C37 style mic using Dale's capsule

I'm finally catching up with building mics out of the capsules I bought so I have an excuse to buy more capsules  ;D

After my M49ish FET mic with a Dale M7 (http://www.groupdiy.com/index.php?topic=30406.0), I decided on trying the C37 style capsule I bought.

This is the capsule mount. I molded the dome out of plexiglass, which I heated over a candle. Hey, it's Christmas time 


The circuit is my own design - well there's nothing really new under the sun, anymore, but it's not a copy of anything that I know of. It is an impedance balanced transformerless design with only two transistors (the transformer of the donor mic is disconnected). There are no caps in the direct audio path except for the unavoidable output lytics. The C37 capsule is about 12 dB lower in output than a M7, so it wasn't exactly easy to achieve low noise. I might start a topic in the Drawing Board section about the circuit. There may be improvements to be made, but right now, I'm quite happy with it.


There is a CMOS-based DC-DC converter board on the backside which puts out about 68V for the capsule. The mic is now as quiet as a studio mic ought to be. I have no exact figures, but I'm fairly certain it is below 18 dB-A self noise. (Which is quite a bit lower than Sony C37/C38 mics, but I have no experience with those, so maybe they are better than what the datasheets say.)


So how does the C37 style capsule sound? Well, very different from an M7. It sounds very real and unflattering; you feel a bit naked singing into it. But at the same time there is an unpretentious realism about it that few LD mics will achieve. It sounds a little bit bright-ish in the 4k range, but there's no sibilance. S- and T-sounds are very clear and undistorted. Somehow this mic makes me think of Steve Winwood. I think this is a good mic for a loud and/or forward singer and also for spoken word (if you're going for a realistic sound, not that huge commercial type of voice sound). I wouldn't use it for a crooner type of singer.

Anyway, this build gave me quite some trouble, but in the end I'm very happy with this mic. It is definitely a different "voice" in the mic cabinet. Thanks again to Dale for his capsule wizardry.

Cheers,
Andreas

its just amazing...
I wish i have the cash to get into building mics..

two transistors
OK lets guess

a FET BJT feedback follower(x1) like you can find in the NS app notes(somewhat like the gefell 690) with 100 ohms in both legs allows you to run about 15VDC for the cmos inverter charge pump DC to DC.

Or the km74 type, ber B5 C2 ......

or the 012

or the newer gefells

Nice capsule and you build transformerless?

There are more

It is a kind of KM84 style FET stage meets a DC coupled NPN emitter follower output stage, nothing too fancy, acutally. The FET is a 2SK117 (I tried quite a number of different FETs) and and runs a little hotter than in a KM84 style mic. The biasing was quite difficult, but then again I'm not really an EE, so I have to try out a lot of stuff.

I didn't want to use a transformer for various reasons. Fist, from what I heard, the C37's attraction is not its color but its realism.  So I figured a very clean circuit would do nicely. Also, I wanted to experiment with transformerless designs. Using a good transformer is a convenient way to build a good mic, but when I built my M49 style mic, I felt like I merely put the thing together. It sounds very nice, but that's not really something I achieved, I think. Then, for practial reasons, transformerless seemed a good solution given the low capsule output. With an overall gain of 10-12 dB the mic's sensitivity is comparable to a TLM103 (which is unity gain., I think). Had I used a single FET circuit and step down transformer, I would have had low output or I would have needed a lot of gain from the FET stage, which might have meant more noise.


@3nity: This was a fairly inexpensive affair, the capsule was about 100 bucks and the donor mic was a cheapo china mic for about 60 bucks. As there's no expensive transformer involved, the acutal cost of the electronics part is negligible, so the total cost of this mic is less than 200 (euro-)bucks. It was a lot of work, though.

nice initiative! that is an interesting idea...you know we wanna see the schematic!

Interesting!