Warm Audio WA-67 - Teardown

[Whoops]

What measuring frequency you used? Nickel alloys have no linear permeability by frequency.

The MK-328 uses a different method for measuring inductance, I don't think it uses a fixed frequency it uses Pulses, it's a complex way and I was not able to fully understand it when i read the MK-328 tech docs (ATmega328 tester open source).
I know that it's not precise when measuring inductance, it's more like in the ballpark value than correct.

Can you measure the ratios? It will tell more about the feedback deemphasis

I already soldered the transformer back into the mic's PCB... sorry

what do you wanted me to? to input a 1V And and measure the the voltage in the secondaries?
How could I measure the ratios?

If it's simple I don't mind un-soldering it again and let you know

 

[Moby]

Hey

The MK-328 uses a different method for measuring inductance, I don't think it uses a fixed frequency it uses Pulses, it's a complex way and I was not able to fully understand it when i read the MK-328 tech docs (ATmega328 tester open source).
I know that it's not precise when measuring inductance, it's more like in the ballpark value than correct.



I already soldered the transformer back into the mic's PCB... sorry

what do you wanted me to? to input a 1V And and measure the the voltage in the secondaries?
How could I measure the ratios?

If it's simple I don't mind un-soldering it again and let you know

Hey, dont bother with it. It's cool for other members who want to repair this mic to know what's inside. I believe they did the proper ratio since it sounds as expected.

 

[Whoops]

I discovered another new thing for me,
If you have the WA67 connected and turned on and then you turn on 48V (phantom power) from your mic pre it inflicts low end loss, pretty big low cut.
I was testing another mic and left the 48V on, and when I tried the WA67 I though something was wrong with it, then I turned 48V off and the Sound was back to normal and the Low End was back.

I don't think I ever experienced this before with a tube mic, I don't remember ever noticing this happening with the U67s.
I'm also not seeing at the moment why sending 48V will make a low cut, but there must be a reason for it.

Glad I teach my students to only turn the Phantom power after connecting a mic that needs it, and disconnect it before unplugging the mic, and never leave the 48V on after a session.

 

[living sounds]

You can listen to comparisons between the wa-67 and the Neumann reissue here:

https://www.amazona.de/test-warm-audio-wa-67-grossmembran-roehrenmikrofon/
To my ears these sound very different and the Neumann is very obviously a far better sounding mic.

Here the same reviewer compares the modern U67 vs a vintage one:

https://www.amazona.de/test-neumann-u-67/

 

[Whoops]

B+ measures 191V in this mic,
Neumann states 210 +-2%, so thats from 205,8V to 214,2V.
I don't seed whats the reason to have the B+ this low, I will check the PSU next and see if there's a trimmer to set the voltage to 210V

 

[Whoops]

Soldering Comparison

Neumann vintage U67 (solder on both sides)



Reissue Neumann U67 (Solder on both sides)



Warm Audio WA-67 (Soldering only on one side, it saves time and saves money on solder, less toxic solder fumes and it looks great also)

 

[Whoops]

Both Vintage and Reissue Neumann's meet the NASA Soldering standard,
the Warm Audio on the other end is not going to Space, NASA rejected!

 

[abbey road d enfer]

I discovered another new thing for me,
If you have the WA67 connected and turned on and then you turn on 48V (phantom power) from your mic pre it inflicts low end loss, pretty big low cut.

My distant diagnosis is that DC flows into the transformer's secondary, which I could attribute to one leg being shorted to ground.
Should not be too difficult to trace.

 

[Whoops]

It has to be related to DC flowing in the transformer,
but no winding of the secondaries is connected to ground:

 

[abbey road d enfer]

It has to be related to DC flowing in the transformer,
but no winding of the secondaries is connected to groud:

Well, it sure doesn't show on the schemo, but what about in real life? Time to take out the multimeter.

 

[Whoops]

My distant diagnosis is that DC flows into the transformer's secondary, which I could attribute to one leg being shorted to ground.
Should not be too difficult to trace.

Abbey you were completely correct.
Your post made me think about the situation.
When I was desoldering the transformer I remember seeing a strange solder bridge from one of the outputs to ground, but I though I was not seeing right and didn’t took it seriously.
I re touched that solder and traced the circuit after that.

But after your post I started thinking about it again and I went back to the first photos I took of the circuit before tracing, and yes there was a solder bridge of one of the outputs (black wire) to the ground track next to it.



The Circular trace is ground and the big pin in the middle is the transformer signal output, it was shorted straight from factory.
So this microphone came from the factory with an Unbalanced output because soldering is awfull and the work was done in a rush, then no quality control from Warm Audio seemed to have happened.

