Back to Main 1176 Page
15 October 2004
modified 9 January 2005
revised 31 January 2006
Wiring the 1176LN Clone
Keeping the Hum to a Minimum
There's a feeling of satisfaction you get when you finish stuffing a board as if your
project is nearly complete. Ignore that feeling - there's still a lot to do!
Before you get started
there's something I would
advise you do preferably
before stuffing in the
transistors and ICs.
up the power supply first
and test it.
The power
supply sits in the upper
right-hand corner of the
Gyraf/mnats board.
Build
It shouldn't matter too
much if you've put in
some of the other
components, unless
something is drastically wrong with your power supply. But try to stick with
building up the power supply first. The only semiconductor you should have
installed is the 24V voltage regulator - the 7824.
The components you need to have in place are as follows:
R85
R86
R87
R89
C23
C24
C25
C26
VR1
CR6
CR7
CR8
CR9
CR10
The components are clearly legended on my boards with the component
identifications above. If you are using a Gyraf Rev 7 board, you'll need to refer to
the schematic to identify the parts you need and correspond them to the
component values on the board.
Add a 90� 3 way pin to the three
transformer inputs labelled 24 - 0 - 24 as
pictured on the right. Wire a 3 way header to
your AC power transformer secondary. The
middle wire goes to the transformer center tap
and the other two go to either outside pin.
Which of the other secondary leads goes to
which pin is unimportant. Just make sure all
three leads are connected. I'm sorry that I
cannot give specific details about wire colors
etc as each transformer uses a different color code. Look
most perfect explanation of wiring a typical power transformer
Factory). Example 3 of the linked .gif file is the configuration that applies to the
1176. Plug the 3 way header into the 3 way pins and power up the transformer
primary from your wall socket. Be sure you have wired a fuse to the primary in
case there is a problem!
here for Mark Burnley's
(hosted by DIY
With the negative lead of your multimeter
connected to a ground point
underneath the output transformer on my
mnats board is a convenient spot)
(the square pad
and your
multimeter set to DC and 50 or more volts,
touch the positive probe to the point indicated
on the image on the right. You can click on the
image to see a larger version. You should read
approximately negative 10 volts at this point. If
so, go to the head of the class.
Keeping the negative probe on the ground,
move the positive probe to the point indicated
in the next image. Though it is the 'bottom'
lead of the 7824, for some reason this point is
labelled "2" on the UREI schematic. You should
have +30 volts at this point. If so, proceed
with stuffing the board with the remainder of
the components. You can be fairly certain that
your board won't blow up unless you stuff
things the wrong way around or have shorts
elsewhere. Double check the voltages on the IC sockets before plugging in the
chips.
Wiring the 1176 clone is fairly straightforward and the schematic actually contains
most of the information you need. Deciphering that information can be
troublesome though. I'll try to provide images to match the relevant and important
parts of wiring your 1176 in order to minimize hum.
Central to the idea of eliminating hum from your clone (or any electronic
equipment you design, build or repair) is the idea of eradicating ground loops.
Ground loops occur when two or more paths are allowed to the electrical ground
(also called neutral or earth). When wiring the 1176 you'll want to make sure only
one end of your hookup wire is attached to ground. Hopefully this concept will
become clearer as we go on.
Shielded cable is suggested to wire certain parts of your 1176. Both one and two
conductor shielded cable can be used - each has a specific place where it would be
more suitable but a two conductor can be used in place of single conductor cable.
If you only have one conductor cable you'll need two lengths to do the job of a
two conductor cable. Note that even though the convention is to call it "two
conductor" cable the shield, in fact, conducts too meaning there are actually three
conductors!
For my examples I've used
Canare L-2B2AT
, a good multipurpose hook-up wire.
The images will link to larger versions to provide a closer view of the action. Note
that I have used no less than three main boards and both the Revision F and
Revision G in the images where deemed appropriate. As a side note, please forgive
the quality of the images - I shot them with my Sony DCR PC100 "Megapixel"
Digital Video camera, clearly not the best for still images but very quick and dirty.
