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M-35

Tascam M-35 Operation And Maintenance Instruction Manual

TASCAM
TEAC
Audio
Mixer
Production Products
OPERATION /MAINTENANCE
While this arrangernent of controls rnight help the beginner to understand the flow of signal in the
it
rnodule,
StiII, the wiring sequence rnust be understood
ate.
would be very inconvenient to oper- diagrarns, rnother-board layouts and rnechanical
can be used successfully. So along with the docu­rnentation you
disassernbly inforarntion), we include
will need for service (schernatic
asirnplified
before the more cornplex functions of the M-35P electrical sequence chart called a block diagrarn.
This drawing shows al1 the controls, switches, arnplifying stages and connectors in their
proper order. Learning to read it will provide theanswers to any questions about what cornes where on the
inside. Even though the block diagrarn
is
cate what flexibility,
available in the way of extra circuit
it
can't explain why a connection or
can indi-
switch has been included, or suggest a standard
layout. In the following sections of this rnanual,
we will do our best to describe the
individua1 functions and controls of the M-35, and how they can be arranged in more than one sequence; but, your rnixing needs rnay be best served by an
ar-
rangernent of inputs and sub-systern connections
you work out for yourself. To begin,
we'll start with some basic inforrnation about sound and the nurnbering systerns used to describe
levels in and out of the equiprnent and
impedance-what the terrn rneans and how to dea1 with the details when you rnust connect frorn our gear to other equiprnent. Many aspects will be discussed in the rnost basic language we can use. There
is
a vast arnount of inforrnation available to the beginning sound rnixer but rnuch of it
is
not basic enough to be easily understood,
or
it
assurnes that the reader has an engineering or scientific background and wil "the rnath". Practical
"rules of thurnb" for the
l
be interested in
novice are not generally available. Sornething be-7'
9
-
16
Direct
@
from
subrnaster "Ta~e
ml
15
inn*
17
-
P
solo
14
tween a picture of the outside of the unit and a complete rnathernatical
inside
is
needed. You don't have to build a mixer
frorn scratch, you
analysis of the circuits
just need to know how to
operate one.
However, some nurnbers are unavoidable. The M-35 rnixer does nothing connected to
quite a lot of sophisticated gear.
Mics, tape recorders, power amps, and
useful without being
loud­speakers al1 play a part in the process of rnixingl recording and each piece of gear has its own re­quirernents and problerns. We have tried to rnake this rnanual
as sirnple as technology will allow.
Each section or topic will give you some basic
instruction in the terrninology used in the
pro­cess of rnixing as well as a list of what plug goes into which
jack. Whenever possible, the scientific terrns have been related to understandable cornrnon references.
Understanding what isgoing on inside your
equip­rnent will help you irnprove your sound. Think of this rnanual need al1 of what
is
not necessary to rnernorize find tirne to way you will be farniliar with
as a reference book. You won't
is
here to begin, and it certainly
it,
but do try to
read
it
carefully at least once. That
its
contents. If you
need the nurnbers, they will be there waiting.
Good luck with your sound.
'THE
DB;
WHO, WHAT, WHY
No matter what happens to the signal while
it
being processed,
again by
a
human ear. So the process of convert-
will eventually be heard once
it
is
ing a sound to an electrical quantity and back to sound again must follow the logic of human hear­ing.
The first group of scientists and engineers to dea1 with the problems of understanding how the ear works were telephone company researchers, and the results of their investigations form the
foun­dation of al1 the measurement systems we use in audio today. The folks at Bell Laboratories get the credit for finding out how we power, how quiet a sound an average person
hear, and almost
al1
of the many other details about sound you must know before with it
successfully.
judge sound
can
you can work
From this basic research, Bell Labs developed a system of units that of the system. Sound traveling on wires as
could be applied to al1 phases
elec­trical energy, sound on tape as magnetic energy, sound in air; anyplace that sound stored as energy until some future will again be sound,
can be described by using
the human ear-related system of numbers
is,
or has been
time when it
called "bels" in honor of Alexander Graham Bell, the inventor of the telephone.
is
What
a bel and what does it stand for?
it
is
loud? No,
only 6dB more sound. The unit quantities must follow nonlinear progressions to satisfy the ears' demand.
