STANDARD VOLUME INDICATOR AND REFERENCE LEVEL 133 



S. Temperature Effects 



In the instruments now available, the deviation of the sensitivity 

 with temperature is less than 0.1 decibel for temperatures between 

 50° F. and 120° F., and is less than 0.5 decibel for temperatures as 

 low as 32° F. 



Description of Circuits 



The new instrument by itself does not constitute a complete volume 

 indicator but must have certain simple circuits associated with it. 

 Two forms which these circuits may take are illustrated in Fig. 18. 



uj 3900-OHM ATTENUATOR 



^ Q ABOUT ADJUSTABLE IN 11 STEPS 



D < 800W OF 2 DECIBELS EACH 



2800^^ X 



[600*^ 

 600'^ < 



.> 



COPPER-OXIDE 

 RECTIFIER & 

 INSTRUMENT 



s 



300^A) ABOUT 

 75001JJ 



ABOUT 3900"-^ 

 3900>-iJ 



3900^ 



A. HIGH-IMPEDANCE ARRANGEMENT. RANGE +4 TO +26 VU 

 (FOR A DEFLECTION TO THE VU OR 100 MARK) 



3900-OHM ATTENUATOR 

 ABOUT ADJUSTABLE IN 11 STEPS 

 800UJ OF 2 DECIBELS EACH 



ABOUT 

 600<^ 



ABOUT 3900 W 

 3900UJ 



3900'-^ 



8. LOW-IMPEDANCE ARRANGEMENT. RANGE„-6 TO +16 VU 

 (for a DEFLECTION TO THE VU OR 100 MARK) 



Fig. 18 — Circuits for new volume indicator. 



One volume indicator may, of course, have both circuits with arrange- 

 ments to select either by means of a key or switch. 



Diagram 18A shows a high impedance arrangement intended for 

 bridging across lines. As noted above, about 3600 ohms of series 

 resistance has been removed from the instrument and must be supplied 

 externally in order to obtain the required ballistic characteristics. 

 This was done in order to provide a point where the impedance is the 

 same in both directions, for the insertion of an adjustable attenuator. 

 A portion of the series resistance is made adjustable as shown by the 

 slide wire in the diagram. This is for the purpose of facilitating ac- 



