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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?
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