Remember, decibels follow the ears.
All other quantities of measure must be increased in what­ever units necessary to satisfy the human
require-
ments, and may not be easy to visualize. Sound
is
in air, our beginning reference, the human ear to
4000Hz. Bell Labs measured this value to be
(young men) can detect
the least sound
at
1000
.O002 microbar, so we say OdB = .O002 microbars and work our way perceivable sound to humans" point. Here chart of sounds and their ratings in
up from the bottom, or "no
is
dB, using
a
.O002 microbar pressure change in air as our re­ference
for "OdB".
10,000
pnare druni
t140
1
22
nch
mic inride drum
l
inch
I
bass
drum
powr?Ilc voice
at
1
inch
Ircream)
It means, very simply, twice ear. Twice
The bel
as
loud as what? An obviousquestion.
is
always a comparison between two things. No matter what system of units of ure you are working with always state a value as a reference before you compare another value to
-
it
dynes, webers
doesn't matter, a bel, or ear-
related statement of "twice as loud"
as
loud to the human
at
the time, you must
it
by using bels, volts,
is
always a
meas-
can
ratio, not an absolute number. Unless a zero, or "no
difference" point
is
placed somewhere, no
comparison is possible. There are many positive and definite statements
of reference in use today. But before we go over them, we should divide the "bel" into smaller units. "Twice used
al1 the time. How about one tenth of a bel?
Okay, the decibel
ente,
same as the reference".
"nothing". Now, if you double the power,
twice
as
you double an electrical voltage,
as
loud" will be a little crude to be
loud? No,
it
is,
and O means "no differ-
It
seldom means
it
is
only 3dB more sound. If
is
it
is
that
twice as
10
-1
rquare
newtoiir
newton
rneter
per
per
100
1
square
dvner
dyne
per
100
per
cm. l niicrobar
I
microbar
.O1
microbar
-001
microbar
100'
--
-
...
Home in citv, cantinuour background
:
1
- - - - - -
noire*(carr,
-
"
Homen citv at night
t"
Isoiared recording
Open
icricketr.
rubwavr. rtreet
field, night,
nrect
Auerage
or
no
noirer,
converratlun
TV
studio
wind
etc.)
nolre)
We should also make a point of mentioning that the maximum number on this chart represents
"peak power" and not average power. The
rea­son? Consider if even some monetary part of your recording is distorted, it will cording and
it
is
wisest to be prepared for the
force a re-re-
highest values and pressure even if they only happen "once in
a
while". On this point, statistics are not going to be useful, the average sound pressure selves
"statistics" close to the
is
not the whole story. 'rhe words them-
can be used
as
an example. Say the word
mic while watching the meters and the peak LED level detector. Then say the word "average". What you are see are two good examples of the problems
likely to
en­countered in the "real world" of recording. 'rhe strong peaks in the
"s"
and
"t"
sounds will pro­bably cause the LED's to flash long before the VU meter reads anywhere near "zero" while the vowel sounds that make up the word "average" will cause no such drastic action.
To
allow peaks to pass undistorted through chain of audio parts, the individua1 gain stages must
al1
have a large reserve capability. If the av­erage speech, but extremely percussive sounds may qui re
results. Woodblocks, castanets,
is X than
as
much
X
+
20dB is usually safe for
as
90dB of "reserve" to insure good
latin percussion
re-
(guido, afuche) are good examples of this short
term
violence that will show a large difference between "LED flash" and actual meter movement. When you are dealing with this kind of sound,
it
believe the LED,
is telling you the truth.
Since the reference is assumed to be the lowest possible audible value, positive, and correctly written should sign in front of the number. But omitted. Negative energy value
as
to be of interest to a scientist try-
dB spl is almost always
have
a
+
it
is
frequently
dB spl would indicate so low an
ing to record one cricket at 1,000 yds. distance, and
is
of no significance to the multichannel
is
recordist. Far more to the point "What is
a
microbar?" It
is a unit of measure-
the question
ment related to atmospheric pressure and al­though it down
is
extremely small, it must be divided
quite a lot before
it
will indicate the mini­mum pressure change in air that we consider minimum audible sound. This will give you better idea of the sensitivity of the human ear.
