"U67"-ish microphone

[Maliq]

Wow great thanks for your answer. I still got 2 of those psu's laying around.

Changed the 72V Zener to 62V zeners.

A chance to get the pcb's allready? if you could put up a BOM that would also be nice. Maybe a few more pictures from the mic, if possible. Would love to build one since i'm in need for a different descent tube mic, i'm over here in germany, been to the netherlands pretty often.

Regards

 

[RuudNL]

I had a few PCBs made, but they have all been sold now.
And about the bill of materials: there isn't much in the circuit, so the fastest route is to write down the needed components yourself.
The only 'difficult' parts are the high-value (G.ohm) resistors. (Not every electronics store has them.)

 

[abbey road d enfer]

The only 'difficult' parts are the high-value (G.ohm) resistors. (Not every electronics store has them.)

Fanell have them at a reasonable price:
https://fr.farnell.com/te-connectivity/rgp0207chk1g0/resistance-couche-epaisse-1g-10/dp/2805261
They also have 10, 100, 1 000 and 10 000 Gohm at unrealistic prices!
https://fr.farnell.com/ohmite/um050e100bke/res-10000g-3w-radial-thick-film/dp/2944974

 

[RuudNL]

I usually get them from RS Components.

https://nl.rs-online.com/web/p/through-hole-fixed-resistors/1372742/

 

[Strick9]

This Cascade Elroy power supply I bought for cheap will work, right? I’m pretty sure it’s 120v B+ and 6.3v for the heater. 

 

[RuudNL]

I would measure the +HT output, just to be sure.
The polarisation voltage on the capsule is ~½ of the +HT voltage.
More than 60 volts on the capsule is probably a bad idea...
(If the voltage is more than 120 Volts, you can always change the zener diodes in the power supply.)

 

[ubxf]

Big Thanks to Ruud for this awesome project. It sounds great. Ruud you are a prince.
Here is a picture before wrapping it up

 

[RuudNL]

Good to read that the microphone works (and sounds!) as expected!
Nice capsule by the way!

 

[ubxf]

Thank you, that capsule waited 17 years in my mic locker for your project to come along.
Well worth the wait.

 

[doqmemory]

What does the plate voltage A run at?  I think it was about 75v for U67.

 

[RuudNL]

It depends a bit upon the tube.
HT from the power supply is +120 Volts.
This voltage was chosen so that you can use a standard commercially available power supply.
Plate voltage is usually in the order of 55-60 Volts.
Plenty of headroom anyway!

 

[doqmemory]

I want to try one of these as soon as I can free up a suitable donor body.  With the smaller transformer, this should fit into something like an MXL 2010.  The larger SYT-5 bodies have been out of stock for so long (even the budget YT5 now) that an alternative design like this one is a great option to have.

 

[RuudNL]

Take care that you use a microphone capsule with a single backplate.
Sometimes capsules advertized as ' K67' seem to have isolated backplates.
In this case you have to connect both backplates together.

 

[Ricardus]

I don't see it up there. In fact I don't see much of anything on the site.

 

[RuudNL]

Send an e-mail and you will get an answer what to do!

 

[Kaskelot]

Thanks RuudNL!

Have just been waiting for this. Will start a project with two vintage M7 capsules reskinned by Thiersch.
I was wondering which caps to spend on C8....? I will not have any size restrictions as I am building in a rather large brass cylinder.
I am thinking Mundorf alu in oil and then maybe a Lundahl LL1578XL 10:1.
/Robert

 

[Khron]

Why use M7's with U67-ish electronics (which include high-frequency attenuation)? How dark / dull are you hoping (or intending) those mics to be?

 

[RuudNL]

If you want to use a M7 capsule, I would omit the HF feedback capacitor (C9).
That will result in a 'flat' circuit. (For a K47 or M7 capsule.)

 

[Spencerleehorton]

Might have to give this one a go!! Use up all my spare bits!!!

 

[innercityman]

I am using the microphone with this power supply:

https://www.thomann.de/nl/the_tbone_psu_sct_2000.htm
I replaced the zener diodes to lower the plate voltage.
I suppose that if it will become a kit, the power supply is included.
(Not sure when this will happen, still negotiating ...)

What about this kit you talked about ? Still negotiating ?