JK Audio RemoteMix C+ - Manual (Page 6)

6
Power
RemoteMix C+ is powered by two 9 volt alkaline batteries
located under the cover on the bottom of the unit. Under
normal use, you should get at least 30 hours of continuous
use from a fresh set of alkaline batteries. To test the
batteries, simply press the Battery Test button on the front of
the unit. If the LED lights, the batteries are still good. The unit
may still function if the LED does not light, but there may be
significant audio distortion and a loss of level as the batteries
continue to discharge. It is important to replace both batteries
at the same time with identical batteries. If two fresh batteries
are not available, it is better to use only one good battery.
Since the two battery fixtures are wired in parallel it does not
matter which one gets the single battery.
We also provide a high quality, regulated AC to DC adapter
to power RemoteMix C+ when AC power is available. Simply
plug it into the back of RemoteMix C+ and plug the
transformer into a 110 VAC wall outlet. When the power
connector is inserted into the jack, the batteries are
bypassed. The AC adapter does not charge the batteries.
Operation
Null Adjust (optional)
The RemoteMix C+ can be adjusted to control the amount of
transmit audio that appears on the receive audio jacks. The
recessed fine tuning control is adjusted by inserting a
screwdriver into the back of the unit just below the words Null
Adj. and turning left or right. This is a ten-turn potentiometer.
The null circuit matches the characteristics of RemoteMix C+
with the characteristics of the telephone line. Although much
of the transmit audio can be removed, this is not the
equivalent of a mix-minus output.
The amount of transmit/receive isolation will depend on the
quality of the telephone line. This circuit is factory set to give
an equal mix on an average telephone line, and is therefore
perfect for recording both sides of a telephone interview.
7
To find the absolute null for any telephone line, follow this
procedure:
1. Place a call to a quiet location.
2. Send a signal down the line at moderate levels. This can
be prerecorded music or speech, or a test signal.
3. Connect the From Phone line output to a meter or scope,
or listen to the receive signal over the headphones. Be
sure to turn up the Line Out or Headphones volume
control depending on which method you are using to
monitor the receive signal.
4. On the back of RemoteMix C+, below the words Null Adj.,
there is a hole for a small flat blade screwdriver. This is a
10-turn potentiometer to allow for very sensitive
adjustments. Try to remember the position of the blade,
and the number of turns you are making as you first
adjust clockwise, and then back to the original position,
and then counterclockwise.
The goal is to adjust the null signal until the receive signal
contains a minimum amount of transmit audio. If, on the
other hand, you want a good mix of transmit and receive
signals, you must have someone on the far end speak or
send audio down the line as you adjust for the proper
balance.
5. Factory Setting: To reset to the factory setting, set the
phone line switch to On-Hook, and adjust to find the null.
We have installed a terminating resistor in the On-Hook
position that simulates the average phone line connection
and gives the right mix of transmit and receive audio.
The best tools for this task are 1) an oscilloscope connected
to the From Phone Line output, and 2) a 1 kHz sine wave
generator connected to the To Phone Line input jack.
However, the above procedure will work with a little patience.
Null Adjust (optional)