Linkwitz Mods On Panasonic WM61A Mic

[teleman]

Hi,
I have wired both the 2 wire & the 3 wire versions of the "Linkwitz" modifications on 2 Panasonic WM61A mic capsules.

However I don't quite understand the topology behind of these two methods of wiring.

1.Can someone please explain the topology behind these two different wirings?

2.Which one of these would give,
a.better noise Spec
b.higher SPL
c.lower sensitivity

Thanks.

3 Wire "Linkwitz" mod wiring

[teleman]

Here's the 2 wire "Linkwitz" mod wiring

[zapnspark]

They are both a source follower configuration.
They give identical results. The second version needs only 2 wires but , the capsule case is "hot"
at + 9 volts. That's OK for battery powered applications where a positive ground can be used.

Cheers.

ZAP

[teleman]

Thank you Zap,

If you look at the schematic of the 2 wire Linkwitz mod, only the -9v battary/ dc suppy is used to "bias" Pin 2, ie:source with a 10k
resistor, with both the drain - pin1 & the case/ring tied together to ground along with the + batt. terminal.In other words 2 wire mode will work only on -9v supply!

In the 3 wire mode..it's the Drain-pin1- which is supplied with +9v d.c voltage!(hot), pin2 as a source follower & casing to ground (0v)

In both instances the case is grounded. I, have perhaps misunderstood your statemant.

I've actually tried both & as you've mentioned they seem to "sound" the same!That's why I wondered if both modes would exhbit the same ele/ sound characteristics or not regardless.

Cheers.

[Wavebourn]

I loaded them on gyrators, without any mod. The best signal/noise I could obtain from them. However, the next stage needs to have JFET input in such case.

But for less distortions on high SPL it is better to load them on a stable voltage, i.e. to use them cascoded.

One good option is, to use them modified, loaded on base-emitter of PNP transistor, with feedback to source of it's internal FET.

[scott wurcer]

Originally posted by teleman
Here's the 2 wire "Linkwitz" mod wiring

Just in case anyone wonders why you can't just flip an unmodded capsule (JFET's are symmetric) there is an internal diode on the gate/source not shown.

[teleman]

Thanks Guys!
I've already tried both versions on a non inverting buffer, two stage preamp & both modes work nicely.I just want to know if one Linkwitz mode is better than the other.ie:2 wire or 3 wire? If so I'd love to know why!

Since my preamp is running on +/- 9 volts (2x PP3 battaries) it's no problem to switch biasing or modes.

[zapnspark]

Here is a diagram that shows the various methods for connecting internal fet electret capsules. This might help visualize this stuff.
I have found no measurable difference between either of these wiring configurations. (figure c and Figure d)



Cheers

ZAP

[bigwill]

How do people deal with soldering to the cases of these things? They're tiny! My first attempt at this worked by sheer luck but my second capsule took a lot longer

(Built a linkwitz mic preamp a while ago, haven't played with it for a long time)

[scott wurcer]

Originally posted by bigwill
How do people deal with soldering to the cases of these things? They're tiny! My first attempt at this worked by sheer luck but my second capsule took a lot longer

(Built a linkwitz mic preamp a while ago, haven't played with it for a long time)

I bisect the pad with a fresh XACTO blade then you can solder three wires more easily. I use #30 wire wrap so the insulation does not melt away.