RCA KN-1a anone know about this microphone? dynamic/ribbon?

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ToobieSnack

Well-known member
Joined
Mar 3, 2005
Messages
493
hey does anyone know anything about these mics

they are strange looking
looking down from the top it looks like a tear drop....
or a fat airplane wing...

the screen looks like a remington shaver screen...
it has an tube enclosure that hides the XLR connection
and keeps it attached securely.

at the top of the tube is a simi-circular track
that allows back/forward adjustment of the mic

inside the mic looks like a dynamic from the front BUT!...
it has two tiny wires going into the CENTER ENDS of an OVAL shaped diaphragm!!!!
after removing the trafo/element mount i could see the back of this element....

WOW! it has a magnetic return circuit
consisting of about 1" strap metal arched across the back
then there is this gap that looks suspiciously like:
a RIBBON GAP!!! :shock:

it's almost as if the ribbon is glued to the back of this paper diaphragm!!! :shock:

also there are 2 tiny magnets glued in place...
there is some sort of yellow foam looking stuff covering the area where the ribbon would be... I can't see in there..
I am afraid to disturb it...
I can fix the mic with a single solder to the trafo wire that was snapped...

do these mics sound any good?
I could DEFINITELY convert this into a nice ribbon mic...

I'll try to post or fing some pics on the web

later
ts
 
here is a pic

rca_kn1a.jpg


later
ts
 
yeah i just did this trafo solder and she works wonderfully!! :grin:
Now I have one more mic... :grin:

the windings from the trafo to the element ar the size of house wire .....practically..

it does not have the heavy bass a ribbon would have but
it is very clear and VERY strong output...
would be good for female or background vocals...
OR maybe the guitar at the neck for the highs...
I hope so ....that is what i need... :grin:

later
ts

PS maybe I'll post some inside pics ...... ahhhh who knows ???
 
[quote author="ToobieSnack"]hey does anyone know anything about these mics
[/quote]
Moving conductor.
It is mic designet to overcome problems with ribbon,
what was: gaps between ribbon and pole pieces,
ribbon contact
etc.
It is lower class than ribbon, that mean, it is not studio
mic with tight frequency tolerances, but for vocal can
be hardly enough.

You can not remake it to velocity ribbon. It is pressure mic,
controled via silk piece inside (resistance).

You can it repair, but need historic info about it, parameters, drawings, manuals, etc, somebody can help you.

xvlk
 
thanks for the info xvlk...

the repair was easy just one broken trafo wire

inside it is in good condition.. :grin:

this mic "label" indicates ...250 ohms output impedance....
will impedance matching improve low frequencies?

thanks
ts
 
250ohms is about right for modern mic pre amps. Most modern mic premaps works ok with mics ranging from 30ohms to as high as 500 or 600ohms.
 
hey thanks for your interest

the RCA 74b are super incredible and awesome

i have one and if you go to the following link you will see my work on the TCA 74b :wink: this is an clone of the RCA 74b.....

http://www.groupdiy.com/index.php?topic=7572

the one I built has some innovation added with the ribbon tension adjustment... :grin: and a better trafo

it actually sound as good if not BETTER than my RCA

take a look ...here...enjoy



later
ts
 
[quote author="ToobieSnack"]
this mic "label" indicates ...250 ohms output impedance....
will impedance matching improve low frequencies?
[/quote]

As my teacher says, pressure dynamic microphone is resistance controlled.
Via impedance matching (to resistance) you only can enlarges wideband,
but you control only part of overall system resistance . This part is somewhat about "coupling factor" in the quartz resonators.

You can measure it. Standard way (to measure) is to measure impedancy, then put mass on the diafragm (of speaker) and
then measure the some.
They are formulas for it in standard books...
I not believe, that effect of enlarging width compensate decreased
noise figure, what you do by any load.

But you have no lo freq resonancy like in the ribbon, beacouse of resistance controll.
And this microphone have no proximity, it is omni and if
you want full sound, you must equalize.

Noise figure of some "load" or any what is connected directly
to the mic is poor.

I recomend to you any shelf - equalizer with minimal phase after
mic preamp

Best is simple
Ra : (Rb+C)
Everything different is "synthetic"


xvlk
 
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