Generalmusic AMP 4 User 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
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TechnicalSpecifications,Introduction,TestProcedures&Adjustments
2
BlockDiagram
3
Layout&AssemblyAMP4,AMP8
5
6
Schematics
Layout&AssemblyAMP12,SparePartList
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: (8Ωboth 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
➭4Ω700W, 100Ω100W 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
775mVRMS (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 sug-
gested 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 25Ωand 30Ω.
➭INITIAL TEST:INITIAL TEST:
INITIAL TEST:INITIAL TEST:
INITIAL TEST:
Increase slowly the Variac. The channel output signals must be symmetri-
cal 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 poten-
tiometer, 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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must light at the amplifier output signal clipping.
➭LIMITER CHECK:LIMITER CHECK:
LIMITER CHECK:LIMITER CHECK:
LIMITER CHECK:
Switch on the LIMITER from rear panel: the signal clipping must disap-
pear and the clip led lights off.
Reset the LIMITER to off position.
➭BANDWIDTH CHECK:BANDWIDTH CHECK:
BANDWIDTH CHECK:BANDWIDTH CHECK:
BANDWIDTH CHECK:
Increase the generator level just below to clip, sweep the generator
frequency from 20Hz to 20KHz: the output level must have not detectable
level changes.
Reset the generator at 1KHz 775mVRMS (0dB) sinusoidal signal.
➭CHECK WITH LOAD ATTACHED:CHECK WITH LOAD ATTACHED:
CHECK WITH LOAD ATTACHED:CHECK WITH LOAD ATTACHED:
CHECK WITH LOAD ATTACHED:
Set the Variac at zero voltage, connect a 4Ω700W load and repeat the
previous tests.
➭CURRENT AND SHORT CIRCUIT SENSOR CHECK:CURRENT AND SHORT CIRCUIT SENSOR CHECK:
CURRENT AND SHORT CIRCUIT SENSOR CHECK:CURRENT AND SHORT CIRCUIT SENSOR CHECK:
CURRENT AND SHORT CIRCUIT SENSOR CHECK:
Set the LEVEL potentiometer at minimum.
Connect the scope ch.B GND clip at one of the emitter resistors, side
positive supply rail (R141 thru 145 or also R168,169), located on POWER
board.
Connect the scope ch.B probe tip at the same resistor side transistor
emitter.
Set the scope ch.B sensitivity to 0.2V/div.
Increase the input signal, the output current limiter must keep the emitter
voltages, both half channel, at 0.6Vp approx.
Temporarily short the amplifier output: the current limiter must keep the
emitter voltages, both half channel, at 0.2Vp approx.
Repeat this check for the negative rail connecting the scope ch.B at one
emitter resistor (R146 thru R150 or also R170,171).
If this test fail, check the Q102 (positive) and Q103 (negative) circuitries,
refer to schematics.
➭SIGNAL TO NOISE RATIO CHECKSIGNAL TO NOISE RATIO CHECK
SIGNAL TO NOISE RATIO CHECKSIGNAL TO NOISE RATIO CHECK
SIGNAL TO NOISE RATIO CHECK
Disconnect the audio generator and short the input (pin 1,2,3 of XLR
socket shorted) the output signal (noise) must be less than 2mV approx.
➭OFFSET SENSOR CHECK:OFFSET SENSOR CHECK:
OFFSET SENSOR CHECK:OFFSET SENSOR CHECK:
OFFSET SENSOR CHECK:
Set the Variac to zero voltage output.
Disconnect the amplifier load and the supply connection to MAIN board
(JK107, JK108), short temporarily pin 8 and 9 of JK107, turn on the
amplifier, connect temporarily (by means of a suitable conductor wire)
JK108 pin 7 to +15Vdc, the PROTECT led must turn on in 5 seconds
approx.
Remove the connection, wait until the leds turn off and after some sec-
onds repeat the check with -15Vdc, the led PROTECT must turn on
again.
AdvicesAdvices
AdvicesAdvices
Advices
➭Check the channels one at time to determine which is right (note: if you
have a spare power module that you know as right, use it).
➭If the input sinewave appears to be distorted during the negative cycle,
you can assume that the problem is located somewhere in the circuitry of
the positive rail.
If the positive cycle appears distorted, you can assume that the problem
is in the circuitry of the negative rail.
➭If you have determined that the problem is a short on a rail, you must
check the output transistors.
