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TEST PROCEDURES & ADJUSTMENTSTEST PROCEDURES & ADJUSTMENTS

TEST PROCEDURES & ADJUSTMENTS

These procedures are relative to the ACTIVE versions (amplified loudspeakers)

only.

PrecautionPrecaution

Precaution

➭ To prevent short circuit during any test,

the oscilloscope must be EARTHthe oscilloscope must be EARTH

the oscilloscope must be EARTH

insulatedinsulated

insulated, this occurs because some test require to connect its probe to the

amplifier output, non-compliance may cause damages to oscilloscope inputs

circuitry.

➭ Before removing or installing any modules and connectors,

disconnect thedisconnect the

disconnect the

amplifier from AC MAINSamplifier from AC MAINS

amplifier from AC MAINS and measure the DC supply voltages across each

of the power suppliy capacitors. If your measurement on any of the caps is

greater than 10Vdc, connect a 100Ω 10W resistor across the applicable caps

to discharge them for your safety. Remember to remove the discharge

resistor immediately after discharging caps.

Do not power up the amplifierDo not power up the amplifier

Do not power up the amplifier

with the discharge resistor connectedwith the discharge resistor connected

with the discharge resistor connected.

➭ 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 amplified speaker.

➭

Do not check the amplifier with the speaker connected use only anDo not check the amplifier with the speaker connected use only an

Do not check the amplifier with the speaker connected use only an

appropriate load resistor.appropriate load resistor.

appropriate load resistor.

RemarksRemarks

Remarks

➭ The power supply utilizes a dual bipolar DC rail configuration with low and

high voltages; one positive and one negative low rail (+/-Vcc1) and one

positive and one negative high rail (+/-Vcc2).

Visual CheckVisual Check

Visual Check

➭ Check the speakers for any damaging (cone-breaking, interruption or so).

➭ Before proceed to supply the amplifier check visually the internal assembly,

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 Instruments

➭ Audio Generator

➭ Dual Trace Oscilloscope

➭ Digital Multimeter

➭ Temperature Meter

➭ 4Ω 500W, 100Ω 10W resistors

➭ Variac (0÷250Vac)

AV12A Amplified LoudspeakerAV12A Amplified Loudspeaker

AV12A Amplified Loudspeaker

The following adjustment and notes are relative to this model only.

TECHNICAL SPECIFICATIONSTECHNICAL SPECIFICATIONS

TECHNICAL SPECIFICATIONS

Dimensions: (WxHxD) 436x616x420mm

Weight: 28,5Kg

Power Requirements: (230Vac±10% 50Hz) 210VA

(115Vac±10% 50/60Hz) 210VA

Output Power*: (4Ω) 200W

Max. Undistorted Out*: (4Ω) 80Vpp

Sensitivity: (1W/1m) 97dB

SPL

Max SPL: (continuous) 120dB

SPL

(peak) 123dB

SPL

Frequency Response (amplifier+speaker) 70Hz÷20kHz

(only amplifier -3dB) 10Hz÷60kHz

Input Sensitivity: (0dB) 0.775V

RMS

Input Impedance: (balanced) 30KΩ

(unbalanced) 15KΩ

Voltage Gain: 31±1dB

IMD: (SMPTE 60Hz/7KHz 4:1) <0.1%

THD: (THD+N) <0.1%

S/N Ratio: (unweighted) >100dB

*Note: measured with the limiter deactivated.

SetupSetup

Setup

➭ Connect the Variac between the mains and the amplifier and set it at zero

voltage.

➭ Turn full clockwise the LEVEL potentiometer.

➭ Connect the audio generator to the channel input and set it to 1kHz 775mV

RMS

(0dB) sinusoidal signal.

➭ Place the temperature sensor between heatsink and the PTC (R59).

➭ The procedures that follow must be executed subsequently in the order

specified.

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:

F1-F2=76±2Vac

F3-F4=42±1.5Vac.

➭ Re-set the Variac at zero voltage, turn off the amplifier and put the fuses back

on its holders.

➭ Connect the oscilloscope probe CH1 to the channel output, before RL1, set

it to 20V/div. 1mS/div.

➭ Set up the Variac slowly monitoring the Outputs with the oscilloscope CH1

connected, it should display the sinusoidal input signal amplified with no

distortions, if a distortion occur check the AMPLIFIER board as suggested in

the ADVICES section.

➭ If the protection trips, turn off the amplifier, wait some minutes and disconnect

the supplies from the amplifier module (CN2, CN3 on AMPLIFIER board),

continue to check the supplies.

