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TL Audio Ivory C5021

2-channel Valve Compressor By Paul White
Published September 1998

TL Audio Ivory C5021

Paul White finds the best of both valve and solid state worlds in TL Audio's latest compressor.

TL Audio's C5021 is the latest in the Ivory series of hybrid valve/solid‑state signal processors and combines a dual‑channel compressor with a pair of gates. The valve circuitry is in the preamp and gain control stage of the compressor, while the output and side‑chain circuitry is solid‑state. In theory, then, the user gets the best of both technologies for far less than the cost of an all‑valve design. The preamp valve stage has variable drive allowing the amount of valve 'flavouring' to be adjusted.

Packaged in a nicely‑engineered 2U rack case and finished in 'intensive care' off‑white, the C5021 offers a choice of a high Z jack, instrument level input, an unbalanced ‑10dBu line level jack input or a balanced, +4dBu XLR input. The outputs are also available on both jack (‑10dBu unbalanced) and XLR (+4dBu balanced) with further TRS jacks providing side‑chain insert points for the two channels. A nice touch is the provision of separate input and output gain switches on the rear panel to increase the jack operating level to +4dBu and the XLR to +18dBu. This could be useful for interfacing with digital gear that expects to see a level of around +14dBu to produce a digital full scale reading.

As with other units in the Ivory range, the feature set is simplified compared with TL Audio's Indigo range which it supercedes. For example, the compressor doesn't have variable attack and release controls, just a pair of Fast/Slow buttons, though there is some programme‑dependent element that makes this arrangement rather more flexible than it first appears.

Lightning Tour

The Input Gain control, which sets the drive to the first valve stage, is monitored by an amber LED indicating the amount of drive, while a red LED warns of imminent clipping. Oddly, the compressor comes before the gate. Presumably this is so any noise generated by the compressor is also silenced, though working this way around can make the gate threshold more tricky to optimise. In addition to the Fast/Slow time constant switches mentioned, the compressor section has a fully variable +/‑20dB threshold plus a Ratio control that extends from a gentle 1.5:1 up to a stiff 30:1. A built‑in compressor hold time of around 10ms prevents distortion when working with low frequency sounds, and like some previous TL Audio designs, the soft‑knee gain control circuit combines both feedforward and feedback signals to derive the sidechain signal.

The usual make‑up gain control is fitted to the compressor output. However, a further output gain stage comes in series with this, after the compressor In/Out button, but before the gate. Even when the compressor is bypassed, the input valve stage is still in circuit, so you can use the preamp and gate without the compressor. Gain reduction is shown on back‑lit, circular, analogue meters which may be switched to monitor the output signal level (post all gain controls). The gate section has only a single threshold control with the fully anticlockwise setting effectively disabling it.

The compressor is a great all‑rounder that sounds flattering, yet still very natural...

In Use

The compressor has the same gentle but flattering character as other TL Audio units I've tried. Though there are only two time constant buttons on the compressor, I didn't have any trouble at all getting the effect I wanted. Using the slow attack setting gives instruments such as acoustic guitar, bass and clean electric guitar a bright, well‑defined attack, while choosing the faster setting produces a warmer start to the note. At modest settings, the compressor is both subtle and musical, while with high ratio settings and a fast attack time, it makes an effective limiter.

Being able to bypass the compressor while leaving the valve preamp active is useful, but I'd have liked an overall hard Bypass button so that I could take the whole box out of circuit in one go. The valve stage definitely adds warmth to the sound as you increase the input gain to the point where the amber LED starts to flash, but not in the coarse, muddy way that some competing units do. Bringing in the compressor with the threshold set so as to prevent any compression taking place seems to emphasise this warming effect slightly, presumably as a result of having two valve stages in series.

That leaves just the gate, which seems to have fast attack and a preset release of around one second. For signals with little in the way of background noise, the gate works perfectly, but if you have a noisy signal that necessitates a higher threshold setting, the gate can be provoked into clicking. A more gentle expansion characteristic would have been preferable, but for most routine jobs, the gate is fine.


On balance, the C5021 is an exceptional performer at the price. My only criticism is the provision of a rather fierce gate where a gentler expander would have been more forgiving. The compressor is a great all‑rounder that sounds flattering, yet still very natural, and the tube warmth circuit goes just far enough without letting you overdo the effect. Having an instrument input also means the C5021 works well as a deluxe DI channel, and I used it successfully with both electric guitar and bass.

Once again, a British manufacturer has proved that you don't have to buy an expensive import when the home grown equivalent is often both better and cheaper.


  • Super smooth compressor.
  • Effective tube warmth stage.
  • Offers both line and instrument inputs.
  • Realistically priced.


  • Gate a little fierce at higher threshold settings.


A genuine bargain with very few shortcomings.