APT made both pre-amps and power amps designed by Tom Holman (of THX fame). They are both interesting from the perspective of their design and sound quality.
I have undertaken upgrades on a number of APT pre-amps, and use one in my reference “Lab” system. They have a great phono stage and are both warm and detailed. The pre amp was designed around a number of op amp IC’s, originally the TL072, with each op amp forming a “block” of functionality in the pre-amp. As with many components of this vintage, they do benefit from replacing the electrolytic capacitors and other components. My upgrades include:
- New power supply capacitors of higher capacity
- replacement of all electrolytic capacitors with new audio quality Nichicon (including bipolar and additional capacitance at appropriate circuit points) and Wima film types.
- New IC’s through out all in sockets (including the regulator IC’s)
- New higher capacity bridge rectifier
- Replacement of the relay
all of which greatly enhances the sonic performance and reduces noise and distortion significantly.
I have supplied a number of these, often used with the upgraded NAD 2200’s described elsewhere, which has results in great sounding combination.
The front and rear panels of the APT preamp
The renowned phono section showing the capacitive and resistive termination options for MM cartridges. The infrasonic filter switch is also visible