AttacK VRF1230 – AMLIFIER circuit diagram – adjustments

Preliminary Adjustments

Connect the amplifier to the 127V mains with lamp in series;

 Turn the ON / OFF switch and measure the DC voltages at the source:

 + Vref (pin 6 of the PRC board CNC6): 4.8Vdc @ 127Vac / 4Vdc @ 220Vac

 + 15Vdc: Pin 4 of the PRC board CNC6;

 -15Vdc: Pin 1 of the PRE plate CNC6

 + B and -B (CNC1 and CNC6 of PWR board): +/- 88Vdc @ 127Vac / +/- 74Vdc @ 220Vac;

Enter with 1KHz signal and check with the oscilloscope the signal at the output;

If everything is OK, remove the lamp;

Redo the voltage measurements, in 127Vac and also in 220Vac, as described in item 1.2;

Set the trim trimpot to the anti-clockwise position, POT3 (THRESHOLD);

Set Offset to POT7 (OFFSET) while keeping signal at input and volume all open. To monitor with the multimeter to get 0Vdc on Tp6. Select the smallest DC voltage range available on the multimeter used. After adjustment lock the trimpot with stained glass;

LED Testing:

Set the signal level to 0.8Vrms @ 1kHz. Check the operation of the signal LED and the limiter LED;

Short Circuit Testing:

 Set the signal level until the signal LED is lit;

Measuring the signal at the output, short-circuit the output of the amplifier. At this moment the signal will be cut;

 After the short test, test again, to see if everything is OK;

Frequency Response Test:

Plot the frequency response curve as described below:

NOTE: Use attenuated cable at 20dB

Enter Line Input with flat Equalization: "VRF1230-Flat" curve

Enter Line Input with Open Equalization: Curve "VRF1230-Open"

Enter MIC Input with closed Equalization: "VRF1230-Closed"

 Burn-in test:

If everything OK put in BURN-IN for 2 hours the maximum musical power on load of 4 ohms;

 Final Tests:

After BURN-IN, if no fault, check the limiter value (sinusoidal output voltage value in rms, according to item 3) with the amplifier well heated, if changed, readjust the POT LIMITER. After adjusted lock the trimpot with stained glass;

THD (Harmonic Distortion)

 Sine input signal 0.6 Vrms / 1kHz / 4 Ohms;

With Neutrik measure THD with 22Hz-22kHz enabled filter;

 The value must be less than 0.500%.

S / N (Signal to Noise Ratio)

 Sinusoidal input signal 0.6Vrms / 1kHz / 4 Ohms;

 With Neutrik put in LEVEL and select LEVEL REL (0dBref in SET REF) with 22Hz-22kHz filter enabled. After mute the neutrik;

 The value must be greater than 80dB.

Phase

 Check the phase between the input signal and the output signal.

 Monitor with an oscilloscope channel pin 2 of the input connector;

 Monitor with the other channel of the oscilloscope the amplifier output signal;

Both must be in phase.

 Check List:

Make sure all plates are securely fastened;

Check that the block is securely fastened;

Check if all the wiring connections between the boards are well made;

 Check if silicone has been placed on all capacitors and dissipators of the FNT board;

 Check if silicone has been inserted into all connectors (flat and flexible cables);

Check if all trimpots (offset and limiter) are sealed with stained glass;

 Check that the wiring is not touching any heat-sink;

 Check that the wiring of the block is secured with a well-formed plastic strap;

 Check that the XLR's external connectors are securely fastened;

 Check the grounding of pin 1 of the XLR connectors for the chassis;

 Check the paint (external) of the appliance for risk;