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Korg TP2 & TPB2

Dual Tube Preamp/Optical Compressor
Published April 2005
By Tom Flint

Korg TP2 & TPB2Photo: Mike Cameron

Korg's new valve preamp and optical compressor is available not only as a stand-alone box, but also in a version which can be installed directly into either of their flagship digital multitrackers.

Digital recording is a fantastic innovation, but it does have shortcomings. One of its major problems is that it often lacks what has become known as 'analogue warmth', which was given to recordings of yore by the specific characteristics of valve/solid-state equipment and analogue tape.

While software designers struggle to develop programs which accurately reproduce the beneficial imperfections of vintage equipment, hardware manufacturers have been exploiting the opportunity to sell the real thing to sufferers of digital coldness, so there is now quite a choice of analogue preamps and channel strips on the market, all of which can be used to process and 'warm' audio on its way into a digital setup.

The TP2 is a twin-channel valve preamp with optical compression included, and is clearly designed to appeal to anyone who has an appetite for tubes. The TPB2 is functionally pretty much the same, except that it is designed to integrate with Korg's D32XD and D16XD digital multitrackers. I'll deal mainly with the TP2 here, but there are more details about the TPB2 in the 'Little B' box elsewhere in this article.

Together with a moulded metal heat sink, the TP2's two 12AX7 valves are proudly displayed in a large, clear plastic dome so that they are impossible to overlook. The aesthetic theme is furthered by the two circular VU level meters, which have a definite retro look about them. Despite Korg's visual styling, this unit remains a thoroughly modern bundle of electronics, carefully designed to interface with digital multitrackers and computer workstations, as demonstrated by the optical and coaxial S/PDIF digital outputs on the back. Digitised audio can be output at sample rates of 44.1kHz, 48kHz, or 96kHz, simply by moving a rear-panel switch to the desired setting. Bit depth, however, is fixed at 24.

The Setup

Each of the two preamp channels has its own combi jack/XLR socket into which both quarter-inch jacks and XLRs can be inserted. Phantom power is applied to the XLR at 48V via one switch, while its neighbour reverses the channel's signal phase. Next in the circuit is a 26dB pad button which makes headroom for extremely loud input signals. That's followed by a 6dB/octave low-cut filter operating at 70Hz.

Korg TP2 & TPB2Photo: Mike Cameron

The preamp's valves can either be driven hard for an extremely noticeable saturation effect, or used moderately to add a touch of colour to a signal. The overall level adjustment is made with the Level Trim knob, which provides up to 48dB of attenuation, although further control is offered by the optical compressor. As far as I can make out from the schematic in the manual, the compressor is actually located in the circuit just before the valve. However, it is triggered by the valve's output which is fed back into the circuit via the threshold level control. The level meter is the last component in the circuit before A-D conversion, and therefore allows the user to keep an eye on possible clipping problems.

The compressor itself has just a few controls governing its adjustment. The attack speed of the compressor is determined by a button marked Fast/Slow, although there is no helpful legend to say which one is selected when the button is depressed. The manual reveals that Fast is the upper position, but it doesn't offer any actual timing values for either speed. The Fast setting is, however, optimised for drums, whereas Slow has apparently been set for vocals. Sadly there is no control governing the release time, significantly reducing the flexibility of the compressor. The manual doesn't mention release times at all, so we're left to wonder if there are just two fixed values, or if there is some kind of automatic mechanism at work, with the time varying according to the input signal.

The aforementioned threshold level control is labelled Comp Sens and is adjusted with the use of a rotary knob, together with its own Gain Reduction indicator LED. Korg are aware that the TP2's twin channels may be used to process stereo signals, so they have included a Link button which ensures that the same compression is applied to each channel. In practice this means that when one channel's threshold is set lower than the other, it will be triggered first, and will therefore act as the Comp Sens control for both.

Beyond the preamp and compressor the audio signal is sent to the A-D converter with no further intervention. The analogue signal, on the other hand, can be attenuated independently for each channel by adjusting the two hardware faders.

Little B: The TPB2

Owners of a Korg D16XD or D32XD who are interested in the TP2 have the option of buying its expansion-board equivalent, the TPB2. This has been designed to fit into the spare I/O slot on the front panel of either multitracker, and acts like any other pair of inputs. In terms of processing, the two products are the same, but the TPB2 does away with the output connectors and the two faders, which are no longer needed. The rest of the controls are identically positioned, and differ only slightly in their colour scheme.

The TPB2 version installed in Korg's D16XD digital multitracker.The TPB2 version installed in Korg's D16XD digital multitracker.Photo: Mike Cameron

Installing the TPB2 into a Korg multitracker is very easy indeed, and should only take a minute or two for anyone with a screwdriver to hand. Once the recorder's blanking panel has been removed, the main circuit board is visible inside the metalwork. Mounted on the board, directly beneath XLR sockets seven and eight, is the plastic socket into which the TPB2's lead needs to be plugged. Installation really is just a matter of pressing the plug in place, and the connection provides the preamp with both power and audio connections.

