Guyatone GST-CO4 Ultrem review

  • £379
  • $495

With tremolo back in vogue, Guyatone's optical pedal is just what you need

Image 1 of 2 blank
The Ultrem just might be the best pedal of its type
Image 2 of 2 blank
Plug in a Boss Expression pedal for more options

Our Verdict

Old-school analogue technology and modelling style versatility make one of the best tremolo units around.


  • Warm and convicing sounds. Great fun. Limitless options.


  • Only that over-using tremolo can be annoying.
Buying options

Like that old advert that challenges you to put a sweet in your mouth without chewing, we dare you to try the Guyatone Ultrem Optical Tremolo without playing the theme to Twin Peaks or Johnny Marr's awesome tremolo opening to The Smith's How Soon Is Now?

Where the '70s vibe of the Guyatone Ultron envelope filter (also reviewed on MusicRadar) makes us want to slide over the bonnet of a car arse first like Starsky and Hutch, the Ultrem transports you back to a gentler time of surf music and Roy Orbison ballads.

Not that it's stuck in the past like some aging hippy. Like its brother in charms, the Ultron, this tremolo unit combines vintage and modern technology in a tough little package.

The Ultrem is probably the most comprehensive tremolo pedal on the market. The tap tempo function is so essential. The ability to instantly alter the speed of the tremolo with your foot live or in the studio makes this pedal a very useful tool indeed. Add to that the sheer breadth of tremolo options available - from the subtle wobble of an old valve amp circuit to the maniacal chopping of Green Day's Boulevard Of Broken Dreams - the Ultrem delivers them all beautifully.

And there are many more goodies on offer here. The Ultrem has an auto function that triggers the tremolo effect when a signal is received and stops the instant the input signal does. You'll be playing around with that for hours. That's the beauty of tremolo: it can save a tired chord sequence and turn a well-worn idea into something special.


The Ultrem has six effects modes, some of which can be influenced with an optional Boss EV-5 Expression pedal (£49). For example, in the Pedal Speed/Touch mode the expression pedal varies the speed of the waveform oscillation. Switch to the Momentary Wave mode (and depress the Ultrem's onboard control footswitch) and the tremolo effect engages. Release the footswitch and the effect stops. It's functions like these that make the Ultrem such an awesome piece of kit.

Tremolo isn't an effect you'll use all the time - too much of any effect is a bad thing after all. But the Ultrem beats the boredom factor thanks to the sheer number of sound options available. Use this pedal in interesting ways and it will keep on rewarding you. Sure, it's perfect for retro guitar parts but it can also work its magic on bass guitar lines or added to a backing vocal for some Beatles style experimentation. Run some orchestral string parts through it and set the speed high for some '50s B-movie fun. The options are limitless.

It's tough to match the warmth of a vintage amp's tremolo circuit but Guyatone have nailed it. And they didn't need modelling trickery to do it, just good old-fashioned analogue technology.

Tech Specs

Available Inputs1/4 Inch Jack
Available Outputs2x1/4-inch jacks
Battery/Adaptor TypeNine-volt mains adaptor
Dimensions120 x 188 x 55mm
LFO Wave FormsPulse Saw Tooth Triangle
Manufacturer's DescriptionOptical tremolo.
Weight (g)680