D.W. Fearn VT-3 Dual Channel Vacuum Tube DI
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Add depth, dynamics, and excitement to your recordings without adding noise!
The VT-3 from D.W. Fearn is a dual-channel, all-triode vacuum tube DI ("direct box") for recording electric or electronic instruments. The inputs are designed to provide the proper load impedance for all instruments that have a 1/4" phone jack output. Tube circuitry provides the very high impedance necessary to capture all the details of these instruments.
The outputs of the VT-3 are mic level (150 ohm source impedance at a nominal -30dBV). The VT-3 Direct Box is designed to operate into a high-quality microphone preamplifier like the Fearn VT-1 (#180271) and VT-2 (#180272) Vacuum Tube Microphone Preamplifiers.
Operation is very simple: plug the instrument into the 1/4" front panel jack and take the output either from the front panel XLR connector, or a parallel XLR connector on the back panel. A second 1/4" jack provides an output to feed a guitar amplifier when necessary. A ground-lift switch helps eliminate ground loop buzz, and a switchable high-pass filter gently rolls off frequencies below 100Hz when required.
The two channels are entirely independent and can be used with two different instruments at the same time.
Important Note: Due to heat given off by tubes, D.W. Fearn recommends that you provide at least one rack unit (RU) of space above and below their audio rack products. For proper cooling and a refined look for your rack, we highly recommend using D.W. Fearn Vented Rack Panels (#180296).
History of the VT-3 Vacuum Tube DI
As far back as I can remember, taking instruments "direct" has never sounded very good to me. There always seemed to be a lack of dynamics and a sterile quality to sounds recorded with a direct box (or DI).
The first tube DI that we produced was the VT-I/F Instrument Interface. It was
a beautiful piece in a large, machined-aluminum case that you could drive a truck over. Unfortunately, the cost of that case made it impossible to build the VT-I/F for a reasonable price. Only about 75 were ever made, but the owners loved them, and we kept getting requests for it. After several years of promises to bring out a rackmount version, we finally did so in 2006. The VT-3 is exactly the same as the VTI/F internally, except that we added a switchable high-pass filter and changed tubes from the 6072A (which we use in all our preamps) to the 6N1P, an excellent-sounding tube used in our VT-4 EQ and VT-7 Stereo Compressor.
Before beginning the design of the circuit, I spoke to engineers, producers, and musicians about what they felt was lacking in DI boxes. Almost without exception, they all said, "It's got to have tons of headroom." How much headroom was enough? I spoke to a number of instrument pickup manufacturers and got an idea of the peak output level of a variety of instruments. These figures were confirmed with an oscilloscope placed directly across the output of various electric guitars, basses, pianos, synthesizers, etc.
The first design goal was to accommodate the full dynamic range of sources likely to be connected to the VT-3. Secondly, the design had to be quiet. After that, it was just a matter of designing it to have the type of performance and packaging that audio professionals have come to expect from our other products.
The decision was made early on that the output of the VT-3 would be at microphone level. Although a line-level output is not difficult to design, it would increase the cost. Besides, everyone has mic preamps available. Although the VT-3 will work with virtually any mic preamp, it was designed to complement the VT-1/VT-2 series of preamps (see 180271 & 180272).
We tried the first prototype on a solid-body electric guitar, and compared the sound to several other respected DI boxes. We were astonished at first listen! It sounded very close to the sound of the guitar through a good vacuum tube amp.
This prototype was evaluated by a number of studio friends who made some useful suggestions. These suggestions were incorporated into the second prototype, and the VT-3 design was complete. By the way, our evaluators were very, very reluctant to return the prototype.
Why does the VT-3 sound so good? For one thing, it provides the proper load to the instrument. This is vital for an unrestricted sound. The frequency response is flat from 10cps to 20kc, with -3 dB points at 0.5cps and 90kc. The VT-3 circuit is very similar to the circuit of the VT-1/VT-2, with a different input design. The output is identical to the VT-1/VT-2 but operates at a lower level.
The VT-3 has been used on electric and acoustic (with a pickup) guitars, electric and acoustic (with a pickup) bass, electric pianos, synthesizers, samplers, etc. and it sounds great on all of them. It will not overload on any instrument, although when driven hard, the sound becomes fatter. It has enough gain, and it's quiet enough, for use with very low-level instruments, like fingerpicked acoustic guitar.
The lifeless, restricted sound I thought was part of direct recording is gone. The
VT-3 has depth, fullness, dynamics, and excitement while remaining quiet and under control with any instrument.
Douglas W. Fearn
- All-Triode Vacuum Tube DI
- Simple Operation
- Two Independent Channels
- Provides The Proper Load Impedance For All Instruments That Have A 1/4-Inch Phone Jack Output
- Ground-Lift Switch Helps Eliminate Ground Loop Buzz
- Switchable High-Pass Filter Gently Rolls Off Frequencies Below 100Hz
Pros who can use anything choose D.W. Fearn for the best possible sound.
VT-3 Dual Channel Vacuum Tube DI Specifications:
- Input: 200 mV nominal unbalanced
- Input Load Impedance: 1 megohm minimum
- Minimum Input Level: 5 mV nominal
- Maximum Input Level: 2.3 volts P-P for 1% THD
- Gain: -10 dB
- Frequency Response: Â± 0.2 dB 10 cps to 20 kc, -3 dB @ 0.5 cps and 95 kc
- THD + Noise: <0.3% 20 cps to 20 kc
- Intermodulation Distortion: <0.01% SMPTE
- Noise: minimum 90 dB below output (22 cps to 22 kc bandwidth)
- Output Transformer Balanced (matches 150 ohm input)
- Output Level: -30 dBm nominal
- Maximum Output Level: -12 dBm @ 20 cps
- Crosstalk maximum: -90 dB @ 20 kc
- Power Requirements: 100/120/220 VAC 50/60Hz 25W
- Dimensions: 19"W x 5.25"H x 10"D, (48.3cm x 13.3cm x 25.4cm)
- Weight: 10 lbs (6.82 kg)