D.W. Fearn VNE Operating Instructions Manual Download Page 17 | Manualshive

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D.W. Fearn VNE Operating Instructions Manual Download Page 17

VNE Vacuum Tube Compression Amplifier

HAZELRIGG INDUSTRIES

17

THEORY OF OPERATION

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.

Input transformer

The input transformer is made by Jensen Transformers, Inc. and represents 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. The secondary of is connected directly to the grid of the

first amplifier stage.

Input Amplifier

First

stage

The first stage is a 6072a configured as a Class A voltage amplifier with a gain of approximately
20. Negative feedback from the plate of the second stage reduces distortion, flattens the frequency
response, and makes the gain of the first two stages less dependent on individual vacuum tube
characteristics.

Second stage

The output of the first stage is coupled to the grid of the second stage through a polypropylene
capacitor. This stage operates as a Class A voltage amplifier with a gain of approximately 15.

Output Stage

The  output  stage  operates  as  a  cathode  follower,  presenting  a  comparatively  low  output
impedance  (approximately  450  ohms).  The  cathode  output  is  coupled  through  a  polypropylene
capacitor to the Pulse Width Modulator board.

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Summary of Contents for VNE

Page 1: ...HAZELRIGG INDUSTRIES VNE Vacuum Tube Compression Amplifier Operating Instructions ...

Page 2: ...be Compression Amplifier HAZELRIGG INDUSTRIES 2 How to Contact us Telephone 567 DWFEARN 567 393 3276 Shipping Address 124 Tartan Terrace Chalfont PA 18914 U S A e mail support hazelriggindustries com www dwfearn com ...

Page 3: ...ufacturing products that are fully compliant with the EU RoHS Directive The following products are compliant D W Fearn VT 1 VT 2 VT 3 VT I F VT 4 VT 5 VT 7 VT 15 LP 1 PDB VRP VPF Hazelrigg Industries VNE VLC VDI VPH This declaration is based on our understanding of the current RoHS Directive and from information provided by the supplier material declarations with regard to materials contained in t...

Page 4: ...ZELRIGG INDUSTRIES 4 VNE Vacuum Tube Compression Amplifier Final Test Report Serial Number Mains Voltage VAC Date Tested by THD Noise 20 cps 200 cps 2 kc s 20 kc s Operational Tests Compression Range Attack Release HPF GR Meter Listening Test ...

Page 5: ...mplifier HAZELRIGG INDUSTRIES Table of Contents Warranty 6 Specifications 7 Description 8 Installation 9 Operation 12 Theory 17 Maintenance 20 List of Illustrations Rear Panel Connections 11 Front Panel Controls and Connections 13 ...

Page 6: ...anty but are warranted for 90 days from date of purchase Except as expressly set forth in this Warranty D W Fearn Hazelrigg Industries makes no other warranties express or implied including any implied warranty of merchantability and fitness for a particular purpose D W Fearn Hazelrigg Industries shall not be liable for technical or editorial errors or omissions in this manual nor for incidental o...

Page 7: ...ain unity to 15dB Frequency Response 0 5 dB 20 cps to 20 kc THD Noise 0 05 20 cps to 20 kc Signal to Noise Ratio 78 dB minimum Output low Z transformer balanced Output source impedance 115 ohms Maximum Output Level 22 dBm into bridging input balanced or unbalanced Gain reduction range 0 to 20dB Power Requirements 120 or 220 VAC 50 60Hz 25 W Dimensions 19 48 26cm W 3 5 13 34cm H 14 22 86cm D Weight...

Page 8: ... of vacuum tubes the VNE has a clarity transparency and warmth that solid state compressors lack Its modern design and construction allow the VNE to exceed the performance of vintage vacuum tube compressors It is designed for use in the professional recording environment It accepts a low impedance 600 ohm nominal source impedance balanced or unbalanced line level nominal 4dBm signal There are cont...

Page 9: ... other heat producing equipment for that matter Be sure the side vent slots are not blocked Equipment that runs cool can last for a very long time In tight equipment enclosures be sure there is adequate air flow Forced air cooling will benefit all your equipment The VNE can also be used without a rack placed on a table counter or even on the floor Optional rubber feet are available when requested ...

