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[Antonw]

in article ( http://prosoundweb.com/recording/tapeop/buildmic/buildmic_16 _1.shtml ) very big claims are made on this DIY mike. Now at what goes into the mike its worth its money even if it does a crappy imitation of radio-shack mike, and itll keep me warm this summer if i make a couple, im still curious whether anybody made one and what they thought of it

IF this thing has allready been discussed till death then ill say oops and be off on my merry way again...

Cheers
Anton

[Family Hoof]

I think it has been discussed to death. Most of the discussion was about making them into real mics that used phantom power. That capsule is pretty good and used in a number of other omni mics. There's a mod (linkwitz) that makes it 10 times better and the company Stapes Audio made their first mic out of a modification of this design from the article. They now have another pair that supposedly competes with Earthworks.

[Antonw]

Thanks Hoof, ill have another look in the pit.

Cheers
Anton
[edit: allmost forgot: OOPS]

[chickenbop]

I made a couple.The tapeop mic distorts at a pretty low volume making it unusable for drums .The panasonic capsules are supposed to perform a lot better after the linkwitz mod.There's a thread over at www.homerecording.com about modding the behringer ecm8000 that talks about the linkwitz mod.

[Family Hoof]

Probably those 9V batteries which are limiting the headroom and causing the distortion. After modding my Realistic PZMs from AA batteries to phantom the difference was HUGE! I'm unable to overload them even if I try. I'd imagine the TapeOp mics would have similar results with a real phantom powered circuit in them. B & K have taught us a thing or two about high voltage = better performance.

[Marik]

<Probably those 9V batteries which are limiting the headroom and causing the distortion. After modding my Realistic PZMs from AA batteries to phantom the difference was HUGE! I'm unable to overload them even if I try. I'd imagine the TapeOp mics would have similar results with a real phantom powered circuit in them. B & K have taught us a thing or two about high voltage = better performance.>

Hoof,

Could you please point out which PZM mod are talking about, as there were quite a few around.

PZM mods for phantom power I saw have a Zener which stabilizes voltage at 12V, which is quite close to 9V battery.

[Family Hoof]

My apologies Marik, it was this one. Still supplies about 12V without the use of a zener and that's all the volts those capsule types are rated for. I know the circuit you speak of and I'd imagine it probably sounds better, no? My knowlege of electronics is still mostly voodoo, no thanks to the university for helping this.

Don't get me wrong about the PZMs, they still sound like crap, and even though I also replaced the capsules with the Panasonics mentioned in TapeOp (soon to be discontinued I hear!). I got the mics for free and barely use them but thought it'd be a fun, low-cost experiement. I was mainly just trying to make a point about the higher voltage making a big difference in my previous post.

P.S. This new R/E/P forum never e-mails or notifies me of responses. I'd get back a lot quicker if it did.

[Antonw]

Yeah same here,
and the RSS feed (see xml syndicate button below) doesnt work (last time i checkd) either. Maybe thats a good hting, cause with that id never get to finding a job.

Cheers
Anton

[Consul]

To post my two cents...

The Panasonic electret capsules come with an on-board FET for impedance matching with the outside world. The Linkwitz mod cuts a trace on the capsule which disables the on-board FET. That then allows you to design a much higher-quality circuit around a now more basic electret capsule.

It's not a leap from there to then think about hand-selecting capsules for specific properties, really.

[josh]

Consul wrote on Wed, 12 May 2004 15:33

The Linkwitz mod cuts a trace on the capsule which disables the on-board FET.

That's not what the Linkwitz mod does at all.

see this page for the correct info:

http://www.linkwitzlab.com/sys_test.htm

[Consul]

Well, it does something with the FET:

Quote:

Fortunately, is it possible to modify the external connection to the FET. This involves some delicate work of cutting a trace on the tiny pcb in back of the cartridge and soldering thin, flexible wires to the standard two hookup points...

I wish he gave more detail. Perhaps he's just changing how you can hook the internal FET into an external circuit, to give you more flexibility.

