Respect to you also, man.
Over the years, I have really learned to have a lot of faith in “standard” circuits. These standard circuits and their associated math have been proven to be very solid time after time. All of the standard circuits that I have worked with, test nearly exactly to how they were calculated or simulated. There are, of course, other factors that can skew measured results from the calculations; like active circuit stress with improper resistive or reactive loads, interference or oscillations caused by adjacent circuitry, power supply limitations and PCB layouts are also important. So, there are many variables can cause measured results to vary from the calculated circuit performance (including the test equipment used), but the SPICE simulators of today can take most of those circuit variables into account and allow you to find where the weak link is most of the time. A lot of these simulators can also calculate circuit variances due to ambient temperature changes... very cool stuff! You just have to be diligent to put real life limitations and parameters into the circuit simulations where necessary and to know/understand the device data sheets and design well within those parameters. The only times I have had significant variations with actual circuits and their equivalent SPICE simulations, is when I have designed up to or beyond the operational limits of active devices (so that would be my dummy-head fault, not the circuit itself)…. or with MOSFET’s. I have never been able to successfully simulate MOSFET circuits directly without adding extra ‘fudge’ circuitry into the simulation. After running into discrepancies with these MOSFET circuits, I read that SPICE simulators have issues with some MOSFET circuits. So I do not trust any simulations of MOSFET circuitry now without actual physical verification.
This tilt EQ in the Diamond is a textbook “standard”. When looking at the tilt circuit and the circuits that proceed and follow it, I can see nothing that would skew its measured results from the calculated and simulated results. I am so confident of it, that I will wager a free pedal or a kitten to be proven wrong.
The reason that I asked about the Smoothie using a dual-ganged pot for the tilt control, is because of the cut response in your plot. A “standard” tilt-EQ only has a maximum 6dB shelving boost/cut by design and uses a single gang pot. I have built a pseudo tilt EQ control that used a dual-ganged pot with a heavily modified two-band Baxandall circuit that has a similar cut response to your Smoothie plot. But, although it operated similarly to a one control tilt EQ, it really was just a one control (dual-ganged) modified Bax EQ.
-Frank
