Active dynamic microphone project

[clbzh]

Hello,
I would like to build an active dynamic microphone.
To amplify a didgeridoo in an acoustic trance band.
I have already modified an sm57, first by replacing the transformer with a Tab T58 (magic experience with this new configuration, I highly recommend).
Then I tried the Shure R45 cartridge, we are getting closer.

Now I would like to try something more special for him.
I already have a Shure R115 cartridge. I would like to adapt it to an active transformerless circuit powered by phantom power.
I want maximum bandwidth, minimum distortion and good harmonic response. Balanced and around 200ohms output.
Familiar with a few DIY projects, but I'm no electronics expert.
I am looking for information on solid state amplification, impedance matching, possibly a switchable multi amplification and/or correction eq (if necessary i don't know).
Your opinions on relevance, feasibility and your experiences are welcome.

best regards

 

[kingkorg]

Whatever electronics you use it will introduce distortion and limit max spl. Only thing you might gain is less noise and the mic will be less affected by the pramp used. Don't know how important this is for live use. Simplest and probably most cost/time effective would be to use the guts of something like Klark Teknik CT1 and transplant into your mic.

 

[abbey road d enfer]

I already have a Shure R115 cartridge. I would like to adapt it to an active transformerless circuit powered by phantom power.
I want maximum bandwidth, minimum distortion and good harmonic response. Balanced and around 200ohms output.

Looking for a Cloudlifter Type Thing

Low output ribbon/ dynamic microphone phantom-powered circuit new information

 

[clbzh]

As the didgeridoo is a rather weak source in a louder sound environment, I prefer to stick with dynamics.
With some mixers I feel like I'm only amplifying bass while the subtleties of this instrument are more high mid. Obviously this happens most often indoors.
That's why I would like to use them for live.

That's what I thought I figured out after some research.
But what is not clear to me is do I plug directly into the capsule? It replaces the transformer?
I could read that the transformer was necessary in front of such a low impedance like the ribbon or dynamic capsule.
What about Lewitt or Blue active transformerless dynamics?
If the transformer is necessary, it is better to keep the current microphone which is very good and put this kind of device before the mixer.
Cloudlifters are ribbon boosts? Like an active ribbon circuit?
Mic level output?

I was wondering about the possibility of replacing the function of the transformer and amplifying at the same time.
Is the principle radically different from condenser microphones where the capsule is of high impedance?
A product such as the SE Electronics DM2 let me assume that it was possible to choose its input and output impedance. Obviously fixing them like the CT-1 you speak of.
In the datasheet of THAT1500 series, it is said that it can be used in moving-coil transducer amplifier application.
At first I thought more of a transistor circuit.

 

[abbey road d enfer]

But what is not clear to me is do I plug directly into the capsule? It replaces the transformer?

Plug what?

I could read that the transformer was necessary in front of such a low impedance like the ribbon or dynamic capsule.

Not all dynamic mics need a transformer. Many are transformerless.

What about Lewitt or Blue active transformerless dynamics?

It's very likely that the capsule they use does not need a transformer. The active electronics are there to provide an elevated level, comparable to a condenser mic.

Cloudlifters are ribbon boosts? Like an active ribbon circuit?
Mic level output?

Ribbon mics have a very low impedance typically less than 1 ohm; they deliver a very low level. that's why they must have a transformer.
However, teh design and construction of such transformer makes it quite expensive and somewaht limits the performance.
By including active electronice in the mic, it lightens the design constraints, and allow the mic to deliver an elecated level, comparable to a condenser mic, which is beneficial to teh overall noise performance, since cable noise due to interference and radio frequencie are less disturbing.

I was wondering about the possibility of replacing the function of the transformer and amplifying at the same time.

Some capsules (e.g; most of Shure dynamic capsules) are lower impedance (about 50 ohms), which is not optimum for any mic preamp.
Designing active electronics for such a low impedanceis difficult, mainly because of teh limitations of phantom power, so a transformer is preferred.

Is the principle radically different from condenser microphones where the capsule is of high impedance?

Totally. Super-high impedance creates a totally different set of constraints than super-low.

A product such as the SE Electronics DM2 let me assume that it was possible to choose its input and output impedance.

Not really. Again because of phantom power limitations.

In the datasheet of THAT1500 series, it is said that it can be used in moving-coil transducer amplifier application.

Definitely. They are designed for low impedance (150 to 600 ohms) sources. However, their current draw makes them challenging the limits of phantom power.
Have you looked at teh circuit I propose in one of links I posted?

 

[clbzh]

Perfect, this time it's quite clear!
Thanks to you two.

Have you looked at teh circuit I propose in one of links I posted?

Yes, that's why I wanted to know if they have the same function.
Can I contact you privately for these pcbs?

 

[abbey road d enfer]

Can I contact you privately for these pcbs?

Please do.

 

[clbzh]

Please do.

The forum being remarkably provided with information, I have often found what I was looking for without having additional questions, this post will be my 6th and I cannot yet access all the features. Can you start this conversation please?

I take this opportunity to ask you, where can I find the schematic?

 

[ccaudle]

I have not been able to find any specifications for the Shure R115 cartridge. What is the sensitivity and output impedance?

The impedance balanced single op-amp OPA-Alice style circuit from Rogs should be a good choice for a moving coil buffer.
op-amp phantom powered buffer
Two extra resistors could add gain if desired. Exact capsule specs would determine if that circuit is a good choice or not.

 

[abbey road d enfer]

I have not been able to find any specifications for the Shure R115 cartridge. What is the sensitivity and output impedance?

It's the capsule used in the 55SHii

Impedance 270 r​

Sensitivity -58,0 dBV/Pa​

The impedance balanced single op-amp OPA-Alice style circuit from Rogs should be a good choice for a moving coil buffer.

Most opamps are not adequate for a low impedance source, if noise is a primary concern.
A 270r resistor produces 2.1nV/sqrtHz noise voltage density. OPA 1642 at 5.1 is more than 6dB higher. The balanced output would decrease S/N ratio by another 3dB...
Of course, it should be acceptable in a R n' R concert configuration, but for a more demanding application, a quieter opamp is desirable. the problem is that thses quieter opamps are also power hungry.

 

[ccaudle]

Impedance 270 r​

Sensitivity -58,0 dBV/Pa​

That seems like a good candidate for a buffered transformer. Use a transformer for (nearly) noise free gain, then use a buffer to isolate the transformed higher impedance from cable capacitance and preamp load.

I have never worked through the noise on a traditional simple buffer design, e.g. Schoeps style circuit. Any numbers you can pull out of your head for noise equivalent of something like that?

 

[abbey road d enfer]

That seems like a good candidate for a buffered transformer. Use a transformer for (nearly) noise free gain, then use a buffer to isolate the transformed higher impedance from cable capacitance and preamp load.

It's an option. I think that's the most common approach for existing commercial products.
There may be other circuits using discrete bipolar front ends, running at about 1-2mA, which would result in about 1nV/sqrtHz. The LSK389 dual FET, running at the same quiescent, would also have about the same noise level

I have never worked through the noise on a traditional simple buffer design, e.g. Schoeps style circuit. Any numbers you can pull out of your head for noise equivalent of something like that?

The Schoeps circuit is not particularly quiet, starting with a FET that has about 4nV/sqrtHz noise voltage density, aggravated by the emitter-followers, but OTOH the typical condenser capsule delivers nearly 20dB more sensitivity than a dynamic capsule.
Another issue with the Schoeps circuit is that it has only 6dB gain, which still does not mask the noise of the preamp it is connected to.