Here is the applicable excerpt from the Bob Gallien interview I mentioned above regarding the uniqueness of the GK tone stack:
Q&A with Bob Gallien by Tom Bowlus
We all greatly enjoyed hanging out with Bob Gallien at the Winter NAMM Show, but I couldn’t resist a few more follow-up questions to share with our readers.
Q: Your heads use a serial equalization section. Why is this important?
A: When I started (1967), bass amplifiers used a very simple three-control passive “T” tone stack popular in guitar amplifiers. This tone stack works great for guitars and is the main EQ system in use to this day for guitar. I realized early on that to solve the problems bass players were having (power, punch, and clarity), an entirely new approach was required. A different power amp topology and more detailed equalizer was the answer. The typical way then to get more EQ was to use a graphic equalizer. The problem with this type of equalizer is that it is designed to reduce room resonances, and because of the parallel band configuration, they introduced resonances of their own. These things were never intended to equalize instruments, and for the most part only made the problems worse. I worked on the problem mathematically for several months (over a hundred pages of loop equations, all by hand) and came up with the serial equalizer solution we
use to this day. This equalizer requires a lot more parts, but provides the maximum usable response modification without introducing resonances and nulls of its own. It is popular to test equalizers by sweeping them with a signal generator and showing the response. This type of testing does not really show the important characteristics of an equalizer. In the real world, an equalizer is presented with thousands of frequencies at the same time and in this condition the parallel equalizer will produce many nulls and resonances
that make things sound false. The GK serial equalizer does not have this problem. The proper test method for equalizers is to use square waves for the signal. Square waves contain thousands of frequencies and will accurately show how an equalizer actually behaves. Square waves will show severe ringing in high-Q parallel equalizers, reflecting the artificial character of the resulting sound they produce (as well as all the other undesirable anomalies). These undesirable responses are absent in the GK equalizer, which means it provides useful equalization over the full range of its controls.
Q: I notice that you set up your EQ section “backwards” from the norm, from high to low. Why is that?
A: My first amplifiers that used the serial equalizer (300B, 600B) were hand-wired with terminal strips. In order to reduce noise, a serial equalizer must have the high frequency bands first, so with handwiring the high frequency pots had to come first. I can always tell when the competition has been looking at my designs, because for no reason at all they run their equalizer high to low. To my knowledge, GK is the only company using a serial equalizer, therefore the only company with a reason to run the equalizer from high to low.
Then Boss and DOD followed suit.
