Generalmusic AMP 4, AMP 8, AMP 12 Service Manual
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Index
Soldering point.
Male connector.
Female connector.
M/F faston connector.
Test point.
Supply voltage.
Logic supply ground.
Analog supply ground.
Chassis ground.
Earth ground.
Flag joined with one or more flags
GENERALMUSIC S.p.A. Sales Division: 47842 S.Giovanni in Marignano (RN) ITALY - Via delle Rose, 12 - tel. 0541/959511 - fax 0541/957404
GENERALMUSIC on the NET: http://www.generalmusic.com
Technical Specifications, Introduction, Test Procedures & Adjustments
2
Block Diagram
3
Layout & Assembly AMP4, AMP8
5
6
Schematics
Layout & Assembly AMP12, Spare Part List
4
SERVICE MANUAL
CODE: 270231
Warnings
with the same signal name inscribed.
Address
ATTENTION
Observe precautions when handling electrostatic sensitive devices.
Notice
Service must be carried out by qualified personnel only.Any tampering carried out by unqualified personnel during the guarantee period
will forfeit the right to guarantee.
For a correct operation of the instrument, after having switched off, be careful to wait at least 3 seconds before switching on again.
To improve the device's specifications, the schematic diagrams may be subject to change without prior notice.
All components marked by this symbol have special safety characteristics, when replacing any of these components use only
manufacturer's specified parts.
The (µ) micro symbol of capacitance value is substituted by U.
The (
Ω
) omega symbol of resistance value is substituted by E.
The electrolytic capacitors are 25Vdc rated voltage unless otherwise specified.
All resistors are 1/8
Ω
unless otherwise specified.
All switches shown in the "OFF" position. All DC voltages measured to ground with a voltmeter 20KOhm/V.
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TECHNICAL SPECIFICATIONSTECHNICAL SPECIFICATIONS
TECHNICAL SPECIFICATIONSTECHNICAL SPECIFICATIONS
TECHNICAL SPECIFICATIONS
Dimensions(WxHxD): AMP4 483x88x442mm (2U)
AMP8 483x88x442mm (2U)
AMP12 483x132x442mm (3U)
Weight: AMP4 12.5Kg
AMP8 15Kg
AMP12 18.5Kg
Power Requirements: (230Vac±10% 50Hz)
AMP4 540VA
AMP8 1100VA
AMP12 2000VA
Output Power EIA: (4Ω, 1KHz, 1% THD, both channels)
AMP4 2x 235Watts
AMP8 2x 424Watts
AMP12 2x 562Watts
Max. Undistorted Out: (4Ω, 1KHz, 1% THD, both channels)
AMP4 124Vpp
AMP8 164Vpp
AMP12 190Vpp
Input Sensitivity: (0dB) 0.775Vrms
Input Impedance: (balanced) 20KΩ
(unbalanced) 10KΩ
Voltage Gain: AMP4 31±0.5dB
AMP8 33±0.5dB
AMP12 35±0.5dB
Slew Rate: 20V/µS
Damping Factor: (8Ω both channels) >200
Frequency Response (20Hz÷20KHz) 0,-1dB
IMD: <0.1%
THD: (THD+N) <0.1%
S/N Ratio: >105dB
Crosstalk: (1KHz) >80dB
TEST PROCEDURES & ADJUSTMENTSTEST PROCEDURES & ADJUSTMENTS
TEST PROCEDURES & ADJUSTMENTSTEST PROCEDURES & ADJUSTMENTS
TEST PROCEDURES & ADJUSTMENTS
PrecautionPrecaution
PrecautionPrecaution
Precaution
➭ To prevent short circuit during any test,
the oscilloscope must bethe oscilloscope must be
the oscilloscope must bethe oscilloscope must be
the oscilloscope must be
EARTH insulatedEARTH insulated
EARTH insulatedEARTH insulated
EARTH insulated, this occurs because some test require to connect its
probe to the amplifier output, noncompliance may cause damages to
oscilloscope inputs circuitry.
➭ Read these notes entirely before proceeding to any operation. These
notes are not comprehensive of all damages that possibly occur, but
includes some specifically advices, checks and adjustments relative to
this amplifier.
RemarksRemarks
RemarksRemarks
Remarks
➭ The output circuit is an AB class amplifier with the peculiarity of transistor
collectors connected directly to chassis ground, this permit a major
temperature stability and dissipated power efficiency. The final stage is
oversized to obtain high dynamic and high current with hard loads. To
use the amplifier in bridge mode the power supply is realized with two DC
rails each one for its channel.
➭ All components of channel 1 are marked by A suffix as many all compo-
nents of channel 2 are marked by B suffix.
Visual CheckVisual Check
Visual CheckVisual Check
Visual Check
➭ Use compressed air to clear dust in the amplifier chassis.
➭ Before proceed to supply the amplifier check visually the internal assem-
bly, if appears an evident damage find the most possible reasons that
cause it.
➭ Check the wiring cables for possible interruptions or shorts.
