640 Twin-Servo’s seated in Parliament

Twin Servo Preamp Install photo

November 22nd, 2021

As part of a major refurbishment of a parliament building Canada, 640 Radial Twin-Servo mic preamps and 80 Workhorse Power Racks were installed as the primary audio interface between the major political leaders.

The Canadian parliament needed a preamplifier that would deliver the most natural and uncolored sound possible, while being able to handle extreme dynamics without distortion. Canadian politics can get very lively during debate period, particularly during the question and answer sessions. This means that they had to deliver great performance whether confronted with a whisper or a fist banging on a bench. As these sessions are recorded and broadcast to the Canadian media, minimal noise was of primary concern.

Before the product was packaged, each preamp and Workhorse mixer-rack was individually tested to cover a whole range of criteria to ensure it met the required specifications. The racks were then assembled and put on pallets so that they could be installed immediately with as little delay at the receiving end as possible.

Twin Servo Preamp inside view

The Radial Jensen® Twin-Servo & 500 series preamplifier is an updated version of what may well be the most spectacular preamp ever made.

Rack of Twin Serco Preamops in Parliament

Originally developed by industry icon Deane Jensen in 1988, the Twin-Servo 500 is an adaptation that fits the popular 500 series format. The design begins with the legendary performance of two 100% discrete 990 op-amps cascaded in tandem to deliver 60dB of gain with less than 1/10th the distortion and twice the bandwidth of a single stage design. This maximizes the gain-margin so that no matter what the input, the lowest possible distortion will be realized. This also reduces noise at mid and low levels, a critical advantage for those that record with a wide dynamic range. In order to minimize phase distortion and retain the delicate balance of fundamentals with harmonics, all capacitors have been removed from the audio signal path and replaced by two DC servo feedback circuits. This not only reduces low-frequency noise, but also eliminates the ugly distortions associated with electrolytic capacitors that are especially degrading to low-level microphone signals when used to block phantom power in transformerless designs. To deliver the widest possible bandwidth, Jensen transformers are placed at both the input and output producing a frequency response that extends from 0.2Hz to 150kHz. The transformers further benefit from unmatched common-mode noise rejection from offending devices such as power supplies, light dimmers and motors that may be connected to the same power service.

Features include a convenient front-panel Neutrik combo connector with choice of XLR and ¼” inputs, a dual-gang potentiometer for level adjustment along with a 10 segment LED meter for signal management. This is supplemented with a 180° polarity reverse switch that toggles the absolute phase, a gentle high-pass filter to eliminate excessive resonance, a -15dB pad to prevent overload, and a 48V phantom power activation switch with soft-start to eliminate popping from turning on microphones or accidental connections.


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