Yorkville AP4020 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 AP4020 Parts List 2/16/99 YS # Description Qty. YS # Description Qty. YS # Description Qty.3570 14 PIN SCKT 641261/3 OR W3114T 1 2448 15.0 AMP CIRCUIT BREAKER 1 4629 1/2W 10K 5% T&R RES 8 5906 RED 3MM LED 1V9 20MA .4 SPACER T&R 3 3820 4UH COIL 14AWG ZOBEL HORIZONTAL 2 4800 1/4W 10K0 1% T&R RES 5 5908 GRN 3MM LED 1V9 20MA .4 SPACER T&R 3 3601 RING TERMINAL 16AWG WIRE & #8 SCREW 1 4829 1/4W 10K 5% T&R RES 8 6408 GREEN 3MM LED 1V9 5MA FROSTED 3 3615 STAR RING TERMINAL 18 AWG #10 SCREW 4 4983 1/4W 10K 5%MINI T&R RES 3 6419 BRIDGE 35A 400V WIRE LEAD GI3504 2 3410 RED ON LEFT DUAL BINDING POST TPP4 1 6116 1/4W 10K0 1%MINI MF T&R RES 12 6425 BAV21 200V 0A25 DIODE T&R 4 3415 RED ON RIGHT DUAL BINDING POST TPP4 1 4856 1/4W 12K 5% T&R RES 4 6438 1N4004 400V 1A0 DIODE T&R 11 3918 1/4" SLIM JACK PC MOUNT W/SCREW 2 4901 1/4W 13K 5% T&R RES 4 6825 1N4148 75V 0A45 DIODE T&R 51 3628 PC-MOUNT 250TAB SPEAKON #4SCREW GRY 3 4830 1/4W 15K 5% T&R RES 4 6934 MR854 400V 3A0 DIODE FAST RECOV 20 3657 FEMALE XLR PC MOUNT HORIZONTAL 2 4771 1/4W 17K8 1% T&R RES 2 6439 1N5225B 3V0 0W5 ZENER 5% T&R 2 3860 FAN 80MM X 80MM 40CFM 12VDC 1 6125 1/4W 18K 5%MINI T&R RES 2 6440 1N750ARL 4V7 0W5 ZENER 5% T&R 9 3894 AAVID 5972-B H/S W/TAB B.O. 8 6123 1/4W 20K0 1%MINI MF T&R RES 2 6450 1N5242B 12V0 0W5 ZENER 5% T&R 4 3501 B52200F006 COMP WASH #4 SMALL 23 4832 1/4W 22K 5% T&R RES 6 6822 1N4745A 16V0 1W0 ZENER 5% T&R 4 3552 NYLON SPRING CLAMP 1 6118 1/4W 22K 5%MINI T&R RES 1 6824 1N5246B 16V0 0W5 ZENER 5% T&R 2 3827 SQUARE BUMPER BUTTON BLACK 11 4833 1/4W 27K 5% T&R RES 3 6432 1N5248B 18V0 0W5 ZENER 5% T&R 2 8433 AP SERIES PLASTIC KNOB 2 4840 1/4W 33K 5% T&R RES 3 6429 1N4747A 20V0 1W0 ZENER 5% T&R 1 8661 BUTTON KNOB FLAT GREY 3 4853 1/4W 39K 5% T&R RES 4 6465 1N5250B 20V0 0W5 ZENER 5% T&R 2 3468 8? 3/16 SJT AC LINE CORD STRIP 17" 1 6119 1/4W 47K 5%MINI T&R RES 3 6463 1N5251BRL 22V0 0W5 ZENER 5% T&R 1 3821 HEYCO #1200 STRAIN RELIEF 1 4835 1/4W 56K 5% T&R RES 4 6433 1N5257B 33V0 0W5 ZENER 5% T&R 3 3638 12 CIR CABLE HOLDER .098 1 4836 1/4W 68K 5% T&R RES 4 5101 BC550C TO92 NPN TRANS. T&R 14 3676 8 CIR CABLE HOLDER .098 2 4838 1/4W 100K 5% T&R RES 2 5102 BC560C TO92 PNP TRANS. T&R 14 8701 4-40 KEPS NUT ZINC 20 6120 1/4W 100K 5%MINI T&R RES 2 5103 MPSA06 TO92 NPN TRANS. T&R 3 8793 4-40 HEX NUT ZINC 3 4851 1/4W 120K 5% T&R RES 2 5107 2N5551 TO92 NPN TRANS. T&R 2 8760 6-32 KEPS NUT TIN PLATED 64 4790 2.0W 150K 5%10MM BODY T&R RES 2 5108 2N5401 TO92 PNP TRANS. T&R 4 8800 6-32 KEPS NUT ZINC 2 4886 1/4W 200K 5% T&R RES 1 6854 2N6517 TO92 NPN TRANS. 