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Zoom 503

Zoom 503

Can you get a wall of sound from something the size of a single brick? John Walden plugs in his guitar, inserts his earplugs and finds out.

The 503 Guitar and Bass Amp Simulator is the latest addition to Zoom's 500 series of guitar foot pedals. Its primary aim is to provide both the guitar and bass player with a range of different 'classic' amplifier and speaker cabinet simulations in one convenient box. In addition, a small selection of multi‑effects options are included. While all the 500‑series pedals would seem to be designed predominately for use in live performance, more than a passing nod has been given to studio users. Although a budget price does not necessarily equate to budget sound, the cost of the unit means it is more likely to be of interest to those wanting a simple means of getting diverse guitar or bass sounds either at home or when on the move with their portable multitracker.

What's In The Box?

The 503 is constructed from moulded plastic and measures about 15cm square by five cm high, and seems robust, though I wouldn't advise jumping on it too often. The front panel includes two foot‑operated pedals that are used for patch selection. The central strip includes a two‑digit LED, which displays either the patch number or a parameter value when editing, and a series of small indicator lights. These indicate which elements of the effects chain are active for a particular patch and highlight which parameter is being edited. Pairs of buttons on both the left and right edges of the unit are used in editing patches. These are all clearly labelled.

On the rear panel there are two mono inputs labelled LOW and HIGH, recommended for guitars with humbucking and single‑coil pickups respectively, and a further input which takes a signal from a device like a CD player. This signal is then mixed with that of the guitar and arrives at the stereo output that provides a feed to your guitar amp, mixer or headphones. The only other connection on the back panel is for the external power supply (included in the price) although the unit can also be powered from a standard 9V battery.

The 503 can store a maximum of 24 patches, arranged in six banks of four and labelled A1 to F4. As supplied, banks A to D are configured for guitar and E and F for bass. The heart of the unit lies in the various amplifier and speaker cabinet simulations it attempts to recreate, and a total of 15 amp and six cabinet types are available (see the box below for some examples). Each patch is constructed from 10 parameters (see the 'Patch Work' box), and individual components of the effects chain can be switched on and off as required. These components include basic reverb, delay, chorus/flanger and even a tremelo. A chromatic tuner is among a number of other convenient features included for live use.

In Use

As is explained in the manual, the default setting in roughly half the patches has the cabinet simulation disabled to accommodate using the 503 with a guitar amplifier. Unsurprisingly, therefore, these patches — including patch A1 which is selected on power up — sound fizzy if you hear them straight to headphones. However, a few minutes with the manual is all that is needed to get to grips with patch editing, including activating the cabinet simulation on patches in banks A, B and E. The editing process is straightforward within the limitations offered by the LED.

Having got my virtual speaker cabinets sorted out, how did the 503 sound? The short answer is very impressive. While some of the factory presets were a little toppy for my taste, simple editing soon improved things. Sounds based on the cleaner amp types could be made to be both bright and warm, while the overdriven amp types produce sounds ranging from mild, edgy distortion suitable for blues, through some great grungy, fat sounds suitable for a Metallica impression, to a smooth, really overdriven lead tone which, with a touch of delay, had me trying out some Gary Moore‑style licks. Within any particular amp type, moreover, it is possible to shape the sound you want and alter its tone in a wide variety of ways using the gain, EQ and cabinet type and depth.

Although the chorus, reverb and delay effects are basic, they do add an effective ambience to the sounds, which is useful if you have limited outboard effects available or if the unit is simply being used as a practice tool. The room reverb is particularly effective in this respect, and the simulated mic position (close, angled or distant) also has a noticeable effect on the character of the sound. The noise reduction seems to do a reasonable job and the only problem I experienced was some noise at high gain settings as sustained notes faded to silence. This was probably no worse than the noise generated by a some real amps with a mic stuck in front and, at the price, is a minor criticism.

The 503 performed just as well with a bass. The clean amp types provided a really smooth and solid sound while the 'drive' amps allow a variable amount of overdrive to be added for a more rock orientated feel.

The overall impression is of a more‑than‑ adequate sound that can be created and customised with ease.

The overall impression is of a more‑than‑adequate sound that can be created and customised with ease. All the sounds (both guitar and bass) translated well directly to tape providing a convincing presence either within a mix or in isolation. While the sounds may not be as responsive to picking style as a real tube amp or something like the popular Marshall JMP1 guitar preamp, the 503 is a lot ch eaper. A more direct comparison might be with Korg's Pandora MkII which, for another £70 or so, offers a similar set of amp/cab simulations plus a wider range of multi‑effects. Zoom (among others) also make other units in this higher price bracket.


The amp and speaker cabinet simulations available in the 503 are pretty effective. With the addition of a drum machine and a microphone, the 503 would make it very easy to sketch out your electric guitar‑based song ideas on a basic multitrack. If you are working on a tight budget, want a wall of sound but don't want to be a candidate for Neighbours From Hell then the Zoom 503 is well worth checking out.

Amps And Cabs

Of the 15 amp types, nine are intended for guitar use (G1‑G9) and five for bass (b1‑b5). The remaining model is configured as 'flat' (FL), but allows access to the EQ, or the amp simulation can be turned off completely. Both guitar and bass amp types vary from clean to overdriven. For example:

  • G2 'MS DRIVE'

A 'British' tube stack amp in overdriven mode.

  • G6 'PV DRIVE'

A high‑gain tube stack amp with heavy metal in mind.

  • G7 'J CLEAN'

A clean style combo amp.

  • b1 'TE CLEAN'

Clean bass amp with strong midrange.

  • b4 'AC DRIVE'

Overdriven bass amp sound.

For the 'clean' amp models, the Gain setting adjusts the compressor (guitar amps) or limiter (bass amps). For the overdriven amp types the Gain setting adjusts the distortion intensity.

Four of the six cabinet simulators are designed for guitar (two combo and two stack types) and the other two for bass. The different types are essentially intended to mimic different speaker combinations (for example, a combo with one 12‑inch speaker or a 'wall' of 4 x

12‑inch cabinets!). For each cabinet type, the 'ringing depth' can also be set.

Patch Work

1Amp Type
6Cabinet Type & Depth
7Mic Position & Noise Reduction
10Output Level


  • Wide range of sounds available.
  • Creditable imitations of amp and cab combinations which go well directly to tape.
  • Easy editing.


  • Presets might need a tweak to hear the unit at its best.
  • A little noise apparent on high gain settings as notes fade.


For those working on a tight budget, the Zoom 503 provides an excellent option for getting a range of convincing electric guitar and bass sounds on to a multitrack.