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AUDIOPRO AP-3000 SERVICE MANUAL
M1012 “THE INPUT BOARD”
The input board processes the audio signal from the input jacks to the voltage amplifier board, (M1011).
Each channel consists of a balanced gain stage, defeatable bass boost filter, and a preemphasis filter network.
The balanced input, (XLR Jack) and unbalanced input (phone jack) are wired in parallel to the input of a balanced
operational amplifier, (U1). The gain of this stage is 1.6 (4dB) balanced and 1.6 (4dB) unbalanced. Resistors R1, R5
along with capacitors C1 and C2 form a radio interference elimination filter.
Switch S1 selects a flat or bass boosted frequency response. The bass boost filter provides a 20Hz high pass, high Q
filter response with a +4dB peak at 55Hz. The filter consists of a tee network on the input of U1A along with R9, R10,
R11, C5 and C6. The gain is 1 (0dB) in the passband, (above 100Hz).
Operational amplifier U3B is a high pass shelving filter with a +2dB shelf above 20KHz. This filter provides the pre-
emphasis required to obtain a flat frequency response (to 20KHz) on the power amplifier output at full power.
M1011 "VOLTAGE AMPLIFIERS AND SYSTEM CONTROL"
This board contains:
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Voltage amplifiers to drive the current amplifiers on the M1002 boards.
•
The front panel volume control circuitry.
•
The EMS control system with its associated circuits: Pre clipping and line current sensing heater circuits.
•
Clip and activity LED's. Driver circuitry for the amplifier disable relay (used during amplifier turn on, turn off,
thermal shutdown and current limiting).
Circuit Explanation:
Refer to the schematic of M1011 as the sections of the circuit are explained.
The audio signal enters the board from M1012 through connector MS4. The two channels are marked "L" and "R" for
left and right. The signals are to be considered as differential sources and therefore are marked as L+, L-,R+ and R-.
Since the left channel has the same topology as the right channel we will only look at the left channel.
The signal ("L+") at the terminal block (MS4) passes through the front panel level control (P1) and the desired level
enters the inverting input of U1.
Op amp U1 is an inverting amplifier with a set gain of 2.40 (7.6dB). Built around U1 is a dual purpose circuit controlled
by a voltage divider consisting of R15, R16, R17, R18, R19, R20 and R21. The voltage divider sets two reference
levels, (HDRM & CLP). Reference voltage levels vary with the voltage levels on the +/-100VDC supply rails. As the
amplifier?s output is loaded, the supply rails voltage decreases and so do the reference levels.
Transistors Q1, Q3 the surrounding resistors provide a pre-clipping function that tracks the supply rails through the
HDRM voltage reference and clips the audio signal at approximately 11.2V pk. The clip LED indicator circuit is
connected through D1 and D2 to the output of U1, The bases of Q2 and Q4 are connected to the “CLP” reference
voltage, and when the peak output voltage of U1 (+/-Vp) is enough to forward bias the transister junctions, Q2 or Q4
will trigger the clip led circuit (Q5), and eliminate the clip LED.
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 all three blades can be fully inserted to prevent
blade exposure. Precautions should be taken so that the grounding
scheme on the unit is not defeated.
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 RÉDUIRE LES RISQUE DE CHOC
ÉLECTRIQUE, N'ENLEVEZ PAS LE COUVERT (OU
LE PANNEAU ARRIÈRE).
NE CONTIENT AUCUNE
PIÈCE RÉPARABLE PAR L'UTILISATEUR.
CONSULTEZ UN TECHNICIEN
QUALIFIÉ 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.
Cordon d'alimentation:
Évitez d'endommager le cordon d'alimentation. N'UTILISEZ PAS
L'APPAREIL si le cordon d'alimentation est endommagé.
Service:
Consultez un technicien qualifié pour l'entretien de votre appareil.
IMPORTANT SAFETY INSTRUCTIONS
safe_v3.doc Version 3.5 Mar 98
