Tracing Journal: Xotic SL Drive
Today we’re releasing two new Xotic traces. The Xotic SL Drive is a miniature drive pedal that was released in the summer of 2013. It was designed to emulate the tone of an overdriven Marshall Super Lead (hence SL) Model 1959 or Super Bass amplifier, calling to mind famous users of these amps such as Jimmy Page and Jimi Hendrix.
Here’s a quick demo video from Reverb:
Xotic isn’t exactly known for their original circuits. The BB Preamp and AC/RC Booster are heavily based on the Tube Screamer, while the Soul Driven is half Tube Screamer and half Blues Driver. The SP Compressor is a Ross/Dyna topology. But the SL Drive sounded great, so out of curiosity we cracked one open.
Tracing photos
Xotic has a pretty creative method of packing as much as possible into a 1590A enclosure while still leaving enough space for a 9V battery. Practically speaking, you don’t actually get much extra horizontal space (if any) from a 1590A pedal with side-mounted jacks as compared to a 125B with top-mounted jacks, so the mini-pedal trend is a bit overblown in our opinion. But it’s still interesting, and their style is among the best we’ve seen.
Schematic
Analysis
It’s an original circuit! Yes, each of the high-level circuit blocks has similarities to other pedals—but with 50 years of op-amp design in the pedal industry it’s pretty rare to be surprised by something truly innovative. We’ll settle for the fact that it’s not an obvious clone of anything.
It does look a bit RAT-ish, particularly the hard clipping and tone control, but it’s different enough that we couldn’t say for certain that they referenced the RAT in the design process.
As with Xotic’s other mini pedals, there are some DIP switches on the inside to set certain parameters, making it closer to the Super Bass or Super Lead. Here are the four settings they mention:
They also include recommended drive and tone positions for each of these, but since these are very much rig-dependent as well as being external and easy to adjust, they aren’t critical.
IC type
As with many of Xotic’s circuits, the IC is sanded down, so it’s not known what type they used, but we can make some educated guesses. In the manual, they list the current draw of the pedal at 5mA. Trusting that this is accurate—we didn’t confirm the current draw of our unit—there are only three parts of the circuit that factor into the total current draw: the indicator LED, Q1, and the IC.
For our purposes, we’ll say the LED and Q1 together draw 1mA. It may be more, but not much. But this means we’re looking for an IC with an operating current of less than 4mA.
Among common op-amps, this rules out the LM833 (5-8mA; Xotic uses this in the Soul Driven) and JRC4580 (6-9mA), and certainly higher-fidelity options like the NE5532 (8-16mA) and OPA2134 (10mA minimum). The JRC4558, LF353, TL072, LM358, and LM1458 would all still fit under the limit.
Of these, the LM358 (1-2mA) is probably too low, but the others are all right around 3-4mA at idle, so any of them are contenders, as well as other more obscure types that we didn’t consider. If we’re going by probability, though, Xotic uses the JRC4558 more than any other chip, and at 3.5mA minimum current, it fits right into our formula.
Therefore, we’d say it’s probably a JRC4558. If anyone wants to do any sleuthing work, it’s possible to test the slew rate of an op-amp, which would narrow it down pretty closely—or at least make it immaterial, since two op-amps with the same slew rate will generally sound the same.
Silvanus Amp Overdrive
Releasing today is our version of the SL Drive, called the Silvanus. It’s a close copy of the SL Drive, including the DIP switches. We added a clipping toggle switch, so you can engage the stock diodes or two other extra settings not found in the original. Other than that, it has the same controls as the original unit.
