* use a large surface ground track/fill for this circuit, otherwise the LM3524 will not work reliably!
* mount the two potentiometers through the enclosure, as shown in the picture on the start of this page (these pots are used to control the frequency and duty cycle)
* the driver is based on the LM3524 PWM chip, adaptation to TL494 or some newer chip should be easy (just compare pin-outs). Equivalents: CA3524, UC3524, SG3524. These are classic PWM ICs, and should be available just about anywhere, for cheap.
* to keep oscillator noise low and eliminate errors (those comparators inside LM3524 are sensitive…), use a large ground plane on the PCB
* timing capacitor C1 should be between 1nF and 22nF, 10nF is a good start. The cap must be immediately next to the chip, and connect directly to the ground plane.
* it would be a good idea to place a 3-pin switch between the power section 12V out and the 12V input for this section, together with a two-color LED (red+green) and series 6.8k resistor, to indicate whether this driver section is running or not – i.e. the flyback is running or not.
* the MIC-AMP lead to the BC547B transistor comes from the audio sense section
* I-SENSE is the current sense feedback signal from the MOSFET section and is only a few 100 millivolts, so you should use a thin shielded audio cable for signal interconnection