Recording amp with switchable choice of output tube type
Cornford Amplification, the UK-based maker of high-quality guitar amplifiers have launched a companion to their acclaimed Harlequin 6-Watt, class-A recording amplifier. Their new Carrera model adds a number of features, including a mid-range EQ control, a front-panel send/return effects loop, standby switch and a spring reverb. Most interesting of all, however, is the inclusion of two different types of output tube, one eight-pin type (such as the 6L6 and EL34) and one nine-pin (6V6, EL84), with the user able to switch between them to get different sound characteristics.
The Carrera ships with an EL84 (the same as the Harlequin's single output tube) and a 6L6 on board, offering 5 Watts and 8 Watts respectively, but you can swap these for, say, a 6V6 (like a Fender Deluxe) and an EL34 (typical of most Marshalls), greatly enhancing the amp's versatility in the studio. Although there have been previous amp designs that can accommodate a range of different output valve types (notably the THD models), there's nothing like being able to do it at the flick of a switch to encourage creative experimentation. You can also swap any of the Carrera's three 12AX7 preamp valves for a lower gain 12AT7 or 12AU7 to further fine-tune the amp's gain structure to your own requirements.
In action, the amp sounds every bit as sweet as the Harlequin, but with more scope to lift or de-emphasise mid-range without sacrificing overall drive level. Switching to a different output valve type really does change the vocabulary of the amp, with a 6L6 in particular giving a warmer and bigger sound, especially on cleaner or right-on-the-edge sounds. On all valve types, the overall amp voicing remains just on the dark side, like the Harlequin, making it ideally suited to close-miking. Brighter amps may be better at filling a room, but they tend to sound brittle and harsh when close-miked. The Carerra's 'browner' tones are ideal for the robust directness of an SM57 right against the cone, whilst still rewarding subtler treatments like a ribbon mic or a condenser backed off a couple of feet.
At £999, the Carrera complements the Harlequin in the Cornford range rather than replacing it, and should certainly be on the audition shortlist for any recording guitarist into premium tube amps. Dave Lockwood
SUMMARY: A very successful realisation of the high-quality, low-power guitar recording amplifier concept, with the added twist of switchable output tube types. Nothing else exactly like it on the market; a THD UniValve with a suitable speaker would get you in the same sonic territory, but you'd have to swap over the tube type manually when you wanted a change of character.
Recording satisfying acoustic guitar sounds in the home-studio environment can be difficult, particularly if the part will be prominent in the mix. Most home studios are not acoustically well balanced or quiet enough to allow optimum studio miking techniques to be used. Pickup systems of all varieties each have their own compromises too. Combining a pickup and a mic signal recorded to separate tracks offers one way forward, but often doesn't sound as satisfying as it should because the pickup tends to remain dominant in the mix until it is reduced to the point where it is almost inaudible.
The key to making this work is time alignment of the two signals, which is easily achieved if you are working with a software sequencer (or a reasonably sophisticated hardware digital recorder). Normally, the pickup is heard as the dominant source because its signal always 'speaks' first — the electrical signal from the transducer under the bridge is practically instantaneous, whereas the microphone signal has to travel the distance between the guitar and the mic, and other elements of the sound take even longer as the bridge drives the top into vibration and stimulates the resonance of the body enclosure.
Sound propagates in air at a speed of roughly one foot per millisecond, so if your mic is a foot away from your guitar, delaying your pickup signal by one millisecond would be a good place to start (44.1 samples if you are working at 44.1kHz sampling rate). It is only a starting point, however, for the dissimilarity between the two signals means that there is no exactly 'right' time-alignment point. The different shapes of the waveforms make it quite difficult to decide by eye when the two tracks are optimally aligned. The best solution, I find, is simply the one that sounds best, starting from the nominal '1ms per foot' mic distance compensation and then nudging by ear until the attack of the pickup no longer dominates, but its track continues to add sustain and body to the notes.
Configurable guitar rig multicore system
Where do you turn when you need a multicore that will handle two MIDI lines, a 9V DC power line and a voltage control line? Suddenly needing all of the above for my on-stage electric guitar rig, and finding the idea of four more separate cables running out to my already crowded footswitch position distinctly unappealing (to say nothing of the additional setup and breakdown time), I started to look at making up a custom multicore until I realised that the perfect solution was already available.
Pedalsnake is a multicore cabling system for guitar pedalboard users, with a patented internal shielding system that allows audio signals to share a snake with DC power and switching lines (not normally a good idea!). The multicore is terminated with the necessary variety of connectors for each end, with jacks for guitar and line signals, male and female 2.1mm barrel connectors for power and so on, allowing all your pedal power supplies to remain at the back of the stage with your amp.
