The Atomic boost is based on the TC Electronics Spark ™ and a perfect one knob beginner project to check if you are into DIY. Perfect suited to add some extra gain to your Leads or to get Crunch/driven sounds out of your semi-dirty amp. Especially when your amp tempts to be a little too dark the nuance of brightness it adds can be very handy without making the signal harsh.
There are plenty of equivalents and similar-sounding transistors so I would recommend using dip sockets and start diving into creating your very own tone.
For instance, you can use Q1-4 – BC547 (type a-b-c the higher the letter, the more gains they are) and for Q5 a – BC557C (flip it 180 degrees to the silkscreen!)
2n3906* PNP transistor. Although the original unit presents a BC558c transistor we have experienced better results with the listed 2n3906. You can still experiment with BC558c just by flipping the transistor 180 degrees. A higher gain direct replacement could be 2N5087.
BC549c** NPN transistor. You can try 2N3904, 2N5088, 2N5089 replacement, just take in mind you need to flip the transistor 180 degrees to the silkscreen. The order listed is from lower to higher gain.
For further analysis on this circuit take a look at this thread on Free Stomp Boxes Forum