Teac Tascam Series User manual

INSTRUCTION MANUAL
TEAC Tascam Series
MODEL 15 AUDIO MIXER

CONTENTS
1, INTRODUCTION TO THE-MODEL 15 ..... 1
2, IMPEDANCE MATCHING
—OR, WHAT PLUGS INTO WHAT ........ 2
Mathematical Formulas . .
QuickTest for Safe Loads without using Test Gear. 4
3. THE MODEL 16 FROM MIC IN TO LINE OUTS
3.1 INPUT MODULE
Mic In XLR’ Connectors
Mic: ATT ‘Switch
Line In Jacks
Input Select Switch
SIGUE Ss ascites
Overload L.E.D.
Accessory Send/Receive Jacks
Equalization Controls 7
Aux 1 and Aux 2 Pre-/Post-Fader Function .. .
Input Fader 2... ,.
Direct Out Jack
SOLO ta toss eis
NYNDOGMOGDGAAR AA MURS, Fos. SEM Case ween Te
3.2 BUSS MASTER MODULE
Buss tn Jacks .........
Buss Fri; cag oie st ss. 2
Accessory Send/Receive Jacks ee
Buss Master Fader .
Tape as source
Buss as source ......
Monitor Pan
Aux 3 and Aux 4.
Echo Receive Section
COMDDMOMO
3.3 AUX A MASTER MODULE (CUE}
Aux A Mix Control .. 2.0...
Aux 3 and Aux 4 Push Switchs .
Echo RCV Rotary Control Master
Aux A Master Fader
Aux A Module Back Panel
Aux 3 output jacks
Aux A output jacks . ae
Line out 1~ 4 (buss master outputs) . Sieh fey'e AO!
3.4 AUX B MASTER MODULE (ECHO)
Aux B Mix Control .....
Aux 3 and Aux 4 Push Switch
Aux B Master Fader
Aux B Module Back Panel
Aux 4 output jacks
Aux B output jacks . . al eaeteae
Line out § ~ 8 {buss master outputs) Bh eS 11
Loading Advice ....
3.5 CONTROL ROOM MONITOR MODULE
Monitor A Output Jacks 22... JT
CR MON, Land R Output Jacks 21
Push Switches: 80. ese eevee ti
Control Room Master ......-...-..0- il
Solo: Masteh cos Aadis Beek cw Fisk pshes pai
Solo L.ED. ett
Auxiliary Line tn Jacks 11
3.6 STUDIO MONITOR MODULE
Studio
Studio MON L-R Outputs
Monitor B L-R Outputs
3.7 TALKBACK MODULE
Oscillator Frequency Select Switch
Oscillator Function Select Switch
Talkback Microphone ..........
Studio
Aux A
Slate :
Headphone Select Switch vod
3.8 POWER SUPPLY UNIT
Meter Bridge Connector ...... ib ated esavol
4. STANDARD PATCHES ......... hobtidicine .12
Recommended 8 Track Setup ............ 18
16 Track Remix Patch
with an Unorthodox Stereo Echo ........- 14
Recommended 16 Track Setup ............ 15
5. LEVEL SETTING AND OPERATION CHECK
Line in —» Access send ........ wean VE
Line in —> Direct out of... . 0... cee 7
Line in —> Line out/Aux out ........... 7
Check and adjustment of the input module
QverlQa LED 0 2 055 (oa) he ba arate ated we 18
Aux 1 —» Aux Asend .......... 1.19
Aux 2 —> Aux B send
Line in. —> Line —> Aux 3 —> Aux A send . . 20
Aux 3 —+AuxBsend ............. 24
Line in —+ Line out —> Aux 4 —+ Aux B send, 21
Aux 4 -> Aux A send
Line out —> Mon A left/right
Solo circuit
Control room monitor circuit
Studio monitor circuit . ‘
Echo RCV circuit ......-.....
Meter calibration and LED circuit
Test tone oscillator
Talkback circuit ......
Tape in circuit ...
Mic input (Model 301 Input Module)
Phantom power supply .............+4-

6. EXPLODED VIEWS AND PARTS LIST
Model 15 Main Frame
Model 301. Input Module F
Model 302 Buss Master Module
Model 3034 Aux A Module
Model 303B Aux B Module
Model 304 Talkback Module
Model 305A Control Room Monitor Module .
Model 350B Studio Monitor Module
Model 306 Power Supply Module
Model 307 Filler Module Tei cae Boats
Model PS-15 Power Supply Unit ..........
7, PC CARDS AND PARTS LIST
Input Amplifier PCB
Buss Master Amplifier PCB
Aux A Amplifier PCB
Aux B Amplifier PCB
Talkback Amplifier PCB
Controt Room Monitor Amplifier PCB . 2... . 81
Studio Monitor Amptifier PCB He satin Bea BT:
Power supply PCB. ..... La leah genta ieee 91
Mother board: PCB? .ssasasries cet eed das 95
8. ELECTRONICS SCHEMATICS
Block diagram ........ Boe aed tad hee 97
Modet 301 Input Module ..... Lashegarea OS
Model 302 Buss Master Module . . Se 4 OD.
Model 302A Aux A Module
Model 303B Aux B Module
Mode! 304 Talkback Module .
Model 305A Control Roam Monitor Module... 103
Model 305B Studio Monitor Module
Model 306 Power Supply Module
Meter bridge .......... aerate eves
Model PS-15 Power Supply Unit .....
9, SPECIFICATIONS 109

