Analog-Precision Board

Products by Analog-Precision => Ultimate-Preamplifier by Analog-Precision => Bug Reports and Issues => Topic started by: Tranquility Bass on July 29, 2022, 08:07:26 PM

Title: Volume changing sporadically due to excessive ambient temperature
Post by: Tranquility Bass on July 29, 2022, 08:07:26 PM
For those with the earlier Rev:B2 boards it is possible for the volume to increase dramatically. This is noticeable when the Preamp is exposed to high ambient temperatures and there is poor ventilation inside the case. This is caused by the 1.2V regulator that powers the DAC chip to momentarily shut down until it cools down and starts up again in which time the DAC chip starts in an unknown state. To reduce thermal load on the regulator it is recommended to remove the 120 ohm resisitor R59 near the DAC by skilled personnel who are experience with reworking surface mount boards. This resistor is used to bias the regulator into class-A operation but is not needed as the regulator is sufficiently loaded by the DAC anyway. Removing this resistor will lighten the thermal load on the regulator which is only a small SOT-223 package. For that reason it is recommended to provide adequate ventilation around the DSP board to improve reliability of this circuit. This modification only applies to the earlier Rev:B2 boards and NOT the later Rev:C boards which have substantially bigger regulators and better heat sinking.

Check Board Revision on the bottom right hand side of the board.

Only qualified personnel should Remove R59 from the board as depicted on the images below