EMT-FRANZ 156 User manual

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PDM :- Compressor
EMT 156
EMT156TV

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lnstructic>n Manual
PDM-Cornpressor
EMT156
EMT156T·v
March 1978
Applies to units starting
with serial No. 25 738.
Constructions and circuits are
subject to change without notice!

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'
A Preparatory
A 1 MOUNTING
T his unit is designed to be mount ed in any standard 19" rack corres -
ponding to the standards USAS C 83.9, D IN 41 494.
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The fr ont panel dimensions:
1 9" x 5 1/4 " (size C)
vertical distance be t ween 100unting holes 2 1/4"
required clearance depth 14 1/4".
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The unit is to be mounted using four screws.
The EMT 156 is delivered with the following accessories:
2
2
male connectors,
Cannon XLR 3- 12c
female connectors,
Can9on
XLR 3-llc
Connector, Lumberg sv 3
Connector, Lumberg sv 5
AC mains cable
fus e 0.8 A slo -blo {European standard)
f use 0.8 A slo-blo {USA ~tandardl
fuse holder fo r USA stan dard fuse
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A 2 A.C. MAINS CONNECTION
The unit's A.C. mains socket on the back panel is connected to the
A.C. mains by means of the threeconductor A,C . mains cable which
is supplied.
If there is no plug on this cable, then the user should attach his
own mains plug using the yellow/green wire for the mains ground.
The unit is set at the factory for a mains voltage of 200 to 250
volts and has a o. 4 A slo - blo fuse.
A 3 CHANGING
THE A.C . MAINS VOLTAGE SETTING
1. Open the four quick-release screws
on the back right half panel.
2. While holding down the locking
spring, pull out the power supply
plug-in until the A.C. mains selecting
switch becomes accessible. To change
the mains voltage, pull on the mains
switch knob and then rotate it to the
desired voltage, either 110 or 220 V.
The 110 V position is used with
a voltage
between 100 and 125 V, 50/60 Hz.
The 220 V position is used with
a mains voltage
between 200 and 250 v, 50/60 Hz.
When the unit has been changed to
110 V, the 0,4 A fuse must be re-
place with a 0.8 A slo-blo fuse.

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A 4 GROUNDING
The c as e and the internal electronic ground a r e connected tog e ther
inte r na ll y. The ma i ns cable gro u nd wire is only connected to the
po wer t r ansformer shie l d , a l though it can be connect e d to the case
by me ans of the jumper link on the back panel.
Not e :
The un i t is grounded th r ough the ma i ns cable
only wh en i t is co n nected to an A. C . mains
soc ke t wh ich has a valid ground.
A 5 CO NNEC TI ON OF THE I NPUT AND OUTPUT LINES
The inp ut and output Cannon co n nectors deliver , ed with the u nit
should be co nnected as shown below.
INPUT· Stecker
INPUT· PLUG
A 6 SELECTING TH E REFE RE N CE LEVEL
OUTPUT - Stecker
OUTPUT '- PLUG
The EMT 156 compressor can be connected for any of the follow i ng
peak line levels :
+ 4 dBm
~
1.23 V
+ 6
dB m
~
1.55 V
+ 8 dBm
~
1.95
V
+12
dBm
~
3 . 08
V
+15 dBm ~ 4.36
V
The unit is normally shipped with the output transformer connect ed
for +6 dBm, and therefore , the output transformer taps must be
changec;l if it is to be used with any of th e oth er reference levels
V listed above . If the user ' s referenc e l e ve l do e s not correspond to
the unit ' s, then the picture on the front p anel and the adjustment -
control scales wi ll no longer be accurat e.
Note :
All reference levels co rrespon d to the n ormal
100% modulation point. T his l ev e l is ge ne rally
muc h higher than th e us ual o dB VU r e f ere nce.
(See section C f or details .)

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B
To ch<¥1ge the normal output line level , remove both amplifier
plug-ins at the back panel (left) by turning the quick - release
screws.
The pict ur e below shows how to reconnect the transformer output
wires. Both wi res must be connected to the same level.
15 12 8 6 4 4 6 8 12 15
+dBm
Now, r ep lac e the two plug - ins and connect al kHz sine wave, corres-
ponding to the 100% level, to the input. Connect an A.C. Volt meter
to the output and push the buttons FUNCTION and either MAN or AUTO.
Using a screw driver, adjust the input-LEV EL control of both plu ~- ins
until the output line level is 9o rr ect.
Operation
B l POWER ON
Push the AC POWER button
to turn the unit on or off .
The lamp indicates when th e
unit is on.

