D.W. Fearn VT-1 Operating Instructions Manual
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D.W. Fearn VT-1 Operating Instructions Manual

Vacuum tube microphone preamplifiers
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D.W. FEARN
VT-1
VT-2
Vacuum Tube Microphone
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Operating Instructions

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Summary of Contents for D.W. Fearn VT-1

  • Page 1 D.W. FEARN VT-1 VT-2 Vacuum Tube Microphone Preamplifiers Operating Instructions...
  • Page 2 How to Contact us: Telephone: 610-793-2526 Fax: 610-793-1479 Mail: P.O. Box 57, Pocopson, PA 19366 U.S.A. Shipping Address: 182 Bragg Hill Road West Chester, PA 19382 U.S.A. e-mail: dwfearn@dwfearn.com www.dwfearn.com D.W. FEARN VT-1 & VT-2 Microphone Preamplifers...
  • Page 3 Pocopson, PA 19366 U.S.A. PROFESSIONAL Tel: 610-793-2526 RECORDING EQUIPMENT www.dwfearn.com Fax: 610-793-1479 Certificate of RoHS Compliance D.W. Fearn is committed to manufacturing products that are fully-compliant with the EU RoHS Directive. The following products are compliant: VT-1 VT-2 VT-3 VT-4...

  • Page 5: Final Test Report

    VT-1 / VT-2 Vacuum Tube Microphone Preamplifier Final Test Report Model _______________ Serial Number_______________Mains Voltage ______________ Date ___________________ Tested by ________ VU Calibrated to _______________ dBm Test Equipment ____________________________ Microphone ________________________ Channel b Channel A Frequency Response: Frequency Response: 20 cps to 20 kc/s +/- ___________ dB...

  • Page 7: Table Of Contents

    T a b l e o f C o n t e n t s Final Test Report CE Certification Data Warranty ..................7 History of the VT-1 and VT-2 ............9 1. Specifications ................13 2. Description................15 3. Installation ..............17 21 5. Theory of Operation ..............29 6.
  • Page 8 D.W. Fearn shall not be liable for technical or editorial errors or omissions in this manual, nor for incidental or consequential damages resulting from the use of this material. This instruction manual contains information protected by copyright. No part of this manual may be photocopied or reproduced in any form without prior written consent from D.W.

  • Page 9: Warranty

    During the warranty period, D.W. Fearn will, at no additional charge, repair or replace defective parts with new parts. This warranty does not extend to any VT-1 or VT-2 that has been damaged or ren- dered defective as a result of accident, misuse, or abuse; by the use of parts not man- ufactured or supplied by D.W.

  • Page 11: History Of The Vt-1 And Vt-2

    History of the VT-1 and VT-2 Vacuum Tube Microphone Preamplifiers ONE DAY IN 1991 I was going through some old masters in a closet at home and came across a reel from 1968. It was one of the first studio recordings I ever made.
  • Page 12 It’s the nature of the distortion that makes a difference, too. Solid state circuits run out of headroom when the output voltage exceeds the power supply voltage. The result at this point D.W. FEARN VT-1 & VT-2 Microphone Preamplifers...
  • Page 13 AB comparison of the sound, I am certain that the better modern passive components give the VT-1 a superior sound. The VT-1 has been used for all types of recording — vocals, announcers, acoustic instruments, electric instruments, classical — and it works well with them all.
  • Page 14 The VT-2 was developed in 1995 in answer to requests from a number of our customers for a two-channel version of the preamp. The VT-2 occupies the same amount of rack space, but is four inches deeper than the VT-1. D.W. FEARN...

  • Page 15: Specifications

    Power Requirements 100, 120, or 220 VAC 50/60Hz, 25 W Dimensions 19” (48.26cm) W 5.25” (13.34cm) H 9” (22.86cm) D (VT-2 13” 22.9cm) Weight VT-1 14 lbs (6.35 kg) VT-2 18 lbs (8.16kg) D.W. FEARN VT-1 & VT-2 Microphone Preamplifers...

  • Page 17: Description

    (Unless there is a specific rea- son to address a difference between the VT-1 and VT-2 preamplifiers, the device will be referred to as the “VT-2.”) It is typically used in sound recording studios for recording indi- vidual tracks.
  • Page 19 The VT-2 is designed to operate from 100, 120, or 220-240 volt, 50/60 Hz power. The unit will be shipped wired for the voltage specified in the order, but may be changed in the field D.W. FEARN VT-1 & VT-2 Microphone Preamplifers...

  • Page 20: Rear Panel Connections

    Input and Output Connections See Figure 1. Gold-plated XLR connectors are used for inputs and outputs. The input connec- tors are female and the outputs male. Figure 1. The VT-2 rear panel connectors D.W. FEARN VT-1 & VT-2 Microphone Preamplifers...
  • Page 21 The shield should be connected to ground at only one end of the output cable; however, although not recommended, the shields can often be connected at both ends with- out a problem. D.W. FEARN VT-1 & VT-2 Microphone Preamplifers...
  • Page 22 D.W. FEARN VT-1 & VT-2 Microphone Preamplifers...