1. INTRODUCTION TO THE MODEL 15
The Madel 15 is an audio mixing console designed
to satisfy the requirements of modern multichannel re-
cording. Many of the auxiliary mixing systems needed
are built in and canbe re-routed to do more than one
job. Fast, convenient and complete operation with 8
track or 16 track recorders can usually be accomplished
without ré-patching. However, the process of multi-
channel recording is constantly changing, growing more
complex as an art with each advance in technology. Your
signal processing needs may require a unique arrange-
ment of subsystems. No console has ever been built so
large and complete in its routing that it could solve every
imaginable problem with one button. Someone will al-
ways be able to come up with that unusual situation re-
quiring “just one more mix". In order to cope with these
unpredictable requirements, patch points are provided
throughout all signal pathways on the M-15.
As our mixing console becomes more flexible, the
amount of time needed to understand the available func-
tion increases as well. The main signal path from mic in
to line out is still fairly straight forward. The require-
ments have not changed much since the days of “mono”
but the routing for echo sends, multiple source cue feeds,
and stereo monitoring can be hard to visualize. The be-
ginner often overlooks the significance of connections
that would be immediately obvious to the experienced
recording engineer. If you expect to find that “extra
mix” quickly, you must be prepared to study the layout
of the M-15 thoroughly. In most instances the physical
arrangement of the controls on the top pane! has very
little to do with the sequence of electronic parts inside,
The actual wiring order is the information you need to
understand to use the M-15 successfully. As an example,
if the controls on an input module actually followed the
order in which they are wired, the module top panel
would look like this. We'll put the jacks on the top, as
well as the switches and faders.
While this arrangement of controls might help the
beginner to understand the flow of signal in the module,
it would be very inconvenient to operate. Still, the wiring
sequence must be understood before the more complex
functions of the M-15 can be used successfully, so along
with the documentation you will need for service {sche-
matic diagrams, mother board layouts and mechanical
disassembly information) we include a simplified electri-
cal sequence chart called a BLOCK DIAGRAN. This
drawing shows all the controls, switches, amplifying
stages and connectors in their proper order. Learning to
read it will provide the answers to any questions about
what comes where on the inside. Even though the block
diagram can indicate what is available in the way of ex-
tra circuit flexibility, it can’t explain why 2 connection
or switch has been included, or suggest a standard layout.
In the following sections of this manual we will do our
best to describe the individual functions and controls of
the M-15 and how they can be arranged in more than
one sequence, but your mixing needs may be best served
by an arrangement of inputs and sub-system connections
you work out for yourself.
Good luck with your sound.
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2. IMPEDANCE MATCHING — OR; WHAT PLUGS INTO WHAT
All electronic parts including cabies and non powered
devices (mics, passive mixers and such) have impedance,
measurable in ohms {symbol $2 or Z). Impedance is the
total opposition a part presents to the flow of signal, and
it's important to understand some things about this value
when you are.making connections in your mixing system.
The outputs of circuits have an impedance rating and so
do inputs. What’s good ? What values are best? It depends
on the direction of signal flow, and in theory, it looks
like this:
plug into
OUTPUTS
OUTPUTS
It is generally said that the output impedance (Z)
should be as low as possible. 100 ohms, 10 ohms, the
lower, the better in theory. A circuit with a low output
impedance will offer a low resistance to the passage of
signal, and thus will be able to supply many multipte
connections without a loss in performance or a voltage
drop in any part of the total signal pathway. Low
impedance values can be achieved economically by using
transistors and integrated circuits but other considera-
tions are still a problem in practice.
1, The practical power supply is not infinitely large. At
some point even if the circuit is capable of supplying
more energy, you will run out of “juice”.
2. Long before this happens, you may burn out other
parts of the circuit. The output impedance may be
close to the theoretically ideal “O ohms” but many
parts in the practical circuit are not. Passing energy
through a resistance generates heat, and too much
current will literally burn parts right off the circuit
card if steps are not taken to prevent catastrophic
failure.
3. Even if the circuit does not destroy itself, too high a
demand may seriously affect the quatity of the audio.
Distortion will rise, frequency response will suffer,
and you will get poor results,
++ INPUTS
INPUTS
Inputs should have very high impedance numbers, as
high as possible, 100,000 ohms, 1 million ohms, more, if
it can be arranged. A high resistance to the flow of signal
at first sounds bad, but you are not going to build the
gear. if the designer telis you his input will work proper+
ly and has no need for a large amount of signal, you can
assume that he means what he says. For you, a high
input impedance is an unalloyed virtue. It means that
the circuit will do its job with a minimum of electrical
energy as a beginning. The most “economical” electronic
devices in use today have input impedances of many
millions of ohms, Test gear. For example, voltmeters of
good quality must not draw signal away from what they
are measuring or they will disturb the proper operation
of the circuit. A design engineer needs to see what is
going on in his design without destroying it, so he must
have an “efficient” device to’ measure with.
The classic measurement for Output impedance is to
load a circuit until the voltage drops 6 dB (to half the
original power) and note what the load value is. In theory,
you now have a load impedance that is the same as the
output impedance, If you reduce the load gradually, the
dB reading will return slowly. to its original value. How
much drop is acceptable? What load will be left when an
acceptable drop is read on the meter?
When the load value is approximately seven times
the output impedance, the needle is still a little more
than 1dB lower than the origina! reading.
Most technicians says.” 1 dB, not bad, that’s accept-
able.” We at TEAC must say we do not agree. We think
that a seven to one ratio of input (7) to output (1) is not
a high enough ratio and here’s why.
1. The measurement is usually made at a midrange fre-
quency and does not show true loss at the frequency
extremes, What about drop at 20 Hz?
2.-All outputs are not measured at the same time. Most
people don't have twenty meters, we do. Remember,
everybody plays together when you record and the
circuit demands in practice are simultaneous, All
draw power at the same time.

Because of the widely misunderstood rule of thumb,.
the seven to one ratio, we will give you the values for
outputs in a complete form.
Even though the true output impedance is:
Line Out/Aux Out 100 ohms
CR Mon Out 100 ohms
a Studio Mon Out 100 ohms
Aux A and Aux B Out 100 ohms
Mon A and Mon B Out 100 ohms
' Aux. 3 and Aux 4 Out 400 ohms
Tape Foldback
Equal to tape recorder output im-
pedance connected to TAPE IN.
Direct Out 100 ohms
Access Send 100 ohms
Talkback Out Less than 1 ohms
Headphone Out Less than 1 ohrns
For the practical reasons explained previously, we
feel that 7 :1 ratio is not sufficient. To use this rule of
thumb, you must use this higher value. We'll call this
value the “output load impedance.”
Line Out/Aux Out 1.4k ohms
CR Mon Out 1.4k ohms
Studio Mon Out 1.4k ohms
Aux A and Aux B Out 1.4k ohms
Mon A and Mon B Out 1.4k ohms
Aux 3 and Aux 4 Out 1.4k ohms
Tape Foldback
Equal to tape recorder output im-
pedance connected to TAPE IN.
Direct Out 1.4k ohms
Access Send 1.4k ohms
This is a number that will give good results with the
7:1 method. To go one step further, here are the actual
minimum ohmic values we feel are wise.
Connect no total input impedance load higher than:
Line Out/Aux Out 10k ohms
CR Mon Out 10k ohms
Studio Mon Out 10k ohms
Aux A and Aux B Out 10k ohms
Mon A and Mon B Out 10k ohms
Aux 3 and Aux 4 Out 10k ohms
Tape Foldback
Equat to tape recorder output im-
pedance connected to TAPE IN.
Direct Out 10k ohms.
Access Send 10k ohms
Input impedance is more straight forward and re-
quires only one number. Load is load, and here are the
values for the Modal 15:
Mic Input 20k ohms
Line Input 50k ohms
Echo Receive 20k ohms
Tape Input 40k ohms
Buss Input 20k ohms
Access Receive,
input module 50k ohms
Buss Master module 10k ohms
Line 1, 2, 3 Mon 100kohms
if one output is to be “Y” connected to two inputs,
the total impedance of the two inputs must not exceed
the toad impedance, as mentioned before, and if it be-
comes necessary to increase the number of inputs with
slight exceeding of the load spec., you must check for
drop in level, loss of headroom, low frequency response,
or else suffer a loss in quality, {f one input is 10,000
ohms, another of the same 10,000 ohms will give you a
total input impedance (load) of 5,000 ohms. To avoid
calculations you can do this when you have two identi-
cal inputs to connect to one output.
Take the lower value of the two input impedances
and divide it in half. If the number you have is still 7
times the output impedance, you can connect both at
the same time.
When you have more than two loads (inputs), just
dividing the lowest impedance by the number of inputs
will not be accurate unless they are all the same size but
if you still get a safe load (higher than 7 : 1 ratio) by this
method, you can connect without worry.
MATHEMATICAL FORMULAS
If you must have exact values, here are the formulae:
1
For more than 2 —- Rx=
ab eg te ote
Ri R2 RB Rn
Rx = value of total load
For 2 loads ‘or inputs — Rx= nine
Ri + R2
Finding Impedance Values on Other Brands of Equipment.
When you are reading an output impedance specifi-
cation, you will occasionally see this kind of statement:
Minimum load impedance = X ohms
or
Maximum load impedance = X ohms
These two statements are trying to say the same
thing, and can be very confusing. The minimum load
impedance says, please don't make the number of ohms
you connect to this output any lower than X ohms.
That‘s the lowest number. The second statement changes
the logic, but says the exact same thing.
Maximum load impedance refers to the idea of the
load instead of the number, and says, please, don’t make
the toad any heavier. How do you increase the load?

