Diamond Pedals of Nova Scotia have been making guitar stompboxes for quite a while now. With the Bass Comp, they bring to bass players the high-grade optical compression previously available to guitarists in their Compressor pedal.

What’s in the box? Aside from the Bass Comp, there’s an 18 volt DC power supply, a short, red, power-polarity-reverse cable (more on that later), and a well written, useful, four page manual.

The Bass Comp accepts between 9 and 24 Volts DC, and cannot be battery powered. The included 18VDC adapter provides the recommended operating voltage. Running at twice typical stompbox voltage allows the Bass Comp greater headroom, and should make it play nicer with high output active instruments. Note the pedal power jack is negative ground/ positive tip — if powering via a standard 9VDC adapter, use the included polarity reversal cable.

The build quality of the Bass Comp is excellent. A genuine Hammond cast-aluminum enclosure houses real Switchcraft jacks, Alpha pots, Vactrol opto-isolator, Analog Devices op amp and a slew of discrete transistors. The PCB is very cleanly laid out, and a solid feeling 3PDT switch handles true bypass duties. Inside are two hidden controls: a bypass switch for the EQ, and a hi-cut jumper. In testing with a single 12” bass speaker, I could hear a very subtle difference in the background noise engaging and disengaging the EQ switch, but no difference at all engaging the hi-cut. It may be the lack of perceptible difference was due to the test bass cab lacking a tweeter.

On top of the pedal are knobs for Compression (COMP), EQ, and output volume (VOL). A small toggle selects the pivot point for the EQ, and a dual-color LED indicates that the compressor is engaged (green), and that compression is happening (orange to red, depending on the amount of compression).

The COMP knob resembles the old dbx 163x ‘slider’ compressor and the UREI 1176 Input control: the greater the setting, the higher the level going into the compression circuit, and the greater the compression. Set low, the Bass Comp’s effect on the signal is nearly imperceptible. At high levels, the compression can be very heavy handed. So even though only a single knob handles interaction with the compression circuit, the range of compression nicely covers the ground between ‘not enough’ and ‘far too much’.

Background noise is a common issue with compression. By its very nature, compression decreases signal-to-noise ratio in an audio chain. Happily, the Bass Comp only had objectionable hiss at COMP settings over about 3 o’clock. By this point, there was far more compression than I wanted. In the 9-to-1 o’clock range that worked best for my tastes, unwanted noise was simply not an issue.

The EQ is a dual band, single control affair. Unlike a typical tone knob that only cuts high frequencies, this teeter-totter style EQ boosts frequencies at one end of the spectrum as it cuts those at the other end. As the knob moves counter-clockwise, bass is boosted as treble is cut. Moving clockwise, treble is boosted as bass is cut. At the center detent position, the EQ is flat. The toggle switch selects the pivot frequency (250Hz or 900Hz).

The teeter-totter EQ is a graceful approach to a limited control set. And it sounds good; even fully counter-clockwise, the high end never felt too muffled. That said, the EQ isn’t necessary for my purposes, so I appreciate the internal bypass switch. I would think the EQ would be great in back-lined situations where you might not feel free to adjust a borrowed amp’s EQ control, but outside that, most amplifiers will have more exhaustive and bass-appropriate EQ available.

The (VOL) control is simply output volume. Given the COMP control is essentially input volume, the VOL control works well to pad the output of the compressor down to an appropriate level when bouncing between engaged and bypassed states. Given the high headroom of the Bass Comp, it’s capable of substantial gain, which could be useful for using it as a boost effect, or even as a preamp for a low-output instrument.

I tried the Bass Comp with the included 18 volt power adapter, which worked great with no detectable hum or power-supply related noise. I also tried an old (non-isolated) Vestax pedal power supply (with the included polarity reversal cable). Strangely, the pedal would not power on if directly connected to an amp. If I plugged the output of the compressor into another effect (powered from the Vestax), it would then power without any problem. A little weird, but no biggie—it’s an old power supply I don’t gig with. I also tried powering the unit from a garden variety, 9VDC adapter from a MIDI interface. This also worked fine, again without hum, so I suspect there’s some pretty heavy power supply filtering going on in the Bass Comp. Lastly, I tried this with a Voodoo Labs PP2 (9v output) with the polarity flip cable, which worked fine.

In trying the pedal with different power supplies, I unexpectedly realized I slightly prefer the sound of the comp running at 9 volts vs. 18 volts. Compression appeared to happen at a lower volume, and sounded a little smoother to my ear. The majority of my testing was with passive P and J basses, so these lower output instruments may not benefit as much from the increased headroom as higher output active basses would.

I compared the Bass Comp with the ubiquitous Boss LMB3 bass limiter/ enhancer. To be fair, I’m not a huge fan of the Boss unit, but I do have it on my pedal board at the end of the chain to help even out unwanted boosts from some of the effects I use. The Diamond comp blew the Boss out of the water. Much fuller and more natural sounding. I also compared the Diamond to some rack mount compressors I’ve got floating around. It sounds comparable to dbx’s ‘overeasy’ compression, and fairly close to FMR Audio’s RNC compressor set to a 4:1 ratio with attack and release times set about mid-way. Given the pedal form factor, I was happily surprised at the sound quality compared to these rack units.

Bottom line: I really like the Bass Comp. Streeting at about $250 USD, it’s not the least expensive compressor out there, but for a North American built, boutique pedal using top-notch components it’s more than fairly priced.

Ron Guensche is a bassist and audio engineer in the San Francisco Bay Area.