Lexicon PCM 42 User manual

pem 42
digital delay processor
Owner's Manual

TABLE OF CONTENTS
SECTION ONE — INTRODUCTION
1.0 Description
1.1 Precautions
SECTION TWO — CONTROLS & INDICATORS
2.0 Introduction
2.1 Front Panel
2.2 Rear Panel
SECTION THREE — INSTALLATION
3.0 Mounting
3.1 Power Requirements
3.2 Audio Signal Connections
3.3. Audio Control Jacks
3.4 Operating Levels
3.5 Non-Audio Remote Control! Functions
3.6 Clock Output
3.7. Voltage Changeover
SECTION FOUR — APPLICATIONS
4.0 Interconnecting the PCM 42
41 General Application Notes and Set-ups
4.1.0 Introduction
4.1.1 Echo
4.1.2 Double Tracking
4.1.3 Flanging
4.1.4 Resonant Effects
4.1.5 Vibrato
4.1.6 Pitch Twisting
4.1.7 Stereo Image Placement
4.2 Special Applications of Long Delay
4.2.0 Introduction
CO
4.2.1 Layering and the Infinite Repeat
Mode
4.2.2 Looping Techniques for Live
4.3 Programming and Using the Metronome/
Clock Output
4.3.1 Setting the Clock Rate
4.3.2 Interfacing the Clock with Rhythm
Machines
44 Interfacing to Other Units
45 Delay Lines in Distributed Sound
Reinforcement Systems
SECTION FIVE — BLOCK DIAGRAM
SECTION SIX — SPECIFICATIONS
6.0 Test Conditions
6.1 General Performance
6.2 Interface Information
6.3 Controls and Indicators
6.4 Power and Dimensions
SECTION SEVEN — IN CASE OF DIFFICULTY
7.1 General
7.2 Unit Will Not Power Up
7.3 Unit Powers Up, Gives Improper Display
7.4 Unit Powers Up, But Will Not Pass Audio
7.5 Returning Units For Repair
7.6 Replacement Parts
7.7 Limited Waranty

1.0 DESCRIPTION
The PCM 42 is a high-performance digital delay
line/ processor that features up to 2.4 seconds of high
quality audio delay, expandable to 4.8 seconds with
optional memory. Delay times are indicated by a highly
accurate numeric display, which provides rapid tracking
of ALL changes in delay time. The PCM 42 includes ver-
satile audio patching and remote control facilities, and a
unique synchronizing clock feature that allows highly
musical usage of the very long delays of which it is
capable. Long repeat loops and layering effects which
were formerly confined to the studio may now be used
easily and reliably on stage.
The 42 provides superior audio performance through
Lexicon’s proprietary method of analog-to-digital
encoding. An increased sampling rate gives wider band-
width without aliasing effects. In addition, a new “‘soft-
knee” limiting circuit eliminates the unpleasant distortion
that most digital circuits generate when overloaded.
The PCM 42’s excellent sonic quality, unique features,
light weight, flexibility and ease of use make it the
perfect choice either on stage or in the studio.
1.1 PRECAUTIONS
Although the PCM 42 is a very well-behaved device,
precautions consistent with good practice for any piece
of audio gear should be observed as a matter of course.
SECTION ONE
INTRODUCTION
Before turning the PCM 42 on or off, it is advisable to
lower the volume on your power amplifier or monitoring
system to avoid undesirable transients.
Never connect power sources or audio power
amplifiers directly into ANY of the PCM 42’s phone
jacks. The PCM 42’s inputs are designed for line level
signals. If a guitar amplifier is used as a signal input,
then a suitable attenuator pad must be used to lower
the level of the feed to the PCM 42.
To prevent fire or shock, never operate the PCM 42 in
the rain or in exposed wet locations.
Please read Section Three UNSTALLATION) of this
manual before operating the PCM 42.
WARNING
ALL SERVICING OF THE PCM 42 SHOULD BE
PERFORMED BY QUALIFIED SERVICE PER-
SONNEL. THERE ARE HAZARDOUS
VOLTAGES LOCATED UNDER BOTH THE
TOP AND BOTTOM COVERS OF THE UNIT.
