Sebatron VMP Quad Plus - Audio Technology Review

By Mark Davie   21 February 2018

This valve beast is the perfect character to add to your cast of preamps.

If ever there was a preamp to suit the modern recordist, the Australian-made Sebatron VMP Quad Plus could be it. Let’s face it, these days even the IC-based preamps onboard audio interfaces can sound quite good. Everyone with an audio interface has at least two clean, relatively flexible preamps at their fingertips. What they don’t have is character.

Sebatron’s latest four-channel tube microphone preamp ticks a lot of boxes. It’s affordable, built like a tank, and sonically versatile. It can go from crystal clear class A tube gain to coloured with harmonic distortion.

The preamp runs the tube with a proper High Tension voltage, so the tube isn’t starved for power to achieve artificial breakup. Instead, you get all the clean headroom you can get from a 12AT7. While it’s very low noise, this isn’t the ‘absolute’ cleanest preamp — at the clean end of the scale it can induce 0.05% total harmonic distortion, all the way up to 1% when fully driven — but it’s also no fuzz box. Rather, what you get is tonal versatility without ever destroying your sound.

SOLID TUBE LEGACY

The VMP Quad Plus is built upon the legacy of Sebatron’s VMP4000e quad-channel preamp. Sebatron says the majority of the circuit is almost identical. With the new model you get a wider frequency response, a couple more dB of gain, and a ‘lower reaching bottom end’; but they’re all relatively imperceptible, says Sebatron. One isn’t ‘better’ than the other, it’s more about the control interface.

On the VMP4000e, most of the control is switch-based. With those switches you can pad the input to varying degrees, add brightness as well as ‘air’, and a Deep circuit which boosts sub frequencies to go along with the low cut option.

The Bright and Deep circuits are omitted on the VMP Quad Plus, and the switchable pad is replaced with a rotary pad/gain pot. It also adds the ability to toggle between Normal mode — which uses negative feedback to keep the preamp behaviour predictable and clean while sacrificing a little gain — and Open Loop, which is more coloured and adds 12dB of gain.

It means you can really drive the unit by boosting the gain in Open Loop mode, then wind back the output with the main level control. Alternatively, you can keep it clean by keeping the gain at 0dB in Normal mode and adjusting the output to suit.

I haven’t used the VMP4000e; though I’ve seen it in lots of racks. I’m sure its Bright and Deep circuits are very handy for simple tone shaping on the way in, though the Air and low cut on the Quad Plus provide plenty of adjustment. After using the VMP Quad Plus on a range of material, I’m hooked on the flexible harmonic drive characteristics of this version.

OPEN UP THE VALVES

Sebatron use handpicked modern JJ’s valves to keep quality predictable and high. You can, of course, swap the 12AT7s out for a different brand, or dig into some NOS Mullards to vary the tonal signature of the preamps. It’s as easy as popping the hood and wriggling the tube out of its socket. If you want any kind of similarities across your channels though, you’re going to want to buy some matched stock. The 12AT7 has a gain factor of around 60, compared to the 12AX7’s gain factor of 100. Every tube circuit is built around the tube it’s designed for, but a 12AT7 will usually sacrifice gain for a smoother response. It’s still able to add harmonics to the sound when in open loop mode, but it typically won’t crunch and compress like a driven 12AX7. Definitely don’t swap in a 12AX7 for the existing tube.

The unit does get quite warm, so it’s best to give it breathing space. I didn’t notice any adverse effects on the cleanliness of the preamp with it running for full days of tracking. It’s a well-built device, though Sebatron has moved away from a completely screen printed front panel, to a screwed on version. It doesn’t look quite as nice, but I still like the cream look.

As well as the EQ and gain circuitry it’s got all the bits you need in a workhorse preamp; switchable +48V phantom power, phase flip, and a signal indicator LED. There’s no other metering, but it has loads of head room so you won’t overload the input. Anyway, driving the unit is a big part of the charm.

As far as connections go, Sebatron has gone out of its way to make things easy. There are four balanced mic inputs on the rear via XLR, and a 1/4-inch DI input for each channel on the front panel. This goes directly to the plate of the valve, so while you can use either input to process line level signals, Sebatron recommends plugging in via the DI socket.

On the output side, you can come out at line level via the XLR sockets or separate 1/4-inch outputs, which can handle either balanced TRS or unbalanced cables. Very handy if you’re lugging the unit around and don’t have the right cables.

 

It was a smart move for Sebatron to spinoff a unit dedicated to micro-managing the level of tube flavour imparted on sounds

 

SPECTRUM OF SOUND

I’ve been eager to get my hands on one of these units for a while. It’s Australian-designed and made, and I’ve only heard good things.