In the Pedalsnake CS range, the connectors are all hard-wired, either in off-the-shelf or custom configurations, but the company's G2 range allows the user to attach a selection of tails to set the function of each multicore line. Each of the colour-coded lines of the G2 base snake terminates in a standard MIDI connector, whilst the tails all have a female 5-pin DIN with a short cable leading to the appropriate connector for your application. In my case, I terminated one line with a quarter-inch jack at each end for my voltage control pedal, another line with a male and female 2.1mm connector for power, and left two lines unterminated as my MIDI send and return.
If I were thinking of running sensitive, guitar-level audio down it, I would probably opt for the CS range, with hard-wiring and all-metal connectors, but the G2 range is the one that offers complete reconfigurability and a perfect solution to my particular problem and many others, both on stage and in the studio. Pedalsnake systems start at around £53. Dave Lockwood
SUMMARY: A unique problem solver. The reconfigurability offered by swappable tails adds a great deal of flexibility and ensures that your investment in the basic cable can never be rendered useless by minor changes to your setup.
Tube-based onboard preamp for electro-acoustic guitars
For years now, acoustic guitarists have been choosing tube-based outboard preamps to warm up the signals from piezo-based pickups. The piezo's over-fast attack and non-linear output can be partially mitigated by the tubes' tendency to gently compress (within suitably designed circuits). Now Japanese electro-acoustic specialists Takamine have designed a tube preamp that mounts within the guitar itself!
The CTP-1 Cool Tube preamp addresses the obvious concern about excess heat within the guitar body affecting the wood by running the tube at just a couple of degrees above ambient temperature, using a supply of just three Volts for the heater circuit. In fact, the 12AU7 tube doesn't visibly 'light up' at all, leading some people to wonder whether it's actually doing anything! Running a tube at very low voltage is perfectly valid provided you are not using it as a gain stage. Tubes work by causing free electrons stirred up by heating the oxide coating of the cathode to jump across to the positively charged anode or 'plate', with the current flow being regulated by a negative control voltage, or 'bias', on the 'grid', located in between the two. Applying a small input signal to the grid therefore modulates the flow of electrons to produce a larger version of the signal at the plate... hence, gain!
In a low-voltage circuit, tubes are most likely to be used as harmonic distortion generators, with a low plate voltage used to deliberately increase non-linearity, accompanied by a solid-state stage to provide gain. Takamine's Cool Tube preamp allows you to blend the desired amount of 'tube effect' into the output, but the subjective audible effect is more warmth and gentle compression than distortion. It actually works really well! Takamine's patented Palethetic pickup system, using an array of multiple piezo transducers built into the bridge-plate during manufacture, is already a half-decent-sounding solution, but the sound is still rather brittle, with unnatural dynamics.
Dialling in even a little of the Cool Tube effect, the slightly sterile sound of the pickup system alone becomes far more three-dimensional and complete, almost like adding additional transducers to sense more of the body vibration. I'd hesitate to say that it is significantly more microphone-like, but what it certainly is is much nicer, both to listen to and to play. Low-level detail becomes more audible and sustain is increased, as if using a good compressor. There's a useful degree of variation available too; I found I used about 60 percent Cool Tube in a recording context, for maximum warmth, but only around 30 percent on stage, where I wanted to both retain more edge and minimise feedback.
The CTP-1 conforms to Takamine's Sound Choice modular preamp format found on all their guitars since 1989 and features a built-in tuner as well as the standard three-band EQ with semi-parametric mid-range. It is powered by four AA batteries, giving around 24 hours of playing time — enough to get you through the gig, but clearly not ideal on a long-term basis. An alternate power source switch on the preamp module suggests that external powering will be possible, but no details are currently available. The tube itself is a standard type that should last as long as the guitar in a circuit of this kind.
Many attempts have been made in recent years to overcome the inherent limitations of all acoustic guitar pickup systems, ranging from alternative transducer technologies to on-board DSP modelling. Takamine's Cool Tube approach is undeniably one of the more successful ones. The CTP-1 module costs £209 in the UK and is fitted as standard on Supernatural and Nashville models. Dave Lockwood
SUMMARY: Battery life remains an issue until a phantom powering solution is available, but the Cool Tube circuitry really does significantly improve the sound of Takamine's integrated pickup system. An external tube preamp will get you close, but there is something sonically very nice about the way Takamine have implemented this.