Sound Skulptor forums

Build help and troubleshooting => AB528 Microphone preamplifier => Topic started by: JPK on June 12, 2024, 05:15:00 PM

Title: In case your AB528 doesn't work as expected
Post by: JPK on June 12, 2024, 05:15:00 PM

Check the usual suspects:

• Check you didn't leave the polarity switch on the center position (=mute),
• Forgotten solder joint,
• Bad solder joint (reflow suspicious joints),
• Reversed components (electrolytics, diodes, transistors, IC's). In case of IC's, probably destroyed, better replace,
• Flipped IC's or transistors,
• Trim all the component leads and test pins as short as possible. Nothing must touch the chassis plate.

Check the DC voltages:
First check the supply voltages as described in the setup guide.
Next, without any input signal, connect the voltmeter black probe to the 0V test pin and note the DC voltages you get at the points shown on the attached picture. Compare with the expected results (more or less 10%).

Check the AC voltages:
Send a 100mV, 1kHz sine voltage to the input (measured with the input connected to the source).
Set the gain to 50, OUT to maximum and Z to 1200. Check the AC voltages on:
TP1: 175mV
TP2: 550mV
TP3: 550mV
TP4: 5.5V
Output: 10.9V