Do you have the Cello Pallete or the Audio Pallete?
I think Martin Colloms used an Audio Pallete, not the Cello -Palette preamplifier - but can not be sure anymore. The sound of the two units is completely different, I have owned both long ago. The Cello Pallete Preamplfiier (the cheaper unit, using ICs and potentiometers) was a terrific match with the Cello Duet, but was not competitive with other preamplifiers when used with a non Cello system.
The Audio Pallete was much more refined and sweeter. I found that unless I used some equalization with it, it robbed life to the sound in the flat position when used with non Cello systems. It had a much better building quality than the Palette Preamplifier.