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I i Electronics

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inquiries (405)843-9626 co

orders (800)654-8657

  l

CIRCLE 90 ON FREE INFORMATION CARD 93

.

-

o

FIG. 8 THE REAL-TIME AUDIO ANALYZER as

seen

from

the front It is very clean In ap

pearance and will

look

r ight at home with

your

stereo system.

ter the line. Repeat the process for all of

the LED's that are too low, lowest octaves

first, until all that is remaining is a straight

line and LED's that are too high.

• The procedure is again repeated for the

high LED's, beginning with the lower oc

taves. The resistors removed for the high

LED's are to be replaced with 520K cal

ibrating resistors ,

To re-iterate, the steps are to: a) Find

the lowest octave that has a LED too low.

b) Find the resistor number for that oc

tave. c) Replace that resistor with a 430K

calibrating resistor, d) Readjust level con

trol for straightest line. e) Repeat until

only straightest line with LED's too high

remain. f) Find the lowest octave that has a

LED too high. g) Replace that resistor

with a 520K ohm calibrating resistor. h)

Readjust level control for straightest line.

i) Repeat until only a horizontal straight

line of LED's is visible .

The audio analyzer is now calibrated.

The calibration resistors can now be sol

dered in place and the leads clipped to

proper length.

The addition of the real-time analyzer

to a stereo system, PA, or recording con

sole allows you to see what you're hearing

(or what you're not hearing). It can be

used as a tool when taping (to match tapes

with the original source, or to discover the

playback characteristics of a tape ma

chine). As it reveals the spectral content of

the music played it can be enjoyed as an

educational, entertaining, and colorful

display. R-E

Resistor

R99

R97

R95

R93

R91

R101

R103

R105

R109

TABLE

1

Octave

31.5

62

125

250

500

1K

2K

4K

BK

continued from page

board mounted, the depth of the switch

and potentiometer will determine the

length of the standoffs you'll require . If

you use very low-profile parts for that sec

tion, you'll be able to bolt the circuit

board veryclose to the faceplate. That will

give excellent visibility to the LED's. A

red plastic filter may be glued on the back

of

th e

window

for a professionally

finished display.

Calibrating the analyzer

The

following

resistors should

be

placed in position but not soldered: R91,

R93, R95, R97, R99, RIOI, R103, RI05

and R109. To calibrate the analyzer:

• The unit should be powered up with the

selector switch in the oscillator-output

position  AUX . That will display the os

cillator output.

• The LEVEL potentiometer, RIl3 should

be adjusted until the LED's make the

straightest possible horizontal line with

one LED lit per octave, The level should

be playedup and down until the straightest

line is achieved.

• It is normal for some of the LEO's to be

higher or lower than what is desired .

• Table I lists the resistors for each re

spective octave. Using the chart, replace

the resistor for the lowest octave that has a

LED too low with a 430K calibrating re

sistor. Be sure to remove power from the

unit anyting you replace resistors

•

Readjust

the l evel

control

for

the

straightest possible line . Since all of these

parts are interactive, each change may al-

SPE TRUM N LYZER

FIG.  THECOMPLETED ANALYZER,mounted in a 19-inch rack cabinet. Since most of the compo

nents 'are mounted on the circuit board, there is a lot of room inside the cabinet.