The chips used are JRC 4560's which at the time of construction were the best bipolar chip available but are now hopelessly outdated. The simplest remedy is to change these two chips located just behind the tone controls to current technology ones. The superior BI-FET Analog devices AD-712 can be substituted easily (available from Old Colony Sound Labs 1-603-924-6371) and you will be stunned by the difference!!