2 8720 #8 SPRING NUT 2 4841 1/4W 220K 5% T&R RES 2 5105 MPSA13 TO92 NPN DARLINGTONT&R 1 8797 5/16-18 KEPS NUT JS500 1 6126 1/4W 220K 5%MINI T&R RES 6 5106 MPSA63 TO92 PNP DARLINGTONT&R 1 3797 TO-247 THERMO CONDUCTIVE PAD 4 4843 1/4W 470K 5% T&R RES 2 6814 MJF6668 221D- PNP DARLINGTON 1 3815 TO3 PREGREASED MICA 56-03-2AP 32 4844 1/4W 1M 5% T&R RES 1 6815 MJF6388 221D- NPN DARLINGTON 2 3823 TO-220 THERMO PAD SMALL HOLE 4 4948 1/4W 1M 5% .2"U T&R RES 1 6873 MJE340 TO126 NPN TRANS 6 3846 TO220 THERMO PAD LARGE HOLE 56359B 4 4951 1/4W 4M7 5% .2"U T&R RES 2 6874 MJE350 TO126 PNP TRANS. 6 3580 12 CIR WAFER W/LCK VT 0.1" 1 6132 1/4W 8M2 5%MINI T&R RES 2 6752 MTP10N15L TO220 N CHAN MOSFET 2 3583 8 CIR WAFER W/LCK 0.1" 2 3700 RELAY 2C 01AMP DC24 ???MA PC-S 1 6933 MTP23P06 TO220 P CHAN MOSFET 2 4745 5.0W 0R1 5% BLK RES 12 3721 RELAY 1A 16AMP DC24 022MA PC-C 1 6900 YS6900 (22) TO3 NPN TRANS. 16 4749 5.0W 0R15 5% BLK RES 4 3604 21" 14C-28AWG DIP HDR CABLE .050" 1 6989 MJL1302A T03P PNP TRANS PWR 2 4974 1.0W 0R47 5%FLAME PROOF T&R RES 2 3706 13" 8C-26AWG RIB 1 W/LCK HDR 0.1" 2 6990 MJL3281A T03P NPN TRANS PWR 2 4677 1/2W 1R 5% T&R RES 4 3740 15" 12C-26AWG RIB 1 W/LCK HDR 0.1" 1 6927 YS6927 (23) TO3 PNP TRANS. 16 4973 1.0W 1R 5%FLAME PROOF T&R RES 4 8865 4-40 X 5/16 PAN PH MS SJ500 2 6840 MC33078P IC DUAL OP AMP 5 4688 1/2W 2R2 5% T&R RES 3 8742 4-40 X 3/8 PAN PH TAPTITE JS500 2 5190 MBS4992 TO92 8V5 DIAC T&R 2 4911 1/4W 2R2 5% T&R RES 8 8861 4-40 X 3/8 PAN PH MS SJ500 8 6444 MAC224-4 TO220 40A TRIAC 200V 2 4748 2.0W 3R9 5% BLK RES 2 8741 4-40 X 1/2 PAN PH MS JS500 11 6859 NSL-28AA OPTO-COUPLER 2 4733 5.0W 5R6 5% BLK RES 2 8827 4-40 X 1/2 FLAT PH TAPTITE SJ500 6 6880 4N35 OPTO-COUPLER 4 4605 1/8W 10R 5% T&R RES 1 8871 4-40 X 5/8 PAN PH MS SJ500 8 6478 AS35FN-TO92 TEMPERATURE SENSOR 2 4610 1/4W 10R 2%FLAME PROOF T&R RES 8 8799 #6 X 1/4 PAN PH TYPE B JS500 2 6489 5R0 20% NTC THERMISTOR 2 4875 1/4W 10R 5% T&R RES 2 8832 6-32 X 1/4 PAN PH TAPTITE SJ500 