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Tegeler Audio Manufaktur VTRC

Valve Channel Strip
Published January 2016
By Hannes Bieger

Tegeler Audio Manufaktur VTRCPhoto: Hannes Bieger

Sporting both optical and variable–mu compressors and Pultec–inspired EQ, this German channel strip should make a great recording front end for the modern studio.

Tegeler Audio Manufaktur, so–named because they’re based in Berlin’s borough of Tegel, have their origins in the audio DIY community, but today they offer half a dozen powerful studio processors commercially, including summing mixers, valve compressors and transient shapers. Their Vari Tube Recording Channel (VTRC), whose features and signal–shaping capabilities I’ll discuss here, is one of their flagship products and combines a great deal of the circuitry from their other devices — an interesting mixture of the obvious and the unusual, including some unique ideas — in a single enclosure. The VTRC boasts not only a valve–based preamp and a passive EQ section, but also two different compressors, and thus provides ample facilities to ‘shape’ signals before they hit your A–D converters and hard drive.

Overview

Conceived as a fully featured recording front end, the current version stands on the shoulders of a number of previous iterations, each inching the concept further towards perfection. It relies on classic valve amplification and includes three dual–triode valves in the critical processing stages, but designer Michael Krusch also chose to include a few solid–state components in the signal path, as these were required to implement some of the more complex features. The unit is capable of a maximum amplification of 60dB for microphone signals, and while that’s perhaps not a stellar figure by modern standards, it’s typical of and perfectly acceptable for a valve–based preamp such as this.

Boasting no fewer than 11 detented pots and rotary switches as well as 10 smaller toggle switches, there’s plenty of control under your finger tips. First, the Input pot determines the signal level sent to the preamp stage. The amplification is then adjusted by way of the Gain control, which essentially governs the amount of negative feedback applied to the input valve (an ECC803S type). This way, the pot adjusts not only the amount of preamp gain but also the sound of the input stage — when applying more negative feedback, the output level decreases and, with it, the typical nonlinear behaviour of a valve stage, which we would normally call ‘colour’ or ‘character’. Conversely, when reducing the negative feedback, by turning the pot clockwise, the output gain of the valve stage increases and the character becomes increasingly audible. With any preamp that offers such facilities, it’s great to experiment with the different settings, as there are usually plenty of tonal options waiting to be explored. In this case, according to Tegeler, the palette ranges from ‘old–school’ to ‘modern’ sounds; I’ll let you know my own thoughts on that in a moment.

The centre section of the face plate is reserved for the EQ controls. Inspired by the layout of the Pultec MEQ–5 Midrange Equaliser, the EQ section on the VTRC comprises one cut and two boost bands, each offering bell curves and amplitudes which extend well beyond 15dB at certain frequencies. The low band boosts a choice of seven corner frequencies between 80Hz and 1kHz, all well–chosen for the musically critical frequency range between bass and lower mids. The mid cut and high boost each offer 11 corner frequencies, ranging from 200Hz to 7kHz (cut) and 1.5 to 24 kHz (boost).

Tegeler Audio Manufaktur VTRCMost channel strips offer either no compression at all or a single dynamic control device, but the VTRC comes with two. At first, the signal is fed into an optical compressor, based on a Vactrol cell, and this circuit is followed by a variable-mu section, designed around an ECC802 dual-triode valve. Both sections share the same side-chain signal, yet they can be activated individually or simultaneously, giving the user a number of tonal options. The controls are simple: a single pot adjusts the amount of gain reduction for the entire section, and the time constants can be toggled between the Fast, Slow and Auto settings. In the Auto setting, both modes are combined, with the faster one controlling the peaks and the slower one levelling the overall signal. This way, the signal is kept at bay effectively without risking over–compression. Finally, the output pot controls the level being sent to the next device in the chain (typically an A–D converter in a tracking situation). The output amplifier is based, again, on an E88CC dual-triode valve.

