DIY Preamp for DPA MMC Capsules

[jarvis]

Hey everyone,

I just wanted to share a recent project of mine if anyone is interested in that. I've had a pair of DPA MMC 4011 capsules laying around for a while and I finally got the time to build a decent preamp for them. A year ago I bought bodies on Alibaba, that are very similar to the DPA MMP series preamps but with lesser quality internals and externals. Getting the insides out and figuring out, how I wanted to go about mounting a PCB in there was a challenge, but I came up with a 3d printed mount that mimics the original DPA mount, making ground contact to the body via a thin sheet of brass that I glued to the outside. The circuit is @rogs ' clever and straight forward OPIC, for which I designed a PCB that snugly fits the internal dimensions of the body and I'm pretty happy with how everything turned out. So a big thank you to @rogs for sharing that design!

Best
Jannis

 

[Khron]

How's the noise level? And were those 0201(?)-size resistors chosen on purpose?

 

[jarvis]

How's the noise level?

I didn't measure the noise level without the capsule connected so I can't really comment on that. But I put it side by side with a MKH 40, which is very quiet for a small diaphragm condenser, and the only noise I heard were the fans of my computer, that was in the same room. So in real world application it seems to be sufficient for now. But I may actually do a proper noise measurement in the future.

And were those 0201(?)-size resistors chosen on purpose?

They are 0402 resistors that I had laying around from another project when I designed the PCB and I thought, I'd just use those in the build. But they are really difficult to handle with tweezers and hard to solder with my soldering iron, which has a tip that is about 10 times the size of these resistors. That's why the soldering job isn't the best. I think, I'm going to invest in a hot air soldering station soon.

Best
Jannis

 

[Khron]

I think, I'm going to invest in a hot air soldering station soon.

... Or a finer tip for your iron With hot air you run the risk of blowing them away before (or even after) they stick to the solder...

 

[rogs]

But I put it side by side with a MKH 40, which is very quiet for a small diaphragm condenser, and the only noise I heard were the fans of my computer, that was in the same room. So in real world application it seems to be sufficient for now. But I may actually do a proper noise measurement in the future.....

Th MKH 40 has a published A weighted self noise figure of 12dB(A). The OPIC circuit should perform a couple of dB better than that.
In either case it's 'real world' ambient noise that is going to be the dominant noise source, I suspect?

 

[jarvis]

In either case it's 'real world' ambient noise that is going to be the dominant noise source, I suspect?

In my case it definitely is. The MMC 4011 capsules have a pretty high self noise of ~20 dB(A) irrespective of the preamp circuit and in my recording environment at home that gets drowned by ambient noise. But I guess in very quiet rooms or in some field recording scenarios there should be a noticable difference.

Best
Jannis

 

[rogs]

The MMC 4011 capsules have a pretty high self noise of ~20 dB(A) irrespective of the preamp circuit......

According to the DPA spec sheet the 4011 cardiod mic has a max noise figure of 20dB(A) - and that includes the internal mic preamp.
So, unless their preamp design breaks the laws of physics! - the capsule noise must be lower than that...
Self noise of 20dB(A) does seem a lot for just an electret capsule itself?

 

[jarvis]

Yeah, me saying self noise was irrespective of the preamp circuit is of course misleading and doesn't really convey what I've meant. The original DPA MMP-A circuit, in which these capsules are measured in the factory, is pretty low noise as far as I can tell (jfet into a push-pull stage and impedance balanced out). So I was pretty sure that whatever circuit I'd use these with, I would not get noise specs that far surpass those on the measurement reports my capsules came with.

Best
Jannis