One microbar of pressure change is
slightly less than one millionth of an atmosphere, and you can find it on our chart as 74 dB spl. It is not terribly loud, but As
a
matter of fact, power of conversational speech level is
also used by the phone company to define
it
is certainly not hard to hear.
it
represents the average
at
6
feet. This
norma1 earpiece volume on a standard telephone.
Now think about that minimum audible threshold
again:
.O002 microbar.
That's two ten thousandths of one atmosphere
!
This breakdown of one reference just to amaze you, or even to the quantity of power that moderate sound represent. Rather it is intended to
a
millionth part of
is
not given
provide a feel for
levels of
explain the reason we are saddled with a ratiollogarithm measurement system for audio. Adding and sub­tracting multi-digit numbers might be easy in
a
this age of pocket calculators, but in the 1920's
its
when the phone company began sound and the human ear,
a
more easily handled
research into
system of numbers became an absolute necessity.
Conveniente
for the scientist and practical en-
gineer, however, has left us with a system that
a
requires
great dea1 of complex explanation be­fore you can read and correctly interpret a "spec sheet" for almost any
piece of gear.
Here are the formulae for unit increment, but they are necessary only for designers. And unless you build your own gear, you won't
have to dea1 with them. For power (watts) increase or loss, calculate by the following equation:
10
LOG,,
For voltage, current or pressure calculations:
LOG,,
20
a
v2 v1
=
N
(dB)
One whole atmosphere, 14.70 pounds per square inch, equals 1.01325 bars. So one whole
atmos-
phere in microbars comes out to be 1,013,250.
Once we have this chart, we can see the differ-
ente
between the way humans perceive sound and the amount of pressure. Unfortunately, the "twice
as
divisions on
is
This is how the ear works, and we must adapt our system to it. We
loudspeaker to produce the tivity to sound of the human ear produces strong "energy" illusion that has confused listen­ers since early times. How powerful are the loud­est sounds of music in used such sound the answer so regrettably, consider what would happen one pound of pressure was applied not to your head, but directly to your inner ear. One pound of air pressure variation mount of "power" might do some useful work but not much, make use of it you will away or you will go deaf immediately.
If we reduce our sound power to realistic musical values, we will not be injured, but we will almost nothing (in real power terms) to run the mic with! This low available energy is the reason that high gain amplifiers are required for p hones.
When we take
sound, we do much energy we must the electrical part of our system. that we don't
as
much pressure" of sound to be heard
"twice
a
as
loud". If you plot decibels
a
very funny curve.
dB = 20
5 10
original sound we begin with. The high sensi-
as
a
source of energy to do useful work,
as
operating a car? For any normally "loud"
force it takes to change air
result is nota simple
as
the even
graph, the unit increase you need
VOLTAGE,
OF
PRESSURE
iog,,
-
increase
have no choice if we expect our
is,
it's
a
microphone and "pick up" the
have some leeway in deciding how
have to truly hear the signal while
CURRENT
v1
E
15
20 25 30
RIS~
in
a
sound that resembles
real power? Can sound be
regrettably, no! Perhaps not
is
170dB spl ! This
still only one pound and to
have to stand one mile
have in order to operate
/
wav
even
1 dB
Unit
If wecan decide
if
a-
-
have
micro-
a
we are processing can wait until the electronic devices have done al1 their routing and switching before we need audible sound, we can lower the power of the signal. What Well, we need to have enough energy so that the signal
is
not obscured by hiss, hum, buzz or other unpleasant things we don't want, but not so high that
it
costs a fortune in "juice" or electrical power. This was phone company.
They now system, and even when they started out, ity was not free. They set their electrical power signal reference time, and tronic equipment has gotten better. In 1939 the telephone company, radio broadcasting, and cording industry got together and standardized 1 milliwatt of power standard of related industries. Thus, nal at a 600ohm line impedance will present
voltage of 0.775 volts.