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B 2 CHOOSING OPERATING MODE:
LIMITER, COMPRESSOR, AND EXPANDER
First, push the button FUNCTION, located at the right end of
the middle group of buttons.
B 2a LIMITER: push button LIM.ON
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The unit is now operating as a limiter. Limitinq begins when the
output level tries to exceed the preset limiter threshold . Once
J;,hle poin .t... i _§_ ~ r~acJ:ied, fil1Y_ incr ~ ~se J n_ iEPl!_"lc _le,iTel_ rt:!sults in a
corresponding decrease in _..9~ in __ ~ _s,_.E. ha !.._ _t b~ peak valu _e of _ the
output does not exceed the ~hre~pol 9. .
This can be seen from the diagram. Wit h just th,e limiter function
in operation, the gain remains at unity, corresponding to the 45°
lirie, until the level exceeds the adjustable th:reshold, corres-
ponding to the horizontal line (red dot) . The point of inter -
section at which the 45°line an d the h orizontal line meet is the
level at which limiting begins.
The limiter threshold level can be adjusted with the red control
LIM./THRESHOLD between a relative level of - 2 dB and +7 dB . The
relative level corresponds to t he normal 100% (see A6 Selecting
the reference Level) .
In order to avoid introducing di s tortion, th e maximum input level
should never exceed +24 dnm, regardl es s of r eference level or
adjustments.
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B 2b COMPRESSOR:
push button COMP. ON
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The unit is now operating as a compressor . The compressor operates
on the average program level which approximates the loudness. There
are 3 static parameters, which are located on the front panel, for
controlling the compressor characteristics .
1, COMPRESSOR GAIN
This determines the maximum additional gain by which
medium and low level signals are amplified . At
higher levels compres s ion begins and the gain
is re duced below the maximwn which was set with this
control.
In the above diagram, this corresponds to an upward
paralled shift of the 45° O dB amplification curve
(blue dot) .
The blue COMPRESSION GAIN control allows this maximum
gain to be varied from O dB to +18 dB.
2. COMPRESSION RATIO
This determines the density or dynamic range of high -
level program . In the above diagram, this corresponds
to the slope (green dot) of the compression curve,
which intersects the unity gain line. As the
program level increases, the gain decreases in a dB
linear (logarithmic) fashion starting from the maximum
set by the COMPRESSION GAIN control . At the point where
t he program level equals the intersection of the com -
pression and O dB curve, the gain is (0 dB) unity ; for
further increases in program level, the gain decreases
below unity.
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The
compression
ratio
determines
how
much
gain
change
is
produced
by
a
given
change
in
input
level
.
This
can
be
written
as:
K =
dVin
/
dVout
dB
A
compression
ratio
of
3 : 1 ,
for
example
,
means
that
with
a 3
dB
incr
e
ase
in
the
input
level
,
the
outp
ut
l e
vel
increases
by
only
1
dB
.
The
compression
ratio
is
adjusted
with
the
green
con
-
trol
for
values
between
1.5
: 1
and
4:1
.
3 . ROTATION
POINT/
COMPRESSOR
The
compression
rotation
point
(yellow
dot)
is
the
point
around
which
the
compression
curve
is
rotated,
In
order
that
this
point
be
unaffected
by
changes
in
t
he
COMPRESSION GAIN
or
COMPRESSION
RA~~IO
,
it
is
fixed
on
the
O
dB
(
unity
gain)
curve
.
The
point
can
be
raised
or
lowered
along
the
O
dB
amplification
curve
by
adjusting
the
small
yellow
COMPR
.
/ROT
.
POINT
con
.
~rol
between
-
1.
5
dB
and
-6
dB
.
Adjusting
this
control
results
in
a
parallel
shift
of
the
compression
line
and
it
therefore
changes
the
distance
between
the
compression
and
li.mi
ting
regions,
assuming
that
the
limiter
is
also
in
operation.

