D.W.
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 World Wide Web: http://www.dwfearn.
Ta b l e o f C o n t e n t s History of the VT-I/F .............................................................................. 7 Specifications.......................................................................................... 9 Description..............................................................................................11 Installation ..............................................................................................13 Operation .............................................
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 ©1995 D.W.
L I M I T E D 5 -Y E A R WA R R A N T Y 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-I/F 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 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.
7 H i s t o r y o f t h e V T - I / F Va c u u m T u b e Instrument Interface 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). Frankly, initially I was not very excited about designing the VT-I/F. I assumed that the lifeless sound I was accustomed to was the nature of direct sounds.
8 I have seen how direct boxes can be abused in the studio environment, so the VT-I/F was built to take rough treatment. The case is machined from solid quarter-inch thick aluminum plate, and finished with a tough polyurethane aircraft fin- ish. Why does the VT-I/F sound so good? I’m not entirely sure, but I do know that 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.
9 Specifications (with 200 mV input) Input 200 mV nominal unbalanced Input Load Impedance 1 megohm minimum Minimum Input Level 5 mV nominal Maximum Input Level Gain Frequency Response 2.3 volts P-P for 1% THD -10 dB +/- 0.2 dB 10 cps to 20 kc -3 dB @ 0.5 cps and 95 kc THD + Noise <0.3% 20 cps to 20 kc Intermodulation Distortion <0.
10 VT-I/F Vacuum Tube Instrument Interface D.W.
11 Description The D.W. Fearn model VT-I/F Vacuum Tube Instrument Interface is designed to provide recording professionals with a sonically superior method for recording electric and electronic musical instruments by direct injection (DI). Any instru- ment designed to operate into a “guitar amp” will work perfectly with the VT-I/F. Typical instruments include: electric bass, electric guitar, electric piano, acoustic instruments with a pickup (piano, acoustic guitar, electric violin, etc.
13 Installation The VT-I/F is carefully packed for shipment and should survive all but the most brutal handling. If there is any damage, keep the shipping material for use during any claim for damage with the shipper. Included in the box: 1) The VT-I/F Instrument Interface 2) Line cord 3) This instruction manual Mounting The VT-I/F is designed to be placed on the floor, counter, or table-top. In most cases, cooling will not be a problem, but avoid placing the unit where it is tightly confined.
14 D.W. FEARN 1 VT-I/F Vacuum Tube Instrument Interface ON 0.5A 100/120V 0.25A 220V OFF POWER D.W. FEARN P.O. BOX 57 POCOPSON, PA 19366 U.S.A. 610-793-2526 2 Figure 1. VT-I/F Rear Panel Connections and Controls REAR PANEL CONNECTIONS (See Figure 1) AC (Mains) Power (2) The VT-I/F is designed to operate from 100, 120, or 220 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 if necessary.
15 FRONT PANEL CONNECTIONS (See Figure 2) The VT-I/F has two identical channels, labeled A and B. They may be used indi- vidually or simultaneously. These instructions apply to either channel. The musical instrument output connects to the VT-I/F INSTRUMENT input (2) via a standard 1/4 inch single-conductor (monaural) phone jack. The input is unbalanced. Since the input cables carry very low level audio, it is important that well-shielded cables are used.
16 The OUTPUT connectors (4) are XLR-3 male wired according to AES standard: pin 1 is ground (shield), pin 2 is “high” or “+,” and pin 3 is “low” or “-.” The output is transformer-balanced. The output level is a nominal -30 dBm. This is somewhat 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 connector.
17 O P E R AT I O N REAR PANEL CONTROLS (see Figure 1, page 14) Power switch (1) Primary power is applied to the VT-I/F circuits when the Power switch (1) is in the up position. The amber pilot lamp (5) on the front panel indicates that the unit is on. It takes about twenty seconds for the Interface to start working, but it is suggested that you turn on the power at least five minutes prior to use. The tubes are often noisy until all the internal elements reach a stable operating temperature.
18 ronment. Experiment with the orientation of the instrument to minimize this source of noise. Most guitar and bass players will do this automatically, but with keyboards it may be necessary to rotate and/or move the instrument to find the quietest spot. Fluorescent lights and SCR dimmers are terrible electrical noise generators. Turn off the fluorescents. If SCR dimmers must be used, they will generally pro- duce the least noise in their full-on (brightest) position.
19 1. The VT-I/F must be located near the instrument. Ten feet of cable between the instrument and the VT-I/F should be considered the maximum. 2. Use the best quality cables you can. We don’t believe you have to use eso- teric wire, but do use good quality, well-shielded cables. The input cable shielding is particularly important. The output cable should be a standard balanced mic cable designed for use with low-Z microphones. Gold-contact phone and XLR connectors are recommended. 3.
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21 T H E O RY O F O P E R AT I O N This circuit description refers to only one channel. Both channels are identical, sharing only the power supply. (See Figure 3.) Input section The INSTRUMENT input jack is fed directly to the grid of the first amplifier stage, a selected 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.
22 tive network on the secondary of the transformer provides proper loading and matching to the input of the external microphone preamplifier. The GND LIFT switch disconnects pin 1 of the OUTPUT connector from the internal ground when the switch is in the up position. Power Supplies Primary power from the AC mains is connected to the VT-I/F through a stan- dard IEC power input connector. The Power switch energizes all power supplies. A fuse, accessible on the rear panel, protects the VT-I/F.
23 MAINTENANCE The VT-I/F is built with only the highest quality parts and will prove to be extremely reliable. Vacuum tubes and electrolytic capacitors, however, have a finite useful life and must be periodically replaced. TOP COVER REMOVAL Removing the top cover allows access to the vacuum tubes. Twelve 6-32 allenhead bolts must be removed. Vacuum Tubes A single 12AY7 tube is used in each channel of the VT-I/F. (A 6072 may be used. This is the low-noise industrial version of the 12AY7.
24 Although you could purchase a batch of 12AY7s and select the quietest one(s), it may be cost effective to buy a low-noise tube from the us. Current prices are $35.00 for a selected low-noise 6072/12AY7. We test the tubes in a VT-I/F after a burn-in period and grade them according to noise, microphonic response, and other characteristics. A low-noise tube from us will meet the original VT-I/F specifications. The base pins of vacuum tubes supplied by D.W.
25 TROUBLESHOOTING Most problems will be traced to defective vacuum tubes. However, if normal tests do not easily reveal the problem, feel free to call the factory for assistance. If you lack access to 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.
