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Low Frequency Channel Check

• Set the audio generator to 300Hz 775mVRMS (0dB) sinusoidal signal.
• Connect the CH2 probe tip to D22 cathode and set its sensitivity at 20V/div.

LOW RAIL VOLTAGE AMPLIFICATION 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
ampliﬁ er 2nd stage input R58 side C28). If there is a distortion read the section ADVICES.

HIGH RAIL VOLTAGE AMPLIFICATION TEST:

•

When the output signal (Positive half-wave) is less than 34Vp the voltage on D22 cathode

must remain constant at 40V, when the output signal exceeds 34Vp the voltage must follow
the output signal with 6V offset (see Fig.2 Trace B), to check the negative high rail connect
the probe to D26 anode (see Fig.2 Trace C).

LOAD CURRENT TEST:

• Connect the 4Ω 500W load on the output and repeat the LOW RAIL and HIGH RAIL te-
sts.

LIMITER CHECK:

• Increase the input signal of 10 dB and verify the output voltage and wave shape remain
constant.

BIAS ADJUSTMENT:

• With resistive load connected wait until the temperature reach 50°c.
• Set the level at zero, connect the Multimeter across the resistors R60, then adjust VR1
trimmer to read 6±0.1mVdc.

BANDWIDTH CHECK:

• Disconnect the load. Set the generator at -10dB, sweeping the generator frequency from
10Hz to 10kHz the level changes accordingly Figure5 (1a).

OFFSET SENSOR CHECK:

• Set the Variac to zero voltage output, disconnect resistive load from the ampliﬁ er output,
connect temporarily (by means of a suitable conductor wire) CN1 pin 4 (+15Vdc) to R72
side RL1, the protection circuitry (Q14,15,16) 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 CN1 pin 5), the protection circuitry must open the relay
again.

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 1mV.

High Frequency Channel Check

•  Verify, with the Multimeter, the insulation between the heatsink and the TDA7294 case.
•  Set the audio generator to 5KHz 775mVRMS (0dB) sinusoidal signal.
•  Connect the CH2 probe tip to R260 side IC202 (HF PWR out) and set its sensitivity at
20V/div. 200µS/div.

VOLTAGE AMPLIFICATION TEST:

• Increase slowly the Variac. The channel output signals must be symmetrical respect the
GND without visible distortion and oscillation. If there is a distortion replace the TDA7294.

LOAD CURRENT TEST:

• Connect the 8Ω 500W load on the output and repeat the test.

LIMITER CHECK:

• Increase the input signal of 10 dB and verify the output voltage and wave shape remain
constant.

BANDWIDTH CHECK:

• Disconnect the load. Set the generator at -10dB, sweeping the generator frequency from
10Hz to 10kHz the level changes accordingly Figure 5 (1b).

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 1mV.

H350SA H400SA CHECKING & ADJUSTMENTS

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

Technical Specifications

Dimensions: .....................H350SA (WxHxD) ................................. 475x555x520mm
.......................................H400SA (WxHxD) ................................. 625x540x545mm
Weight: ............................H350SA .............................................. 35.6Kg
Weight: ............................H400SA .............................................. 43Kg
Power Requirements: .........(230Vac±10% 50Hz) ............................ 350VA
.......................................(115Vac±10% 50/60Hz) ....................... 350VA
Output Power*: .................H350SA (6

) ....................................... 250W

.......................................H400SA (4

) ....................................... 350W

Max.Undistorted Out*: .......H350SA (6

) ....................................... 105Vpp

.......................................H400SA (4

) ....................................... 105Vpp

Sensitivity: .......................H350SA (1W/1m) ................................. 96.2dB

SPL

.......................................H400SA (1W/1m) ................................. 95.5dB

SPL

Max SPL: ..........................H350SA (continuous) ............................ 120dB

SPL

.......................................H350SA (peak) .................................... 123dB

SPL

.......................................H400SA (continuous) ............................ 122dB

SPL

.......................................H400SA (peak) .................................... 125dB

SPL

Frequency Response: .........H350SA (ampliﬁ er+speaker) .................. 38Hz÷300Hz
.......................................H400SA (ampliﬁ er+speaker) .................. 32Hz÷300Hz
.......................................(only ampliﬁ er -3dB)............................. 10Hz÷10KHz
Input Sensitivity: ...............(0dB) .................................................. 0.775V

RMS

Input Impedance: ..............(balanced) ........................................... 30K

.......................................(unbalanced) ....................................... 15K

Voltage Gain: .............................................................................. 33.5±1dB
IMD: ................................(SMPTE 60Hz/7KHz 4:1)........................ <0.1%
THD: ...............................(THD+N) ............................................. <0.1%
S/N Ratio: ........................(unweighted) ....................................... >100dB
*Note: measured with the limiter enabled.

