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Chandler TG Channel

Recording Channel
Published January 2005
By Hugh Robjohns

Chandler TG ChannelPhoto: Mike Cameron

This new mic preamp and equaliser unit uses '60s EMI designs to recreate some of the classic sounds.

Chandler is an American company, based in Iowa, which builds mic preamps and related products. Now you might be thinking 'So what? There are hundreds of companies making mic preamps.' However, there are relatively few companies building accurate vintage designs, and even fewer making units based on vintage transistor designs — and most of those are Neve replicas anyway.

Vintage EMI Design

Chandler are a little bit different because they specialise in creating a range of vintage preamps, compressors and EQs based entirely on authentic British EMI circuit designs dating back to the late 1960s. These were used in the first of EMI's transistorised consoles — the TG series — which throughout the '70s and '80s recorded such well-known acts as the Beatles and Pink Floyd at the world-famous Abbey Road Studios in London. But Chandler also go beyond simply using the same circuit designs — they also use the same custom-wound transformers (or as close as it is possible to get), the same hand-wired construction practices, and all-discrete circuitry.

The subject of this review is the Chandler TG Channel, an all-new single-channel model contained in a 1U rackmount unit. It combines the preamp and output stages of the Chandler TG2 preamp with a passive, inductor-based three-band equaliser circuit borrowed from the mastering version of the TG console.

The power supply is a completely independent 1U half-rack box which is priced separately — it can power two Chandler Channels, which increases its cost-effectiveness somewhat. I'm not a fan of separate power supplies, despite the potential performance gains from keeping the mains toroidal transformer well away from the audio transformers. It's a practical thing really — it's just a pain having to find somewhere to mount or install a separate PSU lump. If the unit is installed in a static rack, the separate PSU may be less of a problem, but you still need to have access to the PSU to get at the mains switch, which is often inconvenient.

Construction

The power supply unit is a solid nickel-plated steel box, measuring 194mm front to back. The front panel carries only a fuse holder and the mains switch, while the rear panel is scarcely more elaborate, with just an IEC mains inlet and a pair of four-pin XLRs to carry the DC supplies to a pair of TG Channel units (providing ±24V DC for the audio circuits and +48V for phantom, all with a common ground.) Mains input voltage selection is provided via a switch on the internal PCB.

Internally, the box is well constructed, with a toroidal transformer occupying the left of the case, and a PCB on the right, running the full depth of the unit, to carry the rectification, smoothing, and regulation components for each of the three supply outputs. The internal wiring is very neat, and the hand-soldering looks very solid and secure, but I was dismayed that none of the mains wiring was insulated or shrouded on the IEC inlet, the fuse holder, the mains switch, or the PCB. This is bad practice and there can be no excuse, especially in an expensive product with metal casework everywhere.Power for the TG channel comes via a dedicated external PSU unit, the internals of which can be seen here. The voltage selector switch is at the top left, and on the right-hand side are the uninsulated mains wiring connections.Power for the TG channel comes via a dedicated external PSU unit, the internals of which can be seen here. The voltage selector switch is at the top left, and on the right-hand side are the uninsulated mains wiring connections.Photo: Mike Cameron

The Channel unit itself is built in a very 'traditional' manner. For example, the case has two front panels — a hidden inner panel to which the rotary controls and switches are bolted, and a neat outer 'escutcheon' which carries the control markings. The internal circuit board is supported by a pair of rails running the full width of the unit, and all the switches are wired by hand very neatly back to the PCB. The input transformer is bolted to the left of the chassis near the rear panel, while the large output transformer is bolted to the right of the chassis — both custom devices supplied by the UK manufacturer Carnhill.

The PCB is relatively large, with everything being well spaced out to minimise component interaction, supplemented with a screening ground plane all over the top surface. The rear panel carries only three XLRs. The usual three-pin input and output socketry (the single input socket accommodates both mic and line-level signals), plus a four-pin male socket for the DC power feed from the separate PSU. There is no power switch on the TG Channel unit at all. A sealed relay is used to switch between mic and line input levels. When in mic mode, the input socket presents a standard 2.4kΩ nominal input impedance, which increases to 10kΩ in line mode.

The actual preamp stage appears to be very simple and is claimed to be identical to the EMI TG12428 circuit. It comprises two complementary pairs of BC214 (PNP) and BC184 (NPN) transistors — although a useful proportion of the gain is provided by the input transformer, of course. The output stage appears to be based around another BC214/BC184 pair driving a pair of extremely chunky output transistors in metal cans, although the part numbers have been scratched off so I can't identify them at all. Two more sets of BC214/BC184 transistor pairs are used to provide the make-up gain in the passive EQ stage, which incorporates three large ferrite inductor coils. All of the front-panel rotary controls are switches except the Output level control, which is a normal potentiometer, and most have resistors wired directly across their terminals — again in the 'traditional' way. All in all, the Chandler Channel is very nicely constructed indeed.

