Electret TINY design

[sr1200]

Im thinking of building a few really small electret condensers for "odd" work where normal mic's wouldn't fit or cant be placed easily.  Instead of mounting the capsule up and down (the way it would be on a typical pencil type mic) id like to mount them sideways (side address, think large diaphram design).  May take some experimentation on the part of the placement, cutouts etc on the body, but first things first, I want to get a viable circuit in the mic.  Anyone have any thoughts on this design?  The original was missing the 2 22nf caps (c2 / c3 on my drawing) but was suggested for "better performance".

EDIT: just noticed i have my zener diode upside down...  :-[ :-[

 

[tchgtr]

I have used this circuit to modify my Radio Shack PZMs. It certainly sounds much better than the original RS electronics, and I would compare them now to LDC mics in their sound.
A suggestion... MXL 990, 440 mics are already set up for side-address SDC capsule placement. I'll bet what you are planning would sound better than those mics, tho they may not be small enough for what you require.
Have fun!

 

[sr1200]

Yeah, im lookin for chapstick sized mics.  good to hear that someone has used this circuit though.  Thanks

 

[sr1200]

any suggestions for a replacement for the BC479?

 

[ricardo]

You circuit is missing a few important bits.  Try looking for Alice mike on the web.  For some better versions, look in Zapnspark's directory on Yahoo MicBuilders.

 

[seavote]

google "linkwitz mod" if your not already aware of it. 

 

[sr1200]

Just about exactly what im looking for!  Seavote, do you know if the alice mic schem already incorporates the linkwitz mod? 

 

[sr1200]

one last question here, sorry... is it possible to use tantalum caps instead of the electrolytic?

 

[sr1200]

OK so i found a new schematic from the mic builders board here:

CLICK TO DOWNLOAD SCHEMATIC IMAGE

and from that i created a expressPCB proto (cheapest boards) that contains 5 circuits per board... (DOWNLOAD HERE) if anyone has the time to check my work (i think i got it right) would appreciate it and if anyone is interested in the boards themselves, i dont think I'll be needing 15 of these mics (i MIGHT make 4 of em). But since i have to order min of 3 boards, I'll have a few left over.  There were board prints already done on that site but none with that schematic... oh its also single sided for anyone that would want to etch their own boards...

The thing im not sure the most about is the 2n4416 which i cant tell from the data sheet if the pin view is from the bottom up or the top down... if its top down then the board is wrong and will have to be corrected (or the part will have to live on the opposite side of the board)

 

[seavote]

the alice is a circuit built for a transound capsule that would be too large for your  application. maybe someone who  has used the circuit with a smaller electret can weight in on how it worked out for them. zapenspark has many circuits designed for the panasonic capsules posted over at the yahoo mic builders page. he seems to know his stuff and i believe his opinions are first hand from trial and error. personally id go with one of his circuits.
i'll be watching this after i post. just got it in my email a few seconds after i read your post:

http://www.diyrecordingequipment.com/4458/podcast-1-diy-condenser-microphones-with-scott-helmke/
8) 8) 8) 8) 8) 8) 8) 8)
ps: im just getting around to calibrating those mnats g1176s. ill get themtothe next ny diy meet
8) 8) 8)

 

[sr1200]

Decided to go with the capsule listed on the schematic. Found a decent source for them.

 

[ricardo]

I assume you want to use P48V.  What capsules are you using?  If you are using the excellent Panasonic WM61a omni capsules with built in FETs, good choices are ..

• Alice http://www.scotthelmke.com/alice-schematic.jpg  Remove 2n4416, 1G and TSB165 and just connect your capsule where it says S & D
• The simplest possible circuit with good performance is SimpleP48WM61 in my Files directory in MicBuilders
• Circuits in Zapnspark's directory are the Deluxe versions.  Distinguish between circuits for capsules with FETs and those without.  Worth close study even if you don't use them

The Linkwitz mod is for a capsule.  Some capsules with built in FETS are already modded.  eg the Transounds.

Tantalums are crap.  Bad sound and unreliable.

 

[sr1200]

I realized that the schematic wasnt showing up on all browsers, i added a link in a previous post to a copy of it.

Do you think the Panasonic 61as are better than that TSB165's?  I was reading that the TSB's can potentially handle higher spl's and since im looking to possibly use these on drums, i would want the highest spl's i can get no?

 

[sr1200]

OK so going by Seavote and Ricardo... (seavote for the size issue... and ricardo for the tip on what to change on my schematic)

I have these two things here...

First is using the TSB165, is a longer slightly thinner board (5 per sheet)
LONG ALICE for TSB

Second using the panasonic capsules is only 1/2" thick (thinner if you trim the dead space down on the sides of the boards. (6 circuits per sheet!!)
THIN ALICE for Panasonic

 

[seavote]

the alice is a circuit built for a transound capsule that would be too large for your  application. 

the alice mic is constructed in a 1" diameter pipe.smaller than i thought but maybe ok for what you want. the panasonics are tiny. they are the type of capsules installed in the male xlr bodies  see these:
http://www.karmamics.com/shop/K-Micro-Matched-Pair.html
and similar mics by naiant (who used to frequent the board, some of his schematics were posted but i dont know if their still up)

with mics this small why do you need side address??  were you just lookingto experiment with sound differences due to varying head baskets???
if you decide to order panasonic let me know ill buy some myself maybe get lower price.(need to plan this project because im not far enough backed up with currently planned projects)i'll be doingthis one p2p.  im tired of troubleshooting on pcbs,can get very sloppy after a few unsolder/resolders
8) 8) 8) 8) 8) 8) 8)

 

[sr1200]

I think might do the smaller. The side address thing is because im sick of mics sticking up at odd angles while micing certain percussion. A flat profile is sometimes more desireable. I was also thinking of doing a switchable dual capsule (one side address one front address) that could be switched as needed.  Would need a tiny make before break dpdt. But might be more trouble than its worth. If you want a couple boards when i order em let me know ill just drop a couple in the mail.

 

[ricardo]

This is the SimpleP48WM61 I mentioned from my MicBuilders directory.  The WM61 is stuck in a piece of 1/4" cu tube and the whole thing soldered on the end of 20m of XLR cable with a bit of masking tape and Heat shrink.  The incredibly complex circuit has a grand total of 2 components.

It's not the best possible circuit for a WM61A to P48V but its pretty good.

 

[sr1200]

Yeah thats just about the TINY im lookin for!!  8) 8)

Did you see the layouts i linked?  The panasonic one could possibly fit into a 1/2 tube if trimmed properly. That might just be the way to go with this.  Any thoughts on the 2 way capsule idea?

 

[manulaudic]

Seavote,

Those Karma mics look great ! 22 euros for a matched pair, that is just ridiculous...

Have you tried them?
I have built same style of mic based on Tape-op Magazine running with 9v battery, they were quite good, very neutral though 48v is much more handy.

Manu

 

[sr1200]

OK i revamped the Alice (to be used with the panasonic) board design (there was 1 missing trace).  Tied it to the schematic and got all the components in order, and it seems to be spot on now (the board is 0.4" wide by 3.8")

For PCBExpress heres the pcb file and schematic if anyone wants to play around or order their own (do at your own risk and quadruple check my work first!!)

Alice Panasonic Thin Board
Alice Panasonic Thin Schematic

I'm ordering the boards now.  I'm confident that the file is good though.

Seavote, i ordered about 10 of the panasonic capsules... there wasnt a price break unit like 25 of em.  If you need a couple let me know