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Crown Audio VT-15 manual

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Table of contents for the manual

  • Page 1

    VT-15 Vacuum Tube Recording Channel Operating Instructions D.W. FEARN[...]

  • Page 2

    D.W. FEARN VT-15 Recording Channel Ho w to Cont act us: T elephone: 6 1 0-793-2526 F ax: 6 1 0-793- 1 479 Mail: P .O. Bo x 57 , P ocopson, P A 1 9366 U .S.A. Shipping A ddress: 1 82 Bragg Hill R oad W est Chester , P A 1 9382 U .S.A. e-mail: dwf ear n@dwf ear n.com www .dwf ear n.com[...]

  • Page 3

    D . W . F EARN H AND - CR AFTED PR OFESSION AL RECORDIN G EQUIPMENT www .dwfear n.com P .O. Bo x 57 P ocopson, P A 1 9366 U .S.A. T el: 6 1 0-793-2526 F ax: 6 1 0-793- 1 479 Cer tificate of RoHS Compliance D.W . F ear n is committed to manuf acturing pr oducts t hat ar e fully-com pliant wit h t he EU R oHS Dir ectiv e. The f ollo wing pr oducts ar[...]

  • Page 4

    4[...]

  • Page 5

    D.W. FEARN VT-15 Recording Channel 5 VT-15 Vacuum Tube Recording Channel Final Test Report Serial Number_______________ Mains Voltage 120/240 set to __________________ Date ________________ Tested by ________ VU Calibrated to _______________ dBm Test Equipment ____________________________ Microphone ________________________ Frequency Response: 20 c[...]

  • Page 6

    D.W. FEARN VT-15 Recording Channel 7 Table of Contents R oHS Com pliance Dat a .................................................................. 3 Final T est R epor t ............................................................................ 5 W ar ranty ........................................................................................ 9 [...]

  • Page 7

    D.W. FEARN VT-15 Recording Channel 8 D.W . F ear n shall not be liable f or technical or editorial er r ors or omissions in t his manual, nor f or incident al or consequential damag es r esulting fr om t he use of t his material. This instr uction manual cont ains inf or mation pr otected b y cop yright. N o par t of t his manual ma y be photocopie[...]

  • Page 8

    D.W. FEARN VT-15 Recording Channel 9 Limited 5-Year Warranty During t he w ar ranty period, D.W . F ear n will, at no additional char g e, r epair or r eplace def ectiv e par ts wit h ne w par ts. This w ar ranty does not extend to an y VT - 1 5 t hat has been damag ed or r ender ed def ectiv e as a r esult of accident, misuse, or abuse; b y t he u[...]

  • Page 9

    D.W. FEARN VT-15 Recording Channel 11 History of the VT-15 Vacuum Tube Recording Channel W it h t he success of t he VT - 1/VT -2 V acuum Tube Micr ophone Pr eam plifiers, t he VT - 4 LC Equalizer , t he VT -7 Ster eo Com pr essor , and t he VT -I/F and VT -3 V acuum Tube DIs, t her e w as a gr eat tem pt ation to combine t he f eatur es of all of [...]

  • Page 10

    D.W. FEARN VT-15 Recording Channel 12[...]

  • Page 11

    D.W. FEARN VT-15 Recording Channel 13 Mic Input 150 ohms Input Load Impedance 1.5k ohms Minimum Input Level -65 dBm nominal Maximum Input Level @ 20 cps -30 dBm without pad -5 dBm with 20 dB pad Instrument Input impedance 1 Megohm Line Input Load Impedance 40k ohms Maximum Line Input Level @ 20 cps +25dBm (+35dBm with pad) Gain <60 dB optimum (c[...]

  • Page 12

    D.W. FEARN VT-15 Recording Channel 14 Compression Range up to 30dB Compression method Pulse-width modulator Equalizer: Low-frequency Boost 100 cps, shelving Low-frequency Cut 80 cps, shelving High-frequency Boost 9.8 kc, peaking High-frequency Q 0.6 to 1.7 High-frequency Cut 12 kc, shelving Power Requirements 100, 120, or 220 V AC 50/60Hz, 50 W Dim[...]

  • Page 13

    D.W. FEARN VT-15 Recording Channel 15 2. DESCRIPTION The D.W . F ear n VT - 1 5 utilizes cir cuitr y de v eloped f or t he VT - 1/VT -2 V acuum Tube Micr ophone Pr eam plifiers, t he VT -7 Ster eo Com pr essor , and t he VT -4 LC Equalizer . The Model VT - 1 5 R ecor ding Channel is designed to pr o vide r ecor ding pr of essionals wit h a sonicall[...]

  • Page 14

    D.W. FEARN VT-15 Recording Channel 16[...]

  • Page 15

    D.W. FEARN VT-15 Recording Channel 17 3. INST ALL A TION The VT - 1 5 is car efully pack ed f or shipment and it should surviv e all but t he most br ut al han - dling. If t her e is an y damag e, k eep t he shipping material f or use during an y possible claim f or damag e wit h t he shipper . Included in t he bo x: 1) The VT - 1 5 R ecor ding Cha[...]

  • Page 16

    D.W. FEARN VT-15 Recording Channel 18 t he back panel f or inst allations t hat use separate chassis gr ounding. If gr ound loop hum is detected, a car eful check of t he studio gr ounding scheme is needed. The VT - 1 5 is less suscep - tible to gr ounding pr oblems t han man y studio de vices. Connections The INPUT connector is a XLR-3 f emale wir[...]

