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TL Audio Ivory 2 5052

Dual Valve Recording Channel By Hugh Robjohns

TL Audio Ivory 2 5052Photo: Mike Cameron

TL Audio's monster new tube voice channel gives you mic/ line/ instrument preamp, EQ, compression, limiting, and optional A-D conversion — twice over!

TL Audio's Ivory series has always been one of the company's most popular product ranges, comprising a quad mic amp, equaliser, compressor and various mono voice processors. These units were updated and improved a little over a year ago to create the Ivory 2 series, and all feature hybrid circuitry using one or more valves (running on fairly high anode voltages) combined with conventional integrated circuits. Most of the units can be fitted with a digital output card too, providing internal A-D conversion with 24-bit resolution at 44.1kHz or 48kHz sample rates.

Among the key technical improvements introduced in the Ivory 2 units were quieter line stages and redesigned microphone input circuitry, along with various tweaks to the EQ and compressor facilities on the relevant units. Despite all the changes inside the cases, the clear and intuitive control layouts were retained almost unchanged, and the characteristically rich and warm sound quality was made even better.

I reviewed the Ivory 2 5051 recording channel back in the SOS December 2002, and the subject of this review initially appears to be a dual-channel version of the same unit (but with an output limiter replacing the former's noise gate). In essence the product provides two independent channels with comprehensive stereo linking facilities, and each channel incorporates an input stage with mic, line and instrument inputs, a compressor, a four-band equaliser, and an output limiter.

Naturally, the 5052 is substantially larger than its mono sibling, but there is another, more fundamental, difference worth noting. The 5051 mono processor employed three ECC83 (12AX7) dual-triode valves, and so does this stereo unit — so the number of valve stages per channel has been halved. The 5051 employed a triode buffer in the preamp, two in the compressor (one for gain reduction and another for make-up gain), and three in the equaliser (one for each mid-band and the last for the two shelf sections). In contrast, the 5052 uses one triode for the input buffer (as in the 5051) one for the compressor make-up gain, and one for the equaliser. So while the renowned TL Audio valve sound is still present, the topology isn't quite the same as in the mono unit.

Connections

This enormous 3U rackmount processor is festooned with controls — 39 knobs and 27 buttons in total! The front panel is finished in the traditional ivory colour with clear legends and section identifiers, and the rotary controls are also colour-coded to aid navigation. A pair of round VU meters are provided to monitor channel levels and gain reduction, and each channel also boasts a front-panel unbalanced high-impedance instrument input, through a quarter-inch socket.

Moving briefly to the rear panel, the interfacing comprises a quartet of XLRs which accept the two microphone inputs and two balanced line inputs. A pair of quarter-inch sockets are provided for unbalanced line inputs, and a red button switches all the line inputs as a group between +4dBu and -10dBu operating levels. That's not a typo — while the normal semi-pro level is -10dBV (which equates approximately to -8dBu) TL Audio have decided to employ -10dBu. However, I don't think a 2dB discrepancy in the nominal sensitivity will concern anyone too much!

Arranged below two removable panels (of which more in a moment) two pairs of TRS sockets provide a balanced insert send and return facility for each channel. Next along, two more quarter-inch sockets and a pair of XLRs provide unbalanced (-10dBu) and balanced (+4dBu) outputs respectively. Finally, another pair of TRS sockets furnish an unbalanced insert to the compressor side-chain of each channel. The fused IEC mains inlet is mounted at the top of the panel.

The optional DO2 digital A-D card — which can also be fitted to other Ivory 2 units — can be installed quite simply after removing the left-hand blanking panel (above the output connectors). Although not mentioned in the handbook, the published block diagram indicates the provision of a D-A facility as well. Should such an option become available it would provide a digital input to the processor, which would appear as a line source for the corresponding channel (and mix with any signals present on the balanced and unbalanced analogue line inputs). I presume such an option card would be fitted in place of the (unmarked) right-hand removable plate, and it is an intriguing proposition which would enable the 5052 to serve as a valve processor within a digital environment. However, before the excitement mounts too much, this is not an available option at the moment, and we'll just have to wait and see if a D-A option becomes a reality in the future!

