Topic: Greenmachine Mics (omni) [w/ samples]

[beefstew]

chris: whats the best resistor to use in a DIY batt box for use with the 4.7k mod mics?

thanks for all the knowledge! 

[Church-Audio]

chris: whats the best resistor to use in a DIY batt box for use with the 4.7k mod mics?

thanks for all the knowledge! 

According to Spark'e a 4.7k but when I did the distortion tests originally I was using a 10k I will do some tests this week and show you guys the difference between the two..

[Church-Audio]

WM61A seems to like to draw 0.4mA or so, so 10k would drop 4V.  Also in theory that would create gain in common source configuration.  I did that in one circuit, and if I recall distortion can be worse as you increase the drain resistor too high (too high being 15 or 22k).  Again it depends on the voltage supply; I was doing that with regulated 12V, 9V would probably be OK, until the battery started to drop.  Maybe 6k8 would be reasonable, but 10k is worth a try.  It will be interesting to hear Chris' results.

For anybody using a recorder with a balanced input, one benefit of using 4k7 is you can create a balanced output with a 3-wire configuration.

All I did was simply measure the distortion at 1k at 114db and changed the value of the resistor until I got the least amount of distortion.. There was no math involved or theories Just me changing a resistor until it worked.. It came about because I ordered my capsules I use for my cardioid mics sight unseen I did some tests and I started to freak out... The distortion was hideous.. I though there is no way I can sell my mics with such poor performance so I just started changing resistors until I got what I wanted.. Then all was good I will do the tests with 6.8 and 10k and 4.7 and a few other values if anyone can suggest any other values. and I will post the results with graphs.

[Church-Audio]

I thought we were talking about the battery box supply resistor    I would concur with 4k7 for WM61A source resistor.

Sorry! I was talking about how I came to choose the 4.7k... I was using a 10k when I tested the 4.7k lol if that makes any sense.. So I will do some tests with different bias resistors.

[kuuan]

very interesting thread indeed, thank's a lot Chris for sharing your knowledge, T+!

though I am curious of your resistor/distortion finds, I have two somewhat other questions:

1: how does the Panasonic WM55 capsule compare to the WM61 resp. the mentioned TS60 and TS62 ( WM55 I can gethands on easily here, the others not )
2: what exactly means 'heat shrinking'?

thank's a lot for any input to clarify,
kuuan

[nasarius]

1: how does the Panasonic WM55 capsule compare to the WM61 resp

That's actually a good question. I noticed those while browsing around DigiKey, and they look pretty decent on paper (20Hz-16kHz response), though the capsules are almost 10mm across. I'll probably buy a few in my next order.

I found this, which has a sample that sounds very good.
http://www.mp3forkidz.com/mic/phantxy.html

2: what exactly means 'heat shrinking'?

Heat shrink tubing. Special kind of tube that you put over something (often wires that you have connected), then use a heat gun to shrink it down to 1/2 or 1/4 of its original diameter.

[kuuan]

thank's nasarius, T+!

I believe that the WM55 are not very different from the WM61, the later being somewhat favoured by some micbuilders it seems. Please post if you find out more!
The site you found is very good, the author member of the yahoo group 'micbuilders': http://tech.groups.yahoo.com/group/micbuilders/

thank's for explainingheat shrinking.. I have been doing that but did not know that it was the same which is refered to by 'heat shrinking'.

good luck for anybody building his own mics, it is easy and fun!

kuuan

[Roger Gustavsson]

Well, the WM55 is a cardioid and the frequency response drops a lot, about 20 dB at 20 Hz and 1 meter. The WM61 is linear to at least 10 Hz.

[nasarius]

Well, the WM55 is a carioid and the frequency response drops a lot, about 20 dB at 20 Hz and 1 meter. The WM61 is linear to at least 10 Hz.

Hm, I misstated the response...it's 100Hz-16kHz, and that's all the datasheet shows as well. I'm not sure where you're getting those numbers, but the point is valid; the WM-55A loses 10dB at 100Hz, up to a few dB at 250Hz.

They should be better than the Giant Squid cardioids at least (which, given their size and advertised 100Hz - 12kHz response, are most likely WM-65As).

http://rocky.digikey.com/scripts/ProductInfo.dll?Site=US&V=10&M=WM-55A103

[Roger Gustavsson]

Panasonic WM55 and WM61, tested here:

[kuuan]

thank you very much Roger, and BTW welcome to the forum, you are a very valuable new member.

I know too little, is to say close to nothing about technical specs so I must admit that the test don't tell me much.

I do understand that you say that the WM61 is better....
However i believe that this dhould not discourage poeple do try out the WM55 in case they cannot get hold of WM61, like me. Many mic DIY did use the WM55 also:

http://www.prodigy-pro.com/FORUM/viewtopic.php?p=270393&sid=c0677291ae69a16269e98b4c980bd378
http://www.scotthelmke.com/stereo-mic.html
http://www.mp3forkidz.com/mic/phantxy.html
http://homepage.ntlworld.com/henry01/cheap_soundfield/cheap_soundfield.htm
http://www.mp3forkidz.com/mic/msmicV2.html

I guess you have seen those sites, but I hope somebody might find them interesting,

In noticed that the the WM55 had been modified for 'source follower operation' using a 2,2 k resistor. Please excuse my innocence, maybe I am wrong, but: Is this a similar mod Chris is doing but using a different value for the resisitor?

thank you,
cheers,
kuuan

[nasarius]

Incidentally, I have found that all three Pana capsules are happiest with 4k7 source resistors, but other brands of capsules, especially in the 10mm size, generally like higher values.  It's always worth experimenting.

This got me curious. Are there any good capsules (equal or better than the Panasonics) available to the general public? That is, no more than 10 or so as a minimum purchase from some distributor.

Answering my own question a little...from this DIY site I found Transound capsules:
http://www.jlielectronics.com/transsound/electrets/tsb-165a.htm

But they're 16mm, which is probably too large for most stealth taping purposes. Maybe these, which are about the same size as the WM-55A:
http://www.jlielectronics.com/transsound/electrets/tsb-99a.htm

Or these, which are rather pricey and require an external FET:
http://www.jlielectronics.com/transsound/electrets/tsb-120a.htm

[kuuan]

nasarius I am sure the TSB-165 are really good, I don't know about the others. A quote from Scott Helmke from the micbuilders:

> The TS capsules that are similar to the Panasonic series are basically
> about as noisy. If you go with the ones that require an external FET and
> 1Gohm resistor then there's a huge difference - the TSB-160, TSB165 are
> both this way. The sound of those capsules is a bit on the bright side,
> but you can build a fully professional mic with them.

seen here: http://tech.groups.yahoo.com/group/micbuilders/message/4759

nasarius, if you want to buy some, need to take 10 Pcs and don't want them all, I'd like to take...let's say, 4 pcs, or half of them?

cheers,
kuuan

[powermonkey]

New to all of this as I am, I'm still constantly surprised by the quality of recordings possible from a pair of mics as tiny as these Greenmachine mics.

I'd love to build a pair of my own mics one of these days, but since I've never even considered picking up a soldering iron I think I'll be sticking to other people's work for the time being!

 

[kuuan]

Quite new to all of this I am too, and very surprised at the quality of recordings from a pair of binaural mics as tiny and cheap as the ones I made with two 0,60 USD capsules simply soldered to 1USD earphones. That hardly needs knowledge of soldering, and if you take capsules for 1,50 each and better cables, OK, don't spend 3 USD but 5.

I'd love to have real good mics, but if it is just entry level mics, why spend 50 or 100 USD if I can get the same quality for just 3 or 5 USD!