JDV-Pre™ Using & Applications

The JDV-Pre is an exceptionally gifted instrument preamp that is able to transition from electric bass, to mandolin, to acoustic guitar and adapt to any type of pickup or microphone. As the options are so varied, we recommend that you read the owner's manual to discover all of the possibilities.

For even more details we suggest you read the Workhorse manual. This gets into details such as optimizing signal flow and maximizing connectivity options in the 500 series world. Complete details on using the JDV-Pre 500 module and making connections to and from your 500 series rack can be found in the manual (PDF download).

Using magnetic pickups

Magnetic pickups such as those found on a typical Fender bass are often recorded direct in the comfort of the control room. The JDV-Pre's front mounted ¼" input connector makes this easy. All you do is plug in, turn up the volume and you are set to go.

The JDV-pre is equipped with an Aux output on the front panel. This is used to send instrument the signal to an amp while recording. This enables the guitarist to hear himself play through a distorted amp while you capture the dry clean track on your recorder. The Aux out is transformer isolated to help eliminate hum and buzz caused by ground loops. Ground loops are a common problem when interfacing guitar amps to pro audio equipment.

Drag control brings the natural tone of the instrument to a whole new level by allowing you to replicate the load on the pickup as if connected to an amplifier. This not only makes the instrument sound more natural, it changes the feel of the instrument so that it sounds right. To activate, you simply depress the Drag control on switch. This changes the input impedance from 3.9m Ohms (optimized for piezo pickups) to a variable load that ranges from 22k Ohms to 500k Ohms.

Begin by setting the Drag Control to 12 o'clock. Then turn it clockwise. The sound will become brighter with greater clarity. As you turn it counter-clockwise the tone will warm up and sound smoother. Setting the Drag is particularly important if you intend to Reamp the signal down the way. By adjusting the load, pedals and amps will sound much more realistic.

Using active pickups

Active bass preamp powered by two 9 volt batteries.

Active pickups have been around for years. They have recently become more popular since the advent of 5 and 6 string basses. Although these can sound absolutely amazing, more often than not these instruments are so loud, they will overload the instrument input on most devices. This is because traditional passive basses generally produce around 1 volt while the active counterparts (often equipped with two 9V batteries) can deliver well over 6 Volts! Unless they have enough headroom, you will get distortion. The JDV-Pre addresses the problem by providing plenty of headroom with 30V internal working rails. Connection would be the same as using a passive bass. Drag control will have no effect as the signal is already being buffered by the bass's internal active electronics.

Using piezo pickups

Drag On Variable impedance Works with passive & active pickups

Drag Off 4 meg Ohms Works with piezo pickups

Most piezo equipped instruments sound squawky and harsh. This is not so much the fault of the pickup as it is the built-in preamp that normally accompanies the device and its input impedance. The higher the input impedance, the happier the piezo element will be and smoother it will sound. But as you increase the input impedance, you increase background noise and hiss. It takes very careful signal management and gifted engineering to effectively produce a preamp that has a high input impedance yet low noise.

By disengaging the Drag Control, the JDV-Pre's input impedance elevates to 3.9 meg-ohms, or about four times higher than the typical input impedance found on most instrument inputs. Careful attention is paid to reducing noise while the class-A feed-forward circuit assures the most natural tone. For best results, bypass your usual preamp (and the internal instrument preamp if you can) and connect the piezo directly to the JDV-Pre's ¼" input on the front panel. You will immediately notice a much warmer, natural sounding tone. This is not only effective on acoustic guitars, but equally so on difficult to amplify instruments such as violin, mandolin, banjo and contrabass.

Using a microphone

There is no denying it… capturing the sound of the instrument with a high quality condenser microphone is just about as good as it gets. The real magic lies, not merely with the choice of mic, but in the positioning of the mic inside the room; finding the sweet spot and connecting the mic to an appropriate preamp. The JDV-Pre's XLR input is optimized for mic'ing instruments. But don't be surprised if you end up using it as your go-to mic preamp for vocal tracks too! It sounds fantastically warm and natural and will surely captivate your senses as you start using it.

But what truly makes it a marvel is the way the transformers naturally compress the sound. This is because transformers do not so much distort, they saturate. In other words, as they reach their maximum signal handling capacity, instead of going from say 1% to 100% distortion like an active circuit, the distortion increases gradually. This sounds naturally compressed – some folks call it vintage. On acoustic instruments that are typified with incredible transient peaks such as a banjo, acoustic guitar or mandolin, the transformer gently rounds out the tone.

Connection is made using the rear panel XLR input on your 500 series rack or Workhorse. The JDV-Pre is well suited to accommodate dynamic, ribbon and condenser microphones. To active 48V phantom power, you merely set the phantom ON switch adjacent to the card edge connector before you plug it into your rack. Although phantom power will not harm dynamic microphones, most engineers tend to turn it off when not in use. This helps reduce the pops that are associated when plugging in equipment.

Using the High-Pass Filter

Click to zoom

The JDV-Pre is equipped with a high-pass (low cut) filter that is designed to reduce resonance and excessive low frequency build up from instruments. In fact, it is always on. You just can't hear it. This is because it begins to take effect at 5Hz which of course is well below our hearing threshold. As you turn it up (clockwise) it slowly rises to gently remove unwanted low frequencies.

Using the high-pass filter with acoustic instruments will change your world. Acoustic instruments are resonating devices with all kinds of harmonics emanating from the body, top, sound hole and neck. When recording, these resonances many not even be immediately audible but depending on the play back system, they can turn what could be a wonderful mix into a low frequency mud fest.

The 'Nashville Trick' is eliminating the problem before it hits the recording system. All you do is dial in the high-pass filter until the bottom end cleans up. Play a little more so that you get use to it, and then add some bass back in.

Using the 180º invert switch

A wonderful feature built into the JDV-Pre is the invert switch. This reverses the electrical polarity of the signal by 180º, essentially putting it out of phase. The most common application when recording is when combining two mics to create a stereo field. Sometimes, flipping the polarity can bring certain frequencies in phase resulting in better tone.

Another application is less known and it has to do with using the 180º invert switch to eliminate room resonance. This is primarily applied in live environments where the sound from the PA system may be interfering with echo in the room. This can create a hot spot (room mode) which can amplify certain frequencies. By inverting the phase, you basically move the hot spot thus solving the problem.