diy mics - big fun for all!

[wenzel.hellgren]

What about this circut?

http://members.chello.nl/krabmoer/index.html

Pros/Cons?

[wenzel.hellgren]

heres some more info on powering electrets :

http://www.hut.fi/Misc/Electronics/circ ... ering.html

[leigh]

What about this circut?

http://members.chello.nl/krabmoer/index.html

This is very similar to the original Tape Op circuit, although I'm not sure what capsule is being used here. The schematic shows 3 wires from the capsule. If I'm reading it correctly, the circuit is dropping the phantom power voltage from 48V to about 1V across the capsule, by using the 100k resistor and the capsule in tandem as a simple voltage divider. (My guess assumes a capsule impedance of about 2K). It's a bit lightweight for dependable use, however, as phantom power can vary from 24V to 48V. I'd prefer a circuit with a zener diode, to drop the voltage to a predicable level - see the aforementioned Hicks circuit I'm always talking about in this thread.

Anyhow...

I still don't know quite how to adopt the Hicks circuit (aka Schoeps style aka Scott Dorsey style) for a Linkwitz-modified Panasonic capsule. If you don't know what I'm talking about, refer to the earlier links in this thread. My previously posted schematic is probably wrong.

I am trying to get my head around what's different/better about the modified capsule. It relates to the way the built-in FET is used. The clearest explanation I've found, from the Mic DIYer's list, comes from Bob Cain. The mod makes the FET run as a source follower, and

The source follower linearizes the amplifier by including
the load in a feedback loop with the gate circuit. The
feedback loop gain is proportional to the transconductance
of the FET...

Confused yet? It gets better. For the Hicks/Dorsey/Schoeps circuit, you need both a positive and a negative signal (each side gets sent to one of the output transistors) which means the FET also needs to act as a "phase splitter".

Can one FET both run as a source follower, to linearize the amplifier, and also run as a phase splitter? Or should the capsule's internal FET run as a source follower, with a second, external FET doing the phase splitting?

Despite consulting Horowitz and Hill, I'm still quite in the dark.

This thread is not quite living up to its name, is it....the big fun part is still far away. I started this discussion b/c I needed help with this circuit design. I still do.

Leigh

[leigh]

For those of you who were not killed off by the confusion of the previous post, here are two R.A.P. postings found by searching for the strings "source follower" and "phase splitter".

Both posts are by David Josephson of Josephson Engineering.

Leigh

[leigh]

There's a new schematic of a Hicks/Dorsey/Schoeps style circuit, but for the Linkwitz-modified capsules, up at the MicDIYers board. Look for the thread titled "balanced output from Linkwitz mod". If you're not already signed up as a member of the MicDIY board, I don't know if you can jump straight to the message.

This schematic was posted by Edu Silva of ES2 Audio. It produces a balanced but non-symmetrical output, sometimes called 'pseudo-balanced'. What this means is that, on an XLR output, you've got the same impedance between pin 2 and ground as between pin 3 and ground. This allows you to benefit from the noise-cancelling inherent in most mic inputs' differential amps. However, unlike a true balanced signal, which would have the + signal on pin 2 and the - signal on pin 3, there's only audio signal on pin 2.

Check the follow-up messages in the MicDIYers thread for details about setting the value for the resistor labeled only "RS" in the schematic.

If/when I build this design, I'll be happy to post the actual schematic here. However, I don't want to throw something out here, untested, and have people blindly build it. For now, you'll have to do your own homework over at the MicDIYers board.

Cheers,
Leigh

[jeray]

Maybe i can help. I have a machine shop at my house (lathe, mill, sheetmetal equipment). Maybe i can make some parts for your mic project if needed. No cost, just for fun.

[evan]

This isn't relevant to the issues at hand, but it is about DIY mics:

http://mp3forkidz.com/mic/

Pretty nice-sounding, if you ask me.

[leigh]

Evan,

Thanks for the link. Those are some works of art.

Leigh

[leigh]

Some new links to homemade mic housings. These aren't ideal for the omni capsule project, they're for crystal element mics, but the housings look great:

http://home.houston.rr.com/w5tom/Mic%20Pix.htm

http://home.houston.rr.com/w5tom/Of%20M ... %20Men.htm

[heylow]

Man, you guys! This is a great thread....I wish I could help out but you guys have already lost me technically.