We may have reached the end of the signal path, but we skipped a few useful controls along the way. There’s phantom power, of course, though sadly no status LED indicating whether a potentially dangerous +48V is being applied to the mic input — phantom power has the potential to be lethal to devices such as vintage passive ribbon mics, so the more visible the control status, the better. The VTRC also includes a low–cut filter (80 or 160 Hz) and a polarity–invert switch. The entire concept is rounded out by extremely flexible routing options for the EQ and compressor sections. With a clever configuration of the respective switches the EQ can be toggled before or after the compressor, and can even be applied to the compressor section’s side-chain. (In this last case, though, the face plate controls aren’t self explanatory, and users who refuse to read manuals will most likely miss this feature!)

In general, the VTRC seems to be well laid out, and it’s obvious that many great ideas contributed to the final result. But if I were to express a single complaint, it would be the layout of the front panel. On similar channel strips, such as the Manley Voxbox or Pendulum Quartet, the different processing sections are visually much better defined, and this helps you grab the right control in a critical and hectic tracking situation. This Tegeler device doesn’t offer any such visual guidance to distinguish the different sections, and it gives the same ‘visual weight’ to all the pots and rotary switches that form its main controls too. This isn’t a problem per se, as familiarity will soon overcome this obstacle, but it does mean that I strongly recommend that you make yourself comfortable with the VTRC before using it to track a critical performance!

The layout isn’t all bad, though, by any means. The VU meter is extremely versatile: it can be set to display the preamp output, the EQ output, the main output or the compressor section’s overall gain reduction. Thus, it’s very easy to manage your gain structure at all times — and this is particularly helpful here, since the levels inside the Vari Tube can be set with great flexibility, and the EQ has a lot of power, too.

With a  digital print on the front panel, the unit looks both distinctive and classy. The fully featured channel strip comprises a  valve–based preamp, a  three–band EQ and a  dual compressor sectionWith a digital print on the front panel, the unit looks both distinctive and classy. The fully featured channel strip comprises a valve–based preamp, a three–band EQ and a dual compressor sectionThere’s an XLR/TS combo jack on the front for the mic and instrument inputs, but all other connectors can be found on the back: another mic input doubling the connector on the front, as well as a line input and a line output. The compressor sections of multiple units can be ganged by way of the Link connector.

Overall, the VTRC seems to be well made. The sturdy and flawlessly manufactured enclosure houses quality components, such as specially selected valves made by JJ Electronics. In total, the circuit employs four audio transformers: two dedicated mic and line input transformers (the former made by Pikatron), as well as two more transformers in the vari-mu compressor section and at the main output, all of which are made by Vigortronix, as are the inductor coils of the passive LC (inductor-capacitor) EQ bands.

Most of the ICs on the main circuit board are employed in the compressors’ side-chain circuit or for signal routing but, as I mentioned earlier, there are a few in the audio path. According to Michael Krusch they are mostly used for buffering and impedance matching in the fairly complex circuitry. While purists might have preferred an all–valve signal path, you simply can’t have it both ways — a purist audio path, and also the complex, versatile feature set of the channel strip. In this case, high–quality, very neutral–sounding components made by Burr Brown are used, and these really don’t detract from the valve sound.

In Use

It takes time to get used to the features and capabilities of the VTRC, partly because of the front–panel layout but also, and more importantly, because of the extensive feature set. However, in many respects it’s intuitive too: the design follows a ‘musical’ approach, whereby all gain pots on the unit simply carry a scale from 1 to 10, rather than offering real–world measurements. This encourages the user to think more in sonic and musical and less in technical terms — which is, in my view, as it should be. I view it as one of the qualities of this unit that all its functions remain accessible for all users, no matter how technically trained they may or may not be.

During my tests, the preamp stage always remained very true to the source unless I decided to dial in character using the negative feedback control, and, just as the sound files (http://sosm.ag/jan16media) demonstrate, it can render the character of different microphones very accurately. This is always a sign that a preamp designer has done a good job: whatever colour I might eventually wish to add, I normally like to be able to listen to the source itself and not so much to the preamp’s contribution.