TO AVOID ELECTRICAL SHOCK, REMOVE
THE POWER CORD BEFORE REMOVING
COVERS. SERVICING PROCEDURES CON-
SISTENT WITH GOOD SAFETY PRACTICE
SHOULD BE USED AT ALL TIMES.

SECTION TWO
CONTROLS & INDICATORS
2.0 INTRODUCTION
ly describes the PCI
ee A a AA
aicators. More cet
d applications is conta
2.1 FRONT PANEL
E
F
GH
J
M
P
VW
Figure
2.1 —
PCM
42
Front
Panel
When
the
button
is
out,
the
unit
is
set
for
the short
Re nEROROOM lore range (O0-1200 ms standard, 0-2400 ms with memory op-
The HEADROOM display monitors the audio level tion) and 16 kHz bandwidth. Pushing the button selects
after the INPUT LEVEL and FEEDBACK controls. The the long range (0-2400 ms standard, 0-4800 ms with
display has 5 LEDs which indicate peak levels relative to memory option) with 6 kHz bandwidth, illuminating the
converter overload. The input stage operates normally 6 kHz LED (Fig. 2.1, Q). The numeric delay display
up to 3 dB below the absolute limit, where a 5:1 com- always indicates the actual delay time.
pression ratio comes into play. At 0 dB, the input stage
limits, and further increases in input level will produce C. INPUT LEVEL
no additional input to the digitizer. Even extreme input
levels produce only a soft distortion, rather than clip-
ping. The Headroom Display follows the compressor/
limiter, indicating the audio level actually seen by the
analog-to-digital converter; thus it becomes non-linear
with respect to the input signal when the O-dB LED is lit.
The INPUT LEVEL control adjusts the input gain for
proper matching of the PCM 42’s sensitivity to the input
signal. Set this control so the HEADROOM display
occasionally indicates 0 dB on program peaks, with
average levels at about -12 dB (in the green zone).
NOTE: A rear panel switch provides an additional
BE PEEE TENGE 20 dB of gain for low level inputs, such as the output of
The DELAY X2 switch determines whether the PCM an instrument pickup. For details, see Section 2.2,
42 is in the short (X1) or the long (X2) time delay range. paragraph “|”.

D. FEEDBACK
cloc k\ wise feeds the
Be WECUY FILTER
Engaging the HI CUT
ne OONG low-pass f Nee i
back path. This is useft
aiat ing room am bien CE
ness of highl ly reson
Engag
reverses
fed bac
back signal ats phase c Bich acter
and is typically used for resonant fenuingss sounds:
G. DLY INV
Engaging the DLY INV (Delay Invert) button reverses
the polarity of the delayed sound which ts fed to the
OQUTPUT MIX control (Fig. 2.7, 1).
H. BYPASS LED
In Bypass mode, the Delay signal is cut out of the mix
at the MAIN OUTPUT, and all input to the delay line is
cut off. This LED is illuminated when the BYPASS is ac-
tivated by the optional footswitch or an external logic
signal.
|. OUTPUT MIX
The OUTPUT MIX control establishes the ratio of
direct to delayed sound in the PCM 42 MAIN OUTPUT.
Full counterclockwise position (toward INPUT) provides
100% direct sound from the input preamplifier. Full
clockwise position provides 100% delayed sound. The
control is detented in center position, where the blend
of signals is equal. This point is calibrated for maximum
notch depth during flanging.
J. © RPT
The INFINITE RPT pushbutton causes the PCM 42 to
capture the sound in the delay memory at the first clock
pulse after the button is pressed and repeat that seg-
ment continuously until the button is pressed again
The repeat mode uses the entire delay memory — the
length of the captured segment is independent of the
delay tap selected with the UP and DOWN pushbut-
tons, but changes with the settings of the MANUAL
VCO-SWEEP control and the DELAY X2 pushbutton.
ise ae the infinite repeat mode is enabled not at
nt the button is pressed, but at the first clock
cree (as Ow He the flashing CLK LED at the right of
he di / that time. To See rapid entry into this
rate To a sma
delay time lene section K, below!
il fraction of the total
TI ill not power up in repeat mode. If the
INFINITE RPT button is “IN” at time of power up, the
‘ll not enter the : Ae eat mode until the pushbutton
is released ane press
selected throu
to the rear pane
ee Repeat mode can also be
ry-contact switch attached
REP EAT jack (Fig. 2.2, D}.
