dbx 463X - Page 19

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0A3A Is

an

Inverting

buffer

for

the

signal

through

CR3

with

a gain

of

sinus

two.

Its output

Is

sent to

the

LED

display, the

tip of the Strapping

jack,

and the VCA. R24

Is

added

Inside

the

feedback

loop

to help

protect

this

op-amp from Improper

connections

at

the

Strapping

jack. When

the

Slave

switch,

SI, Is

activated

the

output

of

0A3A

Is

disconnected

and

the

VCA

now

gets

Its control

voltage from

the

signal

externally

connected

to

the

tip

of the

Strapping

jack.

The

control voltage

Is

scaled at

16mV/dB

at

this

point

and

Is

divided

down to

6mV/dB at

the

VCA

by R8

and

R12.

LED

Display

Q1

provides

a

constant current

of

approximately

10mA

for

the string

of

12

LEDs.

The

comparators

IC3, IC4,

and

IC5, shunt

this

current

to

the

-15v

supply

when

the

control voltage (16mV/dB)

Is less

than

the

reference

at

the

minus

Input

of each

comparator section.

When

the

control

voltage

exceeds

the

reference

voltage,

the

comparator

section

becomes

an

open

circuit

and

allows

the

current

to flow through

the

LED

connected

to

that

section,

turning

It

on. All

LEDs

above this

point

will

be

on,

and all

LEDs

below

this

point

will

be

off. When

the

'Slave*

switch

Is

pressed, this

current

Is

sent

to the

Slave

LED,

turning

It

on

and

the

entire string off.

Power

Supply

The

voltage

selector switch,

located on

the

rear panel,

connects

the

dual

primary

windings of

the power

transformer

In

parallel

for

120

volt

operation

and

In

series

for

240

volt

operation.

The

center tapped

secondary

of

the

transformer

reduces

the primary

voltage to about

48v

ac

rms,

which

Is

full-wave

rectified

by the

diodes

CR21, CR22, CR23, and

CR24.

The

plus

and minus 24v

dc Is smoothed

by capacitors

C28, C29, C30

and

C31

and

checked

at TP7

and

TP8.

The

voltage

regulators

VR1

and

VR2

reduce

this

voltage

to

a

constant

+

and

-

15

volts

dc which is

used for

most

of

the

circuitry

In the

463X

and can

be

monitored

at

TP9

and

TP10

respectfully.

The

front

panel

*Power*

LED

Is connected

to

the

-24v

supply

through

R66

and Is used

to indicate

connection

to a

live

sc mains.