There’s something special about COSM. Short for “Composite Object Sound Modeling”, this technology was released by Roland/Boss in 1995 and it has that special grit lacking in many more modern preamps. The Roland GP-100 leveraged COSM like a boss to create an amazing 1U rack preamp adorned with a classy champagne front plate and plenty of usability features meant to please professional musicians. For the most part, it did the trick. Think of the GP-100 as a more professional alternative to the Boss GX-700, which was released a year later.

Knobs and Connectivity

The GP-100 has a built-in power supply which probably works to reduce background hum a tad more compared to the Boss GX-700 with its somewhat burdensome external PSU. The GP-100 also sports a beautiful set of knobs allowing you to intuitively set bass, middle, treble, and all the other traditional basic parameters for its amplifier emulations. Other settings in the GP-100 are elegantly handled using two rotating controllers next to the power-switch, both with push-button functionality as well.

Roland's GP-100 has a great set of connectors in the back, including MIDI in and out. There are two sets of 1/4" stereo outputs for connecting the GP-100 into mixers and power amplifiers. The effect loop in the unit supports two external stereo devices; the one in GX-700 was mono only. An additional input jack also resides in the back panel of the unit. Only some kind of digital output is missing (which would be rare in a device from 1995). The COSM-based Boss VF-1 from 1999 rectified this with its splendid coaxial S/PDIF-connector.

You can extend the expressive capabilities of the GP-100 with Roland's FC-200 foot controller and many other MIDI-based devices.

The Glory of Nineties Roland Preamps

In my book the best amplifier emulations in the GP-100 are the Soldano, the Peavey 5150, and the mighty Roland Jazz Chorus 120. The Fender Twin on offer is also usable, if a bit lifeless. The adequate Matchless emulation in the GP-100 might also come in handy for some. All Roland/Boss units of this era are quite lousy for crunch; they excel in squeaky clean or seriously overdriven tones. One exception is the odd Mesa-Boogie simulation which doesn’t sound that great even when heavily distorted. As for a fairly pleasant COSM-based crunch, the Marshall-emulation ("MS 1959") comes close.

Not all preamps sound wonderful with all speaker simulations. The Soldano and the 5150 are best matched with the virtual MS Stack or Metal Stack speakers. As always, you should apply heavy doses of EQ; you often get the most out of these units by cutting a few dB at 350 Hz, 500 Hz, or 1.25 kHz. Luckily, the GP-100 has a four-band effect for this; the EQ in the GX-700 was a mere three-band affair.

Fun with Algorithms

The GP-100 uses a system of five algorithms each of which consist of a different set of effects. These algorithms are labeled BASIC, DELAY, HARMONY, VINTAGE, and DUAL. There are no modulation effects, apart from chorus, in the BASIC-algorithm. DELAY, on the other hand, offers chorus, phaser, and flanger as well as a fancy four-tap delay. Only HARMONY has a neat four-voice harmonist effect. The VINTAGE-algorithm is the only one to provide tremolo, vibrato, and a rather wretched automated wah.