Like most of Universal Audio’s compact pedal range so far, the Flow is a digital pedal derived from some of the effects found within their larger, more comprehensive UAFX units, in this case the Astra modulation pedal. Mono in and out, with only three controls, there’s either not much to get excited about, or an intuitive and immediate user interface, depending on your viewpoint. I tend towards the latter, especially with regard to guitar pedals.
You can preset Flow to one of three modes: ‘65’ replicating the optical tremolo circuit of mid‑’60s classic amps such as Fender’s Deluxe and Twin Reverb; ‘Square’, which as the name suggests uses a differently shaped waveform to give a harder‑edged, ‘choppier’ tremolo effect; and ‘Dharma’, a harmonic tremolo effect similar to that used in some late ’50s or very early ’60s Fender amps. In this mode, the input is divided with a crossover into separate treble and bass signals, with an LFO modulator then used to pan back and forth between them. When the two channels are re‑combined you get cyclic variations in the frequency response and level that sound a bit like a mild phaser circuit and a tremolo at the same time. That might sound a bit lame but it’s actually a beautiful effect that must have sounded pretty space‑age when people discovered it within their tube amps back in the day! You can hear exactly what it is doing by turning Flow’s Depth all the way up and the Speed all the way down. Play a chord and hear all the top end come and go every three seconds or so, with the bottom end doing the inverse. Not very useful like that, of course, but turn Speed to 12 o’clock and Depth to 10 o’clock and play some chordal parts, and you’ll hear that the effect has a subtlety that avoids both the annoying whoosh of a phaser and the attention‑grabbing throb of a full‑on optical tremolo.
There’s a Volume control to make up for the subjective level drop you get when you activate any tremolo effect: it sounds quieter overall because it is spending half the time attenuated to some degree, and that includes the harmonic tremolo, too, as there is a lot less energy in the treble‑only part of the signal. In their original form these effects are all tube‑based, of course, being implemented within tube guitar amps, and the tube emulation necessary for full authenticity is included with the Flow pedal. A single valve usually takes care of an optical tremolo circuit, but harmonic tremolo requires rather more, up to three dual‑triodes in some designs, which explains why apparently quite simple, very early‑’60s non‑reverb amps can still have an impressive array of five or six preamp tubes.
As with all the UA pedals, there is plenty of headroom for using Flow at line level and especially in a tube‑amp effects loop.
The footswitch, which also offers a switchable buffered or true bypass option, can be set to double as a tap‑tempo facility — very useful in such a rhythm‑based effect. You can still bypass when in tap mode using a press and hold on the footswitch, with the tapped tempo being retained unless you manually adjust the Speed control, so it will still be there even when you bypass.
Top‑mounted jacks and DC input (standard 9V, centre‑negative, 250mA minimum) help keep Flow’s pedalboard real‑estate demands to a minimum, and with very few modern amp designs offering tremolo, the pedal represents a great way to incorporate this classic effect within any setup. As with all the UA pedals, there is plenty of headroom for using Flow at line level and especially in a tube‑amp effects loop; in fact I think it sounds at its best there, replicating the position in the signal flow that the original circuitry would have.
The basic tremolo sounds do exactly what you’d expect, with an adjustment range that covers everything from gently pulsing to ‘machine‑gun’ chopped, but the harmonic tremolo just might surprise you as ‘the subtle effect you never knew you wanted’. I’ve created some audio examples should you want to get a better feel for what I’m writing about and you can find them below.
UAFX Flow: Audio Examples
Audio Example 1
‘65’ replicates a classic Fender tube amp optical tremolo ‘throb’. As with a real integrated amp trem, you have dial-in the tempo manually. In this type of track I’ve always found that it doesn’t seem to matter if you don’t get it quite spot-on, so long as you avoid anything that obviously clashes with the basic rhythm.
Audio Example 2
The ‘Dharma’ harmonic tremolo effect adds some subtle animation to this rhythm guitar part without making it too prominent — I’ve over-mixed it here and taken out some other parts so you can hear it more clearly as in this context I want it to be a fairly gentle effect, with Depth at only 40 percent. There’s a ‘sweet spot’ up to about 60 percent, after which it starts to sound a bit tonally deconstructed, to me.
Audio Example 3
The ‘Square’ setting lends itself well to sequencer-like pulsing parts. Obviously, the exact tempo matters far more here than in the first example. I just audibly lined it up with a click, as it only has to hold sync for the time between one chord and the next with a guitar part like this. This effect is still based on the same ‘65’ optical trem model, however, so it’s not actually fully square-wave modulated — an optical circuit can’t respond like that — resulting in something that sounds a bit more organic than synth pulsing rhythm.