1 5200 _10P 200V 5%CAP T&R RAD CER.2"NPO 4 4930 1/4W 10R 5% .2"U T&R RES 1 8801 6-32 X 3/8 PAN PH TAPTITE SJ500 4 5410 100P 100V 10%CAP T&R BEAD NPO 2 4591 1/8W 22R1 1%FLAME PROOF T&R RES 2 8829 6-32 X 3/8 FLAT PH TAPTITE BO#4 HEA 18 5197 220P 100V 2%CAP T&R RAD CER.2"NPO 1 4607 1/8W 39R 2%FLAME PROOF T&R RES 16 8761 6-32 X 1/2 PAN PHIL MS ZINC CLEAR 64 5412 220P 100V 10%CAP T&R BEAD NPO 13 4899 1/4W 39R 5% T&R RES 6 8806 6-32 X 1/2 PAN PH TAPTITE SJ500 2 5417 330P 50V 10%CAP T&R BEAD NPO 2 4811 1/4W 68R 5% T&R RES 2 8837 6-32 X 1/2 ROUND PH MS SJ500 1 5201 470P 100V 5%CAP T&R RAD CER.2"NPO 2 4590 1/8W 100R0 1%FLAME PROOF T&R RES 4 8824 8-32 X 5/16 PAN QUAD TAPTITE SJ500 2 5416 470P 50V 10%CAP T&R BEAD NPO 2 4859 1/4W 150R 5% T&R RES 4 8869 8-18 X 1/2 THRD CUTTING FOR PLASTIC 4 5422 __1N 50V 10%CAP T&R BEAD NPO 2 6201 1/4W 200R 1%FLAME PROOF T&R RES 6 8999 8-32 X 5/8 PAN PH TAPTITE SJ500 17 5273 __1N5 200V 5%CAP T&R RAD CER.2"NPO 2 4645 1/8W 220R0 1%FLAME PROOF T&R RES 4 8719 8-32 X 3/4 FILLISTER PHIL MS JS500 2 5427 __2N2 500V 10%CAP T&R RAD CER.2" YB 6 4857 1/4W 220R 5% T&R RES 4 8815 8-32 X 3/4 PAN PH TAPTITE SJ500 5 5209 __4N7 250V 5%CAP T&R RADIAL.2"FILM 2 4977 1/4W 220R 5%MINI T&R RES 7 8809 10-32 X 1/4 PAN PH TAPTITE SJ500 4 6451 __4N7 250V 20%CAP AC Y ONLY RAD10MM 1 4606 1/8W 249R 2%FLAME PROOF T&R RES 8 8749 10-32 X 1/2 QDX PH TAPTITE JS500 2 5834 _10N 250V 20%CAP RAD POLYFILM BULK 2 4867 1/4W 270R 5% T&R RES 4 8731 10-16 X 5/8 TYPE B HEX W/SLOT JS500 12 5210 _22N 100V 10%CAP T&R RADIAL.2"FILM 11 4855 1/4W 330R 5% T&R RES 2 8736 5/16-18X2-3/4 GRD 5 HEX BOLT JS500 1 6435 _22N 275V 20%CAP AC X2 RAD BLK15MM 2 4821 1/4W 470R 5% T&R RES 4 8663 11/64 NYLON SPACER (MICRO PLASTIC) 66 5308 _47N 50V 10%CAP T&R BEAD X7R 2 4980 1/4W 470R 5%MINI T&R RES 5 8629 10-32 X 1/4 SPACER PHENOLIC 8 5226 _68N 100V 5%CAP T&R RADIAL.2"FILM 4 4891 1/4W 620R 5% T&R RES 2 3746 21/64 X .250 OD #6 SPACER ALUMINUM 2 5228 100N 100V 5%CAP T&R RADIAL.2"FILM 3 4823 1/4W 1K 5% T&R RES 6 3751 SNAP IN 5/16 SPACER RICHCO 3 5314 100N 50V 10%CAP T&R BEAD X7R 4 4981 1/4W 1K 5%MINI T&R RES 6 3739 CUSTOM .4 LED SPACER 6 5229 150N 63V 10%CAP T&R RADIAL.2"FILM 4 4854 1/4W 1K2 5% T&R RES 1 3743 SNAP ON 0.5" SPACER RICHCO 10 5231 220N 63V 10%CAP T&R RADIAL.2"FILM 2 4718 5.0W 1K5 5% BLK