Controls

The control knobs are all classic black pointers and, combined with a quartet of chunky white buttons and clear, simple white and yellow legends on a dark grey panel — altogether they make for a wonderfully understated vintage look. Everything feels very solid and reliable, and the overall impression is of a high-quality product. The first control is the gain switch, marked in yellow to offer -15dB to +55dB of gain in 5dB steps when in mic mode, and ±15dB (marked in white) for line mode. However, the gain can be adjusted beyond these limits in line mode to deliberately overdrive the input stage if required, which will generate a lot of (possibly useful) third-harmonic distortion — a facility made more practical thanks to the inclusion of the variable output attenuator, which allows the user to maintain sensible output levels.

Surprisingly, there is no level metering of any kind — not even a peak overload indicator — but the Channel has a huge headroom and very high output capability, so optimising the gain structure is not overly critical. The maximum +55dB of gain may not sound like much — especially when the Chandler TG2 offered 75dB from the same circuit — but this is intentional. The EQ stage provides for considerable amounts of bass and treble boost, and so in practice the input gain is likely to be less than might otherwise be the case in a straight preamp. It was also found in the Chandler TG2 that the high preamp gain and lack of an input pad often caused problems when close-miking loud sources with high-output mics. Consequently, the Chandler Channel provides less maximum gain and up to 15dB of attenuation to be incorporated in mic mode at the left-hand end of the gain control.

When pressed, the four independent latching buttons provide 48V phantom power, polarity (phase) reverse, line input mode, and insertion of the EQ circuit. None of the switches have indicator LEDs and it can be hard to tell what condition the unit is in if both switches in each section happen to be in the same state (ie. both pressed in or out). I was also concerned that the phantom power switch remains active even when the line mode is selected. Some solid-state line output stages can be damaged or destroyed if they receive 48V phantom power, and if this was my unit I would modify it immediately so that the phantom supply was wired through the spare bank of contacts on the adjacent line switch. In that way the phantom power could only reach the XLR socket when the unit was in the mic input mode. This is such a simple and obvious modification that I'm surprised no one at Chandler has already thought of it! Can I claim a designer's commission fee?

The Output rotary control is the only continuously variable control on the entire machine — all the rest are switches — and it replaces the fader of the original TG consoles. It is scaled simply from zero to 10 and is located in the circuitry between the input and output stages. So not only can it be used to provide fine level control between the 5dB input gain steps, it can also keep the peak output level under control even if the input stage is driven unusually hard as an effect. The input gain calibrations are correct when the output control is fully open (ie. the maximum clockwise position).

The inside of the TG Channel itself, showing the discrete components and hand-wiring.The inside of the TG Channel itself, showing the discrete components and hand-wiring.Photo: Mike Cameron

The Equaliser

The EQ stage is a three-band semi-parametric design, and each section has its own Off mode at the left-hand end of the frequency-selector switch so that unused sections can be bypassed. The first section provides high boost, with gain ranging from 0dB to +18dB in 2dB steps — there is no high-cut option. This may sound a little restrictive at first, but in practice it is unusual to need to reduce the high end — you almost always want to turn it up!

An even more unusual feature is that the frequency selector also changes the shape of the EQ curve. At the higher frequency settings, which are all marked in yellow (16, 12, 8.1, 6.8, and 5.8kHz) the section acts as a high shelf, using only capacitors in the circuitry. However, at the lower frequency settings (3.9, 2.2, 1.8, and 1.2kHz, all marked in white) it acts as a peaking bell equaliser, using both capacitance and inductance. Not only does the shape of the EQ curve change, but so does the sound character — it's a subtle but useful distinction. In addition, the bandwidth of the bell curve can be adjusted between high and low Q values via a small toggle switch, although the Q also reduces automatically (ie. the bell curve gets sharper) with increasing gain to make the EQ more selective as it is turned up.

It might sound rather complicated, but in practice the arrangement works very intuitively, doing exactly what you would expect of it. When boosting higher frequencies for added air and sparkle, the shelf option is the appropriate mode, and when boosting the upper mid-range to pull out some specific harmonic character of a sound, the bell response allows precise control. If you should need a lot of gain to really pull a sound out of the mix, then you'll also want a narrow bandwidth to ensure accurate control — so all in all these controls just work wonderfully well!

