Pickup Lines
Amp designer and founder of Bulldog Pickups, Hayden Minett, cleans up the fuzzy picture of preamp distortion…
In the formative years of the electric guitar amplifier, manufacturers began settling on designs that, although technically flawed, would ultimately prove indispensable to the instrument’s trademark tones and the evolution of popular music. “They got things wrong in terms of how sensitive the inputs are to guitar pickup signals,” Hayden Minett tells us. Having spent the best part of two decades building pickups and designing amps, he’s been able to draw his own conclusions as to why people aren’t rushing to correct these so-called mistakes. “I’m not entirely sure that things have been refined over the years,” he says. “All these mistakes that happened in the 50s and before have become part of the sound of what we expect to happen when we plug a guitar into an amplifier – we expect it to become a little bit crunchy and a little bit dirty.
“That distortion stems from the fact that ultimately there’s too much power from the pickup going into the amplifier circuitry to create a clean sound. The mismatch between the two is where that sound comes from. You’ve got a pickup coil, which is basically a generator, and it’s generating a small AC signal – a voltage. So you have to think about how you’re going to amplify that tiny signal, and you have to think about the amount of signal going into the amp. One of the most critical parts of the amp’s circuit is the input stage.
“A lot of amps will give their full output power with only a 20mV to 40mV of input signal. Some even less than that. A modern high-power humbucker will happily deliver 400mV, which is about 10 times the signal needed to produce full power from, say, a Fender Twin. And that’s why the amplifier overdrives. Ultimately, it’s got too much gain in the early stages of the amplifier than is needed. If you plug a vintage PAF-style humbucker into, say, a Fender Twin and set it to ‘2’ or ‘3’, you’ll probably start to hear it crunch up a little bit. By comparison, if you plug a vintage Fender-style single coil in, it’s going to be a little more open-sounding and clean. That’s the most obvious way of listening to the output power difference between different types of pickup. It’s purely down to the amount of power generated.
“One of the interesting traits of break-up in a valve amplifier is that before it gets to the point of really clipping and really distorting and sounding like what we call overdrive, it goes through a stage of soft clipping and compressing. You can see it on an oscilloscope starting to round off at the top [of the waveform] and that’s kind of where the fun starts to happen in terms of playing response. You will find the onset of that happens a lot sooner with a higher-output pickup (or if you hit the strings harder on a lower-output pickup), but if you’ve got a really high-output guitar pickup, you just don’t have any headroom at all on some amp designs.
“If you’ve got an amplifier that’s designed to work with higher-output pickups, with all that extra headroom, the clean sound can sometimes be overly bright and almost brittle. If you go for the more metal-orientated amps, they sound great with humbuckers, but sometimes regular single-coil pickups are a bit too bright and you can struggle a little bit – the clean channel can be quite glassy, because they’re more or less expecting you to be hitting it with a high-output pickup. You can often hear the target market of some modern amp designs. But a lot of pickup and amplifier designers are now looking back to how things were done in the 50s and 60s. In fact, that’s probably about 90 per cent of what I do. People increasingly want that original pickup output level. It’s these accidental guitar tones from the early days of rock ’n’ roll that people just keep on returning to.” [RB] http://bulldogpickups.6.ekm.shop
“A lot of pickup and amp designers are looking back to how things were done in the 50s and 60s”