Saturday, February 5, 2011

3- Electrical wiring

Here's the boards before the modification. Note the wires 2 and 4 (marked W2, W4 as silkscreened on the PCB): they're signal ch.1 & 2 and will be cut. W1 and W3 are signal grounds. The red circle is the capacitor to be displaced.





The modified boards. The two INSERT jacks are added and the cap desoldered and placed horizontally:





The detail of the 1/4 jack wiring. This is known as a TRS "tip send ring return" configuration, the standard for most recent mixers for unbalanced mono effect insert point. Dashed line is cut wire W2 above:



There's a 120Ω resistor on the send tip as described in this Mackie mixer schematic I don't know if it's mandatory... Eh I'm a physicist not an engineer!  Thanks to Mike Rivers on Mackie Forums, it's called a build-out resistor and prevents oscillations when cable capacitance is added to signal path.



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2 comments:

  1. nanoOctober 2, 2011 at 11:04 PM

    Could you of placed the jacks in the middle of the sides of the unit instead of the back without having to displace that one cap? Or is there no room there

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  2. Raymond LutzNovember 1, 2011 at 6:41 PM

    @nano yes, there is some room there but the assembly/disassembly would be problematic... see http://insertsfor402.blogspot.com/2011/02/2-lets-get-physical.html : the back of the mixer case is a U shaped metal plate and the jacks would be fixed the side-walls of this U, the problem is that the PCB boards are fixed to the top and are lying _at the bottom_ of the case so you couldn`t remove the back U shaped panel with the jacks fixed onto it without ripping through the board... sorry for my approximate english (and late reply)

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