Given that most pickups are just a coil of wire and some magnets, is there much scope for doing it so wrong that it actually sounds bad, or is the reality that you are just going to get subtle variations in frequency response and distortion that you won't even notice in the mix?
Yes, there is plenty of scope to make pickups that have gross differences in frequency response, microphonics (or lack of), output level and impedance, noise immunity, distribution of even and odd order harmonic distortion, hysteresis and other aspects that all interact dynamically.
Those variations can be as little as as a few percent (subtle), or orders of magnitude (gross).
The amplification and speakers used can reveal or mask differences.
Some of those differences may be due to poor design or manufacturing, and cost cutting.
As the science of pickups has been refined over the last century, many are designed in to accommodate musician's (and engineer's..) vast difference in perception of what sounds "good" or "bad", "wrong" or "right" in an electric guitar.
Art
I'm lost, in the context of an electric guitar pickup that sounds bad... I'll have to look into that synth - thanks for pointing it out.
"Sounds bad" has a lot to do with what you're attempting to do with it. My example would be EVH; as a young musician, the pickups available at the time werent cutting it, as he wanted to play Marshalls with everything at 11 - and have it still sound good. Pickup microphonics dont sound good at high gains, to he - apparently - reconstructed them by coming up with his own wax impregnation process, which held the windings fast in a better way than simply wound onto the bobbin.
So a deliberate way to make pickups sound bad - particularly when used in high gain, high SPL situations - would be to wind them as loosely as possible, giving each winding turn ample opportunity to wiggle some in response to vibration.
A Chinese (sorry China, as you do many things really good) pickup I recently gutted was quickly assembled with hot melt glue. It didnt even stick to the case; I could just push the windings and magnets out by pushing on a pole piece. Another deliberate way to make a pickup crappier than it could have been, just use poor manufacturing technique.
And, I have to suppose that the number of wire turns could be deliberately limited, to just "good enough" to get a usable signal. Saves cost of the wire, time cost of winding more turns. The above referenced pickup didnt seem to have much output and on inspection, didnt seem to have a turn more than they could get away with.
You could use crappy magnets as well and couple them to the pole pieces in a crappy way. that one looked like it just had a couple broken off ceramic pieces - of different lengths - glued to opposite sides of the poles. So you could deliberately do that too.
Perhaps that's the wrong question - one should ask what makes a 'good' guitar pickup sound good? Certainly having the windings fixed (generally by dipping in hot wax) so it's not nearly so microphonic is good, but that's only one aspect.
Pickups were developed during the vacuum tube era, with thousands of turns of thin wire to induce enough voltage through the coil so only a couple of tubes are needed to amplify the signal enough to drive a speaker. This is also rather high impedance (not just the wire resistance, but also/mostly the inductance), and with all the turns of wire, the capacitance between turns adds up and causes the coil to have self-resonance around 5 to 7 kHz, within the audio band. This causes a boost in that band, and this is a substantial part of the electric guitar sound. High-impedance guitar pickups with their imperfections helped create the sound of electric guitar, and that hasn't changed. "Crappy" pickups likely have fewer turns, lower output, and especially a self-resonance at a higher frequency and thus they "don't sound like a guitar pickup should." Even this is simplified, there's a sound difference between single-coil and humbuckers, and the position (distance along the strings from the bridge) also affects sound, thus most electric guitars have several pickups which can be switched to provide different sounds.
Pickups were developed during the vacuum tube era, with thousands of turns of thin wire to induce enough voltage through the coil so only a couple of tubes are needed to amplify the signal enough to drive a speaker. This is also rather high impedance (not just the wire resistance, but also/mostly the inductance), and with all the turns of wire, the capacitance between turns adds up and causes the coil to have self-resonance around 5 to 7 kHz, within the audio band. This causes a boost in that band, and this is a substantial part of the electric guitar sound. High-impedance guitar pickups with their imperfections helped create the sound of electric guitar, and that hasn't changed. "Crappy" pickups likely have fewer turns, lower output, and especially a self-resonance at a higher frequency and thus they "don't sound like a guitar pickup should." Even this is simplified, there's a sound difference between single-coil and humbuckers, and the position (distance along the strings from the bridge) also affects sound, thus most electric guitars have several pickups which can be switched to provide different sounds.
Perhaps so, but were people cranking their amps to 11 in that decade? I mean as a reason why they used wax?
