by Barry Rudolph
The VT-4 follows in the steps of the D.W. Fearn single-channel VT-1 and two-channel VT-2 Vacuum Tube Microphone Preamplifiers with its uncompromising approach to audio processing. In fact, much of the amplifier circuit design is based on those two mic pres. I feel privilege to write about the VT-4 since it's immediately apparent that this hand-made, "labor of love" is in its own special class. Douglas Fearn, who individually inspects, tests, and signs each unit, says that only about six VT-2 pre-amps a month emerge from his factory and he expects to make about twice as many VT-4s since he has already sold many as stereo pairs.
The VT-4 is a single channel equalizer in a three rack space cabinet. Everything about the construction is first class...built to last. The equalizer's chassis is fabricated of heavy-gauge, anodized aluminum plate and the 1/4-inch thick front panel is finished in D.W. Fearn red to match the VT-1/VT-2 units. The large, mil-spec (military specification) control knobs are from original Raytheon designs now manufactured by Electronic Hardware Inc. The heavy duty AC power on/off switch is located on the back panel away from sensitive audio lines and accidental "use" during a recording. The internal power supply fully regulates both the high voltages and DC filament voltage. All controls are semi-sealed, rotary switches using silver contacts for repeatability. No potentiometers are used. All of the audio capacitors are polystyrene or polypropylene and resistors are 1% metal film. The inductors and input/output transformers are custom-made by Jensen Transformers Inc.
The VT-4's passive equalizer circuit is surrounded by Class A mode input and output amplifiers that uses Svetlana 6N1P dual triodes. Both amps are similar with single-ended triode sections coupled to cathode follower circuits. After the input transformer, the input amplifier isolates the passive equalizer circuit whose output is then fed to the output amplifier and followed by the output transformer. The unit is designed to accept balanced or unbalanced signals and output line level, balanced +4dBm signals. LC refers to using, in the series/parallel filter circuitry, inductors or coils (L) and a capacitors (C) rather than resistors (R) and capacitors like most (RC) equalizers that need to keep costs and physical size down. Passive equalizers using LC networks sound noticeable more "open" and smoother.
Getting In and Out
There is a large In/Out switch that toggles the EQ in and out of circuit by substituting an resistive attenuator equaled to the level drop of the passive EQ circuit when all controls are set to flat. This is not a hard-wired bypass and better because you'll hear just the sound of the tube input/output amplifiers sans EQ. It would be stupid to leave an EQ this good patched in bypass mode. I did notice an occasional soft pop when I operated this switch and since receiving my unit (serial #008), a new "make-before-break" switch is now used eliminating all possibility of noise.
The Input Level control adjusts gain of the first amp stage in three dB steps from -9dB to +9dB. For the most part I kept this switch at unity or the center position. Fearn explains: "this control is for maintaining proper headroom within the unit." This control worked just fine for adding level when I was able, by grounding pin 3 of the input XLR connector, to process -10dBv unbalanced signals. If you boost several frequencies at once you may have to dial back the input level to keep from overloading the output amplifier. Of course if you wanted the sound of an overloaded tube stage, you can crank the Input Level up and get lots of wonderful (albeit expensive) distortion. For this purpose, it would be nice to have an Output level control because the unit will put out up to +22dBm.
There are five frequency controls or bands on the VT-4. Gain control knobs are intuitively located directly below each frequency control. Exact frequency selection is different on the VT-4 from all other EQs and contributes to its unique sound. I found myself looking at frequency choice a little differently and making slightly different judgments and decisions throughout the session...decisions and judgments I was very happy with the next day! Douglas Fearn said he arrived at his frequency choices by mostly listening in a musical and subjective way. I'll bet some good old trial and error and a few clip leads went into it as well!
Starting at the left side of the fronnt panel, low frequencies are covered by two controls, Low Boost and Low Cut. Both of these equalizers are shelving types. Low Boost has 20, 40, 60 and 140Hz positions while Low Cut has 30, 40, 100 and 400Hz. These sets of overlapping frequencies make for interesting equalizer "stylings"...different from conventional EQs...even multi-band parametrics. Maybe idiosyncratic and like an old Pultec EQP-1, you can boost and cut in the same frequency ranges! I find, generally, boosting low frequencies by large amounts causes muddiness or boominess. I tried boosting 60Hz and cutting the octave down at 30Hz and I was able to have more bottom without as much boominess.
The next control is the unique bell-shaped Mid Cut. Midrange frequencies available for attenuation are: 200, 300, 400, 500, 600, and 700Hz. You can cut up to 16dB in two dB steps. This is a progressive Q equalizer...as the Mid Cut control is advanced, the Q becomes sharper. This huge range is quite a sound change and I wondered if Doug played electric guitar because I liked this feature for "scooping" out mid range from guitar tracks. My only wish here was a 1.5kHz position in the frequency range selection. As such, the VT-4 does not have a dedicated mid range boost control although the next section, High Boost, does go down to 2kHz.
High Boost is a bell-shaped equalizer with 2, 3, 4, 5, 8, 10, 12, and 16kHz frequency selection positions. You can boost up to 14dB in two dB steps. I would like to see a 1kHz position here then the equalizer would have complete overlapping frequency range selection. High Boost includes a Q or bandwidth control that goes from a broad 0.6 to 1.7 at the sharpest. I found this section just perfect for brightening vocals, guitars or drums. I never got any stridency or harshness no matter how much I wound on the High Boost.
High Cut, the last control, is an shelving equalizer and its frequencies are: 1.7, 4, 10, or 28kHz. 28kHz? 28kHz is just the ticket for rolling off digital artifacts you pick up sometimes. I brighten a guitar track (recorded in Pro-Tools) with the High Boost section and then rolled off at 28kHz to lose some aliasing trash I started to hear. Like Low Boost and Cut, using both High Boost and High Cut at the same frequencies produces a whole other equalizer sound with interesting effect.
A great sounding equalizer with more tone shaping possibilities than most other tube EQs, the VT-4 is crafted and built to last like a Rolls Royce made for the U.S. Government. The D.W.Fearn VT-4, at $3,900 MSRP, makes a fine investment for any recording and mixing studio. D.W. Fearn is located at 182 Bragg Hill Road, West Chester, PA 19382. Phone them at 610-793-2526 or FAX to: 610-793-1479. Web to: www.dwfearn.com.
Thanks goes to producer David Gamson for use of his studio and helping me with my evaluation of the VT-4.
Barry Rudolph is an L.A.-based recording engineer.
Visit his Web site at: www.barryrudolph.com
Input Impedance: 600ohms
Input load Impedance: 20K
Minimum Input Level: -20dBm
Max Input Level @ 20Hz: +26dBm
Frequency Response: +or- 0.5dB from 20Hz to 20kHz
THD: <0.25% 20Hz to 20kHz
IMD: <0.80% (SMPTE)