Roland SIP-301 Bass Pre-Amp

Roland Rack. Click to enlarge.

Introduction to the Roland SIP-301:

In the early 1980’s Roland produced some of its most acclaimed rack mount effects processors. This series included the SIP-300 guitar preamp, the SIP-301 bass preamp, the SBF-325 voltage-controlled, stereo rack-mount flanger, the famous SDD-320 Dimension D chorus unit, the SRE-555 rack-mount version of the RE-501 tape-delay/chorus, and the SPV-355 pitch-to-voltage analog synthesizer.

The SIP-301 is a versatile analog bass preamp. There is a high and low gain input, followed by an excellent analog compressor. The compression can be disabled using a foot switch. After the compression section is an optional effects insert, then a very flexible three-band equalizer, with high and low cut filters. Each band in the equalizer has two selectable frequencies as well. After the equalizer there is another effects insert! Then a volume control which feeds directly to the front panel XLR output, and a master volume control that feeds to a pair of unbalanced outputs, one of the front panel, and one on the rear panel. The master volume also feeds a built-in crossover network, with high and low outputs on the rear panel as well.

The SIP-301 is a fully professional unit that can be used simply as a direct box for Bass or any high-impedance input, or it can be used as a additional processor to add some analog quality sound to any sound source.

Smooth Vintage Optical Compression Circuit:

The SIP-301 compressor provides clean, smooth compression with ultra-low noise and incredible transparency. The compression ratio can be set from subtle to extreme. While it is on you will notice note-to-note levels that are smoother and more consistent, chords and arpeggios that are tighter and more focused, and when used with an overdriven amp, sustain that will last for days. Best of all, you’ll notice minimal coloration to your guitar signal and less of the note-attack alterations so common to other compressors.

At the heart of the SIP-301’s circuit sits are two vintage HTV P873 CdS (Cadmium Sulfur) Photo couplers. This light-sensitive component varies resistance based on the input signal to control the amp gain, increasing gain as the input signal weakens. Most other current-production compressors accomplish this task using a VCA (voltage controlled amplifier), but the multiple transistors packed into a VCA inevitably lead to high noise levels, which means lots of "hiss" from your rig. The SIP-301’s optical circuit keeps the noise-floor low - so low that you can run the unit after a distortion and still retain near-silent operation. With its ultra low-noise level, transparent operation and natural playing response the SIP-301 has the perfect compressor for players who hate using compressors.

All Discrete Componenet Three-Band Active Equalizer:

The SIP-301 equalizer section works just a brilliantly as the compression circuit. Notice that the equalizer is all old-school, using entirely discrete components, with no operational amplifiers in this first-class design. Most modern equipment makes use of off-the-shelf, inexpensive op-amps. This greatly lowers production costs, and makes design easier, but all discrete circuits like the SIP-301 have lower noise, with more precise musical operation, since they are specifically for sonic applications. As noted, this unit works equally well for guitar.

Again, there are two selectable frequencies per band. The selectable frequencies are low band: 35 Hz or 45 Hz, mid-band: 250 Hz or 500 Hz and high band: 4 kHz or 6 k Hz.

Versatile Effects Loops and Output Options:

The SIP-301 provides four unbalanced 1/4” outputs, one full-range output on the front of the unit, and one full-range output on the back. There are two additional unbalanced, active crossover outputs on the rear, with a crossover frequency control. There is additionally a balanced, XLR output on the front. The first volume control functions as the master volume control for the unit, controlling the level of both the balanced and unbalanced outputs. There is a dedicated volume control for the four unbalanced outputs as well.

For stage or studio recording, the master volume control would set the level of the XLR/balanced/recording output going to the mixing console. The unbalanced volume control would be used to control the stage volume, independent of the XLR/balanced/recording output. In addition, there are two independent effects loops, a high impedance send/return on the rear, and a low impedance send/return on the front.

Roland SIP-301 Block Diagram.

• Download the SIP-301 Guitar Pre-Amp Owner's Manual (pdf).

Photos:

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Videos:

Schematics - Repairs - Service Bulletins:

There are no known service bulletins from Roland addressing any SIP-300 problems.

• Download the SIP-301 Service Manual Schematics (pdf).