The 5052's rear connections.The 5052's rear connections.Photo: Mike Cameron

Stereo Linking

The stereo linking facilities on the 5052 are unusually comprehensive. There are three buttons — all with associated LEDs — and each controls the stereo linking of a specific element of the processing. In all cases stereo linking disables the appropriate controls of channel two and employs the channel one controls as the master. At all times, the unit's input and output controls remain fully independent on both channels, regardless of the linking settings, so care is needed to match gains and so forth between channels when working with stereo signals.

The three Link buttons activate the stereo linking independently for the compressor, equaliser, and limiter. This enables each section to be either linked or kept separate, as best suits the task in hand. When working with stereo material it will usually be necessary to link all three sections to avoid unwanted stereo image shifts caused by unmatched control settings. However, there may be occasions — albeit rarely — when processing separate signals or when using one signal to affect another, when independent control of the dynamics and equaliser sections may be useful.

Input Conditioning & Output Level

Returning to the vast front panel, the two channels are laid out identically side by side, with the input and output controls arranged along the top level, with the meters. The controls for the compressor and equaliser are arranged below, and a central section contains the stereo link switches and a rotary switch to determine what the meters are showing.

The input selection for each channel is made with a rotary switch offering mic with phantom power; unpowered mic; line; or instrument. The gain control spans +16dB to +60dB for the microphone inputs; -2dB to +38dB for the DI input; or ±20dB for the line sources. Two buttons activate a 30dB pad on the mic input and a 90Hz high-pass filter (applicable to all inputs), and Drive and Peak LEDs indicate the preamp signal levels. Two more buttons introduce a polarity reversal and activate the bypass mode (with an associated LED). The latter switches the compressor, equaliser and output limiter (and their associated valve stages) out of circuit, but the input section and its valve remains. This means that, if the input stage is being driven fairly hard to obtain an obvious tube thickening, there is no easy way of bypassing the unit completely to determine the effect in comparison with the original signal. It's a small point, but may be an issue in certain cases.

The input signals are conditioned by individual high-quality op amp stages, each section optimised for the appropriate input type and level. A single-triode valve stage completes the input section, and its sonic characteristics are dependent on how hard the input section is driven. The balanced insert point sits between the input section and the rest of the processing, and the send can be used as a direct output if required.

The Output Gain control provides up to 15dB above its centre-detented unity-gain position (handy when feeding a digital recorder directly). At the opposite extreme, the output can be reduced all the way down to silence. The last control in this section sets the threshold for the peak limiter, which is calibrated from zero to +20dBu. This limiter is positioned after the Output Gain knob, ensuring peak levels are controlled regardless of the Output Gain setting. The limiter is activated by pulling the Limiter knob — a green LED illuminates when the limiter is engaged, and a red one lights when it is applying gain reduction.

The circular VU meter is calibrated such that 0VU equates to +4dBu at the balanced output (and -14dBFS from the optional A-D card). A rotary switch positioned below and midway between the two meters determines what is being displayed. The four options are input, output, compressor and limiter — the first two showing the corresponding signal levels and the last two showing the gain reduction applied by the appropriate dynamics section. Of course, the signal peaks may often be substantially higher than +4dBu, which would have the meter needle wrapped around the end stop most of the time! To overcome this problem an additional button reduces the meter sensitivity by 10dB, so that 0VU then corresponds to +14dBu.