I WILL be waiting to see how this stuff turns out though!


heylow

[dayvel]

Hi! I'm the guy responsible for those fine looking mics at the mp3forkidz link mentioned above. I'm currently working an xy set-up using a pair of the Horn cardioids from digi-key (the Panasonic directional capsules just don't have enough low end.) I'm using them in the phase-splitter configuration feeding the back end of Scott Dorsey's mic mod for phantom powering. I'll get back to you after the UPS guy brings the transistors.
One thing you may find interesting is that a properly bent paper clip serves as a good mount for cardioid capsules and makes a surprisingly good contact for grounding the mic case, which comes in real handy for the Linkwitz and phase splitter mods.

[Scodiddly]

First off, many many thanks for this thread... I wouldn't have quite connected the dots from just the Prosoundweb reprint from TapeOp.

I'm currently playing with this stuff on breadboard... actually got it to work last night, phantom power and all. Been a long time since I built anything. I'm going to do the 1/4" pipe thing, of course. I got a couple of the smallest aluminum Bud boxes, which should just fit the circuitry and XLR.

However, check this out: http://store.electrogalaxy.com/vanvs41.html

I originally got one of these from a local photo store for under $4. As a camera tripod it's pretty cool, but it's also a handy source for three pieces of ~1/4" dia. gooseneck, with enough hollow space to run thin wires inside. In other words, absolutely perfect for making clip-on instrument mics.

[Scodiddly]

Hrmmm.

Well, that was a little *too* easy... guess my 'leet DIY skills haven't totally atrophied yet. I made two mics with the phantom power circuit, with 1/4" aluminum tubing (next time brass so I can solder a ground/shield wire?) into the smalled diecast aluminum box available (~1x1x3"). I used a lamp "nipple", which is tubing threaded on the outside and (conveniently!) slightly bigger than 1/4" inside diameter to attach the 1/4" tubing to the box. An XLR lives in the opposite end, and the perfboard with components is stuffed into the middle. I ended up with some huge 1u0 capacitors, but luckily it all just barely fit.

And it only took a box from Digi-key, two visits to the hardware store, one visit each to Radio Shack and the real electronics parts store, and a few bits I already had. Now the fun really begins; I also bought a couple of the above-mentioned Horn unidirectional capsules to play with, and of course I've got a few omni capsules left. Perhaps a 2-channel power supply and a few different capsules on thin wires or something.

[Scodiddly]

Oh yeah... I tried to do that Linkwitz mod on one of the capsules. Cutting the trace was easy... but I couldn't manage to solder a wire onto the case for the third wire.

Anybody manage to do that mod?

[Scodiddly]

Uh oh... Got this email today:

You have purchased the following part number(s) from Digi-Key within the last two years.
The manufacturer has announced this part(s) will become obsolete.

PANASONIC - ECG
? ?Description: MICROPHONE CARTRIDGE 6MM X 5MM ?
? ?Manufacturer Part No: WM-60AY ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?
? ?Digi-Key Part No: P9959-ND ? ? ? ? ? ?
? ?Your Most Recent P.O. No: ? ? ? ? ? ? ? ? ? ?

For more information on possible substitutes, please click on this link
http://dkc1.digikey.com/scripts/us/obs_ ... n=P9959-ND ? ? ? ? ? ?

Last Buy Date: 15-FEB-2004

No direct substitutes that match form, fit and function are available at this time. However, we may be able to suggest alternatives based on your specific application. Please contact our Technical Department at 1-800-344-4539 or email us at Techs@digikey.com if you need further assistance.



-----------------------------------------------------------------------

PANASONIC - ECG
? ?Description: MIC HOLDER FOR WM-63/60A/65A ? ?
? ?Manufacturer Part No: YPM-CH021 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?
? ?Digi-Key Part No: P9898-ND ? ? ? ? ? ?
? ?Your Most Recent P.O. No: ? ? ? ? ? ? ? ? ? ?

For more information on possible substitutes, please click on this link
http://dkc1.digikey.com/scripts/us/obs_ ... n=P9898-ND ? ? ? ? ? ?