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B 2c EXPANDER: push button EXP ON
Operating with the expander section is only meaningful if the
compressor section is also in operating.
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The meaning of "expander' in this application is not relat ed to the
type of equipment used to compensate for compress ion in a companding
system. Rather, the expan er function for low lev e l program and has
a compression ratio less than 1 (an expansion ra tio greater than 1).
The xpander function prevents very low level pr ogram and noise from
being amplified by the COMPRESSION GAIN In thi s way, prog ram level
which is below an adJustable thresh o ld' ~ u na ffe ct ed by th e system
(amplification= 0 dB) and the ef f ec · ve si gnal- to-noise ratio at
the output is the same as at the in put
In the diagram, the line connecting the linear (45°) compression
gain curve to the low-level O dB gain region is called the expansion
line. When operating in this region, an increase in input level
results in a increase in gain (in contrast to the compression region),
until the maximum ga n is reached. A decrease in input level results
in a decrease in gain until the minimum of O dB(unit~ gain is reached .
The gain never decreases below O dB in this region of operation. The
intersection of the expander curve and the o dB(unit0 gain curve is
called the ROTATION POINT/EXPANDE R. This point can be moved up and
down along the O dB line by adjusting the green EXP./ROT . POINT control
between -35 dB _ and -55 dB. Thus, this control affects the range of
program level over which the expansion occurs, and also affects the
range of program over which the gain is kept at O dB (unity).
Push button RATIO 1.5
RATIO 2 . 5
With these two buttons, the expansion ratio, or slope f the expan-
sion curve, is selected This determines the range of input level
over which the gain increase is distributed.

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' B
2d INTERACTION OF THE LIMITER, COMPRESSOR, AND EXPANDER PARAMETERS
There are 5 meaningful combinations of function which may be used.
Individual functions:
LIMITER
COMPRESSOR
LIMITER+ COMPRESSOR
Combination functions: COMPRESSOR+ EXPANDER
LIMITER+ COMPRESSOR+ EXPANDER
The geometric level diagram clearly shows the effect of the individual
compressor and expander functions . We recommend that the user sketch
on the accompanying pre-printed from the particular static characte -
ristics for each application. In this way, a systematic method of
choosing the best parameters for each kind of application can be
; determined and incorrect parameter settings will be avoided. In
addition, by learning to correlate the optical diagram with the
acoustic impression, the user will gain more insight into the best
approach for choosing the optimum parameters for his application .
After a little experience with this approach, the system is easly
adjusted for any kind of problem.
B 2e DYNAMIC CHARACTERISTICS
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1. Attack time
The compressor attack time is adjusted for approximately I/
2 msec at the factory. It can be changed internally within \
the region of 2 to 5 msec. (see SERVICE-appendix)
The attack-time for the limiter and e xp ander sections is
not adjustable. They have the following values:
Limiter
Expander
80 JUSec
Program dependent
2. Release time, manually adjus · ted
The release time for the Limiter, Compressor, and Expander
can be manually adjusted using the three knobs, labeled
RELEASE TIME, ~tjl e push button MAN has been pressed . The
r elease ti ~~s~ ingful only when the program level is
decreasing faster than the setting on the release time
knob. This means, for example , with a setting of 2 sec/10
dB, the gain will increase · lo dD in 2 sec following a
sudden decrease in level . The 10 dB increase in gain will
only occur, however, if the new program level allows for a
10 dB increase . If the new level is such that a 5 dB gain
increase occurs, then the new gain will occur 1 sec after
the program gain change .
The same is true for the expander, except that the gain
increases when the program level decreases. With the
release ti.me set at 3 sec/10 dB , for example , then the
gain decreases 5 dB in 1.5 sec, with a setting of
6 sec/10 dB the gain decreases 5 dB in 3 sec, etc .
In the case of the Limiter, the value of the gain change
corresponds to the change in the input level. If the level
suddenly decreases 10 dB while operating in the limiter
region, then the gain must increase 10 dB so that the
peak output level is the same . Thus, the amount of time
needed for this gain change is easily determined from the
setting on the release time.

