Post by aquin43 on Sept 21, 2022 11:50:18 GMT -5
The ideal pickup model should as accurately as possible reproduce both the impedance and velocity transfer function of the pickup at least up to the open circuit resonant frequency. This requires that both the response to an exciter and the complex impedance be measured. In measuring the impedance, any extra loading on the pickup is to be avoided since it will lead to errors. Phase in particular is important. The method described by ms requires the simplest possible measuring fixture and provides a robust measurement. Phase is not usually measured at all in the frequency response Bode plot but it is desirable that the loading should be the least possible and should be known.
The fitting method used in the Gitec Pickup Wizard program can produce a multi-coil circuit that closely approximates the impedance of a real pickup coil using usually two but sometimes one or three non-coupled inductors. This is a behavioural model, the actual coil is more complicated than that. It turns out, though, that by splitting the input exciter voltage in the correct proportion between the coils the response of the coil to the magnetic velocity signal from the string is well reproduced, at least for pickups without excessive losses in enclosing metalwork.
Other pickups need a supplement to the frequency response and it seems that an extra single low pass step filter is sufficient even for a very lossy pickup.
Here is an Armstrong "Johnny Smith" pickup modeled in this way with eight parameters. This is an extreme example of a pickup with a cover that deliberately attenuates the treble but which isn't tightly coupled to the coil.
The fitting method used in the Gitec Pickup Wizard program can produce a multi-coil circuit that closely approximates the impedance of a real pickup coil using usually two but sometimes one or three non-coupled inductors. This is a behavioural model, the actual coil is more complicated than that. It turns out, though, that by splitting the input exciter voltage in the correct proportion between the coils the response of the coil to the magnetic velocity signal from the string is well reproduced, at least for pickups without excessive losses in enclosing metalwork.
Other pickups need a supplement to the frequency response and it seems that an extra single low pass step filter is sufficient even for a very lossy pickup.
Here is an Armstrong "Johnny Smith" pickup modeled in this way with eight parameters. This is an extreme example of a pickup with a cover that deliberately attenuates the treble but which isn't tightly coupled to the coil.
The brown line is the overall response, the red line the added step and the orange line the core response of the coil. Most pickups don't need anything like as much correction but it is encouraging that such an extreme example can be made to work with a single low pass step. The exciter voltage is applied to the coil sections in proportion to their inductances as fractions of the total inductance.
The coils are not coupled so the total is simply the sum of the parts
The method of introducing the voltages uses a minimum of Spice components. There are other equivalent circuit configurations that are more amenable to non-Spice calculation.