Make the number lower for ohms. Maximum load =
minimum ohms, so read carefully.
When the minimum/maximum statement is made
you can safely assume that the manufacturer has already
done the “saven times is best” ratio calculation, And the
number given in ohms does not have to be multiplied.
You can match the ohmic value of your input to this
number of ohms successfully, but as always, higher ohms
will be okay (Less load). 7
QUICK TEST FOR SAFE LOADS WITHOUT
USING TEST GEAR
tf you don‘t know the exact value input impedance
for a device you want to connect there are still a couple
of ways to test it.
1, Listen to the main signal output {line out or Aux
out) as you remove and re-connect the device to the
direct out. If you hear a drop in level or a change in
the.tonal balance of the sound on the main line out,
the device is likely to be drawing too much current
and is unsuitable.
lf you can get a steady tone to work with, you can
read your VU meter and make this measurement.
Patch the steady tone through the mixer from input
to line out. Set the faders so the tone reads “O" VU
‘on the meter. Now connect the device you wish to
check to the “direct out” on the input module you
are using for the steady tone, If the drop in level on
the meter is more than 0.5 dB, the device has too low
a value of input impedance. It will not damage the
mixer to use it, but it will affect the quality of the
signal on the main line.
Nn
If making the connection to the direct out causes
the main line signal to drop 6dB, the input impedance
of the device is the same as the true output impedance.
You should also know that to make the “disconnect,
re-connect the load” test in. section 1 above, you must
actually pull out the connection. Many devices will affect
a circuit when the signal cable is connected, even if they
are not plugged in the power line, or their power (AC)
switch is in the off position.
3. THE MODEL 15 FROM MIC IN TO LINE OUTS
In our description of the seven different types of
module used in the M-15, we'll disregard the physical
layout and follow the block diagram, or actual wiring
sequence.
3.1 INPUT MODULE
All sixteen input modules are identical and can be
interchanged without modification. An additional 8
modules can be added io the frame at any time. The
extra positions are completely wired, with one excep-
tion. The RMX (remix) position will be inoperative on
the last 8 positions (17-24) because there is no provi-
sion on the tape A or B circuit for the extra 8 busses
necessary. All other features will be identical in the 24
input mode.
MIC IN XLR CONNECTOR
This connector and the small amount of wiring
immediately in front of the input transformer are the
oniy parts of the M-15 that use the 3 wire balanced
type of circuit. The Mic in XLR, the pad of 20 dB that
is switch selectable and the transformer primary are
“balanced”. All circuits thereafter are 2 wire “single
ended”, one hot lead, one ground.
MIC ATT SWITCH
When this switch is set to the left, a balanced pad
lowers the “Mic In" level by 20 dB, Since the maxirnum
permissible input to the transformer is 0 dB (1 volt),
when high output mic’s are used on very loud sounds,
extra external pads may be required to lower the input
signal to safe levels. The input load impedance of the
“Mic In” group of parts is 20 kohms. This circuit cor-
rectly matches 50-250 ohm low impedance microphones.
LINE IN JACK
An RCA jack on the rear of each input module. The
maximum signal you can apply here is +28 dB (25 volt).
The Mic Att switch does not affect this input. The input
impedance is 50 kohms.
INPUT SELECT SWITCH
This switch has 3 positions, left selects the Mic in
XLR, center selects the Line In RCA jack on the back
of the module, and right, marked “w” (remix), selects
as an input one of the “Tape In” jacks on the buss master
modules. Since each input module will receive only one
“Tape In” signal, we'll provide a chart to show which
signal goes to which module.
The “Tape In” A and B systems normally feed the
monitor sections on the buss master modules. The “s#”
{remix} position on the input module will allow you
to route tape playback signa! to the input module for
final mixing without moving the cabies plugged in at
tape A or B to the input “Line In” jacks, in addition,
selecting this “m” (remix) position on the input module
will not disable the normal operation of the monitor.

TAPE A JACK, UPPER ROW
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10
TAPE 8 JACK, LOWER ROW
Signal will go to both circuits at the same time, allowing
separate use of the monitor A and B outputs as extra
mixes. True stereo echo is an obvious first choice, and
the mixdown machine can be monitored using a “Line
In” position on the control room monitor module. Since
the remix position can be selected one module at a time,
a single track may be equalized and monitored without
disturbing “Mic {n” settings on the whale mix, A deci-
sion can be made quickly on the artistic success or failure
of an individual part without the need to place the entire
console in remix mode just to see the effect of corrective
equalization on a single track.
If you examine the input module numbers you will
see that the Number One module is the one closest to
the “Buss Master 1 Module.” The mixing console is
numbered from right to left on the input module section,
but from left to right in the buss master section. This
system has been adopted in order to keep the mixing
console as compact as possible in 16 input configuration.
Expanding to 24 inputs will now add modules to the left
of the ones already installed, and the numbering will
rernain correct, even though inverted.
Since the TAPE IN jack on the buss master module
actually feeds 3 separate mixing positions it will present
a more severe load to anything connected to it than
“Line in“ on the module. TAPE IN's have an input load
impedance of 40kohms, LINE IN‘’s (on the input
module} have an input impedance of 50 kohms.
TRIM
This control witl alter the gain of the first amplifier
in the console. It will affect the fevel of any signal, Mic,
Line, or #. With this pot rotated fully clockwise (right-
ward), the maximum gain of the first amplifier is 48 dB.
In this position, the maximum input signal before over-
load is -38 dB (0.013V). To improve the performance
of this first gain critical stage, for the M-15, TEAC has
elected to build a discrete amplifier with FET inputs
instead of using the standard |.C.’s now available. Sub-
stantial improvements in performance have been realized
as a result. When the pot is in its minimum setting (fully
counterclockwise or leftwards) the gain is reduced to
8 dB and the maximum signal that can be handled with-
out overload wil] be +2 dB (1.3V}.
Remember, these overload figures refer to the input
of the amplifier, not the input plug or connector, Losses
occur, and pads can be inserted before this point. The
maximum signal that can be applied: to the line in jack
is +28 dB (25V) with the Trim rotated fully leftwards,
and -12 dB (0.25 mV) with the Trim rotated fully
rightwards.
OVERLOAD L,E.D.
When signals high enough to make the ACCESS
SEND jack output exceed +15dB are applied to the
INPUT module, this L.E.D. will light up. Trim, or the
Mic Att pad should be adjusted until the L.E.D. remains
out when signal is present. When recording extremely
percussive transient material, it may require full negative
trim and pad to prevent this L.E.D. from flickering on
strong peaks. Changing to a less sensitive mic may help.
On the Aux B Master Module you will find a rotary
switch marked NORM/MIX. This control will alter the
sensitivity of the overload signal L.E.D.'s on the input
modules so that they can be used as a signal indicating
system or tracer. When this switch is set to “MIX” the
sensitivity of the L.£.D. driver is increased by 20dB.
The L.E.D. will now show you which modules have
signal applied to their inputs. To again check for input
overload, you must switch this control back to "NORM."
It affects all input L.E.D.'s simultaneously. F
ACCESSORY SEND — RECEIVE JACKS
The high gain provided by the use of discrete cir-
cuitry in our new mic preamplifier allows us to place a
“patch-point” in this more useful position. The level at
the send jack is-10 dB (0.3V) and the output load impe-
dance is 1.4k ohms. A limiter connected to this point in
‘the M-15 circuit can now be set to a range of compression
that will. not alter when either the equalizer (the next
stage) is adjusted or the input fader is moved (the stage
after the EQ amps). This pair of jacks is not.“normalled”
so, when no device is bridged from send to receive,
jumpers must be in place for signal to flow to the EQ
amps and on through the console, However, since all the
mixing controls lie after the “ Receive” jack, it is possible
to use “Accessory Receive” as an input, and by-pass the
the first gain stage. The only functions that will be lost
are the trim and overload indicators. The signal quality
will improve slightly but it will not be possible to switch
to “Mic In", “Line In” or “m” without re-patching. This
unorthodox patch is suggested for final remix when all
recording has been completed,-and more time for patch-
ing is available. Maxirnum level in will be +18 dB, (8 volt)
input impedance is 50 kohms.

