Mr. Lee,
Thanks! The key turned out to be the Allen head cap screw at the wide end of
the "cone" - I unscrewed that and the whole assembly came apart. I must admit
it was a challenge lining up all the pieces for reassembly; I assume that in
"production" this stage occurred before the side rails and printed circuit
assembly were added.
You had asked for details of my modifications; here's the first installment.
The first page shows the regulator I added to my own microphone; the second
details the changes to the one that's currently under the knife. My goal is to
avoid cutting the foil at the cathode of the LED; I'll let you know how it
works out. I'll try to send a picture of the regulator installed; the
Surf-Board I use requires some surgery to fit into the available space. Pardon
the hand-scrawled schematics!
BTW, it turned out the resistor was fine; a solder joint had given way due to
the resistor leads being inserted an insufficient distance. Reminds one of
working on old British sports cars! ("Why do the British drink warm beer?")
Cordially,
Rudy Chalupa
Pleiades Audio + Electronics
-----Original Message-----
From: Richard Lee <rica...@justnet.com.au>
To: 'Surround Sound discussion group' <sursound@music.vt.edu>
Sent: Tue, Mar 29, 2016 8:04 pm
Subject: Re: [Sursound] Soundfield MK IV Disassembly
> I have a question for the keepers of ancient wisdom: how does one remove
the capsule assembly from a Soundfield MK IV microphone? I have one on
which the 1 kilohm "capsule heater" resistor has gone open circuit. The
cone on the MK V and newer is split and comes apart pretty readily, but the
MK IV cone is solid and it's not apparent how to reach the resistor.
Rudy, It's more than 30 yrs since I took a Mk4 capsule assembly apart so
bear with me I'm pontificating from the wrong orifice.
1 Unsolder the leads from capsule to PCB.
Can't remember if you can reach this from inside as the connections may
be
in the cone section.
If so (!!#*??), you'll have to disassemble the capsule assembly, remove
at
least 2 capsules on their tetrahedron sections and unsolder from the tags
behind the capsule.
Keep the capsules in their little holder to provide some measure of
protection but this is still a brain surgery type operation.
2 The tetrahedron stalk is screwed to a brass block on the PCB. The 1k
resistor is sandwiched to the block/stalk in some way which I've long
forgotten. IIRC, there was another small PCB whose sole purpose was to
clamp the resistor.
3 Removing the tetrahedron allows the cone to come off.
I you have the set of dwgs which were supplied with early Mk4s, there
should be one that makes this clearer (or not).
My apologies for this Heath Robinson design from my mispent youth.
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