K. SET-MODE
The SET-MODE slide sv vitch determines the function
of the display and the U P ag d DOWN pushbuttons. In
normal operation, this switc “ s set to DLY (left) and the
display shows the delay time in milliseconds, while the
pushbuttons increment and decrement the delay tap
selection.
With the SET-MODE switch in the CLK (right) posi-
tion, the UP and DOWN pushbuttons change the rate
of the flashing CLK LED and of the pulses appearing at
the CLOCK output. In this mode, the display indicates
the period of the clock as a fraction of the maximum
delay time (as determined by the DELAY X2 and the
MANUAL VCO-SWEEP settings). The numerator of the
fraction is on the left, the denominator on the right. The
DOWN button cycles the numerator through odd in-
tegers 1, 3, 5, 7, and 9. The UP pushbutton causes the
denominator of the fraction to cycle through binary
values 1, 2, 4, 16, 32, and 64.
L. DOWN BUTTON — DELAY/CLOCK
The DOWN pushbutton decrements the delay tap
value or the denominator of the CLOCK output ratio, as
described in paragraph ‘‘K’’ above. With the SET-
MODE switch in DLY, a short press and release of the
button will decrease the delay time by one increment. If
the button is held in, the selection will decrease approx-
imately once per second. To move rapidly to a new set-
ting, the UP button may be pressed while continuing to
hold DOWN. When UP is released, the increment rate
reverts to once per second.
M. UP BUTTON — DELAY/CLOCK
The UP pushbutton increments the delay tap value or
the numerator of the clock ratio as described above in
paragraphs “’K"’ and “L’’. As with DOWN, the rate of
increase of the delay time may be accelerated by press-
ing DOWN while holding UP. Thus, the direction of
change is determined by which button is pressed first,
while the rapid mode is enabled by the opposite button.

N. DELAY DISPLAY
When the SET-MODE switch is in the DELAY posi-
tion, the DELAY DISPLAY gives a precise 4-digit
display of the actual Gelars ime in milliseconds. With the
SET-MODE switch at CLOCK, it shows display of the
clo ae eee {see seca K above). The delay time
disp is accurate and updates itself very quickly,
stewines it to track all sweep functions as fast as the eye
can follow.
O. CLK LED
The CLK LED flashes in synchrony with the CLOCK
UTPUT on the rear panel. The rate at which the la amp
he is determined by the fraction programmed v os
SET-MODE, DOWN and UP, coupled with the settin
of the VCO-SWEEP controls.
To determine the exact period of the CLOCK, step
the delay tap value upward with UP until the display
ceases to increment, indicating maximum delay time.
(Use the fast-forward function described in paragraphs
K and L.) Note the delay time, and then switch SET-
MODE to CLOCK and read the display as a fraction,
with the numerator on the left and the denominator on
the right. The clock period is equal to the delay time
times the clock fraction. Note that if DEPTH is not set to
QO, or an external modulation is present, the clock rate
will not be stable.
P. co LED
The INFINITY LED is illuminated whenever the repeat
mode is selected by the INFINITE RPT pushbutton or
the corresponding footswitch jack.
Q. 6 kHz LED
The 6 kHz LED lights when the long delay mode is
selected by DELAY X2, indicating a reduction in band-
width to 6 kHz and a doubling of the available range of
delay.
R. MANUAL VCO-SWEEP
The MANUAL VCO-SWEEP control provides con-
tinuous, smooth control of delay times over a range of 3
to 1 by modifying the sampling rate. This control func-
tions as a,manual modulation for flange, chorus and
pitch twisting effects, and for access to very long delay
times.
S. DEPTH
The DEPTH control adjusts the amount of internal
modulation of the VCO, affecting the depth of sweep
r or flange, chorus and pitch-twisting. When DEPTH is
set at “O"', the internal sweep Is inactive. As the DEPTH
control
.
advanced
clockwise
toward
‘'10",
the
range
of the sweep increases to a maximum clock ratio of 3:1.
The DEPTH control interacts with the MANUAL
¥CO-SWEEP control (Fig. 2.1-R). The MANUAL con-
trol has its maximum effect with the DEPTH at 0", and
no effect with the DEPTH control at 10".