EQUALIZATION CONTROLS
The M-15 has 6 frequency, 4 control E.0. divided
into two sections of two knobs each. On the upper sec-
tion, 1OKHz fixed, 3kHz or 5k Hz switch selectable.
On the lower section, 200 Hz or 800 Hz, switch selectable,
and 75.Hz, fixed. The fixed frequency controls will not
work unless their frequency select switch is away from
the center, or “EQ OFF” position. Either side will do
but center is “OFF” for both knobs in a section. The
chart below shows the range for each frequency, boost
and cut.
DIRECT OUT
6) (101
© soLo
AUX 1 AND AUX 2 PRE-/POST-FADER FUNCTION
Both of these Auxiliary Mixing Positions can be fed
from. more than one point in the signal path..To make
their operation clear we’ll use a section of the Biock
Diagram to show the connections. Since there is no
switch, the direction of rotation of the control will
determine which point signal will be derived from.
Counterclockwise (leftwards) rotation of either the Aux
1 or Aux 2 control will draw. signal before the input
fader. if you choose this source, moving the input fader
will not affect the level of your Aux Mix. This is useful
for making up cue mixes for musicians. Nothing is more
frustrating to a player than having the drums suddenly
disappear from the earphone mix during rehearsal. Clock-
wise (rightwards) rotation of either the Aux 1 or Aux 2
control will draw signal after the input fader. This source
is useful for echo mixes. As the input fader is closed, the
echo send will also be reduced, “fading out” will not
leave you with a “ghost” coming from your echo return.
Each control has a detent you can feel at “center”
allowing you to be sure it is completely “OFF” and
drawing no signal from either side.
PRE, PosT
Rotate CCW
(left) to increase
Rotote CW
(right) to increase
oN ON
This type of control is called a'"W” pot. Its use in
the M-15 allows us to eliminate a switch that would
otherwise be necessary to select “pre” or “post”. Both
circuits may be set to the same side safely, either pre or
post. You may have 2 postfader echo sends or 2 pre-
fader cue systems or one of each as the needs of the
moment require. Because of slight differences in func-
tion on the master control of each circuit, we suggest
that you use Aux 1 as your input cue, and Aux 2 as an
echo circuit, but this is basically a recommendation not
@ command. The reasons will become more clear when
we describe the final controls for each function. (See
“Aux A Module”, “Aux B Module” Pages 9 and 10).
INPUT FADER
Controls the signal level of all prior stages. Faders,
also called pots or attenuators always cause loss in order
to control signal level. Gain stages in an electronic device
always run “wide open” at whatever gain they are set
for, unless they have provision for "Trim" or actual gain
adjustment. In the M-15 only two of the many amplifiers
employed actually have “Trim”, the first gain stage or
Mic Pre and the Buss Summing amplifier. When you
advance any straight line fader on the M-15 you are just
reducing the loss it causes. The entire signal flows to the
next stage only if the fader is “wide open”. or up all the
way.
DIRECT OUT JACK
There is no special control for this output on the
top panel. It is “Hot” all the time, and provides an un-
mixed single signal output of whatever has been assigned
to the module. This direct ouput can be used for a variety
of purposes.

1, A subsidiary mix can be made by using an accessory
mixer fed by this output.
2. One mic, one track recording happens frequently,
and using direct out will by pass unneeded summing
networks and amplifiers. Going “Direct” to the re-
corder will result in a cleaner signal.
On the M-15 monitoring wiil be possible by switch-
ing the appropriate monitor section to “ Tape” and listen-
ing to the recorders electronics instead of a buss master,
For metering, either the recorder or an accessory meter
bridge can be used, (MB-20}
Since the amplifier that feeds this jack also feeds the
buss assign network and the post fader cue systems, it is
wise to calculate the total load carefully. The output
load impedance of this jack is 1.4k ohms. The load of the
pre-wired circuits restrict the connection of this output
to a single circuit at a time, unless the equipment you
plan on connecting here is known to have very high
values for input impedance {100 kohms or more).
SOLO
Depressing this pushbutton bypasses whatever source
you have selected on the control room monitor module
and substitutes the signal appearing at this point in the
input module. More than one module at a time may be
selected producing a “Mix” on this buss. Since this
“Mix” goes only to the monitor module, all other line
output functions remain uninterrupted and recording
will not be affected. The Solo buttons latch, push again
to release. Whenever any button is down, an L.E.D
lights on the control roorn rnodule to remind you that
the normal selection function of monitor has been by-
passed. The Solo signal is monophonic, but is distributed
equally between both monitor outputs. You will be able
to set your EQ, but echo return and stereo placement
will be disabled, ~
PAN POT AND BUSS ASSIGNMENT
Each input rodule may only feed signal to four of
the 8 buss master modules at a time. A fifth push switch
in the assignment section marked Buss In 1~ 4 on one
side and 5 ~ 8 on the other will transfer the four outputs
of the switch section from one group (Up - 1 ~ 4) to the
other (Down - 5 ~ 8)
Depressing more than one button will engage the
“Pan" control. This single knob works two faders that
are wired “back to back”. As you rotate the knob, one
fader is turned up as the other is turned down. When the
contro! is “dead center” each fader is still reducing the
signal slightly so that the signal transition through
“center” does not become louder as you “Pan” through
it. When both speakers in a stereo pair are producing
sound, you don’t need as much power to maintain a con-
stant volume. tf only one button is depressed, the pan
control has no effect on the signal. When any two
buttons are depressed, the tower number is “ Panned” to
full on-when the control is turned as far as it will go
counterclockwise, the higher is “Panned” to full on
clockwise.
The “Pan” logic for 3 or 4 button arrays is easiest to
explain with some drawings. If shaded buttons are as-
sumed to be down, the logic is:
me CT
oS
Typical examples of multichannel panning
Since the entire pan logic diagram also transfers to
buss group 5~ 8, panning signal ‘to busses in separate
groups will not be possible, As an example to .“Pan”
between Buss’1, and Buss 6, or between Busses 4 & 5.
MUTE
The mute switch is a program interrupt, and will
affect your recording. When depressed, it disconnects
the output. of the module from the Buss assign section
and the Direct Out Jack, However, the Aux 1 and 2 cir-
cuits are not affected. Cue or echo functions will not be
interrupted. If it is necessary to mute echo as well while
remixing, the “input select” switch will disconnect signal
at the beginning of the chain as long as you have a posi-
tion available that has no signal appearing on its back
panel connector.

