RuudNL

"U67"-ish microphone
« on: May 22, 2020, 10:55:53 AM »
Just for fun, I recently put together a "U67"-ish microphone.
It is a kind of mix between a U67 and a U87.
The microphone works as expected, sounds good and I don't hear any difference between this microphone and a U87ai.
Measured self noise is 2 dB higher than a U87ai. Not too bad, but maybe a better EF86/EF806 could improve this.
I used an original Neumann capsule that I had as a spare.
The microphone is powered from an existing tube power supply, delivering +120 V for HT.
De-emphasis is through feedback from the output. (15 KHz is 5.5 dB down referred to 1 KHz.)

For those who are interested: the schematic is in the attachment.
There is a solution for every problem!

http://www.vansteenisaudio.nl


OneRoomStudios

Re: "U67"-ish microphone
« Reply #1 on: May 22, 2020, 01:05:25 PM »
Very nice. Which output transformer did you use?

RuudNL

Re: "U67"-ish microphone
« Reply #2 on: May 22, 2020, 01:47:21 PM »
This one (3U Audio):

https://www.ebay.nl/itm/3U-Audio-GZT-87-Output-Transformer-for-Condenser-Microphone/111683319855?hash=item1a00d8382f:g:f6kAAOSwiCRUg89Z

Although it has a small core, the frequency response is excellent.
(Measured from 'test input' to output, 20 Hz is only 1 dB down.)
« Last Edit: June 29, 2020, 09:04:31 AM by RuudNL »
There is a solution for every problem!

http://www.vansteenisaudio.nl

Re: "U67"-ish microphone
« Reply #3 on: May 22, 2020, 02:04:07 PM »
This is phenomenal. Thank you for sharing!

RuudNL

Re: "U67"-ish microphone
« Reply #4 on: May 23, 2020, 06:47:22 AM »
Picture of the prototype.


There is a solution for every problem!

http://www.vansteenisaudio.nl

RuudNL

Re: "U67"-ish microphone
« Reply #5 on: June 06, 2020, 02:29:39 PM »
If anyone wants to try my design: I have a few extra printed circuit boards available.
(The PCBs fit into Chunger's 'budget' SYT-5 body.)

Edit June 07: All PCBs found a new owner...
« Last Edit: June 08, 2020, 05:10:02 AM by RuudNL »
There is a solution for every problem!

http://www.vansteenisaudio.nl

Sredna

Re: "U67"-ish microphone
« Reply #6 on: June 06, 2020, 06:59:40 PM »
Great, sent you a PM!  8)
Hmm... in which direction do the electrons actually go?

DjaiTeam

Re: "U67"-ish microphone
« Reply #7 on: June 07, 2020, 09:09:22 AM »
Hi Ruud,

Looking very nice indeed, must sound incredible!
I have a spare K87 capsule doing nothing so why not try this one ;D

Sent you a pm for the pcb.

Best Regards,

Iwan

Re: "U67"-ish microphone
« Reply #8 on: June 14, 2020, 04:33:14 AM »
Nice. I've thought of putting a 1nF capacitor for the high end de-emphasis but in a cheaper FET mic like the BM-600 (or in a DIY U87 clone).

RuudNL

Re: "U67"-ish microphone
« Reply #9 on: June 14, 2020, 05:31:54 AM »
In this design the de-emphasis is done by HF feedback. (120 pF)
There is a solution for every problem!

http://www.vansteenisaudio.nl


Re: "U67"-ish microphone
« Reply #10 on: June 27, 2020, 01:19:56 PM »
Just finished building this mic this week and I am super, super impressed at how it sounds. I had a vintage Neumann capsule (circa 1979) that I put in there with the GZT transformer and  brand new JJ EF806s. Really love the sonics of what I'm hearing. Very quiet. I think I'm going to hit up Bowie for a Telefunken or Amperex and see where it goes. Here's a short clip of it through the UAD Avalon 737.

Bravo, Ruud! Bravo! And thank you for designing and sharing this awesomeness!

https://www.dropbox.com/s/532aon0qnxkvtgh/Ruud67Circuit-1.wav?dl=0

RuudNL

Re: "U67"-ish microphone
« Reply #11 on: June 27, 2020, 02:38:38 PM »
Glad to read that you have got it working and that you are happy with the result.
I compared mine with a 'real' U67, but I didn't hear any difference!
In fact, the LF response is better than the U67. (Because there is no fixed low-cut, we want the full audio range!)
In the meantime I have experimented with some more tubes.
The JJ Electronics EF806S are very good and a NOS Mullard EF86 was even a fraction quieter.
One thing you can experiment with is the de-emphasis capacitor.
I started with 120 pF, but with a Neumann capsule the microphone was a little brighter than I wanted.
So I changed the capacitor to 150 pF.
But yesterday I have built a second version with a non-Neumann capsule and with that one I ended with 100 pF.
So that means you have to 'tune' the capacitor for the capsule you are using.
To be honest, I never was a real fan of tube microphones (usually they were too noisy for me), but this one changed my mind...
There is a solution for every problem!

http://www.vansteenisaudio.nl

Re: "U67"-ish microphone
« Reply #12 on: June 27, 2020, 06:36:31 PM »
If anyone wants to try my design: I have a few extra printed circuit boards available.
(The PCBs fit into Chunger's 'budget' SYT-5 body.)

