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Making the Mixer
For about $20 (if you have
the tools), you can build the above passive mixer for four-or-less
that will work quite well to combine the CD players
signals. A passive mixer just uses resistors to isolate
from each other so they don't cause an impedance mismatch being
all connected together.
An impedance mismatch distorts the sound quality,
changes the frequency response, and usually
affects your volume
level. Passive mixers, like the one described above and below, will
drop the audio
gain just a tad (about 3db), but do not usually distort
the audio. You can make up for the audio drop by
turning your amplifier
or receiver up about 1 notch.
IMPORTANT: You should NOT use a "Y-cable"
because of the player's solid state output. Players not
will clamp their output to ground and cause an impedance mismatch
and drop in volume level as
described above. This effects players
that ARE playing.
We have several links to audio music equipment
supply companies on our web site that sell four, six,
stereo mixers that take up one-or-two rack spaces (19"W x 1.75"H
-or- 19"W x 3.5"H).
These are brands such as Ashly, Rane,
Symetrix, Fostex, and Samson, and run from $210 to $500,
on the features and quality. This is the ideal route, but if you're
on a budget, read on.
The following text-based schematic is for
a four-channel passive mixer. We at Wintek SC, and many of
our other customers have built and tested the passive mixer
below. It works quite well, with no bad side effects.
You can build it with more or less channels if
you wish, but if you need to combine more than four
strongly suggest an active mixer, due to the greater signal loss.
The parts you need for this four-channel passive
mixer are available from Radio Shack, Frys Electronics,
Jameco, Mouser, or other electronic parts stores.
1 - 25-watt soldering pencil (Radio Shack Cat# 64-2070, $6.99)
1 - Roll rosin core solder .5 oz (Radio Shack Cat# 64-001, $1.19)
1 - Nibbling tool (Radio Shack Cat# 64-823, $10.99)
OR optionally (if you feel uneasy with a soldering
iron) you can use:
1 - Solder tape strips (Radio Shack Cat#64-010, $1.59). You wrap
tape around the connection and heat with a match to solder it.
8 - 4.7k ohm 1/4 watt resistors (Radio Shack Cat# 271-1330, 2@$0.98)
(The resistors come 5 to a pack, so you only need two packs)
1 - 4" x 2" x 1" project box (Radio Shack Cat# 270-1802,
1 - Octal Phono Jack Board (Radio Shack Cat# 274-370, $2.19)
1 - 6 foot Stereo Patch cable (Radio Shack Cat# 42-2351, $3.99)
OR optionally you can use:
1 package - Panel Mount RCA phono jacks (Radio Shack Cat # 274-346,
4 in a pack @ $2.59)
Input 1 Left o-----resistor----+
Input 2 Left o-----resistor----|
Input 3 Left o-----resistor----+-------------o Left Output to Amp
Input 4 Left o-----resistor----+ (Left Stereo Patch cable)
Inputs 1-4 Grounds o-------------------------o
Input 1 Right o----resistor----+
Input 2 Right o----resistor----|
Input 3 Right o----resistor----+-------------o Right Output to Amp
Input 4 Right o----resistor----+ (Right Stereo Patch cable)
Each input for each channel must go through a 4.7k
resistor to the output cable to be combined with all
the other inputs
from other players.
Mount the octal jack board onto a project box.
This is done by cutting out a square big enough for RCA
strip to protrude through. This can be done with a drimmel or notch
Cut the plugs off one end of a standard audio patch
cable, strip back the end, and feed it through a hole
in the project
Solder a resistor to the center tab of the four
input jacks as shown above. Then connect the other side of
all four resistors to left output cable. Do the same for the
other four jacks for the right output.
Buss all the grounds of all those jacks to the
shield on the output cable.
It should end up looking like this complete with case. (Pardon the
| CD AUDIO INPUTS |
| 1 2 3 4 |
| +----------------------+ |
| L | O O O O | |-----> Left output to amp CD input
| R | O O O O | |-----> Right output to amp CD input
| +----------------------+ |
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