3.2 BUSS MASTER MODULE
BUSS IN JACKS
ee tnput
r
These two R.C.A, Jacks allow you to add a signal or
group of signals to the input of the Buss Master Module
and route them on to another circuit, if necessary.
Because this connection acts in the same fashion as an
external "Y" cable, care must be taken in calculating the
true load, The output feeding the "Y” will be affected
by the total load of both connections. The Buss In input
load impedance is 10k ohms. Find the input load im-
pedance for the second connection and see Page’ 3,
impedancé matching, for the appropriate formulas.
10 Buss master
BUSS TRIM
Like the trim on the first gain stage of the 1st input
module. When the overall level on the buss becomes too
high, distortion can be induced in the summing amplifier.
Reducing the setting of the Straight Line Master will not
help. Turning this “Trim” control counterclockwise will
lower the gain and increase the headroorn of the sum-
ming amplifier, In extreme cases, it may be necessary to
reduce the level of each input fader. The maximum gain
reduction provided by the “Trim” control is approxi-
mately 20 dB. The normal position is fully clockwise.
ACC SEND/RECEIVE JACKS
Provided for signal processing of the entire Buss
Output, The Jack pair is not connected internally and a
jumper or a device must be completely connected for
signal to flow to the next stage. The output toad imped-
ance of the Send Jack is 1.4kohms. The input load
impedance of the Receive Jack is 10k ohms.
This signal path (in and out) is located behind the
Buss Master Fader. The action of a limiter or compressor
action will not be affected by moving the Buss Master
Fader, but will be affected by “Trim.” At this point in
the circuit we have a complete Buss Master Mix. All
functions of the input module will affect the signal here,
all major and minor patch points are behind us, and as
far as the recorder is concerned, the signal is ready to
record — we are done, The only problem job remaining
is: how do we hear what we are doing? This signal must
go to Our monitor circuits. So, we put an internal con-
nection here to one side of a switch:
MONITOR A SELECT and,
also to MONITOR B SELECT
BUSS MASTER FADER
This fader contro!s the overall level of signals from
the input modules and the echo receive section. When
Buss is selected, echo receive signal enters the signal path
here. Other functions of the echo assign buttons enter
the monitor at leter points in the circuit, See Page 9,
Buss Master Module.
TAPE AS SOURCE
There are two switches that seem to do the same
job, feeding signals to the monitor system, This apparent
doubling of function is provided for several reasons.
Even though the M-15 has only 8 Buss Master Modules,
it has a 16 track monitor system, Setting the monitor
select switch to the left selects “Buss Master Output” as
a signal. Re-setting to the right most position will now
select “Tape” as a monitor, and we need sixteen posi-
tions to monitor the playback of all sixteen tracks.
Because of this 16 track monitor requirement, all moni-
tor controls are doubled and there are two apparently
identical sets of controls. When used as “Buss Master”
monitor they become redundant, but the two sections
are not identical in “Tape” mode. Monitor section “A”
is connected only to Tape in A, and monitor section “B”
only to Tape in B.
BUSS AS SOURCE
tf our basic 16 track setup on Page 13 is used, you
will get a different track on each section of the monitor
or Buss Master Module (one for each), Monitor “A" tape
select will be track 1, Monitor B tape select will be track
9. Both Monitor A and B will see Buss Master 1 when
Buss Out is selected by their Monitor Select Switches.
However, this switch does not control the logic of signat
selection for the Aux 3 or 4 circuits immediately above,
it only works on the straight line fader marked “Mon
Gain” below it. We have provided each section of our
monitor with an output RCA Jack on the back that can
be regarded as an 8 x 2.stereo mix in itself. When using
the M-15 with an 8 track recorder, a great deal of flexi-
bility in monitoring becomes possible for a standard 8
track setup. See Page 13.
MONITOR PAN
The Monitor Pan affects only the monitor mix. It
will not alter the level or pan position on the Buss Master
Output when input panning is done between two busses,
but if both-selected busses are monitor panned to the
same side in your stereo monitor mix, turning the input
pan control will produce no audible result. Input panning
will, in fact, affect what you record, but you won't have
ct

any indication of what you are doing unless the” Monitor
Pans” on the two busses are set one to each side. This
fact can give you a lot of trouble, Work through this
part of the block diagram carefully, it is very complex,
and can take some time to understand thoroughly. *
AUX 3 AND AUX 4
These two potentially independent 8x1 mixing
systerns are subject to somewhat the same logic as the
monitor A and B circuits, but they are substantially dif-
ferent in their mode of operation and signal selection.
The rotation of the Pot itself will determine the source
of signal. Leftwards (counterclockwise) rotation will
select Buss Signal and Level is controlled by further left-
wards rotation. Rightwards rotation will select Tape
signal “A” on the Aux 3 group of controls and Tape
signal “B” on the Aux 4 group. Further rightwards rota-
tion will raise the level of signal. Once again, you have
8 Buss Outs, but 16 Tape Playbacks. The primary use of
these two circuits is “ Earphone Cueing” of tape playback
to musicians making overdubs. For Aux 3 and Aux 4,a
separate Mono Output without a master is provided on
the Aux A (Aux 3) and Aux B (Aux 4) Master Modules.
ECHO RECEIVE SECTION
With 4 buttons and one rotary fader, this subsystern
is essentially an independent input to whatever circuit is
selected by the switches. Each button routes the signal
to a separate point'in the chain. All push switches may
be depressed simultaneously, or used singly. The” Buss”
switch adds the signal ‘to the Buss Master before the
Fader and Accessory Receive Jacks. The Mon A and
Mon B buttons route the signal to their appropriate stereo
monitor sections prior to “Mon Gain” and the “Mon
Pan” pot. Echo, or other fine level signal will then be
affected by these monitor controls, but will not be
recorded, The Aux 1 button routes the signal to a mix-
ing network that has its rotary master fader marked
Echo Rev, Aux A on the Aux A Module. Echo or 8
other line level signals can now be added to the Aux A
Master permitting an Echo return to Cue if the Aux A
buss is used for an earphone feed.
To get the signal in to the-Echo RCV group, use the
Echo RCV jacks on the Buss Master Modules. Each jack
is provided with a foldback (or Y connection) so that a
single echo device may be used to feed several modules
at once. However, you should be aware that you have
“double loaded” the device you have connected, and
foad impedance calculations may prove necessary. *The
input impedance of a single “Echo RCV" is, without
foldback, 20kohms, The end of the foldback route will
affect the total value for input load impedance, see sec-
tion 2. for the proper formulas. The output of one device
ray not be capable of supplying enough current to feed
all 8 “Echo RCV inputs simultaneously.
*There are no amplifiers used to “buffer” or protect
your source of signal connection on any of the fold-
back connections provided on the M-15.
3.3 AUX A MASTER MODULE (CUE)
This system is intended to be used as an earphone
cue. It provides a master fader and summing point for
the Aux 1 on the Input Modules and Aux 3 & 4 on the
Buss Master Modules. Mic signals and tapé playback can
be combined to produce a mano mix. All 8 echo receive
signal positions may be added to this buss as well allow-
ing either an “Echo to Cue” function or additional Sum-
ming. The key to this sytem is the Aux Mix Control.
“AUX A MIX” CONTROL. %
Similar to a panpot, this rotary controi blends two
sources: into one signal. Leftwards rotation gradually
increases the proportion of the Aux 1 signal, rightwards
rotation increases the amount derived fron the push
switch marked “Aux 3” and “Aux 4”, When the Aux Mix
Control is in the center, both systems feed signal to the
Aux A master equally. If you consider Aux 1 to be MIC
signals and the switch selected Aux 3 and Aux 4 systems
to be used for tape playback, adjusting the balance be-
tween a singer (new mic cue) and the playback of a
partially completed recording (tape playback) can now
be accomplished by turning one balance control. More
vocal in the Cue, turn the Aux Mix to the left. More
signal from Tape, rotate to the right. On the Block
Diagram it looks like this.
AUX A
ECHO RCV
co)
AUX A
MASTER
AUX 3 AND AUX 4 PUSH SWITCHES
Both of these may be down (selected) at the same
time. If néither one is engaged, no signal will be sent to
the right side of the Aux Mix Blend Control.
ECHO RCV
This contro! is the master for all 8 Echo Receives
marked “Aux A“ on the Buss Master Echo Receive sec-
tion. One or more of the Echo Aux A selects must be
engaged and signa! brought up by the Echo Receive Pots
on the Buss Masters for signal to flow to the “Echo
RCV” for finai level adjustment to the Aux A buss.

