIC 4 5834 _10N 250V 20%CAP RAD POLYFILM BULK 2 4891 1/4W 620R 5% T&R RES 2 8999 8-32 X 5/8 PAN PH TAPTITE SJ500 17 5210 _22N 100V 10%CAP T&R RADIAL.2"FILM 11 4873 1/4W 680R 5% T&R RES 1 8719 8-32 X 3/4 FILLISTER PHIL MS JS500 2 6435 _22N 275V 20%CAP AC X2 RAD BLK15MM 2 4823 1/4W 1K 5% T&R RES 6 8815 8-32 X 3/4 PAN PH TAPTITE SJ500 5 5308 _47N 50V 10%CAP T&R BEAD X7R 2 4934 1/4W 1K 5% .2"U T&R RES 2 8809 10-32 X 1/4 PAN PH TAPTITE SJ500 4 5226 _68N 100V 5%CAP T&R RADIAL.2"FILM 4 4981 1/4W 1K 5%MINI T&R RES 2 8749 10-32 X 1/2 QDX PH TAPTITE JS500 2 5228 100N 100V 5%CAP T&R RADIAL.2"FILM 3 4854 1/4W 1K2 5% T&R RES 1 8731 10-16 X 5/8 TYPE B HEX W/SLOT JS500 12 5314 100N 50V 10%CAP T&R BEAD X7R 4 4824 1/4W 1K5 5% T&R RES 2 8736 5/16-18X2-3/4 GRD 5 HEX BOLT JS500 1 5229 150N 63V 10%CAP T&R RADIAL.2"FILM 4 4988 1/4W 1K5 5%MINI T&R RES 4 8663 11/64 NYLON SPACER (MICRO PLASTIC) 66 5231 220N 63V 10%CAP T&R RADIAL.2"FILM 2 4791 1/4W 1K54 1% T&T RES 4 8629 10-32 X 1/4 SPACER PHENOLIC 16 5882 220N 250V 10%CAP RAD POLYFILM BULK 4 4808 1/4W 2K 5% T&R RES 4 3746 21/64 X .250 OD #6 SPACER ALUMINUM 2 5255 __1U 63V 20%CAP T&R RADIAL ELE.2" 3 6113 1/4W 2K 5%MINI T&R RES 2 3751 SNAP IN 5/16 SPACER RICHCO 3 5259 __4U7 63V 20%CAP T&R RADIAL ELE.2" 6 4847 1/4W 2K2 5% T&R RES 2 3739 CUSTOM .4 LED SPACER 6 5281 _10U 16V 20%CAP NONPOLAR T&R .2" 2 4804 1/4W 3K 5% T&R RES 4 3743 SNAP ON 0.5" SPACER RICHCO 5 5629 _10U 160V 20%CAP RADIAL ELECT BULK 4 6124 1/4W 3K 5%MINI T&R RES 2 3859 1/2 PLASTIC HEX SPACER #4 2 5945 _10U 63V 20%CAP T&R RADIAL ELECTR 2 6136 1/4W 3K3 5%MINI T&R RES 4 3858 3/4 PLASTIC HEX SPACER #4 4 5260 _22U 50V 20%CAP T&R RADIAL ELE.2" 10 4744 5.0W 3K6 5% BLK RES 8 8667 SHOULDER WASHER SWS-229 LENGTH 1/8 4 5961 _33U 16V 20%CAP NONPOLAR T&R RAD 12 4756 1/4W 4K120 0.1% *** T&R RES 2 8818 3/4 OD X 5/16 ID X .08 THICK WASHER 2 5267 100U 25V 20%CAP T&R RADIAL ELE.2" 3 4681 1.0W 4K7 5% T&R RES 2 3511 #6 FLAT WASHER NYLON 4 5619 330U 100V 20%CAP RADIAL ELECT BULK 4 4827 1/4W 4K7 5% T&R RES 8 8491 #10 SPLIT LOCK WASHER BO 4 5630 330U 25V 20%CAP RADIAL ELECT BULK 6 4943 1/4W 4K7 5% .2"U T&R RES 1 8850 #10 INT TOOTH LOCKWASHER BO 4 5618 470U 25V 20%CAP RADIAL ELECT BULK 1 4982 1/4W 4K7 5%MINI T&R RES 5 3502 NYLON FLAT WASHER OD.158ID.110H.070 2 5896 4700U 80V 20%CAP RADIAL ELECT BULK 16 4887 1/4W 7K5 5% T&R RES 5 3436 DPDT PUSH SW PCMT H BREAK B4 MAKE 3 3587 DPDT ROKR SW QUIK 250" AC/PWR IEC65 1 3705 4P3T SLID SW PCMT H 1 1197 AP4040 T?RD 1

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550 Granite Court, Pickering, Ontartio CANADA L1W-3Y8 4625 Witmer Industrial Estate, Niagara Falls, New York USA 14305 SERVICE MANUAL 1 Yorkville Sound- http://www.yorkville.com 550 Granite Court, Pickering, Ontartio CANADA L1W-3Y8 4625 Witmer Industrial Estate, Niagara Falls, New York USA 14305 SERVICE MANUAL 1 Yorkville Sound- http://www.yorkville.com Y Yo or rk kv vi il ll le e A AP P4 40 04 40 0 P Po ow we er r A Am mp pl li if fi ie er r M M1 11 12 29 9 T TH HE E I IN NP PU UT T B BO OA AR RD D The input board processes the audio signal from the input jacks to the volume control board, (M1128). Each channel consists of a balanced gain stage, switchable subsonic filter, and a stereo / mono / bridge switch. Looking at the left channel, the balanced input, (XLR Jack) and unbalanced input (phone jack) are wired in parallel to the input of a balanced operational amplifier, (U4). The gain of this stage is 0.82 (-1.3dB) balanced and 1.6 (4.0dB) unbalanced. Resistors R25, R27 along with capacitors C11 and C12 form a radio interference elimination filter. Switch S1 selects the cutoff frequency of the hi-pass subsonic filter. The subsonic filter provides a 20Hz or 40 Hz high pass filter. The filter consists of a tee network on the input of U3 along with R10, R28, C29 and C30, C33 and C34. The gain is 1 (0dB) in the passband, (above 100Hz). The audio signals from the input board M1129 pass through the 14 conductor cable to board M1128. M M1 11 12 28 8 V VO OL LU UM ME E C CO ON NT TR RO OL L B BO OA AR RD D This board contains: - the front panel audio gain controls - the front panel indicating LEDs (power, protect, activity and clip). - the audio limiters Circuit Explanation: - The left channel of the circuit is explained. (Refer to the schematic of M1128 as the sections of the circuit are explained.) The audio signal out of M1129 passes through volume control P2 and the desired