Although the D16XD which Korg sent me had the TPB2 already installed, I found that it didn't work at first. This turned out to be because the software needed upgrading to version two or above. The review model also didn't have a CD-RW drive installed, but I was able to run a USB cable from my PC into the back of the D16XD to perform the upgrade. This required placing the recorder into its 'slave' mode, copying some files into the relevant folder, and then loading the system. The accompanying PDF manual provided all the instructions for this process, and I'm happy to report to anyone with an old OS that the upgrade was trouble free.

Once the upgrade was done the two new inputs were available from the input/output assignment page, from individual channel pages, and from the master channel assign page. Having the TPB2 fixed neatly in the chassis of a multitracker, operating like any other set of input channels, is very convenient, and will be an attractive prospect for many D-series owners who have a lack of desk space, or do a lot of location recording. The downside, however, is that it takes up an expansion slot that could otherwise give the multitracker eight additional inputs. Another thing to bear in mind is that the TPB2 can only be used with the Korg multitrackers, which means that if you sell your recorder then you'll have to say goodbye to your valve friend too, so in some ways the TP2 is the more flexible option, even if it does cost a little more.

In Use

I first tested the TP2 by recording several layers of backing vocals and then a lead vocal using an Audio Technica condenser mic running from the preamp's phantom power. The effect of the valve was immediately obvious, giving a clean, bright sound to the recording without sounding harsh or thin. Turning up the gain allowed me to drive the preamp into varying amounts of distortion, which I controlled through the intensity of my vocal performance. Fortunately, even quite severe distortion sounded extremely musical, and reminded me of the kind of vocal effect commonly used in the 1960s to make a voice sound aggressive.

The compressor sounded very smooth, and clamped down on extreme signal peaks reliably and noticeably when the threshold was lowered. Although the Slow attack setting is optimised for vocals I found that the Fast mode worked equally well on the voice, if not better, particularly at moderate settings.

Seeing that the Fast setting for the compressor was intended for use on drums and percussive material, I sent a stereo drum track through the inputs to see how it performed. This mode was indeed quick enough to grab the start of a snare hit, and to quell the ferocity of hi-hat. All the same, I found the Slow setting valuable too, as it retained the crack of the snare hit, but still appeared to take hold of the sound, albeit slightly later, giving it a degree of shape. I also tried cranking the preamp level up high to apply some of that valve distortion to drums, while fending off peak overload with the compressor. The effected drum signal became ever more dirty and coloured as the gain was increased, and would probably be of use to certain dance and hip-hop productions.

The sweetest-sounding guitar amps are usually of the valve variety, so I was keen to try my guitar through the TP2 using the Hi-Z button to provide the appropriate impedance. Optimising the settings for guitar did take a minute or two, but the result was a rather pleasing sound, once again reminiscent of that subtle soft distortion heard on many recordings from the 1960s. Driving the valve hard was also possible, although the compressor needs to be used quite heavily to avoid nasty clipping at the S/PDIF output. For subtler sounds the compressor was best turned off or set with a high threshold to allow the natural dynamics of the guitar to shine through.

When compared to a proper guitar amp the TP2 is limited, having no independent level and gain pots, no EQ, reverb, or speaker cabinet. Nevertheless, by adding a little reverb after recording, the sound becomes far more believable, and many workstations do offer cabinet simulation in their effects arsenal. As for the EQ, it's a matter of adjusting the guitar tone and pickup selection to suit.

In terms of the rest of the controls, everything did what it should in a simple but effective way, even though the lack of button-status information was annoying. It also has to be said that the position markings around each rotary knob are inadequate, as they have no numerical scale. The only control that wasn't effective enough was the low-cut filter, which, I think, needs to be slightly steeper and set higher to act incisively on more material.

Conclusion

At times the TP2 is frustrating to use, having so few controls, many of which could do with better labelling. Korg could add greatly to the product's usefulness by changing the Fast/Slow button to a rotary knob with, say, 10 attack and release presets labelled helpfully. Limitations aside, the TP2 really does sound very good indeed, and there is a lot to be said for that! As a general-purpose studio workhorse, it does leave a little to be desired, but when viewed as a creative tool for adding that extra something to a recording the TP2 really makes sense.

Priced at £399 in the UK, this unit is not as cheap as some voice channels or channel strips with many more features, but it has to be remembered that there are two channels on offer here instead of the one. As such, the asking price seems pretty reasonable. I should also briefly mention something about the compact design of the TP2, as Korg have obviously made efforts to fit both channels in a pretty small box that sits neatly on the desktop. However, compact as it is, my preference would still be for a rack version.

Overall, though, even though I have more sophisticated valve gear, specifically built for guitars and vocals, I still find myself desiring the TP2, and speculating quite how good some aspects of my recording could really be if I were using it on a regular basis.

Published April 2005