Edit June 07: All PCBs found a new owner...

hello ruud, will you publish the PCB layout for self-etching?  Cheers

RuudNL

Re: "U67"-ish microphone
« Reply #13 on: June 28, 2020, 04:38:07 AM »
If you can wait a little: there is a company thinking about selling this design as a complete kit.
(That would save you also the time and effort ordering all the separate parts.)
There is a solution for every problem!

http://www.vansteenisaudio.nl

Re: "U67"-ish microphone
« Reply #14 on: June 28, 2020, 06:03:33 AM »
If you can wait a little: there is a company thinking about selling this design as a complete kit.
(That would save you also the time and effort ordering all the separate parts.)

Very interesting, thanks again 👍

Ricardus

Re: "U67"-ish microphone
« Reply #15 on: June 28, 2020, 11:40:23 AM »
If you can wait a little: there is a company thinking about selling this design as a complete kit.
(That would save you also the time and effort ordering all the separate parts.)

TAKE MY MONEY!!!   :D
Audio mastering for hire..

Re: "U67"-ish microphone
« Reply #16 on: June 28, 2020, 04:07:38 PM »
Just for fun, I recently put together a "U67"-ish microphone.

Hey, very nice  :)

Do you have a personal opinion on your implementation of the high frequency network vs the original?

I have a new U87Ai here that I'm looking to U67-ize and am looking through the various schemes that used the K67,  the valve SM69 has the simplest of the lot but perhaps not enough?


Note to self:  Don't let c**ts wind you up

Gus

Re: "U67"-ish microphone
« Reply #17 on: June 28, 2020, 04:42:12 PM »
I have installed U67 like HPF in phantom powered microphones(basic cut and paste) some with an added low pass as well.

Waveborne posted a circuit  years ago adding a 67 like network to a MXL IIRC this was before people chased him away.

I don't get removing the HPF.
 
Yes SOLO male voice often sounds better but how does it sit in the mix?

If the room is not treated there is often a lot of low frequency junk that you don't want. If you turn the filter on you will see a drop on the metering depending on how well the room is designed. If it is in a house I would keep the filter on.


Re: "U67"-ish microphone
« Reply #18 on: June 28, 2020, 04:58:29 PM »
I have installed U67 like HPF in phantom powered microphones(basic cut and paste) some with an added low pass as well.

Waveborne posted a circuit  years ago adding a 67 like network to a MXL IIRC this was before people chased him away.

I don't get removing the HPF.
 
Yes SOLO male voice often sounds better but how does it sit in the mix?

If the room is not treated there is often a lot of low frequency junk that you don't want. If you turn the filter on you will see a drop on the metering depending on how well the room is designed. If it is in a house I would keep the filter on.

 I agree on the HPF, the Neumann U67 version is actually pretty clever but I'll look for Wavebourne's circuit, thanks :)
I was just curious about Ruud's implantation of the hi frequency attenuation vs the u67 scheme.

I think the idea behind Neumann omitting that particular stuff - HPF- on the SM69 might be to do with it being a stereo microphone designed for far/mid field full range recording but, dunno?

Cheers.
Note to self:  Don't let c**ts wind you up

RuudNL

Re: "U67"-ish microphone
« Reply #19 on: June 29, 2020, 04:35:41 AM »
The Neumann SM69 didn't use de-emphasis or a high-pass filter and used a K67-style capsule.
Because this microphone was mainly intended for 'distant miking', the theory was dat high frequencies would undergo a certain amount of attenuation as a result of friction with the air molecules.
As a result of this, the high frequencies would be more attenuated than the lower frequencies, that have more energy.
The air damping for high frequencies would act as a 'natural de-emphasis'.
(If you listen to a musical event on a distance, you will notice that you mainly hear low frequencies, this is the same effect.)

The U67 has a fixed high-pass filter, that can be removed by cutting a jumper wire.
It seems that everybody disables the high-pass filter, in order to obtain a better LF response.
Also, this has an influence on the phase linearity at low frequencies.
But even without a high-pass filter, subsonic frequencies are attenuated by the transformer.
There is a solution for every problem!

http://www.vansteenisaudio.nl


 

Related Topics

  Subject / Started by Replies Last post
16 Replies
11551 Views
Last post January 13, 2005, 02:20:33 AM
by bradzatitagain
76 Replies
36758 Views
Last post July 16, 2005, 04:17:56 PM
by louder
3 Replies
1998 Views
Last post May 18, 2005, 05:32:47 AM
by nacho459
1557 Replies
285855 Views
Last post July 01, 2020, 12:23:09 PM
by FarisElek