Mic and line inputs are on the rear — the mic input is duplicated on the front channel, by a  ‘combi’ XLR connector that also caters for TS instrument inputs.Mic and line inputs are on the rear — the mic input is duplicated on the front channel, by a ‘combi’ XLR connector that also caters for TS instrument inputs.The overall preamp character, then, is one that I’d describe as detailed and open. In its most neutral state it sounds pretty well–balanced, perhaps with a slight, airy emphasis of the top end. When you’re reducing the negative feedback, though, the sound gets gradually darker, softer and thicker, and a blooming (lower) mid range comes into play. This worked well enough with an already rather soft–sounding Neumann U67, but it really helped to warm up the thinner-sounding Neumann TLM103, shifting its rather analytical charm more towards the ‘creaminess’ of the vintage U67. For all that versatility, though, this is no distortion box. The whole colour palette remains rather civilised and sympathetic to the source.

Three dual–triode valves, three inductors for the passive LC filters and four audio transformers combine to form the beating heart of this channel strip.Three dual–triode valves, three inductors for the passive LC filters and four audio transformers combine to form the beating heart of this channel strip.With gentle peaking curves, wide overlapping bands and plenty of frequency options, the three filters prove a powerful means to shape any signal. They may be inspired by the Pultec circuitry but this isn’t an outright clone. I have the impression that a classic Pultec sounds even sweeter and more lush, but I really like the contoured, precise character of this equaliser, too. There was just one practical thing that bothered me a little: while the boost pots work just as you’d expect (the more you turn them up, the more energy is added in the respective band), the cut filter’s neutral state is when its control is at its rightmost position, which means you have to turn it anti-clockwise to activate the cut. This approach works well and logically for a normal parametric EQ with a centre detent but it’s unusual for a Pultec-type EQ, so I found it rather counter–intuitive.

Tegeler Audio Manufaktur VTRCBy contrast, the compressor section is easy to set up and a joy to use. Just dial in the desired amount of compression, choose one of the time–constant settings and call it a day! I found it great to have both circuit options: the smooth, elegant opto compressor and the slightly more aggressive variable–mu type. Both circuits do a good job on their own but it’s also fun to combine them. If you do that, you must remember that the gain reduction of both compressors will be stacked, so you’d most likely have to adjust the threshold of the first when activating the second. Both compressors work well as gentle levellers during tracking and mixdown, and they can either be used to tame or to accentuate transients with the different time-constant settings. I have the feeling that both compressors are pretty ‘grabby’, though: even the smoother opto circuit seems to behave more like, say, an Inward Connections Vac Rac than a Teletronix LA–2A.

Conclusion

All in all, then, the Vari Tube Recording Channel offers many signal–shaping facilities, and is capable of producing great–sounding results for both tracking and mixing applications. The basic, open and detailed character of the preamp suits a large number of sources, and these results can be refined in a number of ways when bringing the EQ and compressor sections into play. Given the sheer number of features, the build quality and the sonic qualities, this German–made channel strip is offered at a very fair price. While I may not personally be a big fan of the front–panel layout, for the reasons I’ve explained, it’s nothing I couldn’t get used to and, ultimately, the sound quality itself would always be the deciding factor for me. The VTRC, then, is a great, versatile device that doesn’t seem at all expensive given the extensive facilities and great sonic quality that’s on offer.

Alternatives

There are many valve–based channel strips with EQ and compressor sections, and every one has its own strengths. While the Tegeler Vari Tube has more features than most, it’s in the more ‘comfortable’ price bracket. The Universal Audio LA–610, the Thermionic Culture Phoenix HG15 and the Manley Core are also comparatively affordable but have more limited feature sets. The Tree Audio The Branch, Retro Instruments Powerstrip, Manley Voxbox, Gyraf Gyratec II and Pendulum Quartet and Quartet II offer plenty of features but the no–expense–spared approach means they cost a lot more.

Published January 2016