Sennheiser 421 question

[geoff]

Sennheiser 421-U (older, longer-body version).

Replacing the body - yes, I sourced a brand new body ! have the service
manual, such as it is.

Polarity issue - the wiring from capsule to the rotary-switch/XLR
module shows R going to an outside 'land' on the PCB wafer, ground being
the opposite side, and B going to the middle.

However pin 2 from on the XLR goes to the middle land that the capsule
Bl should go to, and vice versa. Colours of those wires internal to the
module also seem reversed.

Is this a deliberate polarity reversal, or has somebody been inside the
XLR module and swapped the R and B wires inadvertently ?

If the apparent polarity reversal is an error, can I just swap the more
accessible wiring around , ie is the switch circuitry symmetrical ?

Yes, I could check it out with a scope and a puff, but not convenient
just now ....

Grateful any knowledgable advice.

geoff

[Scott Dorsey]

geoff > wrote:
>Sennheiser 421-U (older, longer-body version).
>
>Polarity issue - the wiring from capsule to the rotary-switch/XLR
>module shows R going to an outside 'land' on the PCB wafer, ground being
>the opposite side, and B going to the middle.
>
>However pin 2 from on the XLR goes to the middle land that the capsule
>Bl should go to, and vice versa. Colours of those wires internal to the
>module also seem reversed.
>
>Is this a deliberate polarity reversal, or has somebody been inside the
>XLR module and swapped the R and B wires inadvertently ?

Remember that as shipped from the factory, the 421U and 421L were wired
pin 3 hot for positive diaphragm displacement. So a lot of people over
the years went in and swapped leads in order to make them conform to the
more common standard.

Which of course becomes wonderful when you have a mix of modified and
unmodified 421s on the same job.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."