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Summary of Contents for DW FEARN VT7
- Page 1 D.W. FEARN VT-7 Vacuum Tube Compression Amplifier 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-7 Compression Amplifier...
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Page 3: Final Test Report
VT-7 Vacuum Tube Compression Amplifier Final Test Report Model _______________ Serial Number_______________Mains Voltage ______________ Date ___________________ Tested by ________ VU Calibrated to _______________ dBm Test Equipment _______________________________________________________________ Channel B Channel A Frequency Response: Frequency Response: 20 cps to 20 kc/s +/- ___________ dB 20 cps to 20 kc/s +/- ___________ dB THD+Noise: THD+Noise:... -
Page 4: Table Of Contents
T a b l e o f C o n t e n t s Final Test Report ................3 Warranty ..................7 History of the VT-7 .................9 1. Specifications ................11 2. Description................13 3. Installation ................15 4. Operation .................17 5. Theory of Operation ..............23 6. - Page 5 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.
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Page 6: Warranty
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-7 that has been damaged or rendered defective as a result of accident, misuse, or abuse; by the use of parts not manufac- tured or supplied by D.W. -
Page 7: History Of The Vt-7
History of the VT-7 Compression Amplifier Compression (or limiting) is sometimes seen as a necessary evil in the recording process. Often it is used to compensate for less than optimum performance or recording technique. However, when used appropriately, there is no question that good-sounding compression can add loudness, power, and improved impact to a recording. - Page 8 A look inside the VT-7 reveals a very full box with several densely-packed circuit boards for the gain control driver circuitry, interspersed with eight vacuum tubes. Because of the very high frequencies involved in the control circuitry, there are many surface-mount (SMT) com- ponents.
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Page 9: Specifications
S P E C I F I C AT I O N S I I n n p p u u t t 6 6 0 0 0 0 o o h h m m s s o o u u r r c c e e ( ( n n o o m m i i n n a a l l ) ) b b a a l l a a n n c c e e d d o o r r u u n n b b a a l l a a n n c c e e d d I I n n p p u u t t L L o o a a d d I I m m p p e e d d a a n n c c e e... -
Page 10: Description
D E S C R I P T I O N The Model VT-7 Vacuum Tube Compression Amplifier is designed to provide recording pro- fessionals with a sonically superior signal processing device. It is typically used in sound recording studios for processing individual tracks or, when the channels are linked, as a stereo compressor. - Page 11 D.W. FEARN VT-7 Compression Amplifier...
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Page 12: Installation
I N S TA L L AT I O N The VT-7 is carefully packed for shipment and it should survive all but the most brutal han- dling. If there is any damage, keep the shipping material for use during any possible claim for damage with the shipper. - Page 13 Power The VT-7 is designed to operate from 100, 120, or 220-240 volt, 50/60 Hz power. The unit will be shipped for the voltage specified in the order, but may be changed in the field if nec- essary. (See the Maintenance section for detailed instructions on changing the primary volt- age).
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Page 14: Operation
O P E R AT I O N Input Since the input cable will be carrying high quality audio, it is important that a well-shielded cable is used. You should strive to minimize the number connectors, patch jacks, switches, etc. between the source and the VT-7 input. Output The output of the VT-7 is line level, transformer balanced. - Page 15 CONTROLS (see Figure 2.) The Threshold control adjusts the point where compression begins. With the con- Threshold trol all the way down, there is no compression and the VT-7 operates as a straight amplifier. As the control is turned clockwise, the amount of compression increases. This can be moni- tored on the VU meter (in the GR position), or by ear.
- Page 16 right as the signal becomes louder in one channel compared to the other. This would be dis- concerting on a stereo bus, but could be interesting on individual stereo tracks. When operating in the Link position, only the left side (Channel A) controls are operative.
- Page 17 The center part of the voltage selector is a fuseholder. A flat blade screwdriver is neces- Fuse sary to remove the fuse. For 100 and 120 volt operation, the fuse is 2 amps. For 240 volt oper- ation it is 1 amp. See the Maintenance section for fuse replacement information. Bench Test If desired, test the VT-7 before installation.
- Page 18 SUGGESTIONS: You have chosen to use the VT-7 because of the superior sound it provides. To gain the max- imum benefit from your investment, it is important that you hook up the VT-7 so that other factors do not adversely affect the sound quality. Except for extremely short Attack and Release times, the VT-7 will provide quality sound with any settings.
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Page 19: Theory Of Operation
T H E O RY O F O P E R AT I O N Input section Line level (low source impedance, balanced, +4 dBm nominal) audio enters through the XLR- 3 female INPUT connector to a bridging input transformer. The load imposed on the source is 32k ohms and is constant regardless of the frequency. - Page 20 The output of the first stage is coupled to the grid of the second stage through a polystyrene capacitor. This stage operates as a Class A voltage amplifier with a gain of approximately 20. Output Stage The output stage operates as a cathode follower, followed by a custom output transformer built for D.W.
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Page 21: Maintenance
M A I N T E N A N C E The VT-7 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 replaced eventually. - Page 22 Although you could purchase a batch of 6072A tubes and select the quietest one(s), it may be cost effective to buy a low-noise tube from the us. Current prices are $54.00 for a select- ed low-noise 6072A, and $15.00 for a tested 6N1P. We test the tubes in a VT-7 after a burn- in period and grade them according to noise, microphonic response, distortion, and other characteristics.
- Page 23 Gain Reduction meter calibration The adjustments for the VU meter “0” calibration in the “GR” position are located on the PWM board. Contact the factory for complete adjustment instructions. Note that the meter calibration can be off but the VT-7 will continue to operate normally otherwise. Some drift- ing of this adjustment is normal, and the reading will change as the VT-7 warms up over a period of an hour or so.
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