It hasn’t disappointed, the VMP Quad Plus is very clean when operating in Normal mode, with a solid representation of every source. Like any preamp, it’s a matter of suiting the source, but there’s a lot of sources it does suit.

On vocals, the slight bit of compression from adding harmonics helps them both come forward into focus while immediately bedding them into the track. It helped the vocals feel like they belonged.

I did a few recordings where I passively split the output of a Shure SM7 into the VMP Quad Plus and the preamps on a Focusrite Red 8Pre. It’s Focusrite’s flagship interface and no slouch when it comes to the analogue input side. In this mode, the vocal compression was less pronounced than when comparing the recordings made with a condenser. Probably because the less sensitive SM7 does a bit of levelling out itself.

I slapped it up on drums in the classic crush mic position above the kick. It’s a great spot to get a quick balanced mono kit sound. In this instance I was recording a pretty dry drum sound, with a heavily dampened snare in that ’70s close-sound vein. Without the heavy compression I’d usually employ, the Focusrite had slightly more presence to the snare sound, which came across a little cardboard-y in this instance. The Sebatron, on the other hand, contained the snare a bit more while bringing out the woody body of the close sound. It sounded a bit spongier and perfect for the overall drum sound. While just right for that sound, I’d prefer something a tad more snappy for ‘big’ rock drums.

While there are caveats for using the preamps to record a stereo configuration — lack of linearity in open loop mode, and non-repeatable controls — in practise it works fine for non-critical applications. The controls have enough markings around them to get you in the ballpark, and with a critical ear to your centre position, it’s fine. It’s still best to keep it in the normal position to avoid any drift in amplitude and non-linearities; all the things negative feedback keeps under control. I did, however, use it to amplify the signal of a stereo passive ribbon in a Blumlein configuration, and had to use it in Open Loop mode. In that mode I found it harder to keep the mic’s stereo centre pointed at the vocal than it was to line up the two preamp gains. When using the preamps to add character to a line level source you’ll have to line up the two channels with some pink noise. In this case, stepped controls would have been indispensable so you don’t have to constantly recalibrate whenever you make a change to the gain structure.

The variation in colour between the two extremes of clean and full harmonic colouration is relatively dramatic. Recording two passes of an acoustic guitar — one in normal negative feedback mode with gain control set to 0dB and the output control adjusted to match, the other in open loop with the gain all the way up and output control managing the level into my DAW — gave me two quite distinct sounds. The clean tone was everything I usually hear from the guitar, plenty of low end from the dreadnaught shape, but a bit flat overall. The gained up version added a lot more excitement to the mid range of the sound. All in all, it was a much better rendition of the strummed guitar without getting boxy.

The DI input is another very flexible tonal tool. I initially tracked some bass through both the Focusrite and Sebatron and was surprised to hear how similar there reproduced the low end. They both sounded full and tight. After a bit more experimenting with some guitar tracks into some plug-in amp simulation I soon realised the Focusrite sounds slightly saturated, which was a nice touch for an interface DI. The Sebatron could easily match that tone, or drive much harder for a very forward sound, which added some very usable twang and presence. On the other end, in Normal mode, the input was wide-ranging and glassy.

SEBATRON SPINOFF

I really dig what Sebatron is doing. The VMP Quad Plus is not only a great idea, but it’s well executed. Character is everything in music making today, so it was a smart move for Sebatron to spinoff a unit dedicated to micro-managing the level of tube flavour imparted on sounds. All of the things a lot of manufacturers miss, like phase flip, or robust connections, are all the things that makes the VMP Quad Plus even easier to recommend. Whether you don’t have any outboard preamps or have an entire rack of them, there’s a spot in there for the sort of versatile tube character the VMP Quad Plus can impart.



VMP2000eVU - Audio Technology Review

by Sean Diggins

I've always been keen to use a Sebatron preamp, but somehow the opportunity has never presented itself. I have several friends who own them and regard these Australian preamps most highly, but strangely, most of them are in the US, where Sebatron enjoys a reputation for high quality valve processors at a competitive price. Here in Australia, the company sells units largely by word of mouth, but its lack of vigorous advertising means the brand is less well known than its more famous foreign competitors.

After finally getting my hands on one I can happily report the Sebatron VMP-2000eVU exceeded my expectations and represents excellent value for money, particularly within Australia. Refreshingly bereft of gimmicky bells and whistles, this two channel preamp combines the right features to deliver years of reliable, quality audio: good parts selection, good build quality and a design which is as close to plain wire as you can get for less than $2,000.