  • Page 17

    D.W. FEARN VT-15 Recording Channel 19 4. OPER A TION INITIAL SET-UP IS CRITICAL for getting the best performance from your VT-15! The VT - 1 5 has tr emendous v ersatility , but wit h t hat v ersatility comes t he potential f or f or v er y un pleasant sound. Think of t he VT - 1 5 as a small studio chain in one bo x: mic pr eam p, com - pr essor ,[...]

  • Page 18

    D.W. FEARN VT-15 Recording Channel 20 Control Set-up In put togg le switches: Mic/Line switch - as appr opriate f or t he sour ce 0/-20 switch - 0 1 50/Lo-Z switch - 1 50 (unless y ou ar e using a non-st andar d im pedance mic) +48 switch - on f or phantom-po w er ed condenser mics, ot her wise off R e v/Phase switch - do wn (no phase r e v ersal) [...]

  • Page 19

    D.W. FEARN VT-15 Recording Channel 21 6. A djust t he Eq contr ols f or t he desir ed sound. (R emember to use t he Boost and Cut tog et h- er to shape t he sound.) 7 . Switch t he VU meter back to t he VU position. 8. A djust t he Gain contr ol f or a nor mal indication. P eak s should rar ely go into t he r ed (0VU). This pr ocedur e will pr o vi[...]

  • Page 20

    D.W. FEARN VT-15 Recording Channel 22 C ONTR OLS (see Figure 1 .) The VT - 1 5 fr ont panel is divided into t hr ee main ar eas of contr ols. On t he left is t he In put sec - tion, to its right is t he Com pr essor section, fur t her right is t he Equalizer section, and f ar right is t he output and po w er section. Input Toggle Switch Section The[...]

  • Page 21

    D.W. FEARN VT-15 Recording Channel 23 es t he polarity of t he output of t he VT - 1 5. A det ailed discussion of t he application of phase re v ersal of individual micr ophones is be y ond t he scope of t his manual. Ev en when t her e is only one micr ophone being r ecor ded, it ma y be useful to tr y t he “R ev erse” position of t he Phase c[...]

  • Page 22

    D.W. FEARN VT-15 Recording Channel 24 add distor tion to lo w fr equency sounds. (This is tr ue of all com pr essors.) A f ast r elease time adds density to t he sound, often wit h t he com pr ession becoming mor e obvious. Long r elease times mak e t he com pr ession less obvious and mor e natural, but can “punch holes” in t he lo w er le v el[...]

  • Page 23

    D.W. FEARN VT-15 Recording Channel 25 should r esult in “0 VU” on a pr operly aligned r ecor der . (This r ef er ence le v el can be chang ed; see t he Maintenance Section.) This is a tr ue VU meter , and conf or ms to AS A St andar d C1 6.5- 1 954. In t he GR position, t he VU meter monitors t he amount of g ain r eduction (com pr ession). As [...]

  • Page 24

    D.W. FEARN VT-15 Recording Channel 26 1 . Use t he best quality mic cable y ou can. W e don’t belie v e y ou ha v e to use esoteric wir e, but do use a good cable designed f or lo w im pedance micr ophones. A quality cable wit h gold-cont act connectors is best. 2. Ther e should be no additional cables, connectors, junction bo x es, patch jack s,[...]

  • Page 25

    D.W. FEARN VT-15 Recording Channel 27 5. THEOR Y OF OPER A TION Preamp Section Input section Micr ophone le v el (1 50 ohm sour ce im pedance, balanced, -50 dBm nominal) or line le v el (600-ohm sour ce, +4dBm nominal) audio enters t hr ough t he XLR-3 f emale INPUT connec - tor to t he In put selector switch bank. In t he 0 position, t he in put i[...]

  • Page 26

    D.W. FEARN VT-15 Recording Channel 28 r esponse, lo w phase shift, ex cellent squar e w av e r esponse, lo w distor tion, and high noise immunity . The secondar y of is connected dir ectly to t he grid of t he first am plifier st ag e. First stage The first st ag e is a selected 6072 configur ed as a Class A v olt ag e am plifier wit h a g ain of a[...]

  • Page 27

    D.W. FEARN VT-15 Recording Channel 29 VU Meter and Meter Amplifier A tw o-st ag e IC operational am plifier is used to isolate t he VU meter fr om t he VT - 1 5 output. An output sam ple is deriv ed fr om t he primar y of t he output transf or mer . The meter calibra - tion is set wit h a 20-tur n trimmer potentiometer . R ef er ence le v el (0 VU)[...]

  • Page 28

    D.W. FEARN VT-15 Recording Channel 30[...]

  • Page 29

    D.W. FEARN VT-15 Recording Channel 31 6. MAINTENANCE The VT - 1 5 is built wit h only t he highest quality par ts and will pr o v e to be extr emely r eliable. V acuum tubes and electr olytic capacitors, ho w ev er , ha v e a finite useful lif e and must be r eplaced e v entually . Top Cover Removal R emo ving t he top co v er allo ws access to t h[...]

  • Page 30

    D.W. FEARN VT-15 Recording Channel 32 Tubes also sometimes de v elop a micr ophonic r esponse — t he y will r espond to ambient noise and vibration. This can be an insidious pr oblem since measur ements in a quiet r oom will indi - cate per f ect per f or mance. Gently t apping t he tube shields while listening to t he output at a nor mal monitor[...]

  • Page 31

    D.W. FEARN VT-15 Recording Channel 33 Troubleshooting Most pr oblems will be traced to def ectiv e v acuum tubes. Ho w e v er , if nor mal tests do not eas - ily r e v eal t he pr oblem, f eel fr ee to call t he f actor y f or assist ance. If y ou lack access to a qual - ified service technician wit h v acuum tube equipment r epair experience, y ou[...]