Anyone know if/where you can buy electret capsules with no internal FET?

Sorry, it's been a very long and tiring week, and it's only wednesday. I'll try not to be so stupid in the future.

[josh]

I hope I didn't imply you were being stupid javascript: insertTag(document.post_form.msg_body, '', ' ');

Indeed the Linkwitz mod changes the way the internal FET is wired, but does not eliminate it.  Some experimenters have spent a lot of effort trying to figure out a way to neutralize the internal FET in an electret capsule and use an external FET.  It's no small feat to do so.

I don't know of any electrets available without internal FET, but I'm nothing even close to an expert.  The most common "good" Panasonic capsules have internal FETs.

[Consul]

josh wrote on Wed, 12 May 2004 11:21

I hope I didn't imply you were being stupid

No worries. I should've read closer.

Quote:

Some experimenters have spent a lot of effort trying to figure out a way to neutralize the internal FET in an electret capsule and use an external FET.  It's no small feat to do so.

Maybe this is Earthworks' big secret...

I'm not too sure if I want to build a matched pair of electret microphones (like the Linkwitz mic) just yet, anyway. I hear they are good choice, though, if you want to capture a nice and natural drum sound.

I don't even know how one might go about matching up a couple of capsules...

[Marik]

<My apologies Marik, it was this one. Still supplies about 12V without the use of a zener and that's all the volts those capsule types are rated for... Don't get me wrong about the PZMs, they still sound like crap, and even though I also replaced the capsules with the Panasonics mentioned in TapeOp (soon to be discontinued I hear!).>

Hoof,

No apologies neccessary.
Actually, properly modified Realistic PZMs can sound very good. But, since there are some confusions let's start from the beginning...

<    http://prosoundweb.com/recording/tapeop/buildmic/buildmic_16 _1.shtml ) very big claims are made on this DIY mike. Now at what goes into the mike its worth its money even if it does a crappy imitation of radio-shack mike, and itll keep me warm this summer if i make a couple, im still curious whether anybody made one and what they thought of it>

Anton,

The biggest problem is that in this configuration internal FET of the capsule is in its stock  connection and works as a common source amplifier in self-biasing mode. In this connection it has a very limited dynamic range and highest input capacitance possible for a given FET, which loads input signal (think of this as a cap used in a -10 pad  in condenser mics). Another disadvantage is that output impedance is high (around 2-3K depending on a capsule), so you cannot run long cables and there is a serious mismatch with input impedance of mic preamplifier. In order to overcome all these, the very first thing is to make a Linkwitz mod. Basically, you disconnect source of the FET from capsule's ground and reconnect the FET as a source follower. It greatly increases overload capabilities of the capsule and makes its sound less muddy. Then, in order to bring the output impedance to more 'conventional' 200 Ohm, you have to make an output buffer. Realistic does it by means of transformer. Since it is a poor quality one, here it would be a much better idea to make a transformerless output.
As Chikenbop has already mentioned, I had a big thread on HR forum about ECM8000 mods, which would be relevant to PZMs, as well, and the thread has a lot of discussion in depth on all these things. Have a look:

   http://homerecording.com/bbs/showthread.php?t=111051&pag e=1&pp=25

Also, although it is not in the thread, I cut a resonator from the Panasonic capsule, and the capsule sounds much more natural.

<Some experimenters have spent a lot of effort trying to figure out a way to neutralize the internal FET in an electret capsule and use an external FET. It's no small feat to do so. I don't know of any electrets available without internal FET, but I'm nothing even close to an expert. The most common "good" Panasonic capsules have internal FETs.>

Josh,
Although it is quite tricky, I took apart Panasonics and rebuilt it using external 2SK170. It doesn't work. Since capacitance of the capsule is very low, any stray capacitance (wiring, or input capacitance of bigger FET) will load the capsule and its low output becomes unusable. That's the reason why with capsules THAT small,  there ought to be an internal surface mount sized FET.