T. WAVEFORM
The WAVEFORM control selects the
modulation:
type of VCO
1. Full counterclockwise rotation selects sinusoidal
modulation: the delay time smoothly increases
and decreases at a speed governed by the RATE
setting.
2. Setting the control at the center detent selects
envelope-follower modulation: the delay time
changes in response to the level of the input
signal.
3. Full clockwise rotation selects square-wave
modulation: the delay time jumps instantaneously
up and down according to the setting of the RATE
control.
4. Intermediate positions of the control blend either
sinusoidal or square-wave modulation with
envelope-follower modulation.
U. RATE
The RATE control adjusts the low-frequency
oscillator (LFO) that controls the frequency of the sine-
or square-wave modulation. With the WAVEFORM
control in the center (envelope-follower) position, the
RATE control will have no effect.
V. RATE LED
The RATE LED flashes on and off to indicate the rate
of the LFO and to allow playing in synchronization with
the delay sweep.
W. POWER SWITCH
This latching pushbutton turns the AC power on and
off. On power-up, the delay time is automatically set to
O ms, the infinite-repeat function is turned OFF, and the
clock ratio is set to a value of 1/2. All other switch and
control settings remain as they had previously been set.

2.2 REAR PANEL
Figure 2.2 — PCM 42 REAR PANEL
A. POWER CONNECTOR
The POWER connector accepts standard IEC power
cords. Before plugging in the AC cord and applying
power, check the adjacent d plate to ensure that the
set operating voltage matches that of the AC mains.
B. VCO REMOTE JACK
The VCO input jack allows remote operation of the
MANUAL VCO-SWEEP control by means of a foot con-
troller (optional), or an externa! control voltage (range O
to +10 Volts; O Volts = maximum delay, + 10 Volts
= minimum, linear over a range of 3:1). The VCO jack
accepts a standard 1/4” phone plug for control
voltages, or a stereo tip/ring/sleeve plug when used
with the optional foot controller (Lexicon A-CP-41 Foot
Pedal). When the plug is inserted, the MANUAL VCO-
SWEEP is bypassed and has no effect.
C. BYPASS SWITCH JACK
The BYPASS function provides a means of quickly
switching the delay signal out of the MAIN OUTPUT
mix, while at the same time killing the feed to the delay
circuitry itself. The BYPASS jack accepts a 1/4” phone
plug and the BYPASS is activated when the tip of the
plug is shorted to the sleeve, or when a TTL logic ‘0" is
present at the tip.
D. co REPEAT SWITCH JACK
The INFINITE REPEAT function is activated by a
momentary switch closure or the falling edge of a TTL
compatible clock pulse. The unit remains in repeat
mode until another closure or pulse arrives OR the front
panel INFINITE REPEAT pushbutton (Fig. 2.1, J) is
released from a depressed position. The BYPASS func-
tion and the INFINITE REPEAT mode may be controlled
with a single Lexicon A-FS-41 Dual Footswitch
Assembly, or any combination of one latching
(BYPASS) and one momentary-contact (INFINITE
REPEAT) switch.
E. CLOCK OUTPUT JACK
The CLOCK OUTPUT jack provides a TTL-compat-
ible square wave output suitable for clocking many
automatic rhythmic devices and sequential controllers.
The rate of the clock is a fraction of memory Capacity at
the current sampling rate, programmable from the front
panel. This allows synchronization of external devices
to the delay period. (See Sections 3.6 and 4.3.2.)
F. DELAY OUTPUT JACK
The DELAY OUTPUT is an unbalanced tip/sleeve
jack carrying the output of the delay line at line level,
unmixed with any of the direct signal. (See Sections 3.2
and 4.4.)
G. DIRECT OUTPUT JACK
The DIRECT OUTPUT is an unbalanced tip,’sleeve
jack which carries only the input signal after preampli-
fication. This signal is at system line level.
H. INPUT JACK
The INPUT jack is a balanced, differential input which
accepts a 1/4” tip/ring/sleeve phone plug; unbalanced
sources can be accommodated by simply substituting a
tip/sleeve phone plug. A high input impedance allows
the PCM 42 to interface with either low or high im-
pedance sources.
|. GAIN SWITCH
The GAIN Switch matches the PCM 42's ‘nput sen-
sitivity to the signal source. Engaging the switch in-
creases sensitivity by 20 dB for sources such as electric
pickups, high-output microphones, and some electronic
instruments.
