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

kingkorg

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?


D. J. H.

The standard way to reduce much of the noise and distortion in audio gear in 1955 was to have a couple of beers.
 Anything else was too fiddlesome and too expensive.

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.
D. J. H.

The standard way to reduce much of the noise and distortion in audio gear in 1955 was to have a couple of beers.
 Anything else was too fiddlesome and too expensive.

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


 

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