To determine which transistor devices are bad, use a soldering iron to lift
one leg of each emitter pin and measure the emitter-collector resistance
on each device. Unsolder and lift one leg of each base pin and check the
base-collector resistance of each transistor and replace any that measure
as a short.
If all the transistors are OK, unsolder and lift one leg of each diode and
check them.
Check the circuit board for open foil traces.
Use the Multimeter as Ohm-meter to check the resistors, particularly the
base and emitter resistors of damaged transistor.
TO92TO92
TO92TO92
TO92
2SC1815, 2SA10152SC1815, 2SA1015
2SC1815, 2SA10152SC1815, 2SA1015
2SC1815, 2SA1015
1=Emitter
2=Collector
3=Base
TO220TO220
TO220TO220
TO220
2SC2336, 2SA10062SC2336, 2SA1006
2SC2336, 2SA10062SC2336, 2SA1006
2SC2336, 2SA1006
1=Base
2=Collector
3=Emitter
4=Collector
TO264TO264
TO264TO264
TO264
2SC3281, 2SC4029, 2SA1302, 2SA15532SC3281, 2SC4029, 2SA1302, 2SA1553
2SC3281, 2SC4029, 2SA1302, 2SA15532SC3281, 2SC4029, 2SA1302, 2SA1553
2SC3281, 2SC4029, 2SA1302, 2SA1553
1=Base 2=Collector 3=Emitter

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GENERALMUSIC S.p.A. Italy SCHEMATIC DIAGRAM AMP 4
Layouts & Assembly
DRW: BOCCATO
APP: BODINI REV: 19-1-99
DISK: 70 PART: 1/1CKD: RICCI
DWG:
ALL RIGHTS ARE RESERVED, NO COPIES OR
REPRODUCE THIS DOCUMENT WITHOUT
WRITTEN CONSENT BY GENERALMUSIC.
GENERALMUSIC S.p.A. Italy SCHEMATIC DIAGRAM AMP 8
Layouts & Assembly
DRW: BOCCATO
APP: BODINI REV: 19-1-99
DISK: 70 PART: 1/1CKD: RICCI
DWG:
ALL RIGHTS ARE RESERVED, NO COPIES OR
REPRODUCE THIS DOCUMENT WITHOUT
WRITTEN CONSENT BY GENERALMUSIC.
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GENERALMUSIC S.p.A. Italy SCHEMATIC DIAGRAM AMP 12
Layouts & Assembly
DRW: BOCCATO
APP: BODINI REV: 19-1-99
DISK: 70 PART: 1/1CKD: RICCI
DWG:
ALL RIGHTS ARE RESERVED, NO COPIES OR
REPRODUCE THIS DOCUMENT WITHOUT
WRITTEN CONSENT BY GENERALMUSIC.
Spare Part ListSpare Part List
Spare Part ListSpare Part List
Spare Part List
Code Ref. Description
AccessoriesAccessories
AccessoriesAccessories
Accessories
277328 Owner’s Manual AMP-Series
AssemblyAssembly
AssemblyAssembly
Assembly
PHC667000 14 Front Panel (AMP4)
PHC667001 20 Front Panel (AMP8)
PHC667002 28 Front Panel (AMP12)
PHC667003 7 Knob
PHC177000 4 Handle
PHC120000 Screw for Handle
PHC238000 3 Transformer (AMP4)
PHC238001 16 Transformer (AMP8)
PHC238002 23 Transformer (AMP12)
PHC230000 1 070-20279-500-0 Mains Coil (AMP4)(AMP8)
PHC230001 21 070-20289-500-0 Mains Coil (AMP12)
110291 5 Power Switch
141200 12 Speakon Neutrik Socket
PHC110000 6 80x25mm 24Vdc Fan
PHC110001 24 120x25mm 24Vdc Fan
PHC110003 Thermal Switch A85-03PN6308
PHC110004 Thermal Switch B50-03PN6471
BoardsBoards
BoardsBoards
Boards
PHC768004PHC768004
PHC768004PHC768004
PHC768004 99
99
9Inputs BoardInputs Board
Inputs BoardInputs Board
Inputs Board
PHC768005PHC768005
PHC768005PHC768005
PHC768005 Controls Panel BoardControls Panel Board
Controls Panel BoardControls Panel Board
Controls Panel Board
PHC768006PHC768006
PHC768006PHC768006
PHC768006 Power-on Led BoardPower-on Led Board
Power-on Led BoardPower-on Led Board
Power-on Led Board
PHC768007PHC768007
PHC768007PHC768007
PHC768007 22
22
2Supply Board (AMP4)Supply Board (AMP4)
