207d
instruction Manual
Aphex Systems Ltd. Model 207D
Page 24
207d
2-ch tube mic preamp with adc
Page 25
Aphex Systems Ltd. Model 207D
lines as low impedance and unbalanced lines as high
impedance. The fact is, however, that both balanced
and unbalanced lines are operated at low imped-
ance in modern practice owing to the fact that all
output stages have become low impedance. A few
exceptions might be outputs from passive mixers,
instrument pickups, electric guitars and some key-
board synthesizers. It is generally ideal to drive any
audio line from a low impedance and receive into a
high impedance. Generally, a minimum 1: 10 ratio is
possible. This is called “bridging”. This has become
modern practice and all balanced inputs are normally
running 10K ohms or higher impedance. Because of
these developments, it is now no longer as critical to
consider impedance when dealing with interfacing
pro line level equipment (impedance “matching” is
mostly a requirement of the past).
A word on impedance and interfacing adapters:
If you are connecting between two line level devices
and they have different connectors (example: 1/4”
phone to XLR or vice-versa), you do not need to use
an impedance matching transformer. With very few
exceptions you are strictly dealing with a difference
in connector types and should only use hard-wired
adapters (or cables) for this situation.
APPENDIX D: Standard Cable Wiring
In relation to 1/4” phone jacks, you may see the terms
“TS” and “TRS” as abbreviations. Here is a what that
Appendices
TABLE 1 - BALANCED & UNBALANCED CONNECTOR WIRING STANDARDS
3-Pin XLR
1/4” TRS Phone
Standard Wiring Convention (Balanced)
Pin-1
Sleeve
Ground/Shield (Earth, Screen)
Pin-2
Tip
Positive (Signal, High, Hot)
Pin-3
Ring
Negative (Signal Reference, Return, Low, Common)
1/4” TS Phone
RCA
Standard Wiring Convention (Unbalanced)
Tip
Center Pin
Positive (Signal)
Sleeve
Shell
Ground/Shield (Signal Reference/Return)
means: TS refers to the Tip-Sleeve or “mono” 2-
conductor type and TRS refers to Tip-Ring-Sleeve or
“stereo” 3 conductor type 1/4” phone connectors.
This applies to jacks (female connectors) and plugs
(male connectors).
Note: We recommend using only conventional
1/4” phone plugs with the Model 207D and with
all other audio equipment. Professional patch bay
cords using brass PJ055 telephone type plugs are
designed only for patch bays and will not make
proper contact with standard 1/4” phone jacks.
The following instructions show all the different ways
you will probably ever need to hook up your 207D as
well as any other equipment you may own. You will
see that connecting balanced outputs to balanced
inputs is ultimately simple and the same cable will
work for all flavors of output stages.
Connecting a balanced output to an unbalanced
input requires a little more knowledge and care.
You should refer to your equipment manuals and
determine the type of balanced output stage that is
provided, then use the correct “transition cable” as
depicted in this section. Improper transition cables
can cause crosstalk, hum, and distortion problems
within your system.
TYPES OF BALANCED OUTPUTS
Believe it or not, there are at least 5 types of balanced
output stages in use today. They may be placed
into two main classes: transformer balanced, and
R