Once again, we owe you an explanation. Why does Why 600 of them and not some other value? What's a volt? Let's look
1. The logic of ZERO on the meter is another hangover from the telephone company tice. nia, the significant information to a telephone company technician in Boston is signal level drop? meter says ZERO company) that there has been no loss in the transmission, and level is one milli-watt of power, but the gain or loss is in the information the meter was posed to display, so the logic of ZERO made good sense, and that's what they put on the
dial. We still use it even though cal ence level described matter what actual power so firmly set in the minds of everyone in the audio world that change.
2.
One ohm of electrical energy. The exact reasons for the choice of 600 ohms nected to the demands of the circuits used
have the world's biggest audio mixing
it
it
say ZERO on the meter? What isan ohm?
When you start a phone call in Califor-
for anything else, and the idea of a refer-
it from point to point and we
is a good value for a reference here?
a
big consideration for the tele-
electric-
as
low
as
was practical
has lowered over the years
as
OdBm, and this is still the
at
one thing at a time.
If so, how much? When the
it
indicates (to the phone
al1
is
well. The reference
as
a
"no loss" ZERO, no
is
being measured
it
is
probably never going to
is
a
unit of resistance to the passage
as
a
standard are con-
at
as
a
OdBm sig-
-
did the
it's
not logi-
the
elec-
re-
prac-
sup-
is
L
a
''
. .
for long distance transmission and are not simple or easy to explain. Suffice that the worst
possible thing you can do to
it
to say
piece of electronic equipment is to lower the resistance
it
is expected to work into (the
load). The lower the number of ohms, the
a
harder it is to design you think about
"load", the truth
stable circuit. When
is
just the
opposite of what you might expect! O ohms
a
"short circuit", no resistance to the pas-
is sage of signal. If this condition occurs before your
signal gets from California to Boston, you won't be "get there",
able to talk- the circuit didn't
it
"shorted out". Once again, tele-
phone company logic has entered the language
on a permanent basis. Unless the value for
is
ohms
infinity (no contact, no possible energy flow) you will be better off with a higher value, and many working electronic devices
have input numbers in the millions or billions
of ohms.
3. A
volt is a unit of electrical pressure, and by itself is not enough to describe the electrical power available. To give you an analogy
-
that may help, you can think of water in a
hose. The pressure is not the amount of water,
and fast the
Increase
ance, or
less
flow will depend upon the size of
hose (impedance or resistance)
as
well.
the size of the pipe (lower the resist-
Z)
and pressure (volts) will drop un-
you make more water (current) available to keep up the demand. This analogy works fairly well for DC current and voltage, but alternating current asks you to imagine the water running in and out of the whatever frequency your "circuit"
at,
and
is
harder to use a menta1 aid. Water
has never been known to
at
10,000 cycles per second.
flow out of a pipe
nozzle
is
working
at
This reference level for a starting point has been used by radio,
in audio because the
television, and many other groups
telephone company was the
largest buyer for audio equipment. Most of the
companies that
built the gear started out working for the phone company and new audio indus­trie~,
as
use
they came along, found
as
much of the ready-to-hand stuff
it
economica1 to
as
they could, even though they were not routing signals from one end of the world to the other.
a
choice for quality audio. Not so. A 600 ohm, 3-wire
a
necessity for the telephone company, but the primary reason audio
quality. It is noise, hum and buzz rejec-
transformer-isolated circuit
it
is
used has nothing to do with
is
tion in really long line operation (hundreds and hundreds of
Quality circuitry. In fact, when
miles).
audio does not demand 600 ohm, 3-wire
shielding and isolation are not the major consideration, there are big ad­vantages in using the 2-wire system that go well
beyond cost reduction. It is, herently capable
than 3-wire
of much better performance
transformer-isolated circuits.
Since TASCAIVI M-35 mixer a
signal from a mic to a recorder, we think that
is
a
the 2-wire system tionally
accepted standard (IEC) for electronics
wise choice. The interna-
as
a
system, in-
is
designed to route
of this kind uses a voltage reference without speci­fying the exact load
reference
is
this:
This is now the preferred reference for
it
O = l
is
expected to drive. The
volt
al1
elec­tronic work except for the telephone company and some parts of the radio and ness.