level enters U2 through pin 6. U2 is set for a gain of 5 (14dB) when the volume control is in the fully clockwise position. The AP4040s defeatable limiter is built around LD8. LD8 is an opto-resistive cell comprising of an LED that shines on a photocell. As the LED in the LD8 becomes brighter, the resistance of the photocell decreases, placing more of the audio signal on pin 5 (non-inverting input) of U2. This audio voltage gets subtracted from the signal on the inverting input and less signal appears on the output of U2. Transistors Q5 and Q6 along with the surrounding passive parts provide the attack and release time constants of the limiting function along with the drive currents for the clip LED and the LED inside LD8. When an audio signal on the output of the power amplifier section (on board M1146) enters clipping, pulses representing the duration of the clipped portion appear at LCLIP. These pulses turn on transistor Q6, and Q6 provides current pulses to turn on clip LED LD6. The pulses also pass through R7 and D6 to charge C3 and C36. When the voltage across C3 reaches 0.5 volts then Q5 turns on providing a cur- rent into the LED of the LD8 limiting the audio signal at U2. The charging (attack) and discharging (release) times of the limiter are 80mS and 3.5 seconds respectively. Resistors R50 and R7 provide the charging path, and resistor R51 provides the dis- charge path. The limiter can be defeated by placing the limiter switch (S2) in the in position which disconnects Q5 and the charging / discharging circuitry from V+. The activity LED circuit consists of Q1 and the surrounding circuitry. The audio sig- nal enters the activity LED circuit through R2. R2 and C21 form a differentiator that turns Q1 on illuminating the activity LED whenever the audio signal increases in ampli- tude. A constant current flows through R55A, R55B and when Q1 is off, the collector current then flows through D1. From M1128 the audio signal passes through a 12-conductor ribbon cable to circuit board M1147. On M1127 an operational amplifier U201 re-references the ground for the audio sig- nal from LREF or RREF to the corresponding LOG (left output ground) or ROG (right output ground). U201 also provides DC correction for DC offsets appearing on the out- put binding posts. Feedback from the output binding posts appears on LFNB or RFNB. Through R203A or R203B the DC offset achieves a gain of -1 from U201. The DC off- set of opposite polarity on the output of U201 will compensate for the DC offset in the amplifier section on M1146 resulting in 0 volts DC on the output binding posts. - The audio signal continues to M1146 via an 8-conductor ribbon cable. M M1 11 12 26 6 T TH HE E V VO OL LT TA AG GE E A AM MP PL LI IF FI IE ER R A AN ND D C CU UR RR RE EN NT T A AM MP PL LI IF FI IE ER R This board contains: - a voltage amplifier section - a current amplifier section - amplifier current limit section - DC output protection - heatsink temperature sensing Voltage Amplifier Section The voltage amplifier amplifies the audio signals voltage from 6.8 volts peak (at the output of U201) to approximately 98v peak, which is required to drive the current amplifier section. The current amplifier provides the current required for the 98v peak signal to drive 1200 watts into 4 ohms out of the binding posts. Before the circuit is described in detail here is a quick rundown on the signals path through the voltage amplifier stage. Refer to the schematic of M1146. Lets consider that a positive going AC signal is present at the SIG input. The positive going signal will turn on the positive side of the voltage amplifier. The signal at the SIG input turns on Q12A (through R40A, D14A and D13A). The collector of Q12A pulls down on the base of Q14A turns this transistor on further and allows a greater current to flow out of Q14As collector. This increase in current passes through Q15A and its collector to emitter voltage decreases. The collector of Q15A now being more positive in voltage turns the base of Q18A on causing an increase in Q18As collector current resulting in test point 1 going positive. As the positive side of the amplifier was turning on the negative side would have been turning off. This is how test point 1 was able to move positive following the input signal. The reverse would hold true if a negative going signal were present on the input of the voltage amplifier.