That decade was the primetime for and dominated by acts like Les Paul & Mary Ford. Les, I've recently read was in staunch opposition of any distortion. His low Z "studio" balanced pickups - intended to go direct into the recording console - didnt have the flavor of the high Z ones (possibly for reasons, as benb stated) and by modern standards were relatively dead and flat sounding.
I find it interesting that the mass gestalt training for how a guitar pickup should sound didnt end up what 'effin Les Paul thought they should sound like. I mean there's a guy that knew a little something about electric guitar, recording, effects - if there's anyone with such mastery of knowledge. His entire vision of how things "should" be didnt happen; we all got trained on something else.
Apparently, you cant take one of the low-Z recording Les Pauls and just stick a matching transformer on it, plug the Hi-Z out into a Marshall and get the same thing as you would with the Hi-Z humbuckers in the same guitar. So to deliberately make a guitar pickup that sounds like crap and no one wants, would be to do it in a way that produces a different sound than what we've all been trained to hear for the last 60 years or so.
Yes indeed ! I saw and heard many guitar pickups that were really sounding bad, with a wrong design, the wrong materials...
This one below - a floating Jazz pickup for Archtop guitar - was an abomination : an unpotted winding on a plastic bobbin, surrounding a simple ceramic bar magnet. A thin, squealing, lousy tone, plus low output level, hum and microphonic adverse noises...
... Until I had it rewound - or rather rebuilt - by Kent Armstrong (https://www.armstrongpickups.com/). He installed one of his fine smooth sounding low profile Jazz humbucker design in the casing, and voilà - a true Jazz tone à la Johnny Smith or Jim Hall :
T
These fellows wrote an AES paper with measurements:
RAFAEL C. D. PAIVA, JYRI PAKARINEN,1, AND VESA ALIMAKI
Acoustics and Modeling of Pickups
You can see the results of impedance and capacitance in pickup response:
Note the ~+10 R/C (resistive/capacitive) peaks vary in frequency from ~3KHz ("biting") to past 20kHz ("airy") and the 10kohm (low impedance) pickup starts rolling off below 1kHz and is more than -10dB by 10kHz ("dark").
The 1kohm pickup rolls off at an even lower frequency, and has a fraction of the output level.
The guitar cord used in conjunction with the pickup adds series capacitance and resistance, resulting in different R/C curves for any of the high impedance pickups. The old coily cords could lower the peak frequency, while cutting out the "hash" frequencies that are boosted in many guitar speakers.
These are huge differences of over +/-15dB, more variation than many tone controls have when used to their maximum boost/cut, even before looking at the different pickup locations.
Nothing subtle, they are the reason for using several different pickups.
The R/C frequency variations are only one aspect of many, but are the easiest to "see".
Art
When people were using the Bassman for guitar rather than bass the levels got loud. Actually go listen to some of the blues from the time and you will hear some distortion.
Even further than 11! The early Fender Champion amps had volume controls that went to 12!
At the high impedance of a guitar pickup, a few ohms' cable resistance is insignificant. The capacitance, on the other hand, is (around a few hundred pF) in parallel with the pickup's inductance (when the volume control is full on, as it often is), lowering the frequency of the resonance peak, thus making the sound depend partly on the cable. What's even worse is when the volume is turned down, the volume control's added resistance (total control resistance is usually 250k for single-coil guitars, 500k for humbuckers) is in series with the inductance (at this point it's just a signal generator), making an R-C lowpass filter. This is easily audible as the treble dropping away as the volume control is reduced. One can add a "treble bleed" capacitor between the volume control's high connection and the wiper that helps with this, though the tracking of the treble won't perfectly match the tracking of the lower frequencies.
Anecdotally >
I have heard of really good results using some of today's more 'pricy' active pickups 🙂
I have heard of really good results using some of today's more 'pricy' active pickups 🙂
Just being curious: do you happen to know if they looked into iron losses? I don't know anything about guitar pick-ups, but for some moving-magnet cartridges, iron losses contribute substantially to the damping of the resonance with the cable.
I guess Rl is the resistance loading the pick-up (amplifier and passive volume control combined). With a too low load resistance, the cut-off frequency of the low-pass filter formed by the pick-up inductance and load resistance gets low.
Assuming Rl is the load resistance, I guess that's due to voltage division between the resistance of the pick-up itself and of the load.
Iron losses in fact dampen the resonant peak. That is why some old pickups fitted with simple iron screws sound dull imho.