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TL Audio Ivory 2 5013 & 5051

Valve Signal Processors By Hugh Robjohns
Published December 2002

TL Audio have updated their popular Ivory-series processors in response to feedback from their user base. We try out two of the updated units to see what's new.

Ivory 2 series 5013.Ivory 2 series 5013.The Ivory series has been one of TL Audio's most popular product ranges, boasting a variety of units including a quad mic preamp, an equaliser, a compressor and various mono voice processors. All feature hybrid circuitry incorporating one or more valves (running on sensible HT voltages, too!) in the signal path. The range has recently been totally updated, with a lot of small but important changes, to form the new Ivory 2 range.

Ivory 2 series 5051.Ivory 2 series 5051.Photo: Mike CameronTo investigate the latest tweaks I was supplied with a pair of Ivory 2 models. Although a few of the changes apply only to specific models, there are a great many which affect the entire range — for example, an optional new digital output card can be fitted to any of the revised units, there is an improved DI input across the range, and the line level I/O circuitry has been redesigned to lower system noise. Some of the changes to specific models include all-new microphone input stages, improved EQ facilities, and revised compressor parameters. So this is not just a cosmetic makeover, but a substantial redesign of significant elements of the entire range — although the core attributes of the Ivory products (sound quality and usability) have been retained.

5013 Dual Valve Equaliser

This unit was first reviewed in the pages of Sound On Sound in June 1998, and the new model looks little different at first glance. The controls for the two channels are arranged one above the other on the clean 2U front panel. On the left-hand side is a DI input and gain control with Drive and Peak LEDs. The former indicates how hard the valve circuitry is being driven and the latter illuminates a generous 5dB before clipping. As mentioned above, the DI input is a revised design with a higher input impedance (1MΩ). However, it can still accept a wide range of sources, since the input gain control provides a -2 to +38dB gain range (±20dB for line inputs).

TL Audio Ivory 2 5013 £528
  • A worthwhile makeover of this popular unit.
  • Improved flexibility of EQ functionality.
  • Fat function a useful enhancement.
  • Digital output option.
  • Still no individual band bypass facilities.
This revised Ivory 2 equaliser incorporates a number of beneficial improvements to both functionality and technical performance, without sacrificing the sonic quality or user-friendliness of the justifiably popular original. Representing good value for money in the UK, this well-built unit will serve well in any installation.


This particular unit incorporates a single dual-triode valve — an ECC83 — half of which is employed in the input stage immediately prior to the EQ section (remaining in circuit even if the EQ is bypassed). This is a useful facility if the source only requires a little 'valve warming' rather than full equalisation. The other half of the triode is used to provide gain recovery for the EQ section, and is switched in and out of circuit with the EQ. The input stage is followed by four bands of fully parametric equalisation, each with a ±15dB gain range, centre frequency control, and variable Q. This last covers a slightly sharper range than the original version, with the broadest setting being 0.8 (previously 0.5) and the narrowest being 7 (formerly 5). The four bands overlap in their frequency ranges nicely: the bottom covers 30Hz to 1kHz, lower mid-range is 100Hz to 3kHz, upper mid-range spans 1kHz to 12kHz and the top 3kHz to 20kHz.

Pulling the LF or HF band's Q control offers a new shelving response.Pulling the LF or HF band's Q control offers a new shelving response.Photo: Mike CameronWhereas the Q parameters have been tweaked in a minor, albeit useful, way there is a far more significant alteration to the EQ section. The design now includes a facility to switch the top and bottom bands individually to operate as variable-frequency shelving filters — a facility which was sadly missing from the original model, although available on some other TL Audio units sharing similar circuitry. The new filter switching is effected by pulling out the Q control knobs on the appropriate bands — a very elegant solution with a nicely weighted switch action exuding quality.

The output controls to the right of the unit include a global EQ bypass and associated LED (but there are still no individual band bypass switches, unfortunately) and a ±20dB output level trim control. There is also another new addition to this section: a Fat button and associated LED. This new mode introduces an overall equalisation characteristic (separate to any specific EQ settings) in the form of a gentle 'smile' curve — a subtle lift at top and bottom extremes with a mild dip in the mid-band to maintain overall energy levels. This is a nice idea, and will certainly have its uses, although I suspect many users will simply leave it switched in all the time! The rear panel is much as before, except for the optional digital output module, of which more in a moment. The analogue I/O is at line level only on the 5013, but both balanced and unbalanced interfaces are provided, on XLR and quarter-inch jack sockets respectively. Separate buttons for the input and output interfaces change the nominal operating levels between +4 and +18dBu (equating to -10 or +4dBu on the unbalanced interfaces).

