Dbx 165A Service Manual

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MODEL 165A

Compressor/Limiter

all»:

SERVICE MANUAL
(Preliminary)

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RBK OF £1.5th SHOCK

no "07 OPEN
DO NOT EXPDSE TO RMN 0R MDiS'lURE

CAUTION: TO REDUCE THE RISK OF ELECTRICAL SHOCK. DO NOT REMOVE (:0an (OR BACK).
NO USER SERVICEABLE PARTS INSIDE. HEFER ssavrcma TO QUALIFIED SERVICE PERSONNEL.

WARNING: TO REDUCE THE RISK OF FIRE OR ELECTRICAL SHOCK. DO NOT EXPOSE THIS APPLtANCE T0
MIN OH MOISTURE

This symbol. wherever It appears. This symml. wherever it appears.

alerts you to ma presence 0! umnsulalad liens you '0 important open-rung
dangerous voltage inside me andosura - voltage and maintenance hsnucfions in

ma! may be sufficient to consume a ask or shank. me accompanying Itaratwa.
Read me annual.

Manufactured under one or more of the following U.S. patents: 3.377.792; 3.681.6l8; 3.714.462; 3.789.143;
4.097.767; 4.329598: 4.403.199; 4.409.500; 4.425.551; 4.473.795. Omar patents pending.

This abs-branded producx his been mmutacwrud by AKG Acoustics. Inc.

ARC is a registered nadermrk of Akusliche u. Kim-Gem: Ges null-L. Austria.
All undamarks Ire properly of their respacnve companies.

This manual is pan number 9602241302

® Copyright 1993 by AKG Acoufiics. Inc. 100 - FE - 1/93

dbx Professional mam
A division of AKG Acoustics. Inc.

1 x53 Alva-no SuecL San Leandro. CA 94577 USA
TekphonHDSIOBSI-BSD manna/3510500

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Fig. 0 - Signal Input I Om! Jacks With A Normalling
Jack For The Detector Input Dotted lines indicate location ol
osmonal mull jack lporallel wired) lor leading input ol auxiliary
device with same program as 165 Signal trout.

Output Connection

The output of the dbx 165 is designed to feed balanced
or unbalanced 600 ohm or greater loads. The output
stage is single ended, so that in normal operation. the
l-l signal wulut terminal is internally connected to the
It) terminal. Men the system bypass swimh is engaged.
the signal input: are directly connected to the signal
outputs (to a balanced input would produce a balanced
output).

Grounding

For maximum hum rejection. avoid common ground
ing at the input and output (i.e.. double grounding). One
method that usually works is to ground the shield at the
165's output Ground I?) terminal and also ground it at
the input of the following device. 'Do not connect the
shield at the 165's input Ground seminal: leave the
input shield connected only to the output of the device
feeding the 165.

Stereo Coupler Gable

When you wish to link two Model 165's 1or processing
a stereo program. a cable must be constructed to ioin
the Stereo Coupler connectors on the two units. Use the
mating connectors supplied with each Model 165. and
wire the cable awording to Figure 7. Use connectors
supplied with units. or equivalent (Cinch-Jones
P-312-CCT). The cable should be 6-pair. listed 24 ga.
wire with shield (Belden 9506).

Once the cable is connected to the two 165' , it may
be left in place at all times. When both units' Stereo
Coupler switches are placed in "master" mode (bimon
OUT). the 165's operate completely independently:
stereo operation is achieved simply by switching one of
the two units to "slave" mode (button IN. Slave LED
ON).

Input Impedance I Termination

There is sometimes a misunderstanding regarding the
nature of matcl'ling and bridging inputs. the use ol
terminating resistors. and the relationship between
actual input impedance and nominal source impedance.
Most electronic outputs work well when "terminated"

15 $YtIE° WWI-II IL!

Mill-D

Fig. 7 - mar-o Coupler Gable
NOTE: The cable lot the ob: Model 1521': not compatible with

the Model 165.

by an input (connected to an input) having the same or
a higher actual impedance. Outputs are usually over.
loaded when terminated by an impedance that is lower
than the source impedance, When the input impedance
is nearly the same impedance as the source. it is known
as a "matching" input. When an input is 10 times the
source impedance. or more. the input is considered to
be a "bridging" input.

