Linkwitz Mods On Panasonic WM61A Mic

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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
 

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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.
 
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.
 
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.
 
bigwill said:
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.
 
Bigwill,
I wrapp a thick rubber band around the handle of a pair of pliers. ply it open,then insert the capsule in the gap to keep it cool while soldering it. I also use one of these cheapo helping-hand(s) with a magnifying glass ...very handy indeed!

It helps if you apply a little conductive silver on the tiny ground trace/capsule casing as well before soldering.(Maplin sells a small vial) Lead free solder is better for this task I gather, 'cause it contains a little silver in the brew!!

I use only 16-18 strand 1.3-1.5mm soft sheath signal wire, similar to ribbon/network cables.These wires are a bit expensive, but don't exert any strain on the capsule either.The wire/sheath should have little or no capacitance as possible, otherwise it'll just add to the mic's capacitance & will contribute to the noise spec as well!!

Most importantly,it's best to use a 15w-18w soldering iron with a 1.3mm or 1.5 tip at the most!
 
scott wurcer said:


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.

I think will was talking about soldering to the case, which the linkwitz pages suggest. I also found this difficult to do without fears of nuking the capsule, so with my latest one I just roughed up the edge of the case and twisted a stiff single core wire around pressing the contact against the case, sounds flakey but it has maintained a good connection for quite a while now.
 
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I bought 10 I think I've destroyed (and possibly lost) a quite a few (I think I only have two unmodded ones left).... One thing I read (can't remember if it was on the linkwitz site or elsewhere) suggested using conductive glue instead of soldering... not sure where you get it though.

One of the problems is that it is very easy to damage the seal on the mic capsule, this can be because of the cutting, or because of overheating. I think the suggestion of using the big rubber band on the pliers and using them as a heat sink is a great one as is the one of cutting the track with an exacto and soldering to both sides of the track as this should reduce the risk of both of the things that can cause seal failure. I might try again on one of my remaining capsules, I've been suspicious about whether my mics have been working correctly or not. Have had quite mixed results with my measurements and changing mic capsules has made quite big differences. Hopefully will be getting back to doing some testing in the not too distant future, provided I can keep the momentum going, and the new house we are looking at comes off :)

Tony.
 
FWIW, I've always found these small capsules a disappointment because the noise floor isn't that low. It's just the nature of the beast. The 1/2" B&K capsule on our SPL meter at work is about 25 dB better, but the mic alone costs about $1K!! The big studio condenser mics you can get for about $70 (imports) have a great noise floor, but the response is invariably tweaked to sound "good", not flat. I haven't yet found the perfect diy measurement mic.
 
Here's another excellent link on wiring a modified WM61A capsule.

http://www.airraidsirens.com/posts/wm61a.html

I do it a little differently in that,I don't shave off the casing,but solder both the the ground pin & the exposed ring together while keeping the capsule clamped in a pair of pliers & under a magnifying glass.

Winding the solder end of the wires a couple of times on a 5-6mm screw,bolt or any suitable thin rod, making a"spring" before soldering will definitely reduce the capsule picking up unnecessary mechanical vibrations & will further reduce the wires coming apart by accidental pulling.

Sealing the back of the capsule with soft silcone or any soft suitable glue will further help to keep the wires intact & most importantly will reseal/close any holes one may have exposed inadvertantly while soldering, since this will have a significant effect in the low freq.response & sensitivity of the mic capsule.
 
One of the microphones I modified with the two wire method had far less dynamic range than another - it would clip far earlier, confirmed with a scope. I guess this was due to the heat, although I had it in one of those helping hand mounts like teleman mentioned

Something to keep in mind
 
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