  • Page 23: Installation

    If the device being fed by the VT-2 has an input termination switch, that switch should be in the “off” position. D.W. FEARN VT-1 & VT-2 Microphone Preamplifers...
  • Page 24 In the “0” position, the VT-2 can accept up to about a -30 dBm input sig- nal at 20 cps with full gain (53 dB) without an increase in distortion. D.W. FEARN VT-1 & VT-2 Microphone Preamplifers...
  • Page 25 +48 on will not damage any properly wired balanced mic, some ribbon mics have reportedly been damaged when connected or disconnected from phantom powering. Also, some engineers feel that the performance of some dynamic mics may be subtly degraded with the phantom power on. D.W. FEARN VT-1 & VT-2 Microphone Preamplifers...
  • Page 26 VU Meter and VU Meter ON/OFF (5 & 6) The VU meter (6) measures the output level directly across the secondary of the output transformer, through an isolation amplifier. It is calibrated so that a +4 dBm output will indi- D.W. FEARN VT-1 & VT-2 Microphone Preamplifers...
  • Page 27 VT-2 to produce hiss, pops, and microphonic “clanks” as the internal elements of the tubes expand from the heat. Correct any ground loop problems before proceeding. D.W. FEARN VT-1 & VT-2 Microphone Preamplifers...
  • Page 28 A quality cable with gold-contact connectors is best. 3. There should be no additional cables, connectors, junction boxes, patch jacks, etc. between the mic and the VT-2 input. D.W. FEARN VT-1 & VT-2 Microphone Preamplifers...

  • Page 29: Typical Studio Interconnections

    VT-2 (Use this configuration only VT-2 if the console functions are absolutlely required) VT-2 (Recommended only if pro- cessing is necessary while cutting the track) Figure 3. Typical Studio Interconnections with the VT-2 D.W. FEARN VT-1 & VT-2 Microphone Preamplifers...
  • Page 30 D.W. FEARN VT-1 & VT-2 Microphone Preamplifers...

  • Page 31: Theory Of Operation

    In the Normal position, input/output phase (polarity) is maintained (which must be inverted due to the design of the circuit). The balanced output is polarity reversed in the Reverse posi- tion. Switching is accomplished with a sealed, gold-contact instrumentation relay with bifur- cated contacts. D.W. FEARN VT-1 & VT-2 Microphone Preamplifers...

  • Page 32: Block Diagram

    Input transformer The input transformer is custom-made for D.W. Fearn by Jensen Transformers, Inc. and rep- resents the state of the art in transformer design. It exhibits extremely flat frequency response, low phase shift, excellent square wave response, low distortion, and high noise immunity.
  • Page 33 The Power switch energizes all four power supplies. A fuse, accessi- ble on the rear panel, protects the VT-1/VT-2. The Pilot lamp is a type 1819 bulb, operated far below its rated voltage of 28. The life of the bulb is lengthened, and the light output is more compatible with other modern studio equipment.
  • Page 34 This regulator is located on the Meter Amp PCB. B+ Supply Two separate regulated voltages are required for the plates of the VT-1/VT-2. The B+ is fil- tered with long-life, low-leakage, computer-grade filter capacitors before being regulated and extensively bypassed and decoupled.

  • Page 35: Maintenance

    6-32 allen-head bolts must be removed (phillips-head machine screws are used on the VT-1). When replacing the cover, position it so that the slotted ventillation holes are over the tubes (towards the back on the VT-2, to the left when facing the unit on the VT- Vacuum Tubes Four 6072A tubes are used in the VT-2.
  • Page 36 A low-noise tube from us will meet the original VT-2 specifications. The base pins of vacuum tubes supplied by D.W. Fearn have been chemically treated for low contact resistance and oxidation prevention. When handling these tubes, care should be taken to avoid removing or contaminating the treatment.

  • Page 37: Location Of Vu Meter Calibration

    VT-1/VT-2. See Figure 5 on page 38. 6. Replace the top cover. Be sure the ventillation slots are over the tubes (towards the back).
  • Page 38 If the VT-2 should develop a problem during the five-year warranty period, call the factory for return shipping instructions. We will repair and return your VT-2 quickly. Note that the war- ranty does not cover vacuum tubes, which must be periodically replaced. D.W. FEARN VT-1 & VT-2 Microphone Preamplifers...

  • Page 39: Line Pad Instructions

    L P - 1 L i n e P a d A c c e s s o r y The LP-1 Line Pad is an accessory for the VT-1 and VT-2 Vacuum Tube Microphone Preamplifiers that allows the preamp to accommodate a line-level signal of approximately +4 dBm.

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Vt-2

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