3. Subdecay Octasynth
There's something to be said about the size of this unit, as it’s the only pedal in this list that comes in an MXR (1590B) sized enclosure. That isn't to say that its feature set is limited in any way, but if a player requires a rich, yet pared-down synth sound for one or two parts, this is it. The filtering and subsequent pitch generation sound much more like a Roland TB303/MC202 than a Moog Prodigy. If that isn't a familiar sound, take a listen to Josh Wink's "516 Acid." This acid-laden bleep-bloop isn't the only thing the Octasynth is capable of, but it excels at this. If for some reason, you find yourself a guitarist in dire need of acid house sounds, look no further.
4. Red Witch Synthotron
One of the most all-in-one synth solutions on the market today, the Red Witch Synthotron offers a feature that not many pedals have ever offered: a sample-and-hold filter. Only one other pedal (to my knowledge, the Maestro FSH-1) has ever offered sample-and-hold filtering, and that box goes for a pretty ridiculous amount on the used market. Though the Synthotron is an expensive unit, the price isn't nearly as high as the Maestro and contains much, much more. For example, the Synthotron offers actual synth-esque amplitude modulation, which is a key feature on many old analog units, and rarely, if ever, implemented for stompbox use. While tremolo is a form of amplitude modulation, the Synthotron's AM sounds different from a typical trem. Aside from those features, the Synthotron features two standard oscillators with mix control.
5. Electro Harmonix Microsynth/Bass Microsynth
Another effect released during the golden age of hardware synths, the Microsynth and its bass-friendly counterpart don't share the same type of circuit topology as the Korg X911. The latter is an actual synthesizer, boasting control voltage inputs and such, where the Microsynth is an effects processor built to accept an instrument level signal. It's hard to think of a pedal that predates the Microsynth for these type of sounds that didn't require its own roadie (Ludwig Phase II) or didn't fall apart when looked at funny (Maestro USS-1). That said, the Microsynth can be called the granddaddy of synths in a pedal, a title its held since the mid-'70s. And because of its year of production, this baby is—and 40 years later, continues to be—all analog. The sound? It does the job at about 95 percent, not bad for something so old. The pedal continues to be a big seller to this day.
6. Pigtronix Mothership
One of the more complicated models on the list, the Pigtronix Mothership operates under the same principle as the aforementioned Maestro USS-1. That is to say, two different (exhaustive) effects combine to approximate a synthesizer sound. (The USS-1 contains five.) The difference is that while the Maestro sounds like five different effects in series, the Mothership absolutely nails it. The two effects in the Mothership are an intelligent ring modulator and a sub-octave generator. Ring modulators can be tricky, because they rely on the pitch of an internal oscillator, which is normally tuned to Bb. This makes anything not played in the key of Bb sound like a dissonant mess. The Mothership skirts this by offering a multitude of tuning controls for the internal oscillator. Don’t be scared away by VCO controls, they just mean “voltage controlled oscillator,” much like the ones found in any synthesizer worth its salt.