Tube microphone project with vintage M7 capsules after RuudNL

Kaskelot · Oct 17, 2023

Thanks to RuudNL i now dare start a tube microphone prodject. His original post is at "U67"-ish microphone

A couple of yers ago I was given two lollipop ELA MZ 032 with low serial # 467 and 833. I had them re-skinned by Thiersch. I started to look for a shematic that could work with M7s and be simple to build. Have now aquired some parts and am bereadboarding them. I recon I will spend a bit on signal caps so please give some suggestions.
They will one day get rather large shiny brass casings. The tubes will have internal suspension instead of the spiders you usually find on tube microphones.

Thansks in advance for some tips.

rock soderstrom · Oct 17, 2023

Welcome to the forum Kaskelot!

If you want to set up your microphones, you urgently need housings for the capsules that act as Faraday cages, otherwise you will have problems with strong noise sounds.

Your great M7 capsules would rather harmonize with linear microphone circuits like U47 and similar IMHO.
Try what you like best, in the end its your decission. DIY

For the capacitors, decent ERO MKP or MKT types are not particularly expensive, avoid super expensive "high-end" caps, put your money rather in quality mic bodies, which after the capsule are the most important part for a microphone.

RuudNL · Oct 18, 2023

With a M7-style capsule (or a K47) you should remove the HF feedback capacitor.
And yes, you will need good screening for the capsule and the high impedance parts. (Faraday cage.)
I already can hear the hummmmmmm......

Kaskelot · Oct 18, 2023

Thanks! Aware of the hum but I wanted to first build something open and accessible so I could easily tweak. The capsules are 400 # apart so I anticipate a lot of fine tuning to get a stereo pair.
What voltage would you suggest for the capsules?

Kaskelot · Nov 15, 2023

rock soderstrom said:
Welcome to the forum Kaskelot!

..and thanks GroupDIY for letting me in.
I have started on a cage for the breadboard with copper tapeing bottom.

Have bought the resistors: Dale 1/2 watt.
Thinking about MCAP Supreme Silvergold.oil for C8, 1 uF.
You can see my sketch for the casing at my homepage: Workshop. I have made contact with a machine workshop that is willing to machine the pair. It turned out that the manager was related to a member of a rock group I sang in during the 70ties. He is also a musician.
Any suggestions for the pF caps? The casing will be pretty big but do you think it will work?