Remarks

• The power supply utilizes a dual bipolar DC rail conﬁ guration with low and high voltages;
one positive and one negative low rail (+/-Vcc1) and one positive and one negative high rail
(+/-Vcc2).

Setup

•  Connect the Variac between the mains and the ampliﬁ er and set it at zero voltage.
•  Turn full clockwise the LEVEL and X-OVER potentiometers.
•  Connect the audio generator to the channel R input and set it to 150Hz 775mVRMS (0dB)
sinusoidal signal.
•  Place the temperature sensor between heatsink and the PTC (R59).
•  Connect the CH1 scope GND clip to CN2 pin 6 (SGND terminal) and the probe tip to R72
side RL1 (PWR out), set its sensitivity at 20V/div. 10mS/div.
•  Connect the CH2 probe tip to D25 cathode and set its sensitivity at 20V/div.
•  The load resistor is disconnected.
•  The procedures that follow must be executed subsequently in the order speciﬁ ed.

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=102±2Vac
  F3-F4=60±1.5Vac.
•  Re-set the Variac at zero voltage, turn off the ampliﬁ er and put the fuses back on its
holders.
•  Set up the Variac slowly monitoring the Outputs with the oscilloscope CH1 connected,
starts from 2/3 of nominal mains voltage it should display the sinusoidal input signal ampli-
ﬁ ed with no distortions, if a distortion occur check the AMPLIFIER board as suggested in the
ADVICES section.
•  If the protection trips, turn off the ampliﬁ er, wait some minutes and disconnect the
supplies from the ampliﬁ er module (CN2, CN3 on AMPLIFIER board), continue to check the
supplies.
•  Finally verify the DC supplies on SUPPLY board:

CN2 pin 5 (+Vcc2)

=+71±2Vdc

CN3 pin 1 (+Vcc1)

=+42±1.5Vdc

CN3 pin 5-6 (-Vcc1)

=-42±1.5Vdc

CN3 pin 4 (-Vcc2)

=-71±2Vdc

CN2 pin 3

=+15±1Vdc

CN2 pin 2

=-15±1Vdc

•

If one or more voltages don’t correspond, check the rectiﬁ ers, capacitors and transformers

disconnecting them from circuitry, refer to schematics.

Channels Check

• Verify, with the Multimeter, the insulation between the heatsink and the transistors col-
lectors.
• Verify, with the Multimeter, the PTC resistor value (R59), it must be between 50Ω and
200Ω.

INITIAL TEST:

HIGH RAIL CHECK:

•

When the output signal (Positive half-wave) is less than 34Vp the voltage on D25 cathode

must remain constant at 40V, when the output signal exceeds 40Vp the voltage must follow
the output signal with 6V offset (see Fig.2 Trace B), to check the negative high rail connect
the probe to D26 anode (see Fig.2 Trace C).

LOAD CURRENT TEST:

• Connect the 4Ω 500W load on the output and repeat the INITIAL and HIGH RAIL che-
cks.

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
ampliﬁ er 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 ampliﬁ er output signal is 50±2Vp, increasing the input level
the output signal must keep the same level, this is due to the limiter-compression circuitry
(IC2, DL1, IC1).

BIAS ADJUSTMENT:

• With the 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 15±0.1mVdc.

BANDWIDTH CHECK:

• The bandwidth of the ampliﬁ er board only is linear within the audio range (20Hz-20kHz),
but in this case is limited by the X-OVER circuitry on CONTROLS & CROSSOVER board.
• Figure 4 and 5 show the LowPass and the HighPass response, check the correspondance
with it for some frequency values (50,100,150,300 for example).

OFFSET SENSOR CHECK:

• Set the Variac to zero voltage output, disconnect resistive load from the ampliﬁ er 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:

• Disconnect the audio generator and short the input (pin 1,2,3 of XLR socket shorted) the
output signal (noise) must be less than 1mV.

Advices

•  If you have determinate 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.
• 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 low rail.
•

If the positive cycle appears distorted, you can assume that the problem is in the circuitry

of the negative low rail.
• If the high rails appear distorted or are not modulating as shown in ﬁ gure, then the
problem probably exists somewhere in the circuitry of the respective (+ or -) defective high
rail. Refer to the schematics.

Reliability Check

Before reassembling the ampliﬁ er and before deliver it to the user, it is a goal verify its re-
liability with the following checks:
• Switch off the ampliﬁ er, or leaving it switched on but operating with greatest caution,
carefully shake the boards and connections inside it using an insulated tool (for example
the handle of a screwdriver) to ﬁ nd wrong contacts and so on.
• Turn on the ampliﬁ er and verify that it operates correctly.

Burn in Check

• Connect the appropriate load resistor to the output and a noise signal generator to the
input, set it to C or A weighted pink noise with a 4:1 (12dB) of crest factor and 0dB peak
level.
• Leave the ampliﬁ er switched on at least 2 hour and ﬁ nally check its correct functionality
after the test.