High Impedance: The Nature of the Beast

First, we all have to understand that the earth is not the center of the universe as well as a pickup is not the center of your sound. This requires a 180 degree turn from the nonsense that clever marketeers invented to create a need in the mind of the buyer for something he really doesn’t need. In commercialism, it’s called "Sales Psychology." I simply call it "BULL."

What we do need is realistic information that helps the consumer to make an intelligent decision.

Every day we can read the mythology about antique pickups and how they were designed to have that "very special sound." Let’s face the facts: they were nothing more than a good amount of copper wire wound around a magnet till there was enough voltage to drive an amp. The sound was not desirable -- all lows and no highs. (Plug your guitar into an audio amp and try for yourself.) Now the input EQ of the amp was modified till there was a usable sound, and each company adjusted the input EQ of their amps to match their own pickups. The final result depended on the guy who set the input EQ of the amp. Already in the early days of the electric guitar, there were no standards.

Until 1950, most pickups had an inductance below 1 Henry, and till the 60s, the average cable length was below 10 feet. This all changed after 1950. The Gibson P-90 had an inductance of 6.4 Henry and Leo’s Tele bridge had close to 4.0 Henry. The Gretsch Filtertron averaged 1.6 Henry, and Gibson’s PAF varied between 4.2 and 4.8 Henry. The real trouble started in the early 60s when the first heavy duty 20’ cables arrived on the market, and players plugged Gibsons into Fender amps with the volume on 10. Everything was mismatched, and the mismatch was called sound. ( I remember that, during the same period, teens put wide, oversize tires on Volkswagens and believed it to "boost the power of the car!" Logical thinking was replaced by illusions and make believe.)

Now, let’s see how pickups function.

A pickup is a simple AC generator (the source) that converts the mechanical energy of a vibrating string into a multi-frequency electrical signal. (Fundamental plus the harmonic spectrum.)

Output and sound depend mostly on the following factors:

#1. Internal losses like eddy current loss, hysteresis loss and ohmic loss.

#2. External losses are caused by load resistance and cable capacitance in relation to the source impedance. In simple words, low load resistance, high cable capacitance and a high source impedance result in high output losses which increase with increasing frequencies.

#3. Cut off and resonance frequencies

The resonance is the result of source inductance and cable capacitance. If the resonance frequency is between 3 and 5 kHz, the sound will be bright and harsh, especially with a pickup in the bridge position.

#4. Frequency and resonance of the guitar which can be altered by using lighter or heavier strings.

#5. The Fourier Spectrum

A vibrating string represents a standing wave. Standing waves do not propagate energy. The total energy is concentrated in the antinodes of a vibrating string. The timber of plucked string instruments depends on the position and the angle of the attack which is solely in the hands of the player. On an electric guitar, we must also consider the position of the pickup. An experienced player can shift the antinodes of a vibrating string in relation to the position of a pickup with various picking techniques.

To achieve the widest variety of sounds, all parts of the chain (guitar, strings, controls, cable, amp and speaker) must be considered as a total, capable of reproducing a wide range of frequencies. There are two ways to achieve this: We either keep both the inductance of the pickups and the cable capacitance as low as possible or we introduce 2-way pickup systems where the high impedance part reproduces the lows and the low impedance part reproduces the highs, just like a 2-way speaker system.

We are paying today for the biggest blunder that the guitar industry made.

In the mid-30s, in Berlin, at the Telefunken Research Lab, Georg Neumann and his team of engineers designed the condenser microphone and the first tape recorder with magnetic pickups. To achieve a true reproduction of sound, they had to use low impedance. In 1947, the low impedance tape recorder was introduced in the US, and a new company called Ampex started to produce them. A few years later, the major recording studios were using tape recorders; by the early 50s, the whole world, with the exception of the guitar industry, had switched to low impedance, and it was called High Fidelity -- or just Hi Fi. The guitar industry did not recognize the advantage of low impedance and did not make the switch. Today, a change to low impedance is virtually impossible. There are too many amps and guitars floating around, and we are stuck with all the disadvantages of high impedance.

Let’s see how we can make the best out of it.