am..Brew

•
Special atte ntion has been given to the ground
bus. The signal line grounds are run together
to the upper right comer o f the board (as
viewed from the component side-see Figure
connect the outputs
of an HF rig , 2 meter
rig, and a phone
patch . to the inputs
of the mixer. You
can then use an output
to connect a tape
recorder. You can
adjust the inputs for
proper level s. and
record any ofthe input
sources without
constantly changing
patch cords and adjusting
levels. You
can use another outeo
" ••
•, • ............. , ,".1
•
- ""~
0
. ~
-ec
••
"
Figure 4. Gain/frequency graph of low-pass
filter. The cia-offfrequency is defined as 3 dB
betow the nominal. The nominal gain here is
12 dB. so rhe cut-off is 9 dB. which occurs
around 6 kHz..
1"' RIG
I 12" A I,.
11:m
I. .....
I
. 1 1,.Pf
I
.~ " .
~H ~~o 1""1
I
I
,,,
I ,
I
• I
AuDIO
" " ER
I
I
::9,H.
" OI.II< T[ O
_ u£.
FIgure 5. Suggested hook-up for the Four
In/Fi ve Out mixer. You can monitorboth rigs
f rom Ih~ same remote speaker.
6). The power grounds from the op amps
are run together and terminate at the same
corner. There are two connections at this
point. One is for the power ground which is
ru n with the +VDC wire. The second is for
the connection [0 the enclosure. This should
be the only connection to the chassis, thereby
eliminating ground loops within the audio
circuits.
What Can You Do ",Uh It?
Applications are not limited to repeaters. In
the shack. multiple sources are often combined.
You can replace the board-mounted
trimpots with panel moun! pots, for easy adjustment.
If the wire lengths exceed a couple
of inches, be sure to use shielded wire. If you
are driving the mixer from a speaker output.
provide a suitable load for the source. Let me
know ifyou come up with any unusual applications
.
One example is to
P,"
R1-R10
Rll
VR1-VR8
Cl-C4
CS,Cl1
C6-Cl0
U1-US
D1
D2
Parts and Price List
Description
Total parts price listed above: $8.91
put with a small audio amp for a remote
speaker . This allows you 10 monitor both rigs
on one speaker (see Figure 5).
Construction of the Mixer
The mixer, built from readily available
pans, is designed for case of servicing. You
can obtain pans mail order or from Radio
Shack. Construction isn ' t critical; perf board
is fine.
(like to keep the inputs on one side of the
board , and the outputs on the other (see Figure
6 ). This makes troubleshooting much easier.
If space is at a premium, you can make
the mixer smaller by using miniature components.
The primed circuit board for this project,
with sche matic and compo nent layout, is
available for S15. including shipping. I hope
this project will solve some of your audio
problems. DI
10k 5% 0.2SW
1.2k 5% 0 .2SW
lOOk vertical trimpot
4 .7~F2SVDC
0.01 ~ F SOV DC
47~F 2 5V DC
MC14S8 duai 01' amp
0 .200~ LED
1N4003 1 Amp diode
Jameco
(except as noted)
$0.06 ea.
O.06ea.
0.59. (Radio ShaCk)
0.12 ea.
0.06 ea.
0 .15ea.
0.39 ea.
0.12ea.
0.11 ea.
INPUT
tt
# 10
tt
0 IZSlVR '
o@~ 10K b- 0-1 ro« f-<
8 ~ V RS ~
@o1 W ' f-- --I '0' f-
# 20 o C2 ,
0'
..., 10 K f-< (;) 0-1 A2K f--
., ro« H 02 f-o 0
VR6~
c2l0°
U4
0
0 ,•
a
IS71 VR2 (00 ~---O_2
'
+ VOC} TO POWER
NO SU PPLY
I
0 GROUND TO CHASSIS
AT THIS POINT ONLY
~
0 #'
# 3 0
O@oj
VSlVR' e
10K ~ .,
[3 (- Cll -) I
0
VR7 ~
8
0
"'0
'0' f-o •
8'
us
' 0 0 ·3
#4 0
GJ 9+
VRSk]
C4 oj
0
0(8
'0' l- -1 '0' f-
IV IVR4
@ =+G
• 0 0#4
0
'-----" OUTPUT .5
40 73 Amateur Radio • J uly. 1989
Figure 6. Mixer component layout.