Page 10: ...see Figure 1 The INPUT connector is XLR 3 female wired with pin 1 ground pin 2 or high and pin 3 or low The input matches 600 ohm nominal line level 4dBm nominal balanced or unbalanced signals The input uses a top quality Jensen line bridging transformer The OUTPUT connector is XLR 3 male wired with pin 1 ground pin 2 or high and pin 3 or low The VNE is optimized for feeding balanced bridging inpu...

Page 11: ... pin 2 of the output with the Phase Reverse switch set to Normal Grounding and Shields A full discussion of proper studio wiring schemes is beyond the scope of this manual but in general the Input mating XLR connector must have the cable shield connected to pin 1 With most microphones this shield must also be connected to pin 1 at the microphone end of the cable Whether the shield is connected to ...

Page 12: ...e to load impedance than solid state units The VNE design was optimized for feeding a balanced bridging input 20k ohms or greater When feeding a 600 ohm load there may be a slight degradation of some of the specifications In modern studio equipment bridging line inputs are universal If the device being fed by the VNE has an input termination switch that switch should be in the off position The VNE...

Page 13: ...mes into the VNE then immediately goes back out without going through any internal circuitry In the In position audio will go through the amplifiers and compression circuitry In the HPF position a high pass low cut filter is inserted in the sidechain This makes the compression less bass sensitive and may be useful on sources that have a very heavy bass content The roll off of bass sensitivity is a...

Page 14: ...thout gain reduction Experiment with the Attack control on percussive material to see how it changes the sound Generally speaking a fast attack time is best when complete control of the maximum instantaneous level is required This might be desirable to protect a digital input from overload However a more natural sound is usually obtained with a slightly slower attack time Long attack times can be ...

Page 15: ...for hum buzz or other noise For the first few minutes after a cold start it is not unusual for the VNE to produce hiss pops and micro phonic clanks as the internal elements of the tubes expand from the heat Correct any ground loop problems before proceeding The controls should be set as follows The numbers refer to Figure 2 on page 12 Power 9 On Threshold 1 9 o clock Input selector 2 IN Attack 5 1...

Page 16: ... you hook up the VNE so that other factors do not adversely affect the sound quality Except for extremely short Attack and Release times the VNE will provide quality sound with any settings But like any instrument you will find the best adjustment of the controls by experimenting The starting adjustments listed above will get you started Now play with the controls to find the sound that fits your ...

Page 17: ...d directly to the grid of the first amplifier stage Input Amplifier First stage The first stage is a 6072a configured as a Class A voltage amplifier with a gain of approximately 20 Negative feedback from the plate of the second stage reduces distortion flattens the frequency response and makes the gain of the first two stages less dependent on individual vacuum tube characteristics Second stage Th...

Page 18: ...lypropylene 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 an output transformer The output impedance is 115 ohms Power supplies Primary power from the AC mains is connected to the VNE through a standard IEC power input connector The Power switch energizes all five power supplies ...

Page 19: ...Low voltage Supplies This supply provides 15 15 and 5 volts for the solid state circuitry in the Pulse Width Modulator B supply Two separate regulated voltages are required for the plates of the VNE The B is filtered with long life low leakage computer grade filter capacitors before being regulated and extensively bypassed and decoupled The negative side of the supply is grounded ...

Page 20: ... in headroom should indicate the need for replacement Tubes sometimes develop a microphonic response they will respond to ambient noise and vibration This can be an insidious problem since measurements in a quiet room will indicate perfect performance Gently tapping the tube shields while listening to the output at a normal monitor level should reveal nothing more than a slight clank On a peak rea...

Page 21: ...e the equipment becomes obsolete The electrolytic capacitors used in the VNE typically will last at least twenty years If there is a measurable and or audible increase in 120 cps noise the filter capacitors should be suspected They should be replaced with new capacitors of equivalent capacitance and voltage rating and the replacements should be specified for a minimum ten year service life Electro...

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