Long distance electronic transmission still
is
in need of the 600-ohm standard.
television busi-
If your test gear has provision for inserting a 600
load, be cure the load is not used when
ohm working on TASCAM equipment.
Now that we have given a reference for our "0" point, we can print the funny curve again, with numbers on it, and you
can read voltages to go
along with the changes in dB.
,"
20
log,,+
curve
Must we use this
telephone standard for record­ing? Its use in audio has been so widespread that many
people tiave assumed that
it
was the only
All electronic parts, including cables and non­powered devices (mics, passive mixers and such), have impedance, measurable in ohms (symbol
is
or Z). Impedance presents to the flow of signal, and to understand some things about this value when
the total opposition a part
it's
important
OUTPUTS
S2
-
plug into
you are making connections in your mixing sys­tem. The outputs of circuits rating and so do inputs. What's good? What
values are best? signal flow, and in theory,
-
It depends on the direction of
INPUTS
have an impedance
it
looks like this:
It
is
generally said that the output imped-
ance
(Z) should be ohms, 10 ohms. The lower, the better, in theory. A circuit with ance will offer a low resistance to the passage of signal, and thus will be able to supply many multiple connections without in performance or a voltage drop in any part
of the total signal pathway. Low impedance values
ing transistors and integrated circuits, but
other considerations are
practice, such as:
1. The practical power supply
2.
can be achieved economically by us-
nitely large. At some point, even if the circuit ergy you will run out of "juice".
Long before this happens, you may burn
out other parts of the circuit. The output
impedance may be close to the cally ideal "ohms" but many parts in the
practical circuit are not. Passing energy through a resistance generates heat and too much current will
right off the circuit card taken to prevent catastrophic failure.
is
capable of supplying more en-
as
low as possible. 100 a
low output imped-
still a problem in
is
not infi-
theoreti-
literally burn parts
if steps are not
a
loss
Inputs should have very high impedance
as
high
as
nurnbers,
1
million ohms, more, if
A high resistance to the flow of signal at first sounds bad, but you are not going to build the gear. input will work properly and has no for a large amount of signal, you can assume that he means what he says. For you, a high input impedance isan unalloyed virtue.
It means that the circuit will do
a
minimurn of electrical energy as a begin­ning. The most "economical" electronic de­vices in use today have input impedances of many ample, voltrneters of good quality must not
draw signal away from what they are
uring, or they will disturb the proper opera­tion of the circuit. A design engineer needs to
destroying
device to measure with.
millions of ohms, test gear for ex-
see
what is going on in hisdesign without
it,
possible (1 00,000 ohms
it
can be arranged).
If the designer
so he must have an "efficient"
tells
its
job with
you his
need
meas-
3.
Even if the circuit does not destroy itself, too high a demand for current may ously affect the quality of the audio. Dis­tortion will rise, frequency response will suffer, and you will get poor results.
The classic rneasurement for output impedance
load a circuit until the voltage drops 6dB
is to (to half the load value is. In theory, you now have a load im­pedance
ance.
If you reduce the load graudally, the dB
reading will return slowly to
How rnuch drop left when an acceptable drop
ter!
original power) and note what the
that is the same
is
acceptable? What load will be
as
the output imped-
its
original value.
is
read on the me-
seri-
When the seven times the output impedance, the
still a little more than 1 dB lower than the origi­nal reading.
Most technicians say "1 dB, not bad, that's ac­ceptable". We at TEAC must say wedo not agree. We think that a seven-to-one ratio of input to output (1) is not a high enough ratio, and here's why:
load value (input Z)
is
approxirnately
needle is
(7)
1. The measurement range frequency and does not show true loss
at
the frequency extremes. What about drop
at
20
Hz?
2. All outputs are not measured Most people don't have twenty meters, we do.
Remember, everybody
you record and the circuit demands, in
are simultaneous. All draw power
tice, same time.
