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Zoom RFX300

Effects Unit By Paul White
Published November 1999

Zoom RFX300

Paul White foresakes his towering effects rack for a budget processor that looks for all the world as though it would float in the bath!

Zoom started their career by building (pretty impressive) mid‑market effects processors, but these days they seem to have shifted their sights firmly towards the budget guitar player and home recording markets. Their RFX300 looks like a stomp box, but is in fact a stereo studio effects processor, which can be powered either by batteries or the included wall‑wart power supply. (If ground loop hum turns out to be a problem, you can often outwit it by shifting to battery power.) Unlike Zoom's guitar processors, this one is designed to accept line‑level signals, which it can do via either jack (unbalanced) or phono connectors as both are provided; the left jack socket will also function as a mic input, with up to 56dB of gain. The effects themselves appear to be generated from a mix of the left and right inputs, but the dry component of any stereo signal fed through the box retains its stereo integrity. For mono operation, use the left input jack only.

Despite its budget appearance, the Zoom RFX300 features 18‑bit, oversampling 44.1kHz converters, and handles (‑10dBv) 0.775 Volt line levels. A 12‑position rotary switch is used in combination with illuminated Bank A/B buttons to select 24 different effects types or combinations, and separate input and output level controls are fitted, with a red LED to warn of input clipping.

The effects are adjustable to a limited extent, but you can't store user patches and there's no MIDI — in much the same way as there was no power steering, air conditioning or ABS on the Sinclair C5. A single rotary control adjusts one parameter for each effect type; status LEDs let you know whether this is time (for such things as delays or mode rates) or something else that's patch specific.

A Variation/Tap button works in conjunction with this control so that time‑related effects can be sync'ed by tapping in the tempo manually. Where the effect is not time‑related, this button switches in a second variation on the original effect. Finally comes the mix control; if an effect with no mix parameter is selected (such as compression or one of the mix EQ presets), this adjusts a parameter more relevant to the effect, for example, compressor threshold or mic amp enhancement.


Most of the effects are pretty conventional: the selection includes Hall, Room, Plate and Ambience reverbs plus Delay, Pitch Shift, Chorus, Flanging and Phasing. On top of that you get a number of EQ treatments for mix processing, vocal processing or guitar cabinet simulation. There are also some dual programs such as Flanger/Reverb, Delay/Reverb, Chorus/Reverb, Compressor/Delay and Compressor/Detune, though the lack of control when dual programs are selected can be frustrating.

When I first patched in the RFX300, I dialled in Ambience and fed in my guitar via a DI box — and the sound was absolutely amazing. Then I realised the send to my Lexicon PCM90 was also turned up! After switching off the Lexicon, the sound was understandably different, but the surprising thing, considering the cost of the RFX300, is that the reverbs were still pretty impressive, even with the decay time turned down to emulate small rooms. Not only that, but the pitch‑shifter was noticeably less glitchy than the ones found on some far more expensive units (though still a trifle warbly), the chorus and flange had a nice organic sound to them, and even the phaser sounded approximately like its analogue equivalent. The various EQ settings were reasonably well suited for the jobs they were designed to do, especially the guitar cab simulator, and though the rotary speaker emulation isn't the world's best, it's still very usable. Obviously the effects aren't in the same league as those offered on serious rack processors, but they are musically viable and fun to use.

...the surprising thing, considering the cost of the RFX300, is that the reverbs were still pretty impressive, even with the decay time turned down to emulate small rooms.

Of course, every Achilles has his heel, and the RFX300's weak spot is that the sound breaks up horribly if you let the input overload. With transient signals such as clean guitars, it can be very difficult to to control the peak levels except by patching a limiter before the input. The other side of that particular coin is that you nevertheless need to drive the input as hard as you can, because despite the 18‑bit spec, the signal‑to‑noise ratio isn't that great. With properly optimised levels, and at what I would imagine to be a typical monitoring level, a low‑level hiss/hum is plainly audible when nothing else is playing. An analogue limiter built into the effects chain input would help a lot, but few designers do this.

In brief, then, the effects sounded rather better than I expected and the noise is no worse than anything else at this price, but you do have to be very careful with your levels to get good results. Great for demos and usable for independent CD releases if you're careful.


  • Very respectable effects quality, especially the reverb and modulation effects.
  • Exceptionally easy to use.
  • Cheap!


  • Prone to overload.
  • Limited effects editing.


The Zoom RFX300 is certainly cheap, but it's also very cheerful. If you're careful with the input level setting, the effects are surprisingly good for something so inexpensive.