Panasonic WM61-A usage revisited

[ashok]

Some thoughts on using the WM61-A mic capsule.
I wanted to make it as simple as possible. The modifications on the Linkwitz site might be ideal for measuring very high SPL at low distortion. I find that for DIY application even 90 db sounds quite loud at 1 meter and so the standard configuration appears to be good enough. It is also usable up to 134 dB ! Distortion might be higher but the FR measurement capability should be OK I think. You couldn't possibly sit around at 134dB at 1 meter ! Close miking is a different matter.
Rane has a MIc1 which appears to use a Panasonic mic capsule or something very similar. The supply is 3 volts to 9 volts with a Drain resistor of 2.2K ohms. Specs seem to be similar to the Panasonic capsule.
The mic has a 40 feet hard wired cable and goes to an external mic preamp. So I guess we can do the same thing.Bias could also be from the preamp,located away from the mic. If the mic cable has a very high capacitance , then it might help to use an op amp at the mic itself.
The standard configuration has an output of about 17.78mV/Pa ( 17.78mV@ 94dB ). If used in the modified form as shown on the Linkwitz site , the output would be 6.67mV/Pa . This configuration is however easier to use with higher capacitance cables ( or longer cables ) with less HF loss.
With an assumed capsule Zout of 500 ohms and load of 10K ohms and 3000pF capacitance ( worst case ) the 20 Khz response is down by < -0.2 dB .
The standard configuration might need a buffer opamp at the mic capsule to maintain good HF response with high capacitance loads.

Has anyone made any comparisons with the standard usage of the mic capsule and the Linkwitz modified capsule ?
Cheers.

[ashok]

I can't find my Panasonic mic capsules !

If anyone has used it in the standard configuration ( unmodified) with a 10 K resistor and a 9 V battery supply, could you tell me what dc voltage is obtained at the capsule output ( capsule and 10K junction)? Thanks.

[ashok]

Hmm.......No comments from anyone !

I found my WM61 capsules and discovered that they were 61-B's ! Yuck. I guess that isolating the ground terminal might be more difficult with this. Anyway the initial use is in the standard form and that should not be a problem.

Here is what I found.
Supply voltage Load resistor DC voltage at the Drain.

9.8 volts 10 K ohms 4.9 volts
9.1V 10 K 4.29 V
8.6V 10 K 3.88 V
7.7 V 10 K 3.1 V
4 V 2.2 K 3.1 V

So this would mean that we can dispense with the input coupling cap. A buffer will be required here to ensure that HF roll off doesn't happen too early with long lines. I will probably use a 40 feet cable.

So to work it just needs a 9 V battery at the mic and one resistor and the opamp ( OPA134 .......or TL071 ? ). For the sake of protection and supply filtering we can add two capacitors and two resistors. I'll check out what my junk box has to see if I can do it all smd. Should make it pretty small.

Looks like ETF uses a similar capsule and they say max level >120dB . So it appears that for high power tests or very close measurements the capsule has to be used in the modified form.

Shall sit down tonight and chop up another capsule and see what happens.

[Aucosticraft]

Ashok, where did u buy it from ? Pls can you share it with me?

[jamikl]

I would like to know where the capsules can be bought in Melbourne or in the rest of Australia.

Please keep us posted with your findings Ashok.
jamikl

[ashok]

If I remember correctly , I bought this one from DigiKey Corp. | Electronic Components Distributor | United States Home Page .

This whole project came to a grinding halt due to various other unrelated problems. Subsequently I forgot about this thread though the need to build the mic was still on my mind. I even bought new brass tubes to fit them in.
( I have another readymade mic so the urgency was not so great !)
Will post details soon.
Cheers.

[Garyepe]

Originally Posted by ashok

I can't find my Panasonic mic capsules !

If anyone has used it in the standard configuration ( unmodified) with a 10 K resistor and a 9 V battery supply, could you tell me what dc voltage is obtained at the capsule output ( capsule and 10K junction)? Thanks.

Hi

Please check our website . We have the capsule the same as Panasonic.

And we also have the broadcasting capsules which have a more better performance than usual type ECM(Electret Condenser Microphone)

And please contact with me if you need , Thanks a lot.

Gary