➭ Finally verify the DC supplies on SUPPLY board:

CN2 pin 5 (+Vcc2) =+54±2Vdc

CN3 pin 1 (+Vcc1) =+29±1.5Vdc

CN3 pin 5-6 (-Vcc1) =-29±1.5Vdc

CN3 pin 4 (-Vcc2) =-54±2Vdc

CN2 pin 3 =+15±1Vdc

CN2 pin 2 =-15±1Vdc

➭ If one or more voltages don’t correspond, check the rectifiers, capacitors and

transformers disconnecting them from circuitry, refer to schematics.

Channels CheckChannels Check

Channels Check

➭ Verify, with the Multimeter, the insulation between the heatsink and the

transistors collectors.

➭ Verify, with the Multimeter, the PTC resistor value (R59), it must be between

50Ω and 200Ω.

➭

SETUP:SETUP:

SETUP:

Connect the CH1 scope GND clip to CN2 pin 6 (SGND terminal).

Connect the CH1 probe tip to CN3 pin 2 or 3 (PWR out).

Connect the CH2 probe tip to D20 anode and set its sensitivity at 5V/div.

Set the LEVEL potentiometer full clockwise.

The load resistor is disconnected.

➭

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 as shown in

Fig.1

Trace A

(

Trace B

shown the amplifier 2nd stage input). If there is a distortion

read the section ADVICES.

➭

HIGH RAIL CHECK:HIGH RAIL CHECK:

HIGH RAIL CHECK:

Connect the CH2 probe tip to D25 cathode and set its sensitivity at 20V/div.

When the output signal (Positive half-wave) is less than 22Vp the voltage on

D25 cathode must remain constant at 28V, when the output signal exceeds

22Vp the voltage must follow the output signal with 6V offset (see

Fig.2 Trace

), to check the negative high rail connect the probe to D26 anode (see

Fig.2

Trace C

➭ Connect the 4Ω 500W load on the output and repeat the INITIAL and HIGH

RAIL checks.

➭

GAIN ADJUSTMENT:GAIN ADJUSTMENT:

GAIN ADJUSTMENT:

Set the generator level at -10dB (0,245V

RMS

), adjust the trimmer VR2 on

INPUTS board to obtain an output level of 14.5Vp (10V

RMS

➭ Re-set the generator level at 0dB (0,775V

RMS

➭

SIGN/COMP SENSOR CHECK:SIGN/COMP SENSOR CHECK:

SIGN/COMP SENSOR CHECK:

Set the LEVEL pot to minimum, set the scope timebase at 1V/div. 1mS/div.,

then increase the level and check the SIGNAL/COMP led activity: it must turn

on (green light) when the amplifier output is higher than 1Vp.

Set the scope at 20V/div. and increase the level, check the led: it must change

from green to red colour when the amplifier output signal is 36±2Vp, increas-

ing the input level the output signal must keep the same level, this is due to

the limiter-compression circuitry (IC2, DL1, IC1).

➭

BIAS ADJUSTMENT:BIAS ADJUSTMENT:

BIAS ADJUSTMENT:

With resistive load connected wait until the temperature reach 50°c.

Set the generator level at zero, connect the Multimeter across

the resistors

R60, then adjust VR1 trimmer to read 13±0.5mVdc.

➭

BANDWIDTH CHECK:BANDWIDTH CHECK:

BANDWIDTH CHECK:

Switch alternatively the generator frequency to 100Hz and 10kHz, no level

changes must be detectable respect 1kHz.

➭

OFFSET SENSOR CHECK:OFFSET SENSOR CHECK:

OFFSET SENSOR CHECK:

Set the Variac to zero voltage output, disconnect resistive load from the

amplifier output, connect temporarily (by means of a suitable conductor wire)

CN2 pin 3 (+15Vdc) to R72 side RL1, the protection circuitry (TR14,15,16)

detect the DC voltage and open the output relay (RL1) within 3 seconds

approx.

Remove the connection, wait until the relay switch on and after some seconds

repeat the check with -15Vdc (available on CN2 pin 2), the protection circuitry

must open the relay again.

➭

SIGNAL TO NOISE RATIO CHECK:SIGNAL TO NOISE RATIO CHECK:

SIGNAL TO NOISE RATIO CHECK:

Brand	LEM
Model	Avalon AV12-4
Category	Speakers
Language	English

LEM Avalon AV12-4 User Manual

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LEM Avalon AV12-4 Specifications

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