The Ice Box has several super cool controls that no other mic preamp has: the COOLER, BOILER and PRESENCE.
Watch the video demo: YouTube Video
Although these controls are easy to hear when you are playing "live" through the Ice Box, some of the Video Demo was not recorded well enough to hear the effect. Please see the oscilloscope traces below to visualize tube overload.

Circuit Description
Vacuum tubes “boil” electrons off the cathode so current can flow through the tube. The “BOILER” control increases the flow of electrons through the tube. The “COOLER” controls an optical compressor in a proprietary configuration that affects tube loading and provides harmonic enhancement. The "PRESENCE" controls a filter circuit that increases overdrive. These controls push the tube closer to overload to celebrate that sweet tube sound.

The Ice Box uses a minimalist circuit design which follows the straight wire with gain approach and avoids integrated circuits entirely. Fast transient response is maintained by eliminating the feedback circuits universally used in integrated circuit designs. The vacuum tube is the optimal transducer interface as it captures the wide dynamic range from microphones, or instruments, in the most musical way. Microphones and guitar pickups are transducers, which transform sound or motion energy into electrical energy. Transducers typically have a low level output which needs to be amplified to line levels for mixing or recording purposes. This preamplifier amplifies the low level signals cleanly, while gracefully handling the enormous dynamic peaks characteristic of microphones and pickups in the hands (or throats) of real performers. Since the input stage is a vacuum tube, standard microphones take on a tube mic flavor. This circuit has retro written all over it and celebrates the vintage sound.

Pushing the tube a little produces a wonderful sound quality. It is the holy grail of both live sound and recording engineers. Many, unfortunately, use mixing console channel strip preamps along with various processors in an attempt to sweeten the sound. The fortunate few have already discovered there is no substitute for the vacuum tube transducer interface of old that this circuit embodies.

Boiler Off - sine wave


Boiler On - notice notch


Ice Box with Output and Photon Cooler Meters