AUX A MASTER FADER
Final level contro! of all Aux A signals.
AUX A MODULE BACK PANEL
The-simplest method of describing these connections
is to consider them in their physical sequence, frorn top
to bottom.
AUX 3 OUT
A separate output without a master for the Aux 3
8x1 group. The output load impedance is 10 kohms.
The reference level is -10dB, 0.3 voit.
AUX A OUT
Final output of the Aux A. Buss: output load im-
pedance 10 kohms, Reference level -10 dB; 0.3 volt.
LINE OUT, 1-4
Final outputs for Buss Masters 1 through 4. Output
load impedance 10kohms, Reference level on these
jacks can be internally altered by a switch inside each
module, LOW = -10 dB, 0.3 volt
HI = -2.2dB, 0.775 volt
When the M-15 is assembled, the switch is set at the
Lo position.
3.4 AUX B MASTER MODULE (ECHO)
The primary use of this subsystem is as an echo
send. It is identical to the Aux A module in ail respects
except one. It has no echo receive capability. The knob
located in the “Echo RCV” position is a switch control-
ling the input module overload indicator sensitivity, as
described on Page 9. In the “Norm” position the input
overload sensitivity is +15dB. In the “MIX” position
the L.E.D.’s wil! flash when the signal reaches the lower
level of -5dB, providing visual indication of the presence
of signal on the input module, even if the fader is all the
way down.
AUX B MIX CONTROL
Same as Aux A Mix Control, but rightwards rotation
selects Aux 2 pots instead of Aux 1. Leftwards rotation
selects Aux 3 and Aux 4 push switches as signal sources,
Again, as in Aux A, either Mic or Playback can be
favored as a signal. quickly. When no echo is needed,
this system can be used as a second earphone mix for
musicians.
AUX 3 AND 4 PUSH SWITCHES
Both may be depressed at once, If neither switch is
down, rightwards rotation of the Aux Mix Pot will mute
the system. If number Aux 2 pot on the input-side is
open {passing signal), leftwards rotation of the Aux Mix
Pot will mute the system. Always check your sources of
signal.
AUX B MASTER
This fader controls the final level at the Aux B Out-
put Jacks.
CAUTION
Since the Aux 3 and 4 circuits may also select “Buss
Out” as a signal source, a circular assignment (feedback)
is possible on this system if the Echo Receive Section is
set to pass Echo Return to the Master Buss Outputs.
Before you begin, it is wise to make sure that you have
not inadvertently formed such a loop. Careful thought
and study of the Block Diagram will show several pos-
sible causes of trouble. One switch position may be
useful, but another impossible with any really complex
patch. The many exterior connections on the M-15 back
to the Aux Systems are useful and necessary, but not
completely fail safe as regards looping. If flexibility is
desired, the risks are unavoidable. Take care!.
AUX B MODULE BACK PANEL
Quitputs from top to bottom, as in Aux A,
AUX 4 OUT
A separate output without a master. for the Aux 4,
8x 1 group. The output load impedance is 10 kohms.
Reference level is -10 dB, 0.3 volt.

AUX B OUT
Final output of the Aux B buss, output load imped-
ance is 10 kohms. Reference level is -10 dB, 0.3 volt.
LINE OUT 5-8
Final outputs for Buss Masters 5-8. Load informa-
tion and impedances are identical to Line Outs 1.& 4.
LOADING ADVICE
Since the double output jacks are connected to the
same gain stage, any device connected to one pin will
affect the output capability of the other pin. To deter-
mine the true value of loading on the mixers final stage,
the input impedance values of both devices must be con-
sidered even when only one of them is being used. For
this reason we suggest that you unplug anything con-
nected to the final stage that you are not using when
you make your most criticat mixes. The output load
impedance of this stage is 10 kohms.
It's always a good idea to use as small an amount of
electronic stages as you can, If you don’t need a circuit
for its control or function, bypass it and your sound will
improve.
3.5 CONTROL ROOM MONITOR MODULE
MON A OUTPUTS
These RCA Jacks provide a stereo output without
a master fader for the upper monitor section on the Buss
Master Modules. The output level is -10 dB, 0.3 volt
The output load impedance is 10 kohms.
"CR" MON, L AND R OUTPUTS
This pair of outputs should normally be connected
to the control room power amplifier, although other
uses are possible as well. The output load impedance
is 10kohms. The output level is -10 dB, 0.3 voit.
PUSH SWITCHES
There are seven push-to-latch, push again to release
switches on this module. Directly or indirectly, they
allow you to monitor all of the mixing positions of the
M-15. This circuit is a mixer in itself provided with an
active summing circuit. All of the push switches can be
engaged simultaneously or in any cornbination. The
circuits are stereo for Monitor B, Monitor A and the 3
Auxiliary Line In Pairs and Center Feed Mono for the
Aux A and Aux B positions.
CONTROL ROOM MASTER
This rotary contra} provides a master volume for the
“CR Mon” Stereo Output.
SOLO MASTER
This rotary control sets the volume of the Solo
circuit.
11
SOLO LED.
When one or more Solo push switches are depressed
‘on the Input Modules this L.E.D. will fight. No monitor
signal wili be heard other than “Solo” until ali Solo
switches are in the up position.
AUXILIARY LINE IN JACKS
3 stereo pairs are provided to allow the monitoring
of 2 track recorders or other subsidiary mixers without
the necessity of disrupting assisgnments or patches
elsewhere on the M-15. These Jacks also feed the push
switches on. the adjoining Studio Monitor Module. It
has no inputs on its back panel, only outputs.
3.6 STUDIO MONITOR MODULE
Basically identical to the Control! Room Module
in its function, this module-is provided primarily as a
separate master control for a set of loudspeakers in the
studio proper. It can also be used as separate mixer.
Its push switch Jack duplicates the signals found on the
Control Room Module.
STUDIO
This rotary control is the Studio Master Volume.
STUDIO MON L-R OUTPUTS
For connection to studio power amplifier, or other
necessary circuits. The output load impedance is 10k
ohms. The output level is -2.2 dB, 0.775 volt.
MON B L-R OUTPUTS
These RCA Jacks provide a stereo output without
a master fader for the Module “B” section on the Buss
Master Modules, The output level is -10 dB, 0.3 volt.
The output load impedance is 10 kohms.
3.7 TALKBACK MODULE
OSCILLATOR FREQUENCY SELECT SWITCH
A frequency test oscillator is provided for setting
up tape recorder levels and checking circuit continuity.
Since it is not internally connected, a pair of RCA Jacks
are provided on the back so oscillator signals: can be
patched in where needed.
OSCILLATOR FUNCTION SELECT SWITCH
This 3 position switch determines the status of the
test oscillator. Left appties a 40 Hz tone to the slate
button, Center is off, and Right applies the output of
the device to the rear panel Jacks.
TALKBACK MICROPHONE
A microphone: is built in to the top panel allowing
the control room personnel to communicate with the
performers. The microphone output may be set at dif-
fering levels with the 3 volume controls provided.