Because of the widely misunderstood rule of thumb you the
Even though the true output impedance may be
low, say 100 ohms, for the practical reasons ex­plained previously, we feel that the 7:1 ratio not sufficient. To use this rule of thumb, you must use "output model M-35:
ACCESS
-
the seven-to-one ratio - we will give
values for outputs in a complete form.
a
load impedance". For example, in our
SEhID
LINE OUT
higher value. We'll call this value the
is
usually made
at
plays together when
1.4k
ohms X 7 = 10k ohms
1.4k ohms X 7 = 10k ohms
at
a
mid-
the same time.
prac-
at
the
is
level, a loss of headroom, low frequency response,
or
else
suffer from a bad recording. If one input
10,000 ohms, another of the same 10,000 ohms will give you a total input impedance (load) of 5,000 ohms. To avoid
following when you have two inputs to con-
the
nect to one output.
Take the lowervalue of the two input impedances and divide
7 times the output impedance, you can con-
still
nect both not using the true output impedance, we are ing the adjusted number in group impedance.
When you just dividing the ber of inputs will not be accurate unless they are
al1
the same
(higher than 7 : 1 ratio) by this method, you can
connect without worry.
If you must have exact values, here are the for-
mulae:
it
in half. If the number you have is
at
the same time. Remember, we are
have more than two loads (inputs),
lowest impedance by the num-
size.
For more than 2
calculations you can do
l,
output load
But if you still get a safe load
:
is
us-
is
a
This the 7:1 method. To go one step further, here are the actual minimum ohmic wise. Connect to TOTAL INPUT
LOAD
ACCESS
LINE OUT
Our specifications usually show 10,000 ohms
a
"Nominal Load Impedance" and you can that we arrived dividing 10,000 by 7. Any number higher than
10,000
Input impedance requires only one number. are'the
MIC IN
I-INE IN ACCESS RECEIVE 220k ohms BUSS IN
If one output puts, the total impedance of the two inputsmust not above, and if it becomes necessary to number of inputs with load specifications, you must check for a drop in
number that will give good results with
values we feel are
IIVIPEDAIVCE
higher than:
SEhID 10k ohms
10k ohms etc.
as
see
at
the first column above by
is
less load.
is
more straight forward and
Load
is
load, and here
values for the M-35:
600 ohms 50k ohms
12k ohms
is
to be
"Y"
connected to two in-
exceed the load impedance, mentioned
increase the
slight exceeding of the
RX=-j 1 1 1
-+-+-+
R1 R2 R3 Rn
=
RX
For 2 loads or inputs
Finding Impedance Values on Other Brands of
Equipment
When you are reading an output impedance spec-
ification, you will occasionally
statement:
Minimum
Maximum
'rhese 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
lower than X ohms. That's the lowest IVUM-
any BER. The second statement changes the logic, but says the exact same thing.
Value of Total Load
load impedance = X ohms
or
load impedance = X ohms
....
see
this kind of
+--
Maximum load impedance refers to the idea of the
LOAD instead of the number, and says: please don't make the do you lower for ohms. Maximum ohms, so
When the you already culation. And the number given in ohms does not
have to be multiplied. You can MATCH the value
of your input to this number of ohms ly;
load).
Occasionally, a manufacturer will want to show you that right idea and will give the output impedance and the correct output impedance
will give the recommended lowest
pedance.
7
times and will be whatever the specific circu it
in question requires.
increase the load? Make the number read carefully.
minimum/maximum statement is made,
can safely assume that the manufacturer has
done the "seven times
but
as
always, higher ohms will be okay (less
7
times the output
load this way. They will call the
It
may be a higher or lower ratio than
LOAD any heavier. How
load means minimum
is
best" ratio cal-
successful-
Z
is
not quite the
the true impedance and then
LOAD im-
REFERENCE LEVELS
We should talk about one more reference, a prac-
tical
one.
a
Anyone who hasever watched
around wh ile recording knows that
is not a fixed value of energy. and can range from "no reading" to "good grief" in less you the numbers for gain, headroom and in the M -35, we must use a steady signal that will not jump around. We use and start it out put, our beginning reference level. All levelsafter
the rnic input will be higher than this, showing that they will come to the
line-out and the reference signal there will be
-
louder than 94dB spl, or your rnic will produce
more electricity from
-60dB, al1 these numbers will be changed. We
have set this reference for rnic level fairly low. If
you examine the sound power or sound pressure
musical instruments are louder on the average than 94dB spl, and most commercial mics will
produce more electricity than the sound pressure of 94dB, so you should have no
problems getting up of "OVU" on your recorder.
time than
have been amplified, and eventually we
10dB, our "line level" reference.