J. FEEDBACK CONTROL JACK
The FEEDBACK CONTROL jack provides two distinct
functions. When used with a tip/ring/sleeve plug and a

n onan 41) or any potentiometer, the
o the ee remotely. it can
uxillary input which is combined
without gain conte (nominal line
ions 3.3 and 4.2.2
A ss main |
= =
ae)
eS
See Secti
NOTE: THIS FUNCTION IS INDEPENDENT OF THE
F ai NT PANEL FEEDBACK CONTROL. RUNAWAY
DBACK CAN RESULT IF BOTH CONTROLS ARE
RAISED AT THE SAME TIME.
K. MIX CONTROL JACK
Like the FEEDBACK CONTROL, the MIX CONTROL
jack { ai 35 dual functions. With a potentiometer o
foot pedal, the user can raise and lower the volume
the delayed signal in the MAIN OUTPUT mix. ae
delay effects can be faded in and out at will. This jack
can also be used to inject an external signal into the out-
put mix. (See Sections 3.3 and 4.2.2.)
L. MAIN OUTPUT
The MAIN OUTPUT is an unbalanced tip/sleeve jack
whose signal level is determined by the adjacent con-
trol. It carries the blend of di rect and processed signal
which is set with the front panel OUTPUT MIX control
(Fig. 2.1, I).
f
M. OUTPUT LEVEL
The OUTPUT LEVEL control adjusts the MAIN OUT-
PUT level from its maximum of +179 dBV (9 V rms)
down to full attenuation. This control should be ad-
justed to provide the maximum level to the monitor
system, amplifier or console without clipping its input
stage.

ADEQU
TOM AND , whether or not it 's
k-mounted, This is of particular importance if the
s mounted above power ampli er heat
gener: 2Ng gear.
Since the PCM 42 processes low-level audio signals,
if iS advisable to locate it away from strong elec-
tromagnetic fields, such as those generated by power
transformers, motors, fluorescent ballasts, etc.
3.1 POWER REQUIREMENTS
The PCM 42 is set at the factory to operate at either
100, 115, or 230 volts (50 - 60 Hz). The factory-set
voltage is indicated on the rear panel next to the power
receptacle. The maximum power required is 20 watts.
Units set for 100 or 115 volts are fused at 1/4 ampere,
230-volt units at 1/8 ampere.
THE OPERATING VOLTAGE SHOULD NOT BE
CHANGED EXCEPT BY A QUALIFIED SERVICE
TECHNICIAN.
The PCM 42's power cord has a standard three-pin
IEC connector to simplify adaptation to power sources
in various countries, and to provide chassis-to-mains
grounding according to accepted safety standards.
SECTION THREE
INSTALLATION
3.2 AUDIO SIGNAL CONNECTIONS
r stereo (or
>} Plugs for Input
ad this Ssupsection fo
or foot pedal cor é
e proper cable for each
ensure that YOU are
function.
IGE UTD ruSsed WA
g (Tip = signal high, | Ring = signal iow,
Sleeve = shield ground).
it can aiso be used with unbalanced input sources
when fed by a T/S phone plug (Tip. = signal high,
Sleeve = sana ow! shi ield). This creates a traditional
single-ended inpu
NOTE: if a T/R/S plug is used with a
source, be sure to short the ring and sl
together.
single-ended
eeve terminals
OUTPUTS
The MAIN, DIRECT and DELAY audio outputs (Fig.
2.2, L, G and F) are unbalanced (single-ended), and are
intended for use with a T/S phone plug. Load im-
pedances of 5 kilohms or higher can be driven to full
levels; loads as low as 600 ohms may be driven without
loss of signal quality, although the output level will be
reduced slightly. lf the PCM 42 is used to drive
microphone level inputs from the DIRECT or DELAY
outputs, it will be necessary to insert a 20- or 30-dB pad
at the input to the driven device. The MAIN OUTPUT
has its own level control.

3.3 AUDIO CONTROL JACKS
The PCM 42 has two audio control jacks which are
wired in T/R/S configuration. In both of these, the
sleeve iS a common ground, and a single-ended, buf-
fered delay output appears on the ring. The tips of the
jacks are connected to different input patch points in
the PCM 42.