RES 4 3859 1/2 PLASTIC HEX SPACER #4 2 5882 220N 250V 10%CAP RAD POLYFILM BULK 4 4988 1/4W 1K5 5%MINI T&R RES 6 3858 3/4 PLASTIC HEX SPACER #4 4 5255 __1U 63V 20%CAP T&R RADIAL ELE.2" 3 4791 1/4W 1K54 1% T&T RES 4 8667 SHOULDER WASHER SWS-229 LENGTH 1/8 4 5259 __4U7 63V 20%CAP T&R RADIAL ELE.2" 6 4683 1.0W 1K8 5% T&R RES 2 8818 3/4 OD X 5/16 ID X .08 THICK WASHER 2 5281 _10U 16V 20%CAP NONPOLAR T&R .2" 2 4808 1/4W 2K 5% T&R RES 6 3511 #6 FLAT WASHER NYLON 5 5629 _10U 160V 20%CAP RADIAL ELECT BULK 4 4847 1/4W 2K2 5% T&R RES 2 8491 #10 SPLIT LOCK WASHER BO 17 5945 _10U 63V 20%CAP T&R RADIAL ELECTR 2 4804 1/4W 3K 5% T&R RES 4 8850 #10 INT TOOTH LOCKWASHER BO 4 5260 _22U 50V 20%CAP T&R RADIAL ELE.2" 10 6124 1/4W 3K 5%MINI T&R RES 2 3502 NYLON FLAT WASHER OD.158ID.110H.070 2 5961 _33U 16V 20%CAP NONPOLAR T&R RAD 8 4826 1/4W 3K3 5% T&R RES 4 3436 DPDT PUSH SW PCMT H BREAK B4 MAKE 3 5267 100U 25V 20%CAP T&R RADIAL ELE.2" 3 4756 1/4W 4K120 0.1% *** T&R RES 2 3587 DPDT ROKR SW QUIK 250" AC/PWR IEC65 1 5630 330U 25V 20%CAP RADIAL ELECT BULK 6 4827 1/4W 4K7 5% T&R RES 8 3705 4P3T SLID SW PCMT H 1 5621 470U 63V 20%CAP RADIAL ELECT BULK 4 4982 1/4W 4K7 5%MINI T&R RES 6 3417 PC SCREW TERMINAL PC MOUNT 1 5618 470U 25V 20%CAP RADIAL ELECT BULK 1 4887 1/4W 7K5 5% T&R RES 5 7584 SQUARE-CUT O RING FOR AP AIR FILTER 1 5895 6800U 63V 20%CAP RADIAL ELECT BULK 16 4663 1/2W 8K2 5% T&R RES 2 8432 AP SERIES AIR GRILL 1 4520 10K TRIM POT (ENCLOSED) 2 4990 1/4W 8K2 5%MINI T&R RES 2 1196 AP4020 T?RD 1 4390 _10K AUDIO DETENT STYLE"P22"16MM 2 4762 1/4W 9K760 0.1% *** T&R RES 8 = critical conponents

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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 02 20 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 AP4020s 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 M1126) 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 M1127. 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 8.1 volts peak (at the output of U201) to approximately 70v peak, which is required to drive the current amplifier section. The current amplifier provides the current required for the 70v peak signal to drive 1200 watts into 2 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 M1126. 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.