The Lumin project is a workalike of the BBE Sonic Stomp / Sonic Maximizer. It’s based on work done by Bajaman (documented on FSB) and Sebastian Montti (stm) on DIYStompboxes in recreating the functionality of BBE’s proprietary NJM2150AD chip.
I intentionally designed this circuit around six dual op-amps instead of a quad and a dual like most other comparable projects. Your quad op-amp choices are pretty limited, but with duals you have a lot of other options like the NE5532 or OPA2134 if you want to try something different.
This project also has a midrange knob, giving you an additional frequency band to play with, and optional switches that allow you to change the frequencies for the Process (high) and Contour (low) knobs.
The BBE 482i Sonic Maximizer rack unit first appeared on the scene in the late 1980s and quickly achieved legendary status among sound engineers for the way it imparted clarity on the signal—often described as sounding like a blanket was lifted off the speaker cabinet. The circuit is said to create “frequency-dependent time alignment” so that the audio frequencies hit the speaker in a more optimal way. Many professional audio setups even outside the music industry utilize the “BBE process” to enhance sound quality.
The later Sonic Stomp is a stompbox version of the rack unit that was originally released in the late 1990s or early 2000s. The circuit itself is identical to the single-channel rack unit, but intended for use with guitar or bass.
Both the Sonic Stomp and the Sonic Maximizer use a specialized chip, a NJM2150AD, which was designed by BBE and manufactured by JRC/NJR. The datasheet for this chip is readily available, although the chip itself can only be obtained from BBE—but the datasheet tells enough of the story that the circuit can be easily replicated with a relatively small number of components.
The NJM2150AD is a nearly-complete analog circuit composed of opamps, resistors and capacitors all put onto one chip, ostensibly to keep their secrets (sort of like a very expensive version of gooping)—but it certainly didn’t hurt their manufacturing costs either.
The circuit itself is a state variable filter, which splits the signal into three parts (low pass, bandpass and high pass), applies a treatment to each of the frequencies, and mixes them back together. The original unit provided knobs to control the low and high portions of the signal. It’s extremely easy to add a control to the bandpass path for frequency adjustment of the midrange, and my project incorporates this modification.
- The original Sonic Stump project by Bajaman on freestompboxes.org ↩
- Two fantastic technical descriptions by Sebastian Montti (stm) on diystompboxes.com regarding the behavior of the state variable filter: #1, #2 ↩
- One of the earliest breakdowns of the technology behind BBE’s proprietary chip ↩