STUDIO
Level control to the studio monitor module.
AUX A
Level control to the Aux A Buss.
SLATE
Level control to all Buss Master Outputs. The mo-
mentary push switch group determines which circuit will
receive the final output of the talkback microphone.
HEADPHONE SELECT SWITCH
This switch determines the source of signat for both
the (1 watt) back panel headphone jack and the (100 mW)
front panel headphone jack. The left position selects the
output of the Control Room Module, the center position
is off, and the right position selects the output of the
Studio Monitor Module. The rotary contro! immediately
below the switch provides a master for both headphone
jacks.
3.8 POWER SUPPLY UNIT
The M-15 uses an independent power supply module.
Before any operation can take place the multipin con-
nector must be plugged in and power apptied. The master
A.C. Switch and all fuses will be found in this outboard
module.
METER BRIDGE CONNECTOR
The multipin connector must be plugged into the
proper receptacle on the back of the mixing console for
the meters to function.
4, STANDARD PATCHES
The standard patching setups described here are not
rigid commands. Rather, they are provided with the
hope that they will stimulate your imagination when
you have mixing needs that cannot be solved with the
Standard Setup. Line Level is Line Level, whatever the
source, and many Line Level inputs to the Model 15
offer a route toa mix that will be used for a function
other than the one that is labelled on the top panel. The
Jacks on the back are there to be used. Patching is not
a crime and may be used to improve the quality of your
12
signal by bypassing unneeded controls, or by making
additional contrat possible in unorthodox ways.
Most people tend to look for a “permanent” set of
connections when they set up 4 mixing system and it is
true that the logic of control function just on the top of
the mixer takes some time to become familiar with, but
multichannel recording has many mixing requirements.
A permanent patch will severely restrict flexibility.
Don't be afraid to re-plug. There is nothing wrong with
the concept. !f you can examine the system needs of
each mode of operation and re-patch the M-15 to suit,
you can get better results.
For this reason we suggest that you plan on access
to the back panel of the mixer. Don’t set up the system
in such a way that you “hide all that mess”. Leave your-
self room to get at afl the connectors. You will need all
the options you can get.
|f your Cue or Monitor requirements can be reduced
to one 8 signal group, extra functions can be performed
with the mix on the second 8 signal group. Does the
Singer need all 5S tracks of drums in the Cue? If not, a
separate Echo Feed to Cue may be possible.
In all patching and connecting of 2 wire single
ended circuits two Basic rules are worth remembering.
1. Keep your cable runs SHORT | —as short as possible.
Installing a patchbay behind the engineer will require
at least 20 foot runs and is not recommended. To the
left or right side will allow much shorter runs, and
wisest of all is to use our PB-64 mounted on top of
the Meter Bridge itself. This location will permit the
shortest lengths of cable run, and will improve your
sound. Incidentally, short runs cost less, also a bene-
fit. TEAC low loss cabie is available and its low
capacitance per foot and superior insulation has
been designed with systems like this in mind. It is
welt worth its extra cost. The use of 3 conductor.
professional cable such as Belden 8H51 should be
avoided, Even though it is of excellent quality, it is
not the right idea for 2 wire systems. If you are going
to make up your own cables we would suggest our
500 ft. bulk rolls or cable such as Belden 8218.
Solid core insulator, low capacity wire is what you
need. Foam filled 2 conductor is not recommended,
as the center conductor will cut through most foam
with time, the capacitance will go up, and eventually
the cable will short circuit. Don’t use it.
2. Multiple Output Connections require impedance
matching calculations, Make sure you are not asking
too much of your output stages. Permanently con-
necting several cables to a single output may produce
poor quality. If you are not using a patch, unplug it!
Convenience ray cost you quality, unless you are
sure that a multiple connection is well within safe
limits. Use the section on impedance matching in this
manuai, abide by the limitations it covers, and you
will get better results.

RECOMMENDED 8 TRACK SETUP
WITH 2 ECHO SYSTEMS
The monitor System can now be divided into 2
separate groups and a different function assigned to each.
Monitor A will perform Contrai Room functions
and Buss/Tape comparisons. Aux 3 will now allow Play-
back Cueing for Overdubs.
Monitor B will give you 4 Stereo Echo Mix that is
separately controllable at all times, and may be recorded
along with the Dry Signal if desired. (Re-ptug Echo RCV
to the buss you wish to use). For clarity, it is shown
connected only to Buss 5 and 6, with Jumpers to 3 and
4, Aux 4 will provide a Mono Echo Mix to be used in
the Earphones so musicians may hear a more musically
pleasing sound. Route the Aux 4 mix to the Aux B
Master by depressing the appropriate push switch on the
Aux B Master Module. The Aux B Master will now act
as a Master Mono Echo Send when the individual Aux 4
“w" pots are rotated rightwards to receive signal only
from the Aux 4 section. Echo will also be possible from
the input modules of the M-15 if the Aux B Mix Control
is used as described on’ Page 10. The Mono Return is
added to the Cue Buss with Echo RCV #1 Pot, Switch
“Aux A.
Since each Buss Master Line Out is double, you may
attach a 2 track to the spare jack, We show Buss § and 6
connected, since their meters are more or less centrally
located on the Meter Bridge, but any two will serve. If
you work closer to them when mixing, use 1 and 2, or 7
and 8. Suit yourself.
To stereaecho _
Connect as needed Playback from 8 track
Mono echo. Buss cue system To cue amp 8765 432
tor setup
Power
TEST TONE
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2 track 68752431)! Stereo echo return
playback To 8 track inputs for mixdown
Cantro! room To 2 track stereo
power amp mixdown recorder
BUSS iN
Mono echo return
(any input, return to cue}
a
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bout
Cea tnitline et

