Avionics failure yesterday...

Well, I haven't posted here in quite awhile. I'm an IFR-rated PP with
about 400 hours currently. Lately flying about 8 hours a month on
average.

Had an interesting experience yesterday: a "hard" avionics failure
complete with something popping/blowing/burning. Flying a very nice,
new (2000) rented 172SP, there was a pop, the audio panel went dead,
and then an acrid odor in the cabin.

After the couple seconds of stark surprise I flipped the avionics
master off. When it appeared there was no real smoke and the smell
disappated I tried cycling the master. Nothing bad, but no audio panel
(completely dead) and thus no radios.

I had just traversed a class C area and was still on with approach when
losing the stack. I also happened to be damned near over an
uncontrolled field (a generally busy one though approach had called out
no traffic and none was visible in the pattern 1000' or so below me).
I decided that I should really land there and pulled the throttle out.
#1, home field is controlled and I had no radios. #2, since something
had definitely 'burned' under that panel, I wanted the airplane on the
ground.

Of course I couldn't get the WX there with no radios. Airport has a
4/22 and 14/32. Local winds were generally N-NW. After a slow 180 to
lose alt I was more or less lined up with 4 and decided that would
work. However, on short final I noted that I was crabbing a good 30d
and was high as well, though I could have lost the remaining alt with a
slip and full flaps easily enough. However, since though I was now
NORDO it was not an emergency situation, I decided to do a climing 270
turn into 32, which I did, and was on the ground pretty quickly, all
the while looking around everywhere for traffic (none).

Taxied to the FBO and grabbed a car back to home airport (45 minute
drive - was on local sightseeing flight with a coworker and
girlfriend).

Overall, in retrospect, I was largely happy with my performance as I
didn't panic or anything of that sort (inexcusable) and got the
aircraft on the ground pretty quickly. However, I should have done at
least one thing differently: I should have either left the avionics
master off or, if leaving it on as I did once determining there was no
danger, I should have squawked 7600. I never changed my squawk. I
elected to leave the panel on mainly to give ATC the benefit of my
return, being right on the border of their airspace, and didn't change
the squawk because I didn't really think of it. Priority was landing
and getting out of the airplane.

Oh, I'd also verified the extinguisher on board and had it at the
ready.

Haven't heard back from the owner yet (local FBO) but I'd imagine a
resistor or cap in the audio panel itself went. No breaker had popped
(the audio panel doesn't have its own breaker).

Lessons learned:

1) ALWAYS have handheld with me. I own one - I'd left it in my own
152, which is what I usually fly. Nothing but laziness in not taking
it with me. (What could go wrong on a short, local flight, after
all?!)

2) Take a bit of time to think about a squawk in any lost-comm
situation. Really, it would have taken 5s to change the squawk and I
had plenty of time.

Would welcome any comments on the experience.