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I
The sca l es for the release time should be interpreted as
meaning the rate at which the gin changes from the old
value to the new value with a de rease in program . The
time for this change to occur is obviously dependent on
the program changes as well as on the static parameters,
since these two factors determine the necessary change in
gain.
3 . Release Time , automatically controlled
The ~utomatic release time funtion is activated by pushing
the button AUTO located under the release - time controls.
In this mode , the effective release time is automatically
determined as a function of the program. In the limiter
funct i on , this time i is determined by the number of times
the limiter is activated in a giv n time, nd also by the
density of peaks which occur in a region between the
l imiter threshold and 2 dB below . If the peaks seldom
exceed a value -2 dB relative to the threshold, then the
release time is made very short Whereas , if the peaks
app r oach the t hreshold relatively often, then the release
time approaches infinity.
In the compression function the release time is determined
by the "Densi t y" of the program , i.e . by the relationship
between the average to peak le el . When the program is
dense having a small dynamic range , the releas~ time is
made long . Alternatively , when t e peaks are much greater
than the average level , the release time is made short.
For high level program, the el ase time of the expander
function is made a function of the ~ompressor release
t i me . In this way , when the evel suddenly decreases from
a normal value to zero, the rate of gain decrease for the
expander exactly matches the ra e of gain increase for the ~
compressor . Thus, the total gai approaches o dB (uni y) ~
without a sudden increase or de rease in the program noise
level, an gain - modulated no·se is avoided.
~~ expander release time for low level programs is
proportional to the program level. This avoids noise -
modulated program and program - modulated noise since the
rerease time is relatively long . With higher level programs
this is no longer a problem and the release time becomes
increas ngly shorter.
For a 1 three functions compressor, limiter and expander,
the release time - is actually composed of a short and a long
part The long part determines the extention of the
short term release .
B 3 METERING MODE
The mete has twC'
scales .
.I, •

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B 3a THE LOWER SCALE
The instantaneous gain of the entire unit is shown on this scale. If
the program level is between the rotation points of the compressor
and expander, the gain is greater than O dB and the meter points in
' the left of center part of the scale , For program level below the
expander rotation po int, the pointer indicates the center of the
scale, o dB High level program which causes the compressor to operate
abuve the rotation point, and also peaks above the limiter threshold,
result in the meter showing a gain of less than O dB, the right of
cenL~r part of the s~ale
It is important to realize that the contribution from the limiter
and compressor functions cannot be distinguished Therefore, gainn
less than O dB (unity) can be caused in part by both the limiter
and the compressor
B 3b THE UPPER SCALE
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1.s·..;s.·1,s
IBUS(TIN(
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•
When the button ATT/s is pushed, located at the left side of the
middle series of buttons, the instrument is operating on the upper
scale. In this mode; the meter shows the number of times per second
the limiter section has reduced the gain This shows the
limiting, in dB, caused by the peak exceeding the threshold. It is,
in general, unreasonable to have the limiter function operate too
frequently, for excessive limiting the input level should be reduced.
More than 10 limiting operations per second, full scale reading on
the meter., means that the average level is too high , Under certain
special conditions , however, this may be desireable (see Section
C Application Example) ,
B
3c ZERO ADJUSTMENT FOR THE METER
Mechanical Zero
With the unit turned off, carefully turn
the screw located directly under the meter
until the pointer is exactly at the left
end of the scale.
Electrical Zero
Remove all input program to the unit, push
button FUNCTION, and now adjust the control
SET ZERO until the pointer is exactly at
zero the middle of the scale.
'
..

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B 4 PUSH
BUTTON TEST
+
This mode allows the two multipliers to be balanced . Remove any in~ut
program , push button TEST, attach an A.C . volt meter to the output of
each c hannel. The symetry control BAL., located at the back near the
output connected , should now be adjusted so that the 50/60 Hz output
sig n al is a minimum (approximately -36 dB).
It is recommended that this adjustment be made after the unit has been
operating for a few minutes . After the unit has rea~hed temperature
equilibrium with the environment, this adjustment should again be
corrected to achieve optimum balance . Durtng normal service , the TEST
mode should be checked every so often, especially if there has been
a large temperature transient.
B 5 PUSH BUTTON BYPASS
+
When the button BYPASS is pushed, the entire unit is bypassed so that
the input or each channel is connected directly to the output without
any electronic processing of the signal Turning the unit off auto -
matically activates the bypass mode A power failure, therefore, does
not cause an interuption of the program
B 6 PUSH BUTTON AUX.DC
+
This DC voltage is connected to the connector marked EXTERNAL DC using
the 3 pin connected supplied with the unit _ The wiring of the connector
is shown below. The voltage source used to drive this input should be
be t w een O and +7 volts without any AC component . This input loads the
voltage source with a 2.2 kOhm resistance.
ov
(-)