➭ If the damage has burnt a printed circuit board don’t try to repair it,
replace with a new one.
Test InstrumentsTest Instruments
Test InstrumentsTest Instruments
Test Instruments
➭ Audio Generator
➭ Dual Trace Oscilloscope (ch.1 named as A, ch.2 as B)
➭ Digital Multimeter
➭ 4Ω 700W, 100Ω 100W resistors
➭ Variac (0÷250Vac)
SetupSetup
SetupSetup
Setup
➭ Connect the Variac between the mains and the amplifier and set it at zero
voltage.
➭ Set the amplifier in PARALLEL MODE and turn full clockwise the LEVEL
potentiometers.
➭ Connect the audio generator to the channel inputs and set it to 1KHz
775mV
RMS
(0dB) sinusoidal signal.
➭ Switch off the LIMITER from rear panel.
➭ The procedures that follow must be executed subsequently in the order
specified.
Supply CheckSupply Check
Supply CheckSupply Check
Supply Check
➭ Remove the transformer secondary fuses (located on SUPPLY board),
set the Variac to the nominal mains voltage, check with the Multimeter
the AC supply voltages:
AMP4: F601-F602=91±5Vac
AMP8: F601-F602=120±6Vac.
AMP12: F601-F602=144±7Vac.
➭ Reset the Variac at zero voltage, turn off the amplifier and put the fuses
back on its holders.
➭ Connect the oscilloscope probes A and B to the channel outputs before
output relays (R151), and its ground clip to the heatsink set both to 20V/
div. 200µS/div.
➭ Set up the Variac slowly monitoring the Outputs with the oscilloscope
traces A/B, these should display the sinusoidal input signal amplified with
no distortions, if a distortion occur check the POWER boards as suggested in the ADVICES section.
➭ If the protection trips, turn off the amplifier, wait some minutes and
disconnect the supplies (W108 on SUPPLY board) from the channel goes
in protect mode, continue to check the supplies.
➭ Finally verify the DC supplies for each channel on SUPPLY board:
AMP4:
W108 pin 1-2 (+Vcc) =+62±2Vdc
W108 pin 3-4 (-Vcc) =-62±2Vdc
AMP8:
W108 pin 1-2 (+Vcc) =+82±3Vdc
W108 pin 3-4 (-Vcc) =-82±3Vdc
AMP12:
W108 pin 1-2 (+Vcc) =+98±4Vdc
W108 pin 3-4 (-Vcc) =-98±4Vdc
and on MAIN board:
Q130 pin 3 =+15±0.5Vdc
Q131 pin 3 =-15±0.5Vdc
Note: you can measure with the multimeter only the supplies with the
respective channel attached, in effect the supply capacitors are mounted
on MAIN board.
➭ If one or more voltages don’t correspond, check the rectifiers, capacitors
and transformers disconnecting them from circuitry, refer to schematics.
➭ Reset the Variac at zero voltage.
Channels CheckChannels Check
Channels CheckChannels Check
Channels Check
➭ The channel 1 is on the right and channel 2 is on the left of the heatsink.
➭ These procedures are intended for one channel at a time, repeat these
operation for the other channel.
➭
SETUP:SETUP:
SETUP:SETUP:
SETUP:
Connect the ch.A scope GND clip to the chassis or other GND point.
Connect the ch.A probe tip to R151(AMP output).
Connect the ch.B probe tip to IC2 pin 1 (set it at 1V/div.).
Set the amplifier in STEREO MODE and connect the signal generator to
the channel under test.
Set the LEVEL potentiometers full clockwise.
The load resistor is disconnected.
➭
THERMAL PROTECTION CHECK:THERMAL PROTECTION CHECK:
THERMAL PROTECTION CHECK:THERMAL PROTECTION CHECK:
THERMAL PROTECTION CHECK:
Verify, with the Multimeter, if TSW1 is closed TSW2 is opened, and if
NTC1 resistor value must be between 25Ω and 30Ω.
➭
INITIAL TEST:INITIAL TEST:
INITIAL TEST:INITIAL TEST:
INITIAL TEST:
Increase slowly the Variac. The channel output signals must be symmetrical respect the GND without visible distortion and oscillation, trace CH1
shows the output, trace B shows the signal after amplifier input stages.
If there is a distortion on trace A read the section ADVICES and proceed
to check the other channel.
If the signal on trace B doesn't appear correctly check IC1, LEVEL potentiometer, IC2 and their circuitry, see schematics.
➭
SIGNAL/CLIP SENSOR CHECK:SIGNAL/CLIP SENSOR CHECK:
SIGNAL/CLIP SENSOR CHECK:SIGNAL/CLIP SENSOR CHECK:
SIGNAL/CLIP SENSOR CHECK:
Set the LEVEL pot to minimum, set the ch.A scope timebase at 1V/div.
200µS/div., then increase the level and check the SIGNAL/CLIP led
activity: it must turn on (green light) when the amplifier output is higher
than 3Vp.
Set the scope at 20V/div. and increase the level, check the clip led: it
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