The housing is ivory powder coated steel that offers the ergonomic appeal of a 2RU box with very few controls, making everything easy to reach and easy to read. Each channel includes a transformer-balanced microphone input plus a DI input, individual phantom power with LED, passive shelving EQ filters, a 12AT7 vacuum tube gain stage, a switchable three-setting pad, a phase switch, a nice VU meter and a solid state, discrete Class A output stage. Opening the box reveals a sturdy fibreglass circuit board and a pleasing dearth of chips and surface mount devices. I was pleased to see the XLR in/out connectors are soft wired to the board via a connector instead of using direct PCB mounted XLR connectors. It seems like the VMP-2000eVU is more hand assembled than hand crafted (as per the sales pitch) but the assembly is fastidious for a unit in the sub-$2,000 price category. I would have liked to see more wire-to-wire and less connectors, but that would require a price increase that wouldn¡¦t necessarily improve the sound.

Switching on the VMP2000eVU reveals a nice greenish glow from the VU meters, surely worth the extra $400 over the non-VU version! After giving the valves a good warm-up, the first thing I tried was electric bass. Wow! This preamp makes a great bass DI. The valves impart a big character, with plenty of colour, which remains pleasingly clean until driven quite hard (when typical valve distortion kicks in). Although I didn¡¦t have a drumkit handy, I could see this box being great for kick, snare and toms. Acoustic guitar was very clean at lower gain settings, becoming appropriately thicker as the gain was increased. I also really enjoyed using this preamp in series with a speaker simulator for electric guitar.

I used the Sebatron to record male and female vocals through a variety of FET and tube condensers plus some quality ribbon mics. Again, the VMP2000eVU remained quite transparent until it was driven hard, providing flattering vocal amplification and a warm character without being overly thickened by harmonic distortion. The four preset shelving filters come in very handy with vocals, allowing choice between flat/deep/low cut and flat/bright/air (providing a total of nine different combinations). The deep boost and low cut filters kick in below around 120Hz, bright appears to boost at 6 - 8kHz, while air emphasises ultra high frequencies up to (and apparently beyond) the limit of human hearing. I found the air setting to be particularly interesting on female vocals and I applaud Sebatron for providing these simple EQ options with the preamps they provide useful, practical tonal adjustment options without injuriously affecting the signal in the manner of a graphic or parametric EQ.

http://www.audiotechnology.com.au



Sound On Sound Review

by Hugh Robjohns.

Sebatron are an Australian company, who have R&D and manufacturing facilities based in Melbourne. To proclaim their complete faith in all their products, Sebatron are quite unusual in that they offer a 30-day 'return if not completely satisfied for a full refund' guarantee, plus a 12-month warranty on faulty valves and a three-year warranty on everything else. Would that all manufacturers were that supportive. Sebatron seem already to be very well-known in America, where they have acquired a reputation for competitively priced yet high-quality valve products. In the UK they're still little-known, but I suspect that is about to change.

Sebatron's VMP series of preamplifiers all share the same fundamental design concepts and are intended to bring some deliberate character to the recording table, in the shape of classic valve warmth or harmonic richness. However, unlike some valve products, the coloration isn't excessive or overdone in the VMP, and it can be controlled by choosing how hard or gently the preamp is driven. Treat it nicely, and it can be almost transparent — just like proper vintage valve preamps! Part of the secret is that the VMP-series preamps are all discrete hybrid designs, combining valve and solid-state technology, and in such a way that audio quality is paramount.

All models in the range feature transformer-coupled mic inputs plus direct instrument (DI) inputs; switched, passive two-band equalisation; and an active pad circuit that varies the negative feedback around the input valve to control gain and affect coloration. In essence, the valve preamp stage provides 60dB of gain on its own, but by introducing more negative feedback around the circuit, the gain and coloration are reduced, hence the provision of a pad switch rather than a gain switch.

The input stages are built around 12AT7 (ECC81) dual-triode valves, using a traditional high-tension (+300V DC) anode voltage (no starved-anode frippery here!), and the signal path is single-sided Class A throughout. The output stages are discrete solid-state circuits, still operating in Class A up to the balanced output, and powered from relatively high-voltage rails for optimal headroom and transient response.

The construction of the VM series is impressive, with hand-built, single-sided boards that carry mainly the high-quality semiconductor parts. Sebatron use point-to-point wiring for the high-impedance elements of the circuit, in order to avoid the surface irregularities between component and PCB tracks, which they believe degrades the sound quality. The linear power supplies they use are scary beasts, providing around 450V DC for the valve-stage regulators!