Supply Board (AMP4)Supply Board (AMP4)
Supply Board (AMP4)
PHC768008PHC768008
PHC768008PHC768008
PHC768008 1515
1515
15 Supply Board (AMP8)Supply Board (AMP8)
Supply Board (AMP8)Supply Board (AMP8)
Supply Board (AMP8)
PHC768009PHC768009
PHC768009PHC768009
PHC768009 2222
2222
22 Supply Board (AMP12)Supply Board (AMP12)
Supply Board (AMP12)Supply Board (AMP12)
Supply Board (AMP12)
PHC110005 * T5A 250V 6.3x32mm Fuse
PHC110006 * T7A 250V 6.3x32mm Fuse
PHC110006 * T8A 250V 6.3x32mm Fuse
110038 * T15A 250V 6.3x32mm Fuse
110062 * T20A 250V 6.3x32mm Fuse
PHC080003 * KBPC3506 35A 600V Rectifier Diode Bridge
PHC080004 * Ntc type N155P2R5L (AMP8)(AMP12)
PHC080005 * Ntc type N205P010L (AMP4)
PHC768010PHC768010
PHC768010PHC768010
PHC768010 88
88
8Main Board (AMP4)Main Board (AMP4)
Main Board (AMP4)Main Board (AMP4)
Main Board (AMP4)
PHC768011PHC768011
PHC768011PHC768011
PHC768011 1717
1717
17 Main Board (AMP8)Main Board (AMP8)
Main Board (AMP8)Main Board (AMP8)
Main Board (AMP8)
PHC768012PHC768012
PHC768012PHC768012
PHC768012 2525
2525
25 Main Board (AMP12)Main Board (AMP12)
Main Board (AMP12)Main Board (AMP12)
Main Board (AMP12)
PHC080006 * Ntc type TDC05A045L
PHC090000 * A1015GR TO92 LN Pnp Transistor
PHC090001 * C1815GR TO92 LN Npn Transistor
PHC090002 * A1006BQ TO220 Pnp Transistor
PHC090003 * C2336BQ TO220 Npn Transistor
PHC080001 * 1N4934 1A 100V Fast Rectifier Diode
PHC080002 * PB154M Rectifier Diode Bridge
PHC100000 * KF353 Dual J-Fet Operational Amplifier
PHC100001 * M5218 Dual LN Operational Amplifier
PHC100002 * HTVP873-G35-555 Analog Optoisolator
PHC110002 * Relay 24V / 2 Switch 5A 250V
PHC768013PHC768013
PHC768013PHC768013
PHC768013 10-1110-11
10-1110-11
10-11 Power Board (AMP4)Power Board (AMP4)
Power Board (AMP4)Power Board (AMP4)
Power Board (AMP4)
PHC768014PHC768014
PHC768014PHC768014
PHC768014 18-1918-19
18-1918-19
18-19 Power Board (AMP8)Power Board (AMP8)
Power Board (AMP8)Power Board (AMP8)
Power Board (AMP8)
PHC768015PHC768015
PHC768015PHC768015
PHC768015 26-2726-27
26-2726-27
26-27 Power Board (AMP12)Power Board (AMP12)
Power Board (AMP12)Power Board (AMP12)
Power Board (AMP12)
PHC080000 * 1N5404 3A 400V Rectifier Diode
PHC090004 * 2SA1302-O TO264 Pnp Transistor
PHC090005 * 2SC3281-O TO264 Npn Transistor
PHC090006 * 2SA1553-O TO264 Pnp Transistor
PHC090007 * 2SC4029-O TO264 Npn Transistor
Note:Note:
Note:Note:
Note:
Each spare part is single quantity unless otherwise specified.
Asterisk prefix explanation:
Omitted = First level spare part.
One asterisk = Second level, part of previous listed first level part.
Two asterisk = Third level, part of previous listed second level part.
Three asterisk = ............
Any request for not above mentioned part must encompass specific description including:
1) Model name,
2) Section name,
3) Module code,
4) Reference name,
5) Quantity number.
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1212
12
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2121
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2222
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2323
2323
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2525
25
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2727
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