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The fo ll owing curve shows the relationship be t ween the amplification
of t he un it and t he app li ed DC voltage •
Ve r stark un g/d
8
GAI N
+18
+16
+12
+8
+4
0
-4
-0
- 12 .
-
16
-20
- 22
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+1 +2 +3 +4
+5
+6 +7
Glei chspannun g/ V
DC-VOLTAGE
B 7 THE CO N NE CTOR
I NSTR
UMEN T MONITOR
The signal s on this connector allow for external metering and moni -
toring of the in t ernal cont r ol voltages .
1 . C
onnection of a second metering instrument
For external metering, for example in mixing console, the
second meter is connected in series with the inte r nal
instrument . In this application , the jumper between pins
1 and 4 is removed and the meter is inserted with the
-pole connected to pin 1 and the +pole connected to
pin 4,
When the external instrument is removed, the jumper between
pins 1 and 4 must be replace to allow the internal instru -
ment to function .
This external meter must have the following characteristics:
Moving coil movement
Full scale reading 100 ;uA
Int e rnal resistance 2 kOhms or less

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The scale should be similar to the ins~rument supplied in
the un it .
I t
should now be necessary to re-adj u st the electr i cal z ero
with the control SET ZERO as desc r ibed i n s e ction B 3c .
2. Connecting a Monitor Oscilloscope
By monitoring the internal control voltages on pins 3 and 5
of the 5 pin connector, the user can continuously observe
the way in which the unit is operating and can therefore
determine if the parameters are ad j usted for optimum .
On
pin 5 is the control voltage which dete r mines the pulse
duration modulation . Since it is proportional to amplifi -
cation determined by the compressor section , it is a measure
of the average value of the program level in the compressor
and limiter r eg i on.
The voltage on pin 3 is the control voltage for the auto -
ma t ic release time constant and is dependent on the cha-
racteristics of the program material.
Bot h signals (o n pin 3 or 5) can be monitored together with
the input audio program , or the two control voltages can be
compared to each other .
The diagram be low shows the wiring for the INS'I'RUMENT
MONITOR conneccor :
TI ME CONSTANT CONTROL VOLTAGE
PDM CONTRO L VO LT AGE
ov -----
(±) 8
REMOVE STRAP WHEN
CONNECTING AN EX TERNAL
INSTRUMENT

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C Application
C 1 RECOMMENDED ADJUSTMENT OF THE SYSTEM
In order to gain an understanding of the system the user should begin
experim~ntation with the following initial adjustments.
Press the following buttons:
FUNCTION,
AUTOMATIC RELEASE
TIME,
LIMITER .
Set limiter THRESHOLD (red knob) . to desired value. Feed the normal
program to the system.
Press the meter fu nction ATT/sec. If the meter pointer deflects, t he
input program has peaks greater than the nominal O dB. This may or
may not be desirable. Release ATT/s button.
Now, push the COMPR.ON button with the limiter also operating. Adjust
the compression ratio (green knob) to about 2:1 for classical music
and 3.5:1 for ,popular music.
The COMPR.GAIN control (blue) should be set to about 10 dB for no rmal
program . If the program has a good signal-to-noise ratio, than the
COMPR.GAIN control can be set higher. With 18 dB additional gain ,
and a noisy background, the effect of compression is perceived by
changing noise background (pumping). Decreasing the compression {blu e )
and increasin g the compression ratio (green), reduces this noise
" pumping " .
Additionally push the EXP . ON button and choose a RATIO of 2.5:l for
the expander . Adjust the expander rotation point (g rey) w i~h an input
signal of noise alone without program. The EXP.ROT . point is adjusted
so that with the noise alone the meter gai n shown on the meter is zero
dB. In this way, when the program is no longer present, the gain will
return too dB (unity), the effective signal - to - noise ratio at the
output of the compressor will be the same as the original signal-to - noi.se
r atio, and the rushing noise during pauses wil l be eliminated.
Th e system is now ready for operation . Press the ATT/sec meter function
with normal program. Although the input level may have been adjusted
so that limiting does not take place, the compresso r can function to
increase the gain so that the limiter is now forced to operate on the
peaks of the signal. The amount of limiting that takes place can be
adjusted with the compression _ rotation point (yello w). The h igher the
point the more the compressor will increa se the gain and thus the more
often the limiter will be forced t o ope rat e . Unlike norm al c ompressor
and limit er systems, it is in this case desirable for som e l i mi t ing to
take place, especially with progr am signals which have a L ,h ~e ak to
ave rage ratio. ~he limit e r effectiv el y remove s the peaks so that the
average signal level can be increased without overmod ulati ng the channei l
following the system.