I looked at the VMP 2000eVU, which is a two-channel unit (there are also single- and four-channel variations in this series). The single- and two-channel versions can be specified with or without large rectangular VU meters, but other than the metering the channel feature set is identical for all versions.

The complete preamp assembly is housed in a substantial, 2U, rackmounting steel chassis, and it weighs about 4.5kg (for the two-channel version) and measures 190mm behind the rack ears. The vintage-style cream-coloured powder coating is easy on the eye, and makes the control legends very clear to read.

The front panel is divided into separate preamp channels (two in this case). A pair of large, backlit VU meters occupy the areas that would, in the four-channel version, be allocated to channels two and four. To the right-hand side is the mains power switch and power-on light.

Each channel has a simple set of controls, dominated by a large rotary knob, which is labelled Output Level and calibrated arbitrarily from 0 to 10. All of the other controls are silver toggle switches. Starting top left is the pad switch, which effectively determines the preamp's coarse gain, with options of 0, -15 or -25dB (the manual refers throughout to -30dB instead of -25dB, but the attenuation is obviously in that ballpark). As you might expect, given that this switch determines the amount of negative feedback, the lowest gain setting (-25dB) provides a clean, bright and pretty neutral sound, while at high gains (0dB) the sound becomes noticeably more coloured and warmer, as the top end rolls off sooner. On Sebatron's web site they suggest that at the lowest gain setting the frequency response extends between 10Hz and 110kHz (±2dB), which is impressive! Sadly, though. there's no indication of how it fares at higher gain levels. In fact, the manual itself provides no technical specifications whatsoever, and only a very limited subset of the expected information can be found on the company's web site.

Under the gain switch, two more toggles engage a polarity reversal and switch phantom power on (an associated LED warns when this is active). The two remaining switches control a passive EQ section, which is placed in the circuit ahead of the valve gain stage. This EQ is partly to assist in matching the microphone to the amplifier, and is placed before the gain stage to minimise the valve's noise contribution. This unusual circuit topology results in the frequency response of each filter setting varying slightly with the pad-switch gain setting.

Both filter switches have three positions, providing a total of nine possible EQ-setting combinations. The top switch affects the upper end of the spectrum, with positions labelled 'Bright' and 'Air'. The former adds a lift above about 2kHz, while the latter has a higher turnover (about 8kHz). The bass-end switch has positions labelled 'Deep' and 'Lo Cut'. 'Deep' is used to apply some well-judged bass boost (I guess below around about 120Hz), while 'Lo Cut' does as its name suggests in the same frequency region.

On the standard 2000e model, the only other front-panel facility is an unbalanced DI input socket, with automatic source selection taking place when a plug is inserted. However, the VU model has another three-position toggle switch under the large VU meter. This configures the sensitivity of the meter in three ranges (low, medium and high). The medium range is calibrated such that the 0VU mark equates to 0dB at the balanced output.

The rear panel is equipped with an XLR input for each channel, plus both XLR and TRS quarter-inch outputs, and these connectors are all wired back to the PCB, rather than being mounted directly on it, which is always a good sign in terms of reliability. The XLR input can accommodate a line-level signal at a push, but is really intended only for microphones. The output XLR operates at a nominal +4dBu and is capable of providing a whopping +28dBu into a 600(omega) load, while the TRS socket can only manage +22dBu — but it can be used unbalanced without any problems. The manual suggests that the TRS output is ideal for feeding a mixer or headphone amp for zero-latency monitoring while recording. At the left-hand end of the panel is the IEC mains inlet, voltage selector (120 or 240V) and fuse holder.

The Sebatron VMP 2000eVU is quite a fun box for recording all manner of things where musical coloration is desirable. It really adds a lovely sonic flavour to vocals, with a nicely weighted bass-mid range and a smooth, creamy top. In fact it worked well on pretty much all the solo instruments I tried, lending a thick, musical character at medium and high gains, which only rarely seemed to conflict with the sound. It also proved surprisingly good on kick and snare drum mics, producing an excellent, fat sound quality, especially with the EQ switched to Deep to bolster up the low end. The Bright switch helped to emphasise the beater click nicely on kick drums, too.

The EQ facility is very handy, and affords the ability to brighten or warm up the sound tastefully and always in a complementary way. The bass end seems to become fatter and fuller in the Deep mode, without sliding into territory where terms such as boomy or bloated would apply. The Bright and Air switches were very useful not only in adding presence and air to vocals.There's no getting away from the fact that the VMP 2000eVU is a very characterful device, and this is clearly what it was designed to be. In areas where musicality and colour are beneficial, the VMP proves to be a very interesting and creative tool. I also tried running a complete mix through the VMP to add some character to the track, and it worked very well.