Magnetic pickups reviewed
What’s the basic deal?
A pickup device is a transducer (specifically a variable reluctance sensor) that captures or senses mechanical…en.wikipedia.org
What do magnetic pickups detect?
The primary basic principles is: changes in magnetic flux result in voltages induced in coils enclosing that region of flux.
The second principle — which applies to the specific design of magnetic pickups — is that changes in the reluctance of a system will change the flux, and then your coils will detect a signal.
Magnetic circuit , closed path to which a magnetic field , represented as lines of magnetic flux , is confined. In…www.britannica.com
The vital component changing the reluctance in a guitar is the strings.
This is why they need to be ferromagnetic to work at all, and also the right metal to work with a balance output across all the strings.
So, what do the guitar pickups bring to the party?
#1 they all bring pretty much the always the same thing
Pickup designs vary and a lot of hot air seems to be wasted upon the minutiae of the tones generated more on that in other posts, but fundamentally, the analogue pickups all do the same thing.
The pickups in a guitar pickup typically have a thousands of turns — up to around ten thousand of fine copper wire and an impedance of 7–10 kOhms.
From the basic principle of operation, any changing magnetic flux in the environment will be detected by the device and result in a signal when there is only one coil.
Typically, a hum at mains frequency is strong, and often some radio frequency signals can break through and be heard.
The humbucker design uses two coils in proximity to generate equal and opposite noise signals, which are then added to cancel while the guitar signal is reinforced.
The number of turns in a coil is not varied radically, as this would also change the output, which is typically a few 10s of millivolts, presented to a high impedance input.
The trade-off of using more turns in the pickups is that the enhanced signal output is accompanied with the increased reactive properties of inductance and capacitance. The higher these are, the more exaggerated the resonance peak in the pickups’ output.
The position and shape of the resonant peak in the pickup gives it its distinctive tone, hence the birth of the great single coil versus humbucker debate.
The Pickup Parade
So, for the curious, here is a range of pickups cracked open for perusal…
30 Year old single coil
This was the original pickup in a Washburn KC40V.
There is a magnet, around which the coil is wound.
The coil is also wax potted, which should massively reduce the likelihood of microphonic behaviour in the pickup — nice.
The 25 year old Single Coil
This is a pickup wound by a small bespoke UK company a while ago.
They sound really good, a versatile rocky tone.
30 year old Humbuckers
This was also in the KC40V, and was an OK pickup, though not quite with the tone I was looking for.
That’s about it
So, there is little magic going on in a pickup, as we will see in more detail in later posts.