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My wiring scheme for the O2 in a B3-080 Desktop case with RCA's and 1/4 inch jack

Posted 5th July 2012 at 04:23 AM by MrSlim
Updated 5th July 2012 at 04:26 AM by MrSlim (fixed typo)

When I was planning the wiring scheme for the Baby Desktop O2, originally, I thought I would use 3 and 4 pin board mounted posts with equivalent pin connectors so all the flying wires could be disconnected from the board. I realized that would be too much work(and probably even more prone to disconnection so I only made one of the connections removable (the 3 pin P1 jack for the RCA inputs, beside the input J2 connector).
(note to add part #s for the pins and connectors I used)

Make sure you grind off the anodized coating around the holes on the inside of the panel before you mount the RCAs to get a good ground connection.

I used individual pairs of wire from solid core Cat5 cable for all the connections, and in my wiring description, I'll be using the wire colours from the cable I used. (it helped since I built 16 of them.. )

For P1 (for RCA input) I used Brown/white for Right and Blue/white for Left. The square pad(close to the the board edge is Left, middle is ground and the inside pin is Right. I connected both ground wires first to the middle pin on the connector and covered them with heatshrink, as it will be very close to or touching the switch beside it when it is mated to the pins. Solder the left and right wires to the connector and then twist them up and solder them to the RCA connectors.. I only used about 2-3 inches for them.
By putting the RCAs on a connector, everything else including the 1/4 jacks and the volume control can be slid in from the front of the case, and then the board can be pulled out the back to make the final connection to the RCAs.

Also,remember that you need to cut the jumpers under the input connector J2 so that it doesn't short out the input when the jack is not in use.

I made the wires for the 1/4 jack and the volume control about 5 inches long.

The 1/4 Jack connects to P2. The three connections to the jack are Tip(left, I believe, google can confirm), Ring (right) and Sleeve(Ground). The Square pad (closest to the board edge) is Ground, and so is the hole next to it, followed by Tip and Ring. The wire colours I used were Green for Tip(and its partner white/green for ground) and Orange for Ring (with white/orange for ground).
The 1/4 jacks have a very small T R and S beside their appropriate connections. Solder both Ground(white wires ) to S , and the colour mentioned above for Tip and Ring. When installing the wires to P2 on the board, I do Green and white on the middle two first, and then Orange and white on the outer two..

The volume control was the trickiest.. First make sure you remove the cast mounting stud, since it prevents the pot from being mounted flush(you probably already knew that).

Holding the pot upside down (pins up) with the shaft towards you draw yourself a little diagram of the 6 pins. Label the two rows (left to right) Front (closest to the shaft) and Back. Label the pins left to right as Left, Middle and Right.

For the volume control, I used 4 pairs of wires, with the input 2 pairs having ground connected at both ends and the 2 output pairs connected only at the board, and cut back and out of the way at the volume control end(but twisted up with its partner for 95% of the length..

Here's my colour scheme:

Front row:
Left : Brown (with its white-brown ground unterminated at the Pot end)
Middle: Blue (with its white-blue ground connected to Right)

Back row:
Left: Orange (with its white-orange ground unterminated at the Pot end)
Middle: Green( with its white-green ground connected to Right)

I used heatshrink on the middle pins only, and made sure the others were kept separated, when forming the wires when installing the front panel(with the 1/4 and volume control pre-mounted).

If you bought the 15mm shaft volume control, it mounts on the two rows of holes closest to the edge of the board,(so the wires for it would go there). Conversely, if you have the 20MM version, use the back two rows.. (if you straddle them, you end up with Right and Left flipped..)..

The Front wires above connect to the first row closest to the edge of the board, and the Back row connects to the next row. Blue connects to the first row,middle pin and Green connects to the second row, middle pin. Solder them first but don't solder their respective ground wires yet(just have the ground wire for each inserted in the Left hole in each row). (the cat5 wires are small enough that you can insert both ground wires for each row in the left hole, after you have soldered the other 4 rows.

Finally connect Green to first row Right and Orange to second row Right. Insert their ground wires in the respective left holes in each row (there should be 2 wires in each left hole.)..

When you are building the desktop boards, make sure you leave LED D7 about 1/8 to 3/16" high off the board and twist it sideways so it doesn't stick out past the edge of the board (since there is no led hole in the Back(formerly the front) faceplate for the B3.

Somewhere on the O2 Thread(or the Front Panel Group buy) I specified a panel mount LED(need part # here also), and included the proper size mounting hole in the B3 front panel. I can send you a couple of those also if you are planning on using my panel design unchanged. It has pre-installed leads, so you only need to add a 1k resistor inline with the red wire (I soldered it to pin 8 (confirm that this is +12V) on U3 and attach the black wire to ground (I used one of the extra Left holes in one of the unused rows where the volume control mounts.
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  1. Old Comment

    nwavguy said the LED he choosen is a specific one... can we replace it with yours with no issues?

    do you have the part #?

    Posted 5th July 2012 at 04:57 PM by jtktam jtktam is offline
  2. Old Comment
    I didn't replace the original. It is still in the circuit, because it is important to the design. I turned the original sideways so it fit behind the panel. I added This Panel Mount LED in addition just to have a power indicator on the front panel. It's just installed across ground and +12v with a 1K resistor inline with the 12V. (soldered to pin 8 of one of the OpAmps and one of the spare ground pins where the volume control is mounted)
    Posted 6th July 2012 at 02:25 AM by MrSlim MrSlim is offline
    Updated 6th July 2012 at 02:35 AM by MrSlim

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