If I haven’t decided to trace the circuit and take the transformer out I would never have discovered this…

So this was the reason for the Low Cut with phantom power on.

mic shipped with broken capsule mount, a solder bridge… Not Good
I started this thread thinking Warm Audio we’re doing a good product for the price, and with the development of this thread I changed my mind

 

[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

Now I fiured out why this primary inductance value is so small. This meter can measure up to 20H and has the self variable measuring frequency. It probably switched himself to 2khz or more

 

[abbey road d enfer]

So this microphone came from the factory with an Unbalanced output because soldering is awfull and the work was done in a rush, then no quality control from Warm Audio seemed to have happened.

If I haven’t decided to trace the circuit and take the transformer out I would never have discovered this…

So this was the reason for the Low Cut with phantom power on.

mic shipped with broken capsule mount, a solder bridge… Not Good
I started this thread thinking Warm Audio we’re doing a good product for the price, and with the development of this thread I changed my mind

In the 70' s and early 80's, the audio industry was divided in two camps. The very expensive over-engineered products aimed at broadcast, and a herd of new, eager small manufacturers that came with brilliant ideas and very little money.
If you were a brilliant SE with very little money, you would buy from the latter, and be prepared to do your own QC.
Some of these products have acquired legend status, many are forgotten.
Today, you buy e.g. a Rode microphone, you can be confident it works right out of the box, but in 20 years, it will still be only a decent mass-production item.

 

[living sounds]

Wow! No way I am going to buy anything from Warm Audio. Does anyone know of a quality mic on the market that sounds as good as the Neumann U67 but for less money?

 

[Whoops]

Does anyone know of a quality mic on the market that sounds as good as the Neumann U67 but for less money?

Mate I would just build one with Poctop pcbs. You can choose the components and you control every part of the project.

As for commercial mics I really like Advanced Audio, every mic I listened from them was very good, they don’t mass produce. I think they assemble the mics themselves, they re very knowledgeable and passionate about microphones.

 

[living sounds]

Thanks! I've DIYed mics before, but feel this is an area where expertise and proper testing equipment are vital. It's not as easy to get right as a compressor or preamp, as evidenced by all the lousy to mediocre sounding mics out there, even those made by commercial outlets.

Juding from these comparisons I think the Advanced Audio version doesn't do the Neumann thing either, unfortunately:

 

[RuudNL]

I never had a good feeling about the Warm Audio products, but things can be worse!
What to think about this 'construction'? (Golden Age Project)
I would take a lot of creativity to make it worse than this...

In 2018 they sold this 'thing' for €1499 including VAT...

 

[living sounds]

I never had a good feeling about the Warm Audio products, but things can be worse!
What to think about this 'construction'? (Golden Age Project)
I would take a lot of creativity to make it worse than this...

They can't be serious...

 

[Whoops]

Thanks! I've DIYed mics before, but feel this is an area where expertise and proper testing equipment are vital. It's not as easy to get right as a compressor or preamp, as evidenced by all the lousy to mediocre sounding mics out there, even those made by commercial outlets.

I think the problem with cheap commercial outlets is that they have to cut costs, so they cut in a lot of different details of the build.
In this particular case Warm Audio, cut cost on a nice pcb layout, on the factory they used to produce the mics, on the PSu and on the capsule mount.

DIYing you can choose not to cut costs, you can buy all quality parts and if you assemble it well and use good parts I don't see the need to use different test gear than we already have in our worshops. I don't think it's more dificult than doing a compressor that might need calibration or any mic preamp.
Mic circuits are really simple and in the case of the Neumann U67 and U47 everything is pretty well documented that plenty of information all around.

 

[living sounds]

I think the problem with cheap commercial outlets is that they have to cut costs, so they cut in a lot of different details of the build.
In this particular case Warm Audio, cut cost on a nice pcb layout, on the factory they used to produce the mics, on the PSu and on the capsule mount.

DIYing you can choose not to cut costs, you can buy all quality parts and if you assemble it well and use good parts I don't see the need to use different test gear than we already have in our worshops. I don't think it's more dificult than doing a compressor that might need calibration or any mic preamp.
Mic circuits are really simple and in the case of the Neumann U67 and U47 everything is pretty well documented that plenty of information all around.

I understand what you are saying, but there is ample room for things to go wrong. For instance, how do I know the person designing the PCB for those high impedance circuits really understood the challenges and made sure the manufacturer got things right? And once it's built I can't just send test tones from my DAW through the mic and look at the response. You need an anechoic chamber and really good measuring equipment to fully understand what is going on with the mic, don't you?

I've build mics before that sound good, like an ioaudio U47 clone with a Beezneez capsule. But I have no way of actually verifying if it sounds correct, its best, like (or at least close to) the original.

I may still attempt to build an U67 though. A modern Neumann + NOS Telefunken tube is really too expensive...