From this
level
(Spl) chart on page 6 you will see that most
it
takes to blink. In order to give
at
a level of -60dB
last
output of the M-35 - the
you can see that if your sound is
a
sound of 94dB spl than
VU meter bounce
"real sound"
It varies with time
a
tone of 1000 cycles
at
the rnic in-
-
60dB for
noise
a
If you are going to record very loud sounds you
may produce more electrical power from the rnic than the M-35 you estimate this in advance? Well, the spl chart and the rnic sensitivity are to-one basis. If 94dB spl gives - 60dB (1 mV) out,
104dB spl will give you -50dB out, and so forth.
Use the number, on our chart for sound power together with your rnic sensitivity ratings to find out how much level, then check that against the
maximum input the M-35. or line level, there
it into the You will work
!
Most rnic manufacturers give the output of their
mics as don't give the loudness of the test sound in
it's
a
stated
can handle
levels for the various jacks on
If your rnic
is
nothing wrong with plugging
line level connections on the mixer.
need an adaptor, but after that it will
minus-so-many-dB number, but they
as a pressure reference (usually 10 mi-
as
an input. How can
tied together on a one-
is
in fact producing - 10dB
dB,
crobars of pressure). This reference can be found
'
on our sound chart. It
10
dynes per cm2 or 1 Newton per square meter.
For mics, the reference
is
the sound the rnic
94dB spl, the electrical output of
is
given
is
94dB spl, 10 microbars, "0"
is 1 volt (dB). So, if
as
-60dB, meaning so many dB
less than the reference 0=1 volt. In practice, you will see up to about
levels of -60dB for low level dynamics,
-40dB
or slightly higher for the better grade of condenser mics available today. TASCAM recorders and mixers work
-10dB referenced to 1 volt (0.3 volt) so, for
of 94dB spl, will
a
rnic with a reference output of - 60dB
need 50dB of amplification from your M-35 or recorder in order to see "OVU" your meter. Now, if the sound you want to re-
is
cord
/
the rnic will be more powerful and you will need
louder than 94dB spl, the output from
less amplification from your IVI-35 to make the needles on your recorder
read "OVU".
at
(-
l
OdB) on
a
level
segments.
1. As laid out for
2. As wired, but knobs and jacks
convenience.
as
they appear
on the outside.
3. The block diagram, with the controls bered
to correspond to numbers on the first
num-
two drawings.
Even with this "translation system" to help, mul­tiple sources and outputs so when necessary; we will types of drawings to help get the point of
can complicate things,
also include other
a
sub-
system across when we first encounter a source
a
"point" that will be used in may
require re-reading if you are not familiar with subsystems, but we think you
as
early
as
possible.
specific way. This
it
best to advise
THE
BLOCK
DIAGRAM AND GAIN
DI AG RAM
'
Before you begin reading the next section of this manual, flip out the extra fold on page 42. On this page, we
have printed the block diagram. It shows the signal flow through the M-35 and represents in simple form, the actual electron
al1
arrangement of stages from
mic-in to line-out.
the jacks, controls and gain
The diagram on page 43 indicates the gain of
"
reference signal, the noise level, and the available
at
reserve gain or headroom
any point in the signal chain. An experienced audio engineer would be able to operate the M -35 successfully
a
with just these two diagrams and
list
and output specifications.
Any question about function or gain swered by studying the drawings. Will the acces­sory send signal change in level if the input fader
is
moved? No, the signal
is
shown leaving the main line before the input fader. You read both diqgrams from left to right, input to output.
BLOCK
it
a
of input
can be an-
When printed in
its
entirety, a block diagram can look formidable, and tracing a signal path easy, so to aid you in your initial understanding,
/
we'll continue to use our 3 drawing system first shown in the introduction, but in slightly smaller
d
is
not
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