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My efforts in using SE-SE rework boards will be blogged because it has become a distraction from the build thread and is likely to remain the 'path less followed'. Had Owen not encouraged the first of the variants I might have given up on it.
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Posted 11th January 2012 at 11:16 PM by Wolfsin
Updated 12th January 2012 at 11:13 PM by Wolfsin (rename second variant)

When asked where frankenwires were to be filed, qusp replied

Originally Posted by qusp View Post
file it under mutants...

...and their amplifiers
There are two variants of what I originally called the SE-BRGD frankenwire. Both start as rework boards. One gets a pair of LME49860 to replace the LME49990 using the simple surgery below. The + and - inputs to the second 49860 are reversed and resistors adjusted so the gain is equal on both sides. The effect of that reversal is to invert the signal on the second leg so it becomes a mono amp, whose differential outputs are ready to bridge one can.

The second variant, more correctly referred to as the BAL-BALM, requires no rework surgery (so could just as well not even be a rework pcb), just the addition of a tiny adapter to mount an opa1632 and leave off the 49990s. Power connection is not as clean as the first variant. It is effectively half a BAL-BAL, perfect for the audiophile with only one ear.

Originally Posted by Wolfsin View Post
Simple surgery

The attached image shows the pin-out for the 49860 and the underside of a rework SE-SE pcb. Note that the solder mask has been removed from the trace from C24 to U9 and that trace severed and routed to a different pad between C30 and U11. I believe that is the extent of the pcb surgery required. Before and after -- that simple.

To install the 49860, Pins 2 and 7 should be lifted and the others soldered to their matching pad. A blue wire from the pad under 7 to pin 5, and from pin 7 to the pad under pin 2 is all that is left.

Power consumption for a pair is equal to BAL-BAL. A pair of either makes a lower profile bridged mono headamp. For portable applications that might be a bene. A small DC-DC step down supply powers my Roland Edirol (a real 'AA' eater) and is roughly the same shape and thickness. In most other cases the BAL-BAL is likely the better choice.
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