Signal Processing Facilities

The compressor section is based on the same circuitry employed in other TL Audio designs. A transconductance amplifier is used as the gain-controlling element, and another triode stage provides the make-up gain, adding more distinctive valve warmth when driven appropriately. Fully variable Attack (0.4-40ms) and Release (40ms to 4s) controls are provided, although both time constants are also programme-dependent to a degree — which is why the controls are marked simply with Slow and Fast at the extremes. The release section includes a 10ms hold feature which delays the onset of the recovery phase after the signal has fallen below the threshold. This reduces the possibility of dynamic distortion, particularly with bass-heavy signals.

The Threshold control spans +10dB to -20dB, although the actual onset of compression is also dependent on the shape of the knee, which can be selected between Hard and Soft settings via a button. The Soft setting provides the most subtle and 'musical' sound character, while the Hard setting provides a much more aggressive, upfront kind of quality. The compression ratio is variable from a very gentle 1.5:1 all the way up to a very stiff 30:1, and up to 20dB of make-up gain is available to re-establish the peak signal levels after compressing hard.

Along with the Knee button, two further buttons (both with LEDs) switch the compressor section in or out and reconfigure the signal path to place the entire equaliser section in the compressor side-chain for frequency-selective compression effects. The equaliser is a typical four-band design, with another triode buffer driving the output of the equaliser section. The top and bottom bands can be switched between shelf and peaking responses, and offer 15dB of boost or cut (with a 0dB centre detent). The turnover frequencies cover 3kHz-20kHz and 30Hz-1kHz respectively, while the Q value is set to a gentle 1.5 (roughly one octave) when in peaking mode. Unusually, when operated as shelf sections, the filter slopes are 12dB/octave instead of the more typical 6dB/octave.

The two mid-band sections have the same ±15dB cut/boost range, and variable centre frequencies spanning 50-1500Hz, and 1.5kHz-12kHz. Each section also has a variable Q control ranging between 0.7 and seven (from around two octaves down to less than a quarter octave). A pair of buttons (both with LEDs) are provided to switch the equaliser on, and to insert it before (instead of after) the compressor.

Twice As Nice?

The 5052 tech specs and characteristics are very similar to other Ivory 2 units. The input section is clean and quiet when the drive level is modest, although pushing the gain higher produces the desired warmth and character (in other words, second harmonic distortion) expected from a triode valve stage. The amount of 'thickening' is very controllable by manipulating the gain structure through the unit's processing stages. Although not able to match the best esoteric preamps, the mic input passed my 12-string acoustic guitar test quite respectably, demonstrating that it is able to resolve complex harmonic signals well.

The Equaliser section is well designed and flexible, serving well for creative tonal polishing while still having sufficient precision for corrective tweaking of wayward sources. Being able to switch the EQ before the compressor or into the side-chain is useful too. The compressor is also a good workmanlike design, providing gentle or dominant control of dynamics as required. It sounds clean and accurate most of the time, and is always musically complementary when set up carefully.

The quality of construction of this processor, and its intrinsic hybrid sound quality, easily justify the substantial UK cost, although it has little direct competition. Overall, this is a very competent processor, which is easy to use and provides a well-balanced range of facilities — the possibility of a digital input in the future is also an exciting prospect. Whether for tracking, mixing, or mastering, the 5052 stereo valve processor will serve well, bringing a controllable valve character to the party as well as enabling both creative and corrective signal processing through the EQ, compressor and peak limiter.

Pros

  • Competent mic preamp.
  • Versatile compressor with side-chain access.
  • Separate peak limiter.
  • Musical EQ section.
  • Balanced channel insert facility.
  • Digital output option.
  • The possibility of a digital input option in the future?

Cons

  • None.

Summary

TL Audio units always tend to represent good value for money, and their newest processor is no exception. The chunky 5052 dual recording channel does all that is expected, whether tracking, mixing, or mastering mono or stereo material.

information

5052 recording channel, £1173.83; optional DO2 A-D converter card, £149.22. Prices include VAT.

TL Audio +44 (0)1462 492090.

info@tlaudio.co.uk

www.tlaudio.co.uk

Published November 2003