Something à la M49 - S49 microphone project with EF732

[ln76d]

[Adaptation of new topology]

Cardioid only

Based on M49 circuit, using EF732 and Funkwerk Leipzig AU632 and M7 capsule.
Considering 150pF cap from plate to ground - will be tested
PSU is modified Gefell N57.

Schematic updated.

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All microphones projects:
https://groupdiy.com/index.php?topic=62423.0
https://groupdiy.com/index.php?topic=62441.0
https://groupdiy.com/index.php?topic=64687.0
https://groupdiy.com/index.php?topic=62601.0
https://groupdiy.com/index.php?topic=63436.0
https://groupdiy.com/index.php?topic=63682.0
https://groupdiy.com/index.php?topic=62262.0
https://groupdiy.com/index.php?topic=62682.0

 

[micaddict]

Cool!

Sound samples?

 

[ln76d]

Next week. I will put also two other tube mikes samples.

Edit:

Didn't happen

Someday, i promise

 

[micaddict]

Super! 

 

[RuudNL]

10 uF // 2200 ohm is way too low! (Unless you don't want any LF...)
I think 100 uF (or even more) would be better...

 

[ln76d]

Currently working on it
Even 100uF isn't enough for similar to M49 preamp response with feedback.
That's why David Royer didn't use cathode capacitor.
It's not that there's no low end response with 10uF

With feedback output level should be ca 10-12dB lower.
I have not much space to put whole feedback/eq circuit, that's why i choosed simplified circuit.
Am trying right now find some option to use aditional cmponents.
With feedback difference between 10uF and 25uF isn't much.

Edit:
Previous topology based partially on M49C. Currently these parts aren't in use.

 

[RuudNL]

I think I even used 470uF in one of my tube microphones.
There is only a low voltage over this capacitor, so you can use a physically small one.

 

[ln76d]

Yes, i know
I thought, however, i will give a chance to the feedback circuit
It's hard to fit but maybe today i will finish build.

 

[Khron]

Would something like this help, perhaps?

http://cdn.shopify.com/s/files/1/0867/8438/products/rk47-pair.jpg?v=1432508511

 

[ln76d]

Thanks, but rather I was thinking about Neumann capsules.

Maybe someone have manual for first M49 (not B or C version)? Or response graphs?

 

[duantro]

Nice work. What capsule are you using?

 

[ln76d]

M7 but am not sure is it from gefell or berlin but probably gefell.
Currently i disassembled whole microphone and i build it again in a different way.
That's why there's no news here
The body am using is smaller than M49, it's se electronics mini.
Pretty well made, most of brass, different looking little bit, but i do not focus on making clone  only a good mic
I wanted to make switch inside for to "B" or not to "B" option - switching from "broadcast" filters to flat response, but  unfortunately there wouldn't be place for that.

 

[ln76d]

Final version of schematic updated in first post. I hope there wouldn't be more changes.

There wouldn't be resistor feedback with HPF. 
I'm not even sure is it give higher level. It's hard to simulate
If the output level will be too low i will decrease C2 value to 5.6pF.

For EF732/5840, cathode resistor should be 1,6k-1,8k range to get 43V at the plate.

Output capacitor changed for 0.5uF - there wouldn't be any low end drop anyway.
In all mikes which i build or moded (with transformer output) i found that with the lower capacitance always sounds better.
Another things is that i bought really nice MP capacitors. Today i did comparison in different mike - MKP vs MP.
I don't know what is with those old MP but they always sounds a lot better than any MKP which tried.
This is always huge difference!

Still will be trying 600pF LPF filtering cap, but i think that with M7 it wouldn't be necessary.

 

[granger.frederic]

MP are mica / paper capacitors : long life but lower energy density (bigger) , often called PIO (paper in oil) , very usable in a mic ...
stock use in many historical classic mics :  like U47 (bosch) for ex.
better when sealed with glass beads...

 

[ln76d]

MP are mica / paper capacitors : long life but lower energy density (bigger) , often called PIO (paper in oil) , very usable in a mic ...
stock use in many historical classic mics :  like U47 (bosch) for ex.
better when sealed with glass beads...

I know what's MP capacitor i have lot of them in different values, sizes, packages or manufacturers like Siemens, Bosch, Hydra, ITT, RFT, Telpod etc.  In U47 were also used Hydra and Siemens caps not only Bosch
Am wondering how this is possible, that 30-60 years old capacitor can be better than good quality polypropylene!

 

[Khron]

Hey, it's "vintage" - "of course" it's better! ;D

 

[ln76d]

So try some leaky vintage electrolytic caps
These aren't better
With MP it always sounds clearer, especially in mid and high frequency range and this is realy audible - you don't have to choose what's best - you know it for the first listening
That's why i really like A/B test with switch!