The most obvious change to the rear panel is a removable blanking plate to facilitate the installation of the optional DO2 digital output card. If fitted, this board converts the outputs of the two channels to S/PDIF with 24-bit resolution at either 44.1 or 48kHz sample rates (controlled by a rear-panel slide switch). A word-clock input on a BNC is provided for synchronisation with an external master clock source, and the A-D is calibrated such that analogue output levels of +18dBu equate to 0dBFS (digital full scale). The digital output is via a single phono socket.

5013 rear panel.5013 rear panel.The technical specification of the unit is very similar to the original, its bandwidth flat to within a decibel from 10Hz to 40kHz, distortion below 0.5 percent at unity gain (increasing with the amount of valve drive, but consisting mainly of second harmonic), and a dynamic range of 106dB. There seems to be some confusion about the exact noise performance of the unit, since the handbook and brochures quote different figures, although they are in the region of -80dBu, which is good for a hybrid unit of this type.

Like its predecessor, the Ivory 2 5013 sounds delightfully sweet and musical, with well-thought-out and flexible controls. Adding 'air' or a certain valve richness to a source is easy, and the ability to set the end bands to act as shelving filters is a major improvement to the usefulness of this unit. The introduction of the Fat mode is also welcome — acting almost like a kind of aural enhancer — but I fear many users will end up leaving it switched in all the time and miss out on its more creative possibilities! Although the handbook is very well written and contains a wealth of useful technical and operation information, one very obvious omission is a frequency response trace showing the true nature of the Fat equalisation.

The incremental improvements to the DI input and general noise level are welcome, of course (if hardly earth shattering), but the very competent new digital output module will be widely appreciated, I'm sure, and open important new markets, both for this device and its siblings.

5051 Mono Valve Processor

Again, the Series 2 5051 processor looks little different from its antecedent (reviewed in SOS February 1998), but there have been several significant improvements. The most important are probably the new mic input stage and the option to use the DO2 A-D card, but there have also been incremental changes to the dynamics section with hard/soft-knee switching for the compressor and a new optical gate circuit.

TL Audio Ivory 2 5051 £528
  • Quieter mic preamp than previous design.
  • More flexible and responsive dynamics.
  • Digital output option.
  • None at this price.
This revised Ivory 2 processor incorporates several significant improvements over the original design, without sacrificing anything in the process. Like its predecessor, it is a comprehensive and highly competent voice channel, and represents very good value for money in the UK. It would make a welcome addition to any studio.


This unit incorporates no fewer than six separate valve stages, supplied by three ECC83 dual-triode 'bottles'. The first of these valve stages is a buffer at the end of the input circuitry, where most of the drive effect is obtained. Two more are incorporated in the compressor, one as the gain-reduction control element and a second to perform the gain make-up function. The last three stages are used in the equaliser with one triode handling the two shelf sections together, and another pair looking after the two mid-bands individually.

The new version of the 5051 retains all the controls and facilities of the original, including its slightly quirky switched parameter controls, and the 2U panel layout is virtually identical. The input selection switch (mic with phantom power; mic; line; or instrument) is accompanied by a gain control, and two buttons to select a 30dB pad and a 90Hz high-pass filter. Drive and Peak LEDs are also provided. The precise gain range available depends on the source selection: microphone inputs enjoy a range between +16 and +60dB of gain, with -2 to +38dB available for the DI input and ±20dB for line sources.

The next section on the front panel concerns the compressor, although the noise gate is actually next (and correctly so) in the signal path. The compressor is provided with switched Attack and Release controls (four settings each, spanning 0.5 to 40ms attack, and 40ms to four seconds release). Threshold (±20dB), Ratio (1.5 to 30:1) and Gain Make-up (up to 20dB) are all continuously variable controls. A pair of buttons provide a compressor bypass function (with warning LED) and the newly introduced ability to change the knee from a hard to a soft setting. The latter enables a wider range of sonic characteristics to be obtained than was possible previously, ranging from subtle low-ratio soft knees to more aggressive 'in yer face' hard-knee settings.

