D.W. Fearn VT-3 User Manual

VT-3

Vacuum Tube

Instrument Interface

D.W

. FEARN

Operating Instructions

How to Contact us:

Telephone: [phone]

Fax: [phone]

Mail: P.O. Box 57, Pocopson, PA 19366 U.S.A.

Shipping Address:

West Chester, PA 19382 U.S.A.

e-mail: [e-mail]

www.dwfearn.com

182 Bragg Hill Road

Table of Contents

History of the VT-3 ................................................................................ 7

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

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

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

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

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

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

List of Illustrations

Rear Panel Controls and Connections ....................................................15

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

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

Notice

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 guide

may be photocopied or reproduced in any form without prior written consent from D.W. Fearn.

Copyright ©2006 D.W. Fearn & Associates

LIMITED 5-YEAR 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-3 that has been damaged or rendered defective as a result of

accident, misuse, or abuse; by the use of parts not manufactured or supplied by D.W. Fearn; or by unau-

thorized modification of the VT-3. Vacuum tubes are excluded from the 5-year warranty, but are war-

ranted 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 fitness for a particular purpose.

History of the VT-3 Vacuum Tube DI

As far back as I can remember, taking instruments “direct” has never sounded

very good to me. There always seemed to be a lack of dynamics, and a sterile qual-

ity to sounds recorded with a direct box (or DI).

The first tube DI that we produced was the VT-I/F Instrument Interface. It was

a beautiful piece, in a large, machined-aluminum case that you could drive a truck

over. Unfortunately, the cost of that case made it impossible to build the VT-I/F for

a reasonable price. Only about 75 were ever made, but the owners loved them, and

we kept getting requests for it. After several years of promises to bring out a rack-

mount version, we finally did so in 2006. The VT-3 is exactly the same as the VT-

I/F internally, except that we added a switchable high-pass filter and changed tubes

from the 6072A (which we use in all our preamps) to the 6N1P, an excellent-

sounding tube used in our VT-4 Eq and VT-7 Stereo Compressor.

Before beginning the design of the circuit, I spoke to engineers, producers, and

musicians about what they felt was lacking in DI boxes. Almost without exception,

they all said, “It’s got to have tons of headroom.” How much headroom was

enough? I spoke to a number of instrument pickup manufacturers and got an idea

of the peak output level of a variety of instruments. These figures were confirmed

with an oscilloscope placed directly across the output of various electric guitars,

basses, pianos, synthesizers, etc.

7

The first design goal was to accommodate the full dynamic range of sources

likely to be connected to the VT-3. Secondly, the design had to be quiet. After that,

it was just a matter of designing it to have the type of performance and packaging

that audio professionals have come to expect from our other products.

The decision was made early on that the output of the VT-3 would be at micro-

phone level. Although a line-level output is not difficult to design, it would

increase the cost. Besides, everyone has mic preamps available. Although the VT-

3 will work with virtually any mic preamp, it was designed to complement the VT-

1/VT-2 series of preamps.

We tried the first prototype on a solid-body electric guitar, and compared the

sound to several other respected DI boxes. We were astonished at first listen! It

sounded very close to the sound of the guitar through a good vacuum tube amp.

8

This prototype was evaluated by a number of studio friends, who made some

useful suggestions. These suggestions were incorporated into the second proto-

type, and the VT-3 design was complete. By the way, our evaluators were very,

very reluctant to return the prototype.

Why does the VT-3 sound so good? For one thing, it provides the proper load to

the instrument. This is vital for an unrestricted sound. The frequency response is

flat from 10 cps to 20 kc, with -3 dB points at 0.5 cps and 90 kc. The VT-3 circuit

is very similar to the circuit of the 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 VT-3 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 instrument, although

when driven hard, the sound becomes fatter. It has enough gain, and it’s quiet

enough, for use with very low level instruments, like finger-picked acoustic gui-

tar.

The lifeless, restricted sound I thought was part of direct recording is gone. The

VT-3 has depth, fullness, dynamics, and excitement while remaining quiet and

under control with any instrument.

Douglas W. Fearn

October 2006

VT-I/F Vacuum Tube Instrument Interface

D.W. FEARN