Warm Audio WA-67 - Teardown

[Mworthin]

A couple years back i bought a sheet (A5-sized or so) of some adhesive-backed rubber, maybe 2mm thick or so, for the purpose of damping mic body tubes. Haven't yet gotten around to actually using it yet, but that might be a cheap-ish option?

As long as the heat from the tube doesn’t weaken the adhesive and there’s room enough inside the tube, anything that increases the damping should improve the resonance.

That video is really sobering…it is enough to make you want to machine a new body tube than try to fix the old one. I can’t imagine using those faux 67s on something like piano, which is how Keith Jarrett’s “The Köln Concert” was recorded. A notch filter might not be enough.

 

[Gus]

What is up with the 4.7uf? What up with the transformer? it is not the same shape.
I wonder if they know how to adjust the circuit for a different capsule and transformer.

 

[kingkorg]

One important thing, once the mic is assembled, and base tightened the mic will not ring anywhere close to that shown in the video.

Simple way of additional damping is to add some material such as foam to the vertical brackets of the mic that will touch the sleve. Rode nt1 is a perfect example.

BM800 sleve is made perfectly and should not ring at all. Very close to u87.

 

[Whoops]

it is enough to make you want to machine a new body tube than try to fix the old one.

Why? it's just a matter of damping nothing more, it's an easy fix

I can’t imagine using those faux 67s on something like piano,

Although I did the video to showing the ringing when "you tap the body",
I have many doubts that this would present any problem during recording,
when I'm recording no one is tapping the microphone like I did it in the video.
And without other proof or more testing I doubt frequencies from the Piano will make the body ring.

So as is I will not have any problems in using the WA67 in Piano or any other instrument.

which is how Keith Jarrett’s “The Köln Concert” was recorded.

I personally don't really like the Piano sound in that record, a Piano has much more low end than what is presented on the recording, the Piano sounds metallic, there's too much reverb and the choice of reverb is also not inspired.
The playing and the music are quite good though

I use U67s in Piano all the time and the sound is much better than it's presented in that recording, so I'm sure what I don't like was not due to the mics used

 

[JW]

It was cold though.

 

[Whoops]

It was cold though.

I'm pretty sure about that

 

[living sounds]

I personally don't really like the Piano sound in that record, a Piano has much more low end than what is presented on the recording, the Piano sounds metallic, there's too much reverb and the choice of reverb is also not inspired.
The playing and the music are quite good though

It was a bad piano:

https://en.wikipedia.org/wiki/The_Köln_Concert
Thanks for showing your findings, very interesting indeed. Is there any consensus on a manufacturer that makes the best sounding affordable U67 clone?

 

[Whoops]

One important thing, once the mic is assembled, and base tightened the mic will not ring anywhere close to that shown in the video.

I was aware of the ringing when the mic was assembled and had the base tightened,
I though it was too ringy so I just dismantled it to understand were the high pitch ringing was coming from, and discovery it was from the outer tube, and maybe a bit from the lower ring..
So assembled it rings also, much more than a Neumann mic, although much less of course than the video I showed tapping the body tube alone.

If this presents a problem in recording conditions or not I don't know, maybe isn't really a problem, but also doing some damping doesn't cost anything and will not make anything worse, so there's nothing to loose.

 

[Whoops]

It was a bad piano:

https://en.wikipedia.org/wiki/The_Köln_Concert

Oh I see,
thank you so much for sharing that, I was not aware to be honest.
I know that record, since its a pretty well known solo piano jazz record but I never liked the Piano sound.
So now I know why.

"The piano they had was intended for rehearsals only and was in poor condition and required several hours of tuning and adjustment to make it playable.[14] The instrument was tinny and thin in the upper registers and weak in the bass register, and the pedals did not work properly."

 

[Whoops]

Is there any consensus on a manufacturer that makes the best sounding affordable U67 clone?

I don't think there is any consensus between Engineers when it comes to gear...

But the Warm Audio WA67 is affordable and really good sounding.
So it's probably the best or one of the "best sounding affordable U67 clones"

I also recommend checking out Advance Audio microphones, all the mics I've used from them were really good

 

[Mworthin]

Living Sounds beat me to the backstory about the piano.

Whoops, it is good to know that when tightened down, it isn’t an issue.

 

[Whoops]

Whoops, it is good to know that when tightened down, it isn’t an issue.

I don't know if it's an issue or not when recording, it rings less when it's assembled, but it still rings when you tap on the body.
When we are recording we are not tapping on it, so I don't know if it's a problem or not...

maybe some frequencies and vibrations from an instrument will make the body vibrate and that ringing will be recorded, but I don't know if that will happen , I have no proof of that.

 

[Whoops]

I've just traced the circuit of the Warm Audio WA-67 and it seems to be a straight copy of the U67 circuit.
The feedback and the De-emphasis are in place. (So why the Flat K67 capsule?)

 

[Whoops]

And this is the info and measurements I was able to do on the transformer.
The inductance measurement is not precise as the Mk-328 meter has a big tolerance when measuring inductance

 

[kingkorg]

C17 value is the answer. And the capsule isn't flat, it is just flatter and smoother than regular k67. C9 value is still imho an issue.

 

[Whoops]

C17 value is the answer. C9 value is still imho an issue.

Could you please explain mate?

thank you so much

 

[kingkorg]

It is the cap for tuning hf response. Higher value more attenuation. 100pf is in the lower range-less attenuation. Darker sounding capsule needs smaller cap. So it seems right. However cap value is also dependant on the transformer.

The real disadvantage is that you would want more hf from the capsule and more attenuation from the circuit to give you more noise reduction in the end. The whole point of deemphasis network. It works like Dolby NR. Using darker capsule defeats the point of using such circuit.

 

[Whoops]

Thanks for explaining it, now it makes more sense.

What do you think was the reasoning of changing C9 from 0,5uf to 4,7uf?

 

[Moby]

As this is the info and measurements I was able to do on the transformer.
The inductance measurement is not precise as the Mk-328 meter has a big tolerance when measuring inductance

View attachment 88462

What measuring frequency you used? Nickel alloys have no linear permeability by frequency.
Can you measure the ratios? It will tell more about the feedback deemphasis

 

[Moby]

Thanks for explaining it, now it makes more sense.

What do you think was the reasoning of changing C9 from 0,5uf to 4,7uf?

I don't see the reason if the operating point of the tube is the same as the original U67. Generally speaking 1uf is optimum value but 0.5uf does nice (musical) hpf shape.