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.