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lf the user finds the particular program is too sensitive to gain
changes , the compression ratio shou l d be reduced. On the other hand
if the user wants a compression system which produces a very dense
sound, the compression ratio should be increased .
In some application the user may find that he does not wish to use
the automatic release function. lt should be remembered that the
release function has as muc~ if not more effect on the nature of
the compression than does the static characteristics A long release
time results in an almost constant gain, that is the short time
dynamic range is unaffected and the system operates as an automatic
volume control.
On the other hand with a short release time, the gain is continuous -
ly changing and the compression effect is very pronounced. With too
short a release time, there is a sensation of muddiness and distortion.

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D Servicing
D 1 FAULT FINDING
Faulty funct i oning or failure of the unit are most
probab l y due to component failu r e, provided that the
ambient and operating conditions have been normal . Even
when working well within their rated limits, a certain
proportion of electronic components will sti l l fail after
a certain period of operation. In such cases the unit can
often be fully repaired in a short space of time simply
by replacing the defective component .
The £ollowing hi n ts outline certain basic methods for
locating the defective component quickly. Before looking
for a fault in the PDM Compressor EMT 156 , however , it is
advisable quickly to carry out the following checks:
1 . Ar e the AC mains voltage and the incoming signal levels
correct?
2. Have the correct operating functions and parameters
been selected?
3. Is the 5-pin shorting plug on the back of the unit firmly
in position?
4 . Is the noise voltage at the output when pressing the
"TEST" button (no input voltage) below 100 mV (ou tput
transformer in +6 dB position)? (If the noise voltage
is much highe r the four diodes Grl - Gr4 or TS , T6 in
the multiplier may be defective . )
D 1 . 1
MECHANICAL PREPARATIONS FOR FAU LT FINDING
For quick check measurements and adjustments it is generally
sufficient to rem ove the upper cover plate (6 scre w s) . All
pre - se t s are then accessible from above .
IMPORTANT
Removal and replacement of the cover
panels as we l l as handling the open
unit should not be undertaken while the
AC mains are connected.
For extensive checks and measurements the lower cover panel
as well as t he back panel should also be removed by unscrewing
the four retaining screws; the individual pr inted ci rc ui t
cards can now be withdrawn, i f required, by depress i.,g
the locking springs .

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D 1.2 ME ASURING THE SUPPLY VOLTAGES
T he supp l y vol t ages should always be checked first. The
t wo vol t ages should be +10 V and - 10 V measured agains t
0 - V (circuit ground).
IMPORTANT
During all measurements great care should
be taken to avoid short circuiting the supply
voltages even for a short period of time .
Short ci r cuits will generally destroy the
se r ies transistor 2N3053 (T71) in the s t abilize r
circuit in the supply section.
Si nce a ll the chassis parts of the unit are connected to
th e 0- V potential , the 0 - V clip of the test instrumen t can
be a ttached to any part of the metal frame .
T
he +10 V potential can be picked up at the top of the
pow ering printed circuit card at the near e st of the three
l arge soldering lugs which lie side by side (see photograph)
or be tter still it can be picked up at pin 2 (red wire) on
th e co n nector of the expander card .
The
-1 0 V potential is readily available at point 1
(b l ue w ire) of the connector of the expander cassette .
Fig 3 sh ows the position of the expander card . The pin
numbe r s on the printed circuit card connectors are always
c ounted starting at the top (1) and counting downwards .