The obit Model 165 signal input has an actual
impedance of 22.000 ohms in balanced configuration
or 11,000 ohms in unbalanced (it has a highsz' input).
This makes the 165 signal input suitable for use with
virtually any nominal source impedance, low or high.
The dbl signal input vin'll bridge 150-ohl'n or BOO-ohm
(low!) lines.

The db: 165 detector input has an actual impedance
of 500.000 ohms in balanced configuration or 300,000
ohms unbalanced. This very hiya impedance means
the level detector will bridge virtually any nominal
source impedance. It also means that when the jumper
connectors link the detector and signal inputs. the
detector has a negligible effect on me 165's input
impedance as seen" by the source device. The very him
impedance of the detector does sum. however. that
cables from an external processor to the detector input
be kept as short as practical to reduce susceptibility to
hum and RFI.

Terminating resistors are not needed for the dbx 165
signal or detector inputs to operate correctly. but may
be required at these inputs when they are led lrom
devices lsuch as passive eoualiam) desist-led for a
specified load impedance.

The dhx 165 output is capable of driving loads pl
500 ohms or greater. While it may be terminated by a
low impedance. such termination is not required.

"2ie an abbreviation for "innuendo.

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lo.

6.

Threshold LED Indicators '

4.1 with the "STMO COUPLER" switch still to it's IN (SLAVE) Position,
place the "REMOTE" switch on the 165A test box to POSITION 4".

4.2 Measure the DC voltage at the "DVM Banana Jacks" on the 165 test box
and adjust the "OUTPUT GAIN" pot on the db: 165A for .OOVDC. Note that
the BELOW" (GREEN) IED is lit.

15.3 While still pressing the "THRESHOLD TEST" switCh, adjust the OUTPUT
GAIN" pot until the point where the BELOW" LED has just gone
'COHPIEIELY" out and the "YELLOW" LED is lit brightly. The DVM must
read +140+5MVDC.

4.4 while still pressing the rmsmm TEST" switch, adjust the "OUTPUT
GAIN" pot until the point where the "WW" LED has just gone
COHPETHX" out and the "ABOVE" (RED) LED is lit brightly. The DVM
must read +38055MVDC.

Threshold Calibrate
5.1 Place the "STEREO COUPLER to it's "OUT (master) position. Note that

the slave LED is no longer lit.

5.2 Place the "AUTO switch to its "OUT (manual) position. Note that the
AUTO LED is not lit, place the AUTO" switch back to its "IN

(AUTO) position.

5.3 Apply 11012 at +10DB. Place the threshold pot fully CW. Adjust R65
until the red threshold LED is on and then back off on 165 until the
yellow threshold LED just comes on.

5.4 Apply 11012 at 40133. Place the threshold pot fully CW. The yellow
threshold LED must be on.

5.5 Place compressor knob to '4'.

5.6 Place 3.140 fully CH then CCU slightly.

5.7 Apply lKZ ODE (1.00m5). Note: Reading on DB meter (adjust
gain pot for reading).

5.8 Apply 11012 +20DB (lO.VRHS). Meter reading should increase 51)). Adjust
H.140 until the requirements of 5.7 and 5.8 are net.

5.9 Repeat steps 5.7 and 5.8 until no adjustment of R140 is necessary.

5.10 Set the 'COMPRESSION pot fully CW. Apply 11012 at 'O'DB and set the
"OUTPUT GAIN" pot for a convenient reading on the external DB meter.
(e.g. -20DB). Apply 11012 at +20DB. The reading on the external DB
meter must not flange more than 1.593.

System Bypass and Compression Test

6.1 Apply lKKZ at '0' DB and place the SYSTEM BYPASS" switch to it's IN
(SYSTEM BYPASS) position. The external DB meter should read "0"-.2DB.
Note that the "OUTPUT GAIN" pot on the DBX 165A has no effect on this
reading. Place the SYSTEM BYPASS" switch to_it's OUT position.

Meter Calibration - Input Mode

7.1 Shut the power off and set the mechanical zero on the db: 165A meter
for PRECISflY' '0. Set the power back on.

7.2 Apply 11012 at "O'DB. Place the "THRESHOLD pot fully CH. Place the
m switch on the db: 165A to mm". Insure that R125 (R.P.)
will vary the reading on the db: 165A meter from -ll.5 to +1003. Set
3.125 for 'PRECISELY" "0". You might have to change 3169 to a value
between lush and 680K ohm to meet this spec.

7.3 Apply lKI-IZ at -20DB. The dhx 165A meter must read -20j-_lDB.

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