Mic Mods. How Do I Do This

[juan162]

I originally had this in the mics forum, but I really should support the new DIY forum...here goes nothing.

OK, so I have read so many posts here about how people have mod'ed or made their own mics. This is of great interest to me, since I love the satisfaction of making or modifying things into something that I can actually use. For example, I wanted a high end folding bike, so I did my research, bought a 70's Raleigh Twenty, and proceeded to modify it with modern day parts. It's now a great touring machine and I always get great comments from other bikers when I ride it.

In order to gain experience I have been practice soldering and have made myself some stereo electret mics (the kind that uses plug in power) and have been repairing some really cheap wireless mics I bought off of ebay for next to nothing (not the internal guts mind you, but replacing mic wires and connections and resoldering the capsules of broken ones). The minor mods I've done on one of my cheap dynamic handhelds - taking out the inner foam protection and resoldering bad connections - has actually made a noticable difference in sound quality (I still have a stock one that I can compare it to). I have also started reading up on basic electronics. My next project will be to make a phantom powered electret. This will be my first time using perfboard, and I still don't really know how to use it. I'm using this as my starting point:

http://www.stefanavalos.com/micropho...s/diymic01.htm

Anyone have any suggestions on where to look - online, or a book resource - to better educate myself on this stuff? Does anyone have suggestions for me? I'm all ears...or eyes, I guess. I don't really know anyone locally to look to for help so I am hoping for more guidance from the fine folks on this forum who have way more experience than I do.

BTW, I am in on this year's GB and hope to be able to do my own mods when the time comes, hence the work I am putting in now! Thanks in advance,

Juan

[antichef]

wow - thank goodness you moved your post here -- I never would have found it otherwise

I shouldn't be posting because I don't know what I'm doing. but... Can you go buy one of those MXL 990/991 kits? I got one for $50 at Guitar center during one of those big sale days - I see them for $70 sometimes. If so, do it, and think of the mics as disposable (because if you're like me, that's exactly what they will be )

When you get them, take them apart, then do some web surfing -- there are a bunch of howtos, etc. covering them.

Do you have an electronics store in your area that sells individual capacitors and stuff? A Fry's will probably work. I'm lucky enough to have a couple of specialty stores with aisles of caps and resistors nearby, so I started spooking around there. After some web reading, go to a store like this and pick up some parts -- could be as little as a $5 exercise.

Then, go nuts! At one point, I had both the 990 and the 991 sounding pretty good to my ears, but I kept messing with them, and they're both pretty messed up now - a lot of hissy self noise, probably from a bad solder on my part at some point. I still try out new types of caps on them because they're a known quantity, so to speak.

But as a result of the noble self-sacrifice of the MXLs, I have worked confidently and beneficially on a number of other mics without flinching -- it was well worth it.

BTW, I get a 404 on your link.

[juan162]

I fixed the link!

Antichef - That's a good idea. This weekend is actually one of those sale weeekends at Sam Ash...you never know,

Juan

[mshilarious]

A few comments on the schemo:

I don't know if you were planning on using this exact capsule (Transound 165) or not. Be aware that other than a few of the larger TS capsules, most electret capsules have internal FETs. If you are using a capsule with an internal FET, you can omit the external FET shown and the 1G resistor.

If you are using a FET-less capsule, you can reduce the distortion of the circuit by biasing the FET. You can do this by creating a bias supply divided off of the 12V power rail, and use the 1G resistor to feed the FET. You also need a cap to block that bias from the capsule.

Next, you can do with less current through the FET. Try 4k7 for the drain and source resistors.

I don't get why he says the circuit doesn't work with 41V. The Schoeps circuit is fine down to around 18V usually. But this circuit is a little different; compare to this page (scroll down to the phantom power section):

http://www.epanorama.net/circuits/mi..._powering.html

I think the difference in the PNP bias arrangement may account for that. But I haven't build the Alice circuit so . . .

Finally, the body. If you are building a cardioid mic, be aware that the vent size and case size can have a dramatic impact on the mic's frequency and polar response. The Alice mic was pretty much screened on all sides, so it was well vented. This mic has somewhat narrow looking slots. I think he underestimated the difference between that approach and the Alice.

I would take a wild guess that will shift the capsule's resonant peaks a little lower than you will see in the datasheet; it could also suppress highs a bit, resulting in a midrangy mic. It could be mellow, or it could be boxy, I can't say. Again, a wild guess. Be prepared to experiment with vent slot/hole patterns to get a voicing you like.

If you want to try a simpler circuit, perhaps while you work on the body, I have plenty of leftover PCBs from my old mic series; you can build a version of this circuit. Heck, I'll even send the small parts. You can use this with a FET or FET-less capsule, for the FET-less capsule, just omit R5 and R6, and run straight into Q1. I have a mockup mic with TSB1460 with this circuit right now and it works fine. I don't even use the 1G resistor, which is good because those are like $3 each

The PCB is not able to easily support biasing the FET though; you could hack it a bit to make that work. Self-biasing with a cardioid capsule should be good to about 126dBSPL for 1% THD, maybe a little more.

[juan162]

mshilarious,

Wow, thanks for the reply and thanks for the offer of help. I'm continually blown away by the generosity of people on this site. I would definitely like to take you up on your offer of PCB (When I write it that way, it sounds like your offering me some kind of illicit drug) and try your 'simpler' circuit. Of course none of it is very simple to me since I haven't done any of this before. I actually have been playing around with the panasonic WM61A capsules and have a few laying around, so I might as well use them. I'll PM you after I post this.

OK, I think I sent you an email, but I'm not sure. Let me know if you don't get anything.

Juan

[TinNedd]

very yummy thank you

Id like to try that, though new mikes are not that expensive these days and they do have the best components in them?

[juan162]

Originally Posted by TinNedd

very yummy thank you

Id like to try that, though new mikes are not that expensive these days and they do have the best components in them?

I just saw this post today. While there are many solid, low to mid priced mics, the reason I am trying to put together some of my own is so that I can:

1. Better understand how mics work.
2. Learn enough that I can do mods on some of my own mics.

I see you are a newbie. As you get to look at more of the threads on here, you will see that some people have taken these "solid, low priced mics" and upgraded them with mods. What they get are arguably much better mics for not a ton of money. I also ejoy the process of building and/or modifying things. It's fun!

O, and BTW, I recieved the mic parts from mshilarious this past week - I've been so busy with work, this is the first I've been able to really get on the forum in a little while. I will unfortunately have to wait on my own mic fabrication since right this minute life is getting in the way. Thanks again mshilarious for helping me out. I will definitely update this thread once I get building!
Juan