I wanted a way to get a vintage Sunn Coliseum amplifier's tone (having owned one in 1974) without having to lug a large & heavy head around and since no one makes, or has ever made one, I built this exact clone of its preamp in pedal form.
My approach is completely “old school”, by designing and etching my own pcbs for it using 100% thru-hole components (no smd devices) and NOS original transistors for it. It is completely custom hand made with nothing farmed out. The result blew me away and I don’t remember even the original head sounding this good.
The controls consist of volume, lo bass, hi bass, mid and treble with a toggle for two different mid and treble frequencies as well as a bright switch for the overall preamp, and of course, a volume. This pedal has A LOT of output and is capable of driving a poweramp.
The power supply was a very difficult task since the original circuit requires multiple voltages (+30V, +23V and -15V and +9V for the relayed true bypass ). I tried multiple ways to achieve that, using multiple charge pumps and even a 120VAC power transformer but was unsuccessful with either of those methods. The solution was to use a 28 volt power supply with a filter multiplier and then create another circuit to supply all of the necessary voltages.
The circuit uses a Jfet (2N4304) and a PNP transistor (2N4250) (both T-106 button top types) at the front end driving a four BC107B transistor eq section followed by one more BC107B for the output amp.
This pedal is NOT an "emulation" of the preamp, like many pedals these days, but rather, IS the preamp.
Many thanks to Frank Appleton of FEA effects Labs that helped me get this pedal's power issues sorted. It took a lot of work and time to get this pedal where it had to be. This one was designed to look like the original amp as well and is in a 1590XX enclosure with numbered knobs.
Due to the complexity of this build and the cost of the NOS transistors, I have decided not to make any more of them for sale so the buyer will have an exclusive one of a kind pedal. It includes a regulated 28 volt power supply, specifically chosen for it.
The picture on the left is of the pedal that you will receive.
