The Vipre is an all-tube, single-channel microphone preamplifier that precisely matches any microphone new or old with a choice of four different input load impedances. Front panel controls may be used to vary the preamp's actual internal circuitry for different transient response performance characteristics, ranging from the vintage microphone preamps of yesteryear all the way to the super fast performance of modern, high slew-rate mic preamplifiers. The Vipre has a whopping 75 dB of total gain and flat frequency response from 7Hz to 100kHz.

Vipre uses eight tubes for both the Class-A, fully balanced and complementary, differential amplifier and the Class-A, balanced, push-pull output stage. (Keeping the entire signal path balanced from input to the output dictates the use of expensive, multilayer rotary switches rather than cheaper pots.) All eight tubes are thermally insulated and shock-mounted.

The entire unit is hand-assembled and wired using the finest components, switches and, of course, Groove Tubes. There are no solid-state devices, integrated circuits or electrolytic capacitors anywhere in the audio signal path. The cabinet and front panel are finished in matte black and feature large, custom-molded RCA vintage-style phenolic knobs and larger size toggle switches. With its chrome rack handles, a giant old-school style lighted VU meter and overbuilt heft (weight is 32 pounds), the Vipre is one impressive hombre!

The Vipre offers four input modes accessible via the input selector knob. On the far-left side of the panel is an instrument input jack designed for direct recording of guitar, bass or synths. This input feeds a special high-impedance (47-kilohm) circuit centered around its own GT 6205 tube. I liked the fat sound of this direct path and now use it all the time. There is also a -20dB instrument input position for hotter levels, useful for synths or guitars with active electronics. The next mode/position is the fully balanced transformerless bridging input (12-kilohm impedance), which is closer to the input impedance of many modern preamps, followed by the main variable impedance input. Both of these modes use the rear panel XLR connector, and there is an additional rear panel TRS mic/line input that accepts levels 20 dB hotter than the XLR. If both the XLR and TRS jacks are active, then they will mix internally. (They enter the amplifier circuitry at different points.) Toggle switches engage a Phase Flip switch and a gentle, 4dB-per-octave highpass filter starting at 100 Hz.

The Impedance Selector knob selects among 300, 600, 1,200 and 2,400-ohm input impedances by switching between four different sets of primary windings of a specially designed input transformer. This very large humbucking transformer, which is manufactured by Tom Reinchenbach at CineMag, is encased in two mu-metal shielded cans and offers a technically correct way to alter input impedance by using different windings and not by just adding loading resistors.

Why Variable Impedance? Aside from a resistive input level attenuator pad and a phantom power switch, a lot of microphone preamps give the recording engineer just a single control: Gain. Essentially, there is no way to customize or match the microphone preamp to the particular microphone or other source. The preamp's input impedance is just fixed (internally) and is usually high enough that, electrically, it will work okay in most any situation. This seems odd, given the fact that music sources undergo their biggest and most important change in level at this first critical amplification stage. A condenser microphone's output level can require from 30 to 50 dB of gain (depending on the mic and singer) to raise it to a nominal +4dBm line-level ready for any further processing and subsequent recording. Today's 24-bit digital systems require even more gain, better dynamic range and lower noise, all factors that put even more importance on the microphone preamp. Additionally, the same microphones sound different when used with different mic preamps. We all have our favorite mic pre/microphone combinations for specific recording tasks, and many engineers, producers and studios have amassed large and varied preamp collections over the years. Amongst microphones with similar topology Class-A preamps, it is mostly the effects of different input characteristics that we hear. Early audio circuits were designed for maximum power transfer (called the Transfer Function) between units. Input and output impedances would be matched carefully for best efficiency and the most gain. Vintage condenser and ribbon microphones were designed to sound best when loaded or terminated by the specific load impedance of the mic preamp's front end transformer. Modern transformerless, solid-state microphone preamps (as well as most all modern audio gear) have from 10 to 20x higher input impedance than most sources plugged into them. These are called bridging inputs, and they present nearly no load to the microphone source and certainly do not present the load the microphone was originally optimized for.

My favorite controls on the Vipre are the two large, stepped Gain control knobs. The coarse Gain control is graduated in 5dB steps from 20 to 70 dB, and the fine Gain control adds or subtracts from the coarse setting in 1dB steps from -5 to +5 dB. In operation, I set my ballpark gain setting with the coarse control and then dialed in a final level in 1dB steps with no audible pops or clicks when rotating either control. This method offers exact repeatability but does not allow gain riding for smooth changes in level while recording, because, to maintain fully balanced operation throughout, the Vipre has no output level pot.

Between the two Gain controls is a large, lighted VU meter. The RMS reading meter is augmented with two clip LEDs; a green LED lights up at -3 dB before clip and the red LED indicates full clip. The Vipre is capable of +30dBm (24.4-volts RMS or about 1 watt!) maximum output at the output XLR, but there is an additional 1/4-inch TRS balanced output jack from a separate output transformer winding that is referenced to -10 dBv.

To the right of the meter is a unique feature, the VU Meter Range control. The Vipre has a meter driver circuit board for enhanced metering. At the 0VU Meter Range switch position and when the needle reads 0VU, the meter shows an actual +4dBm output level. Three more ranges re-reference 0VU on the meter to +10, +20 and +30dBm levels, respectively. These higher scales provide for accurate measurement when sending super-hot output levels to 24-bit digital systems and without them, the meter would be pegged a lot of the time! Finally, the Expand VU mode broadens the range of the meter from a typical VU meter range of -20 to +3 dB up to a wider -60 to +13dB range. Expanded mode is great for wide dynamic range recordings such as vocals, Foley work and classical music, and makes it easy to see potential problems such as air conditioning or room rumble.

The Rise Time control sets the amplifier's rise time or slew rate. Five different settings range from the Slow position (about 0.75 volts per microsecond, a commonly used setting for vintage audio equipment) to Fast at 6 volts per second, a more typical spec for modern preamps. The net effect of such manipulation is a sort of control over the aggressiveness of the Vipre's sound. I found that percussion and similar sounds were clearer and (apparently) brighter on the Fast mode setting. Slow mode was better for sounds and vocals that tended toward the harsh, and effectively smoothed or rounded out edginess. In use, I found the in-between switch positions extremely subtle and wound up using only the two extremes, Slow and Fast.

The Vipre has a +48V phantom power on/off and the often-overlooked output Mute switch, a feature that is too rarely included in outboard mic preamps. The Vipre has two power switches. The manual states that, to prolong tube life, it is advisable to first power-up the unit with the Standby/B+ switch in standby where the B+ (high voltage) stays off until the filaments have warmed up properly. The manual also recommends that the Standby switch be used during session downtimes and that the Vipre should be powered down with the main Power switch at the end of the day. If you leave the monitor level up on the track you have Vipre routed to, you'll have to FIRST use the mute switch before throwing the B+ switch or a "pop" would occur.

In The Studio