Starting at the input jack, use a two conductor
shielded cable and twist and solder the shield
wire to another short piece of hookup wire.
This will become the one and only point at
which the electrical ground of the main circuit
board connects to the chassis of your unit.
Connect the pair of wires to terminal 1 of the
XLR jack.
Connect the opposite end of the hookup wire
to one of the mounting screws of the jack. You may want to use a crimp "eye"
here or solder lug as I did for a mechanically reliable electrical connection.
Terminal 3 is soldered to the white wire and terminal 2 to the orange wire.
You'll need to wire the input jack to the main board in either of two places,
depending on which option you have chosen. If you have decided to build the
electronically balanced version, which uses IC2, use option A. If you are using
either an OEP or Lundahl
input
transformer, use option B.
Input Wiring Option A (electronically balanced input)
When using the opamp balanced input circuit,
the other end of the input cable is connected
to the main board at the BAL INPUT pads
located near the output transformer. Pay
attention to the polarity! In my example, I've
used three way pins and headers to attach the
cable to the board end. I did this primarily
because the headers easily and effectively
isolate the three wires from each other even
though they are only 0.1" apart. You can solder
the wires directly to the board as well but you need to make sure the insulation
runs flush to the board to avoid any shorts between them.
Now strip a piece of two conductor sheilded
cable and solder it to the input pot (input gain
on the Gyraf layout) pads. The schematic
shows that shielded cable is used here and that
it is connected to the ground at one end and to
the potentiometer at the other. Note where the
shield goes. The wiper (middle lug on the
potentiometer) conductor is the middle pad
which I arbitrarily designated to the orange
wire.
Already we can see that there isn't another practical reason to use pins and
headers like in the previous example. The pads here are 0.2" apart so you would
need a different connector if you were to make them all removable. Also, since
they are 0.2" apart they aren't nearly as prone to shorts as the 0.1" separation of
the pads in the input connector.
The opposite end of this cable goes to the
input potentiometer. Be sure to wire the shield
to the correct terminal. The orange wire goes
to the middle (wiper) lug and the last wire
goes to the lug opposite the shield. I used
small pieces of clear heat shrink tubing to
prevent accidental shorts and for a cleaner
look. You should try to find pots with eye lugs
rather than the PC mount ones I used. Ideally,
the wires should be mechanically secure before they are soldered. It is bad
practise to rely on solder to secure the wires to the terminals. Wrapping the wire
around the PC pins would have been a good idea here...however, this isn't
intended to be a soldering tutorial.
Input Wiring Option B (transformer balanced input)
If you are using the transformer balanced input
(either Lundahl or OEP), you will need to
connect your input jack to the OPTIONAL IN
pads located near the input transformer. Pay
close attention to polarity, which is marked on
the board. Convention states that pin 2 of the
XLR jack is "hot", or positive and that pin 3 is
negative. The shield connects to the pad
marked 0 on the board.
Using a single-conductor shielded cable, solder
the inner conductor to the clockwise lug of the
input potentiometer. Try to expose as little of
the inner conductor as possible.
Strip back enough outer insulation so that you
can reach over to the opposite lug (where the
shield will eventually connect). Cover the shield
wire with shrink tubing to prevent shorts.
Strip back the outer insulation on the other end
of the wire and cut back the shield so that only
the inner conductor is exposed. Put some
shrink tubing over the place where you
stripped back the outer insulation so that there
is no possibility of the shield touching anything
on this end.
Attach the inner conductor to Pad *1 located
right near C19 and R*1.
Solder another single-conductor shielded cable
to the wiper of the input pot. Use a similar
technique to the first wire, exposing as little of
the inner conductor as possible within reason.
Now solder both of the shield wires together
on the counter-clockwise lug of the input
potentiometer.
Finally, solder the remaining wires from the
input pot to the main board as shown.
Remember that Pad 1 at this location is kept
unconnected for the transformer version as
you used Pad *1 instead to connect to the
clockwise lug of the input pot.
From here, you can go on to continue wiring my pushbutton version or go to a
draft version of my rotary switch version wiring page:
Go to the pushbutton wiring page >
Go to the rotary switch wiring page >
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