1

AB528 Microphone preamplifier / Re: AB528 noise

« on: February 18, 2025, 02:24:53 PM »

The problem has been found. The c17 capacitor was damaged and caused leakage.
 

2

AB528 Microphone preamplifier / AB528 noise

« on: February 17, 2025, 07:39:31 PM »

HI? Request assistance.





According to https://www.soundskulptor.com/forum/index.php?topic=498.msg2966#msg2966 The measurement data is within 10%, and LED1 is emitting light. I have checked all the solder joints, positive and negative terminals of capacitors, and positive and negative terminals of diodes, and all of them are set up properly.

A:+3.938v
B:+0.655v
C:+4.6v
D:+5.61v
E:+15.61v
F:-0.458v
G:+14.97v
H:-5.20v
I:-0.458v
J:-13.27v
K:-13.75v
L:+15.52v










Q?current issues



Placing the polarity switch in the mute position will result in noise and background noise.When the switch is not in the mute mode, the background noise still exists, but it is not as strong as it is in the mute mode.

output transformer resistances value

Red-Yellow : 9.3 ohms
Orange-Black : 18.8 ohms
Blue-Green : 18.6 ohms

Resistor between edge connector fingers 2 and 4:37.3 ohms



Noise has always existed, and as the gain increases, the noise will become louder, accompanied by tearing and beeping sounds. This problem has always existed. At first, I thought it was a relay welding problem, but I checked the welding points and found no problems. The SW switch also checked and found no problems.


Under the same environment, everything is normal for TG2-500



Compared to TG2-500, AB528 is more pleasing to me. I think I may need a pair

Salute again.