DOD FX10 Clone

The DOD FX10 Bi-Fet is a simple and incredibly powerful op amp preamplifier/booster. It's a secret weapon in many rigs, as running it after a distortion or fuzz pedal can produce extra heavy or cutting tones. It does a great job of warming up a thin guitar or brightening up muddy pickups. This was a collab with my friend Scot at S&K pedals, who also occasionally helps build our custom shop units. We sold a bunch of these boards but we will be updating the layout into a more compact form for open source availability. The build document references the older layout so in the mean time you can use the schematic and BOM for reference. This is a good beginner to intermediate project. (Build Document - note this is out of date, use at your own risk)

I also drew up an FX10+ which runs at about +/-17V, in case you want more headroom than you'll ever know what to do with. It fits in the same size enclosure and the PCB layout is also on OSH Park. (Schematic)

Mojo Titan

An homage to the almighty Sonic Titan power amp distortion, which uses an LM386 IC for its unique distortion characteristics. This build uses "mojo" parts such as mil-spec resistors and oversized film caps. Does it sound better? Debatable, but it looks rad. The build document has suggested part numbers but feel free to experiment. If you can find one use an LM386N-4 for best results, as other versions can have a sputtery note decay. And use a big enclosure to have more room for tone. (Build Document)

Musicman HD Series Preamp

Simple op amp preamp inspired by the MusicMan HD65, HD130, etc. The topology looks a lot like a Fender preamp, with impedances scaled to suit op amp operation rather than vacuum tubes. These amps are known for their clean tones, but the trashy op amp distortion is in a class of its own. Any dual op amp which is pin-compatible with a TL072 should work. A "bad" op amp like an LM1458 might actually sound better at high gain - the originals used LM307 op amps which are close to the LM301 in design. The original also runs the chips at +/-16V which is possible but takes up a lot of PCB space, so this one uses a charge pump for +/-9V bipolar operation and the gain is reduced slightly to mitigate clipping at the input. Layout verification is pending. (Schematic). 

Magic Missile

This is a six-transistor silicon fuzz/drive with some unusual sounds at extreme settings. It takes some inspiration from the Escobedo/Devi Ever lineage of transistor fuzz (one of the first pedals I ever owned was a Devi Ever Hyperion), which are haphazard yet undoubtedly brilliant. A few such designs feature a PNP/NPN clipping cell which caught my attention. After some breadboarding and SPICE experimentation I discovered that it shuts off the waveform at the peak of each cycle, producing a frequency "doubling" effect unlike a rectifier-based design. 

In this implementation all manner of transistor drive and fuzz tones are available - the input capacitor blend alone can tailor the character across a big range and it even does lower gain quite well. At max settings it produces a slew of unusual harmonics due to the NPN/PNP cell. There exists some condition where the clipping cell produces a delightful octavia-style fuzz at high gain settings, but the effect is dependent on neither beta nor base-emitter voltages and I have not been able to replicate it. My best results were with a 2n2219A/2n2905A pair, which are functionally close to the 2n2222/2n2907. (Schematic)

Modded Maestro Fuzztain

The Maestro Fuzztain features a unique CMOS compressor feeding an op amp drive with feedback clipping. The original had three modes: clean compression, low-gain fuzz, and high-gain fuzz. These were selectable via a rotary which controlled multiple parameters. My friend convinced me to do a modded version with more control, so I broke out the rotary into its constituent controls. The compressor has two level settings, the fuzz has its own gain control, and the fuzz can be bypassed to use the compressor on its own. In classic 70's Maestro fashion it's incredibly well-engineered—check out the peak detector circuit feeding the compressor and the capacitance multiplier in the PSU filtering section. The CD4007AE in the compressor is a bit hard to find but not impossible. NB: the schematic is verified! (Schematic)

Steiner VCF

This filter is best known these days as the multimode filter in the Arturia Microbrute. Has a very aggressive drive sound when the resonance is cranked up. This implementation is pretty close to the one drawn up by Yves Usson here. (NB: His site also has a link to the original article by Steiner describing the operation of the filter, which is quite elegant.) Changes include a redesigned power supply, input buffer, active pregain control, active volume control, some extra low pass filtering to tame parasitic oscillation, and limiting resistors on the sweep control to keep it in the guitar range. A meter is recommended for calibration. (Schematic) 

Headphone Amplifier

Collaborative effort with Nerd Knuckle Effects. The original plan was to make a headphone amp for trade shows, allowing a reasonable approximation of a pedal sound in sub-optimal conditions. The circuit is a combination of three circuit blocks: a fairly tube-like JFET preamp, a speaker cabinet simulator (see the Runoffgroove Condor), and a headphone driver (inspired by the MXR Headphone Amp). Drives headphones fairly well but isn't quite loud enough with low-impedance studio headphones. Will be revisited, possibly with an LM386 or a fancier discrete output stage. (Schematic)

Paradigm Shifter

This is a unique JFET phaser designed by JC Malliet at Viva Analog. I had the opportunity to design the two-layer PCB layout. For more information, see here. An updated layout will be coming soon.