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D.W. Fearn VT-F, Operating Instructions Manual

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D.W. Fearn VT-F Operating Instructions Manual Download Page 3

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History of the VT-I/F .............................................................................. 7

Specifications.......................................................................................... 9

Description..............................................................................................11

Installation ..............................................................................................13

Operation ................................................................................................17

Theory.....................................................................................................21

Maintenance............................................................................................23

List of Illustrations

Rear Panel Controls and Connections ....................................................14

Front Panel Controls and Connections...................................................15

Block Diagram........................................................................................21

Summary of Contents for VT-F

Page 1: ...VT I F Vacuum Tube Instrument Interface D W FEARN Operating Instructions ...

Page 2: ...ct 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 World Wide Web http www dwfearn com ...

Page 3: ...ory of the VT I F 7 Specifications 9 Description 11 Installation 13 Operation 17 Theory 21 Maintenance 23 List of Illustrations Rear Panel Controls and Connections 14 Front Panel Controls and Connections 15 Block Diagram 21 ...

Page 4: ... 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 guide may be photocopied or reproduced in any form without prior written consent from D W Fearn Copyright 1995 D W Fearn Associates ...

Page 5: ...as a result of accident misuse or abuse by the use of parts not manufactured or supplied by D W Fearn or by unauthorized modification of the VT I F Vacuum tubes are excluded from the 5 year warranty but are warranted for a period of 90 days Except as expressly set forth in this Warranty D W Fearn makes no other warranties express or implied including any implied warranty of merchantability and fit...

Page 6: ...o accommodate the full dynamic range of sources likely to be connected to the VT I F Secondly the design had to be quiet After that it was just a matter of designing it to have the type of performance and pack aging that audio professionals have come to expect from our VT 1 VT 2 Vacuum Tube Microphone Preamplifiers The decision was made early on that the output of the VT I F would be at micro phon...

Page 7: ... 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 power supply is virtually identical to that used in the VT 1 VT 2 The VT I F has been used on electric and acoustic with a pickup guitars elec tric 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...

Page 8: ...dulation 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 Crosstalk maximum 90 dB 20 kc Power Requirements 100 120 220 VAC 50 60Hz 25W Dimensions 8 W x 5 H x 12 D 20 3cm x 12 7cm x 30 5cm Weight 15 lbs 6 82 kg NOTE Throughout this manual frequency is specified i...

Page 9: ...VT I F Vacuum Tube Instrument Interface D W FEARN 10 ...

Page 10: ... instruments It is capable of quality reproduction of a wide range of instrument levels The unit does not have the limitations of passive transformer type DIs and has greater headroom and warmth when compared to similar solid state devices It is designed to operate in the professional recording or performing environ ment The output level is hot mic level 30 dBm nominal The output is trans former b...

Page 11: ...les on the bottom The VT I F runs cool cooler in fact than many solid state devices Rack mounting is possible if a shelf is provided If the unit must be mounted in a rack be certain that there is adequate support for both the front and the back of the unit It is heavy and could be damaged if not securely bolted in place and prop erly supported Moderate electrical and magnetic fields in the vicinit...

Page 12: ...t and is required by most electrical codes If ground loop hum is detected a careful check of the studio grounding scheme is needed The VT I F is less susceptible to grounding problems than many studio devices The Fuse is a 3AG type 1 amp for 100 120 VAC operation and 0 5 amp for 220 volts The AC input connector 2 is used with the mating line cord supplied For 120 VAC operation this cord is a Belde...

Page 13: ... should be no additional connectors patch jacks switches etc between the instrument and the VT I F inputs It is important to keep the input lines as short as possible Avoid locating the VT I F where it will be subjected to high sound levels or excessive vibration such as on a drum riser If desired the musical instrument may be simultaneously connected to the input to an external instrument guitar ...

Page 14: ...t level is a nominal 30 dBm This is some what higher in level than a typical microphone Grounding and Shields A full discussion of proper studio wiring schemes is beyond the scope of this manual but in general the shield should be connected to pin 1 of the output con nector The shield should be connected to ground at only one end however although not recommended the shields can often be connected ...

Page 15: ... connectors to the unit internal ground In most situations the GND LIFT switch 3 will remain in the down pin 1 to internal ground position In some situations particularly when an external instrument amplifier is connected to the AMP jack a ground loop may occur This causes a hum or buzz in the recording equipment Placing the GND LIFT switch in the up position may help alleviate this The musical in...

Page 16: ...ed when the VT I F is connected to an instrument and guitar amp simultaneously In this case use the GND LIFT 3 switch to find the proper IMPORTANT When using the VT I F with the D W Fearn VT 1 or VT 2 Vacuum Tube Microphone Preamplifier the VT 1 VT 2 Input switch must be in the 20 dB position unless the instrument level is extremely low With other preamps use the input pad and or reduce trhe gain ...

Page 17: ...ed directly to the recorder through the shortest practical lengths of quality cables Avoid additional cables con nectors junction boxes punch blocks or patch jacks Use gold contact con nectors if possible Do not go through the mixing console unless you absolutely need its features for the track you are cutting 4 In general for superior sound we recommend recording directly to the recorder with no ...

Page 18: ...20 ...

Page 19: ...lected 6072 or selected 12AY7 The input impedance is very high 1 megohm for proper loading of the musical instrument The first stage is capacitively coupled to the grid of the output stage Figure 3 VT I F Block Diagram Output Stage The output tube is the second section of the 6072 12AY7 It is operated as a cathode follower capacitively coupled to the custom output transformer A resis From Instrume...

Page 20: ...engthened and the light output is more compatible with other modern studio equipment The power transformer is custom made for the VT I F and has primary taps for 100 120 or 220 volt operation The VT I F may be rewired for different mains voltages Filament supply The power transformer output is rectified by a bridge rectifier and filtered before being regulated to 12 0 volts by a three terminal reg...

Page 21: ... W Fearn Tube life is difficult to predict but it will probably be measured in years Catastrophic tube failure is rare with this type of device but a gradual increase in noise or distortion or a reduction in headroom should indicate the need for replacement It is recommended that you periodically perform a quick noise and distortion check on the VT I F and compare the results to previous measureme...

Page 22: ...tect your fingers during tube replacement The VT I F should be turned off before removing tubes Allow at least one minute for the filter capacitors to discharge before tube removal or insertion Tubes are made of glass and will break if dropped or even bumped in a critical area Handle with care Electrolytic Capacitors The VT I F is designed and built to last for a long long time and it is possible ...

Page 23: ...o a qualified service technician with vacuum tube equipment repair experience you may return the VT I F to the factory for repair Call first however for shipping information WARRANTY REPAIR If the VT I F should develop a problem during the five year warranty period call the factory for return shipping instructions We will repair and return your VT I F quickly Note that the warranty does not cover ...

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