FEEDBACK CONTROL JACK (Fig. 2.2, J)
The tip terminal of this eo is connected to a patch
point that is mixed with the main INPUT. The input ac-
cepts single-ended, lin Bega ee from a source of any
impedance. Connecting a Lexicon A-CP-41 foot pedal
to this jack places the foot pedal’s internal poten-
tiometer between the ring and the tip, mixing the delay
output with the main input and thus allowing remote
control of feedback or regeneration.
Since the delay-only output on the ring is bu
two-way T/S phone plug may be inserted in thi
mix any other line-level signal with the mai i
without compromising the delayed signal. A T/RY
plug with connections to the ring and sleeve only will
permit the use of either audio control jack as a separate
delay-only output.
="
et
¢
Pe
a
mA&ow
NOTE: The feedback loop enabled by this control
jack iS separate from, and operates in parallel with, the
front panel FEEDBACK control and its associated HI-
CUT and FB INV switches. If the two controls are used
simultaneously, runaway feedback (howling) can occur.
When using the FEEDBACK CONTROL jack with the
foot pedal, turn the front panel FEEDBACK control to 0.
MIX CONTROL JACK (Fig. 2.2, K)
Inserting a phone plug into this jack interrupts the
connection of the delay signal to the OUTPUT MIX con-
trol on the front panel. A foot pedal plugged into this
jack allows the performer to fade the delay effects as
desired from zero up to the setting of the OUTPUT MIX
control. This jack may also be used to insert other signal
processors, ane as equalizers, into the path of the
delayed signal. The input accepts single-ended, line-
level audio from a source of any impedance.
3.4 OPERATING LEVELS
INPUT LEVELS
The PCM 42 can handie a wide variety of input
sources including microphones, electric instruments,
mixer outputs and so on. The high-impedance delay line
input will operate equally well with low- or high-
impedance sources. It is important, however, to set the
10
input sensitivity So that the unit can acco
full dynamic range of the source
i aye e; ~
signa ai/noise ratio and
mmodate the
with
£
To match the PCM 42's sensiti the
source, ae must first set
rear panel. Push the button in (selecting 20 a of extra
ae cee when using sour ue with peak levels ranging
from -23 dBV to 0 dBV (0.07 V to 1.0 V rms). This in-
cludes electric pickups, high output mireropuene coe
level mixer outputs, and some electronic instr pices
instrument preamplifier outputs.
ivity to
input
the 20 dB GAIN switch on the
O
I noul
Ihe button should be out
sources with peak levels rangir
70V to 9.0 Vrms}. This
output Ss, some
puts and some
(unity gain} when using
ng from -3 dBV to +19
includes high level mixer
e electronic instrument/preamplifier out-
direct box outputs.
With the appropriate switch position engaged, adjust
the front panel INPUT LEVEL control for peak
HEADROOM displays of 0 dB, with average levels
around -12 dB.
vel is unknown, Start at the 0 dB
out), and adjust the INPUT
i to otk g the HEADROOM display within
desi red paniaes f the gain is insufficient to achieve
peaks of -6 dB with Ae INPUT LEVEL at maximum, turn
dov he INPUT LEVEL and engage the +20 dB
positio
re signal ley
: iE itimm fA:
SATIN Eee? 1 (Dutton
WARNING
NEVER CONNECT THE PCM 42 INPUT
DIRECTLY TO POWER SOURCES, IM-
PROPERLY ISOLATED AC/DC DEVICES, OR
POWER AMPLIFIERS. DISREGARDING
THESE PRECAUTIONS CAN LEAD TO ELEC-
TRICAL SHOCK, AND MAY DO SEVERE
DAMAGE TO THE PCM 42.
MAIN OUTPUT LEVEL
The PCM 42 MAIN OUTPUT is designed to drive
loads of 5 kilohm or higher impedance at a level of 9 V
rms (+18 dBV). It is possible to drive impedances as
low as 600 ohms, although maximum output level is
reduced to about 5 V rms (+ 14 dBV).
NOTE: Do not use-the INPUT LEVEL control to set
output level.
Once the proper input level is established, the rear
panel OUTPUT LEVEL control can be used to adjust the
MAIN OUTPUT level for a wide range of devices. In
general, best signal-to-noise performance results at set-
tings of mid-scale or higher.