The mid-section affects the lower mid-range frequencies (350, 400, 500, 600, and 700Hz) but provides only cuts of up to 20dB in 2dB steps. Again, it may sound restrictive, but the higher mid-range frequencies can be boosted with the high boost section if required, and in the range covered by this section level reduction is usually required to improve clarity — the middle part of the ubiquitous 'smile curve'. Although there are no markings on the controls, this is another bell-shaped section employing both capacitance and inductance components, and the Q of the filter varies with frequency again, this time providing narrower bandwidths at the lower frequencies and wider, more gentle bandwidths for the higher frequencies.

Finally, the low section applies only boost again, offering either shelving or bell-shaped boosts for different frequency settings — this time both elements are derived from inductor-based circuits. The shelf portion (marked in white) is active for turnover frequencies of 100Hz and 200Hz, providing a gradual slope over a very wide bandwidth. The gain can be increased to +20dB in 2dB steps, with the gain maximising at about 65Hz.

The bell section (marked in yellow) is active for frequency settings of 50, 70, 100, and 200Hz — the lower two being particularly optimised for kick-drum and bass-guitar enhancement. Once again, the Q increases as the amount of gain is increased, making the filter progressively more selective. A useful addition to the low EQ section is a simple high-pass filter (engaged with a toggle switch) to remove unwanted rumbles, with a turnover of 100Hz.

TG Channel In Use

This is a delightfully simple product to use, with all the rotary controls providing very clear visual feedback thanks to the large pointer knobs and well-spaced switch positions. There is no doubt that the unit invokes a certain sound character, so this is not an 'invisible' preamp by any means. Given its heritage, it bears comparison with the early Neve preamps — the transistor circuitry and transformers stamp their characteristic hallmarks on both marques. Like the Neve designs, the Chandler provides that huge, 'larger than life' sound with a warm and full bottom end. The mid-band has a slight but identifiable richness too — presumably contributed by subtle transformer and transistor distortion artefacts.

By driving the input stage harder than normal, the amount of distortion can be increased in a musically enhancing way, but unlike a valve preamp, the distortion here tends to be mainly odd harmonics — the infamous 'transistor fizz'. This can be used to great effect and it is a sound character very much in vogue at the moment, especially for vocals. The Chandler web site refers to John Lennon's vocal on the classic Beatles track Polythene Pam as a good example of the kind of harmonic distortion the Chandler Channel produces when heavily overdriven.

Importantly, this overdriven quality is easy to control, especially as a post-production process when using the line input. In this case, the gain can be cranked up to over-cook the front end, and the output gain control backed off to maintain sensible peak output levels — much like using a guitar amp with separate input drive and output gain controls.

The TG Channel impressed me with its very open and airy high-frequency sound. It is not overly bright — although there is certainly a hint of HF lift — and there is nothing aggressive about the high end at all, but it sounds far more open and extended than I was expecting, with a kind of smooth, almost creamy quality. I understand that the Chandler TG preamp circuitry has a frequency response that is fundamentally flat from 20Hz to 3kHz, followed by a gentle rise up to 16kHz, reaching about +1.5dB — a classic 'air' response, in fact.

The preamp is impressive for injecting character and body into an otherwise sterile sound source — something for which the Chandler TG preamps have already developed quite a reputation. However, pressing the big white button to engage the equaliser raises the game to a whole new level. Passive equaliser circuits have a unique character which I suspect is to do with the huge headroom and accurate transient response inherent in such designs, combined with the sonic qualities of real inductors (rather than the far cheaper gyrator circuitry often used in active designs). The Channel equaliser certainly demonstrates these qualities well, allowing considerable amounts of boost to be applied without the results ever becoming abrasive or grating.

The low-end boost was useful for adding weight and emphasising the body of male vocals, and careful selection of boost frequency could make a 'plain Jane' kick drum sound truly awesome! The ability to thin out the lower mid-band area was very useful too, especially on harmonically dense signals such as electric guitar and some synthesiser string sounds.

I found the high-frequency facilities more useful with bell settings than with the shelf. The preamp is bright anyway, and few of the sources I tried seemed to need any further enhancement in this area. Perhaps the shelf boost was a more important feature in the days of analogue tape recorders. However, the peaking EQ settings in the upper mid-range were very useful for improving the clarity of sources, and really helped to make voices sparkle, or emphasised a breathy intimate character where appropriate.

Chandler Charm

This is a well-built channel unit with a versatile front end and a marvellous EQ section, combined with a full, rich, and airy sound character. Transparent is not a word that can be applied here, but the TG Channel's characteristics are nothing if not flattering and musical. The EQ is sublime in its tonal quality, allowing the key fundamental and harmonics elements of any source to be manipulated easily and creatively, and even extreme settings remain usable. Given its classic form of construction, it's not surprising this is a relatively expensive unit in the UK, yet it compares very favourably to other vintage and high-end units and offers an unusual blend of features and characteristics. If you are looking for something to inject real character and tonal controllability into your recordings, this could be just the box you have been looking for.

Published January 2005