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John Weaver was good enough to send me an advanced copy of their suggested circuit for installing the 2K2 sound system in the K-27 that will be running DC track power.

All the modifications are done to the removable plug-in board and consists of using the 5 volt output from their board to power the chuff optical sensor circuit and the lights.

The smoke unit must not be used in this configuation as it would draw too much current from their battery.

Quoting from John's email

"The loco we had did not sound good without chuff averaging turned on. We
will begin shipping sound for this loco with that turned on. Also note
that with the 2K2 sound board, the chuff trigger needs to be inverted or
you will loose chuffing at high speed.  The trigger pulses are very short.
 We are putting together an installation guide for the K27 which will
include the info I sent to you.  What you have is a very rough version and
we do not consider it representative of our normal documentation.  That
said, we probably won't get our document ready in time to help those like
you who are struggeling to understand the wiring. You can release it if
you like.    If you do please credit that Stan Ames shared with us the use of
the transistor in the chuff circuit to interface with our trigger input.
(I don't know if he came up with the idea, but he did document it and pass
it along). It only applies to DC with Phoenix sound.  Other solutions are
needed for DCC or Remote control. We do not know yet how the extra load on
our battery combined with the normal operating voltage of the loco with
affect how well our battery stays charged.  I think we will be OK on this
as the loco is fairly well geared down.  It is kind of cool that the
lights stay on while the loco is at idle.

Happy modeling,
John Weaver"

Here's the schematic I received. I can't figure how to show a PDF inline, so here's a link

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