The revised optical gate section has but a single control tucked away in the corner of the EQ department. This variable threshold control (with accompanying LED to indicate when the gate closes) can be set from -10 to -60dBu, and is very effective in most cases. Although having access to attack and release settings is often useful, I found no need for them here — small adjustments to the threshold allowed all the control needed to help clean up a slightly noisy source before compressing.

The equaliser is a four-band design with shelving top and bottom bands and two fixed-Q peak/dip sections. The turnover and centre frequencies are set with four-position rotary switches, while the ±15dB gain range is controlled through continuously variable knobs. Like its predecessor, the Q is set to a broad and musical 0.5, and the bands overlap each other nicely. Although some may fear the frequency selections are too limited with only four settings for each band, I found them to be well chosen and easy to use, rarely wishing for alternative values. Although relatively basic, this EQ sounds sweet and enables gentle, creative correction with minimal fuss.

The output section completes the panel, with a rotary output fader (off through to +15dB of gain) and three buttons. The first is an EQ bypass, the second switches the EQ before the compressor — a very handy facility — and the third activates a link buss to enable two 5051's to be used for stereo by sharing their compressor side-chain signals. This feature can also be used to configure an auto-ducker, by using the control signal from one unit (generated even if the compressor is not in circuit) to control the gain reduction of a second unit.

Another four-way rotary switch controls the signals displayed on the vintage-style VU meter. The options are input, output, output +10dB, or gain reduction. The +10dB mode inserts a 10dB pad in the meter signal to allow high output levels to be monitored more accurately — such as would be the case when driving a digital recorder or trying to optimise the noise performance of the optional A-D module. In this situation, achieving near-peak levels on the digital output requires analogue signal peaks of around +15dB (since 0dBFS is aligned for +18dBu), which would leave the needle wrapped around the end-stop of a normally calibrated VU meter.

The rear panel of the 5051, which includes the optional DO2 digital board.The rear panel of the 5051, which includes the optional DO2 digital board. Photo: Mike Cameron

The rear panel is equipped with XLRs for the mic and balanced line inputs, and a third provides a balanced line output. TS quarter-inch sockets are used for the unbalanced line input and output, plus the compressor side-chain link facility. A TRS socket provides a compressor side-chain insert to enable frequency-conscious compression, for example. The line input sensitivity can be configured to operate at one of two nominal levels, courtesy of a button on the rear panel. The balanced input can be switched between +4dBu and +18dBu, the unbalanced input following with -10dBu or +4dBu.

Whereas the 5013 had a rear-panel switch to boost the nominal output level for use with professional digital recorders, level matching must be performed with the output fader on the 5051 — the full 15dB of additional gain usually being required to fully drive a conventionally aligned A-D stage. Naturally, the DO2 A-D card can be installed in the 5051, as with the 5013 already described. However, whereas the 5013 was a two-channel unit, one channel being coded to each side of the digital stereo output, the 5051 is a mono unit. Consequently, both channels of the S/PDIF signal carry the 5051's single output channel signal.

I found the 5051 to sound quiet, clean and very smooth. The valve stages certainly add warmth and character, with a fair degree of controllability through careful use and adjustment of the gain structure. The unit exudes quality in its construction and sonics, and has a musically complementary character, particularly in its EQ and compressor sections. The new mic amp seems to be quieter and to have a little more resolution, although this is only from memory, as I was unable to perform a direct comparison with the original.

Summing Up

Overall, I think TL Audio have done a good job in revisiting the Ivory series. Some of the original omissions in terms of functionality have been addressed, many operational facets have been finely honed, and specific circuit elements have been updated to improve the technical quality. As far as I can see this is a purely positive experience — none of the character or usability of the originals seems to have been lost or diluted at all by introducing these improvements, all of which are useful and constructive. Congratulations all round!

5013 dual-channel valve parametric equaliser £527.58; 5051 mono valve recording channel £527.58; DO2 optional digital output module £149.23. Prices include VAT.

+44 (0)203 086 7330.