Meeting both requirements can go hand in hand, though not automatically.
Since only low frequencies are involved with, the whole design could be implemented on a single-sided PCB. Care has been take to place components on a logical basis, but also to keep tracks and loops small.
Input (transformer) and outputs have been separated buy applying both on opposite sides of the PCB.
This PCB is a dual layer as the line stage is applied on it as well. One layer is used as a screen. Given the audio function, no high frequencies and or currents run here.
On one side the mains transformer, rectification and heater circuit are applied. On the other the gain stage is laid out, with in and outputs again separated from the mains side.
The mains-transformer has a magnetical screen, realized by a metal foil just outside the core. This reduces the hum by a measured amount of 20 dB.
First order calculations have shown that a 4-layer PCB was required to maintain the low value of 3 ps jitter coming from the oscillator.
Copyright © 2001, Marc Heijligers and the DAC group - All rights reserved.