October/November 2015

by Jonathan Pearce

Review: Laney Ironheart IRT-Pulse USB Valve Pre-amp

by Jonathan Pearce

Review: Laney Ironheart IRT-Pulse USB Valve Pre-amp

Analogue to digital convertor technology is now cost-effective enough to be integrated into any aspect of the audio chain. The trend has been towards replacing analogue circuitry with digital solutions, from stompbox effects pedals to PA room correction EQ. With the Ironheart IRT-Pulse, Laney have developed a new hybrid of vintage and modern, aimed at the recording guitarist.

 At a glance, with USB socket and vaguely labelled push-buttons, the Laney IRT-Pulse (rrp $499) seems mysterious, however plug it in and the glow from inside the cage says this is a valve amplifier. For guitarists the next part is obvious –– guitar goes in the input, front and centre. On the amp we have rotary controls for Gain and Volume, a ‘Hot’ mode for more distortion and a Bright switch.

After the valve amp Laney have given us a host of options for what to do with our valve-amplified signal. There is a balanced output, for connecting to a PA system, which also works in unbalanced operation with a guitar amplifier. There is a headphone amplifier with 3.5mm output socket and volume control. And, built into the small metallic-black box, there are analogue to digital (and digital to analogue) convertors that interface with a computer via USB 2.0, making the Pulse a completely integrated guitar recording set up.

For the Pulse to be useful in the studio, it must have good convertors, regardless how good the valve amp sounds. I auditioned the Pulse against my RME Fireface and, remembering the near past when cheap convertors meant that things sounded as though they were playing from under a scratchy woollen blanket, I was very impressed. For playing back pre-recorded music, monitoring via the headphone amp, noise was no issue, and the reproduced audio spectrum was full-range. The Pulse exhibited a slight presence lift from 5Khz compared to the RME, but could not be called harsh.

The Pulse sends two channels, via USB, with a dry DI sound down the ‘left’ channel and the valve amplified signal down the ‘right’. Left and right must be firmware hangovers from the convertor chip’s original design purpose, as they have no correlation to the stereo field here at all, and should simply be considered as input channels one and two. In Reaper (my chosen DAW) I was able to record either one or both, as I wished.

My second test was to compare the DI signal of the Pulse to the Hi-Z input of the RME. My only major criticism of the IRT-Pulse is with this DI signal. My Les Paul Deluxe strummed heavily on an open E chord was able to push the convertor to clipping (0dBFS), and that guitar’s mini-humbucker pick-ups are not as hot as many modern pick-up designs. For a device designed for heavy rock styles, and given pick-ups designed for those styles are typically high output, I was surprised to find this apparent lack of headroom.

Played within these limitations, the RME was noticeably brighter and more dynamic, with a lower noise floor too, but the DI signal from the Pulse was useable, and will be what the Pulse expects to see in ‘Re-amp’ mode (more on which later).

DI concerns aside, the IRT Pulse is a valve pre-amplifier, and in this regard it is excellent. It begs you to go straight to max. gain in hot mode and hoon! The Pulse distorts in a familiar soft-clipping, heavy way, without stepping on the sonic characteristics of your instrument. With the Les Paul it was punishingly heavy for riffs, with the mid-range bark of that guitar fully on show. With a classic Telecaster it was completely different – big lows and highs, unruly and thrilling. Full-on like this the Pulse feels very like a cranked valve amp, compressing with the pick attack and responding to playing intensity. Winding the gain back can produce useful heavy rock tones, but as soon as the gain gets below about 75% the bright switch is needed for air and presence.

Also impressive was the clean sound produced by the Pulse at very low gain. It was broad and did not lack low end or clarity. In fact it inspired me to plug a bass in, which sounded fantastic, eminently recordable. I measured the Pulse passing signal way down to 20Hz, so no worries there.

The two other controls between the valve amp and the convertor are a mid-scoop EQ and speaker emulation. I found the effect of the mid scoop EQ very useful and preferred it most of the time for the relative high frequency boost it creates. Speaker emulation seems to be on all the time when outputting via the ADC, and is only optional for the line output.

To hear the effect I listened via the line output into a line input on the RME. Without the speaker emulation the distortion is raspy and fuzzy, useful in a ’60s context perhaps, but it is assumed that a speaker cabinet or a third-party speaker cabinet emulator will be applied. I tested this using AmpliTube 3 and created useful alternative sounds to the built-in emulation, especially if brighter tones are required at low gain settings. There is a ‘dark’ switch across the line output, which would only be necessary for the brightest of amplifier destinations.

Once the guitar tone has been recorded (DI and amp sound), you can re-amp that signal through the Pulse to further tweak the tone, and re-record the results. The ‘Re-amp’ switch on the front panel routes the left channel coming out from the computer back through the amplifier, which then goes back into the computer in the same way a normal input does, via the ‘right’ channel.

The internal routing required in the DAW to make the re-amp feature work properly is tricky, and unfortunately the user manual is little help. Once set up I immediately used this feature to severely damage a drum sound I was working on (very fun), and along with guitar tones it could be used to dirty-up vocals or anything and everything else that needs valve distortion.

A fully-featured and excellent sounding valve pre-amp, and a decent studio interface for that purpose, Laney’s IRT-Pulse will have a home with many guitarists. The Pulse makes it possible with only two cables, and in silence, to record a blistering valve amp tone, and for that it must be applauded. Alternatives are from modeling amp-interfaces such as the Line 6 POD Studio or software-based alternatives like AmpliTube.