16 TRACK REMIX PATCH WITH
AN UNORTHODOX DOUBLE STEREO ECHO
This setup completely separates the 16 track moni-
tor section from its normal function as a Contral Room
Monitor and converts it to Stereo Echo Mixer with full
gain and pan,
Listening to the mix you are working on will now
be accomplished by using either Aux Line In #1 (Buss
Output 5 and 6) or, Aux Line In #3 (2 track playback).
The Aux A Buss is connected to a Mona Echo device
and returns Echo Signal to “Buss In #5".
The Aux B Buss is connected to a Mono Echo
device and’ return Echo Signal is connected to “Buss In
#6".
Having several Echo Chambers to work with will
allow more sophisticated image placement. Very realistic
and satisfying illusions in stereo are possible by having
signal “Dry” on the left and Echo Return from the signal
on the right. Building an imaginary “Room” or “Stage”
will now be possible, and some otherwise unmixable
tracks become easy to make clear in Stereo when Multi-
ple Echo Systems can’ be used
14
Assign AUX IN 3 for mohitoring
2 track mix, AUX IN | for buss
monitoring 8
To get stereo echo send
master, assign MON A, MON 8
TALKBACK] STUDIO
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BrDoe
ps TALKBACK
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Studio power amp
disconnected
To stereo echo
“To 2 track mixdown To mono echo left
From 2 track mixdown To mono echo right
From 16 track playbock
6 5 2 I 10
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Stereo echo return Mone echo return
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switches to “tape”
Buss Ww
OUT LINE IN
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RECOMMENDED 16 TRACK SETUP
The basic function discussed in this manual assumes.
that you will need to play back what you have recorded
many times before final mixes are made. Since it is
unlikely that you will be recording all 16 tracks at one
time, the fact that the M-15 has only 8 buss master
modules is not a serious limitation. Here we show each
buss master connected to more than one track, Tracks
1 and 9 are on the same buss, #1 and so forth up to
Buss 8 Output, connected to tracks 8 and 16. When you
are ready to mix to stereo, you will have to change your
patch to feed the 2 track, Designed for quick playbacks,
the Monitor A and B systems eliminate the need to
distrupt the Input Module settings you are working with.
Since “Line In" on the Input Module is not used for
playback of your recorder in this patch, these Jacks are
available for any other unit or units you may have. Mov-
ing to “Line In” will, of course, force you to re-set the
Input Controls if you have been using a Microphone as
an Input.
Only one Echo System is shown. Since most record-
ing is done “dry” or without Echo, one chamber should
be sufficient. When you are ready to mix down, more
Echo Systems are likely to be useful, so we suggest you
look at Patch #3. It will help you understand more
about re-mix setups.
There are 2 Stereo and 2 Mono Outputs unused on
this drawing because their systems have been committed
to Cue in Playback and Control Room Monitor. They are:
Mon A — Stereo
Mon 8 — Stereo
Aux 3 = Mono
Aux 4 — Mono
Mono echo send
Connect as needed
for setup
FEST TONE
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To control room
Power amp
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5.
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To cue amp
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To I6 track inputs
9
4
all I6 playback
3
From 16 track outputs
From echo
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(One chamber folded across 8 inputs
may not be possibile due to the
increased load of 8 circuits on
one echo output. Check your
echo specifications.)
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TALKBACK] STUDIO [CONT ROOM) AUX B
16

5. LEVEL SETTING AND OPERATION CHECK
5.1 LINE IN — ACCESS SEND
1. Apply a -10 dB (0.3V) signal to the LINE INPUT
jack on back panel of the Mode! 301 Input Module.
2. Pull out the jumper between ACCESS SEND and
RECEIVE jacks for the channel in which the above
signal is injected, and plug in an AC voltmeter to the
ACCESS SEND jack. The AC voltmeter recom-
mended here should have an input impedance of 50k
ohms or more, input capacitance less than 20 pF, and
maximum sensitivity of -60 dB with a sensitivity
selector switch.
3. Set controls on panel of the Modei 301 Input Module
as follows:
INPUT select switch: LINE
TRIM : At about -20
4. For a normal condition of the circuit, the ACCESS
SEND output should be -10 dB against a LINE IN
signal of -10 dB.
5. If the output is not -10 dB, adjust with TRIM. After
this adjustment, the TRIM knob should be between
10 and 18 dB under normal condition.
6. !f you notice any malfunction, refer to the pream-
plifier (Q1 ~ Q6) circuit schematic and check all
transistor voltages and signal levels.
7. Check all remaining Input Modules in the same way.
8. ‘Measurement of frequency response, S/N ratio,T.H.D.;
Frequency response: 20H2z ~ 20 kHz, within £1dB
S/N ratio More than 84 dB
(using a weighting network}
80dB (measured with a band-
pass filter — 20Hz ~ 20 kHz
A more than 78 dB reading on
an AC voltmeter with a better
than 100kHz range can be
said as normal.
Less than 0.03 %
{at 20 Hz ~ 20kH2)
or, :
or, +:
T.H.D.
5.3 LINE IN LINE OUT/AUX OUT
InpuT MODULE
Ne
mic IN
1. Apply 2 -10dB (0.3V) signal to the LINE IN jack.
2. Plug in an AC voltmeter to the LINE OUT 1 jack on
rear of the Model 303A AUX A Module.
5.2 LINE IN —+ DIRECT OUT
ono 1g
ovpecT out
A asaner oes a0 MoM
1. Apply a -10dB (0.3V} signal to the LINE INPUT Jack.
2. Plug in an AC voltmeter to the DIRECT OUT jack
for the channel-in which the above signal is injected.
3. Set controls on panel of the INPUT MODULE as
follows:
INPUT select switch: LINE
TRIM : To about ~20
EQUALIZER Set to center the 3kHz and
200 H/800 Hz switches. Under
this condition, response will
be flat regardless to setting of
the 10k Hz and .75Hz control
knobs,
INPUT FADER — : “O” scale
4, The circuit isin normal condition if the DIRECT OUT
level is -10 dB against the LINE IN level of -10 aB.
5. If it is slightly off -10dB, adjust by the TRIM knob.
For a normal condition circuit, the TRIM knob posi-
tion should be between 10 and 15 dB.
6. If you cannot obtain the proper reading, check the
circuit,
If the above Item 5.1 check shows normal but the
DIRECT OUT level is incorrect, trouble could be in
the INPUT FADER, and IC's U1 and U4, The gain of
U1-7 and U4-7 is 1, and that of U4-1 is 10dB.
The attenuation of the INPUT FADER set at infinity
should be:
More than 85dB at 30 Hz
More than 75dB at. 1k Hz
More than 58 dB at 10 k Hz
® LINE OUT (0)
@' sux OUT
3. Set the level selector switch (S1~ S4) on the PCB of
the AUX A Moduie to-LO. This selector switch is
located as shown in Page 10.
7