Neumann U67 Clone : D-U67 Tube Microphone Build Thread.

[Whoops]

I’m curious how the fluctuations in my new space affect my mics and if this is something I should consider when setting heater and polarization. Is it a good idea to use a UPS with automatic voltage regulation or is that overkill?
Thank you in advance!

Most people, probably more than 95% don't care at all.
I use my tube mics in a lot of different places so the mains voltage will always be slightly different,
people that work in a lot of different places will have the same situation. I never felt my tube mics to sound different in one place versus the other, neither I ever felt the sound was worse in some places or better in others. So I consider the effects of slightly different mains voltages marginal.
Off course if you will only ever use the Mic in one place, you can easily adjust the PSU for that specific place mains voltage.

Think about guitar players, mostly use tube amps that need Tube Biasing, they set up the Bias as they want in a certain place, but then in every gig they play or any practice room the mains will be different from the place where they setup the Bias to begin with, so the Bias point will be different. No one cares that much, and they sound good in any of those places.

Neumann states the margins of the B+ voltage and Heater voltage of the U67 at + - 2%.
So it means a B+ voltage from 205,8V to 214,2V and a Heater voltage from -6,426V to -6,174V.
Probably it could be even be + an + 5% and you wouldn't be able to tell the difference

 

[egroys]

Most people, probably more than 95% don't care at all.
I use my tube mics in a lot of different places so the mains voltage will always be slightly different,
people that work in a lot of different places will have the same situation. I never felt my tube mics to sound different in one place versus the other, neither I ever felt the sound was worse in some places or better in others. So I consider the effects of slightly different mains voltages marginal.
Off course if you will only ever use the Mic in one place, you can easily adjust the PSU for that specific place mains voltage.

Think about guitar players, mostly use tube amps that need Tube Biasing, they set up the Bias as they want in a certain place, but then in every gig they play or any practice room the mains will be different from the place where they setup the Bias to begin with, so the Bias point will be different. No one cares that much, and they sound good in any of those places.

Neumann states the margins of the B+ voltage and Heater voltage of the U67 at + - 2%.
So it means a B+ voltage from 205,8V to 214,2V and a Heater voltage from -6,426V to -6,174V.
Probably it could be even be + an + 5% and you wouldn't be able to tell the difference

View attachment 106430

Makes a ton of sense but that’s great to validate

 

[guitar4444]

I'm wondering if there would be likely to be any problem with using a single transformer for the supply? So one transformer with separate 6.3 volt and 210 volt windings? I'm presuming it's not going to make a difference. thanks for any help Greg

 

[Whoops]

I'm wondering if there would be likely to be any problem with using a single transformer for the supply? So one transformer with separate 6.3 volt and 210 volt windings? I'm presuming it's not going to make a difference. thanks for any help Greg

It’s great to use one transformer as it takes less space inside the box. But you need 18VAC to 20VAC for the heater rail.

Much easier to get 2 separate transformers for these needs that 1 transformer with the 2 needed secondaries

 

[neowalla]

I'm wondering if there would be likely to be any problem with using a single transformer for the supply? So one transformer with separate 6.3 volt and 210 volt windings? I'm presuming it's not going to make a difference. thanks for any help Greg

I think it's finding those transformers that is the problem. I asked this on this forum before (different thread). The consensus was to buy a second-hand Chinese power supply for an Apex 460 style mic and use the transformer out of it. I searched within the baba space for dual output, dual secondary transformers with no luck at all. I think that is why Dan specifies two separate transformers, but I'll let him speak for himself. If you have a source for them, do tell!

 

[Delta Sigma]

I think it's finding those transformers that is the problem. I asked this on this forum before (different thread). The consensus was to buy a second-hand Chinese power supply for an Apex 460 style mic and use the transformer out of it. I searched within the baba space for dual output, dual secondary transformers with no luck at all. I think that is why Dan specifies two separate transformers, but I'll let him speak for himself. If you have a source for them, do tell!

I've seen some posts about custom toroidals from a manufacturer in the EU. Depending on your enclosure, it would definitely be worth extra $$ for Dany's M49/EF-47 PSU that uses a choke. The NU-67 PSU, if I remember correctly, doesn't take up a lot of room in the enclosure.

 

[wlinart]

I've seen some posts about custom toroidals from a manufacturer in the EU. Depending on your enclosure, it would definitely be worth extra $$ for Dany's M49/EF-47 PSU that uses a choke. The NU-67 PSU, if I remember correctly, doesn't take up a lot of room in the enclosure.

that's audiophonics.fr

 

[dmp]

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So one transformer with separate 6.3 volt and 210 volt windings? I'm presuming it's not going to make a difference. thanks for any help Greg

No, you won't have enough voltage drop with 6.3v to build a u67 correctly.
The heater AC is rectified to -6.5vDC using a 20v AC winding. You might be able to get away with 15vAC

 

[Murdock]

that's audiophonics.fr

No, I think he meant toroidy.pl. It‘s a polish company who produces Custom toroidal transformers at a very good price and really high quality. Top Customer service too.

 

[wlinart]

No, I think he meant toroidy.pl. It‘s a polish company who produces Custom toroidal transformers at a very good price and really high quality. Top Customer service too.

They both are great to have multiple options here i'd say.

 

[TLRT]

We have got a local transformer maker in the EU, for u67 I have 110-220 primary and 20v/200v secondary transformers which works perfectly fine for u67 builds. However I prefer regulated supplies,so 9v secondary is enough for any regulator like lm317.

 

[HerbertR]

We have got a local transformer maker in the EU, for u67 I have 110-220 primary and 20v/200v secondary transformers which works perfectly fine for u67 builds. However I prefer regulated supplies,so 9v secondary is enough for any regulator like lm317.

Agree 6.3V AC Output works for unregulated DC Filament with about 6.3V DC well. But with a Voltageregulater LM7806 or a variable LM317 Regulator you can get troubles to have enough Voltagedifference of at least about 2-3V after Rectifieng, Smoothingcaps..., or the Voltageregulator shuts down. So it is better to drive the Filament PSU with about 9V AC Secondary to stay on the safe side.

 

[Delta Sigma]

No, I think he meant toroidy.pl. It‘s a polish company who produces Custom toroidal transformers at a very good price and really high quality. Top Customer service too.

That's the one! Though I've looked at audiophonics as well.

 

[neowalla]

Hello my fellow tube addicts, I'm thinking of a pair of U67's for my next project and wondering if it is possible/advisable to build a "dual" power supply for both microphones?

 

[Whoops]

Hello my fellow tube addicts, I'm thinking of a pair of U67's for my next project and wondering if it is possible/advisable to build a "dual" power supply for both microphones?

You could do that, but I prefer to have things separate as I might have a session where I only need 1 microphone so I don't want to carry around a bigger and heavier PSU for 2 mics that it's not needed for that job as only 1 mic will be used.

 

[rock soderstrom]

Hello my fellow tube addicts, I'm thinking of a pair of U67's for my next project and wondering if it is possible/advisable to build a "dual" power supply for both microphones?

I also find this question interesting.

First of all, what can you share for the two microphones without losing quality or getting into problems? (such as increasing crosstalk or the like)

You can of course build two completely separate power supplies in one housing, that will probably work without restrictions.

But what about a sharing a transformer for B+ and heating?

Would a common rectification with separate filtering work for B+ and Filament?

Is it sufficient to separate only the last filter stage, as seen in some stereo equipment?

Or just connect both mics to the corresponding common outputs of one PSU?

Null problemo or what could really go wrong? What's your opinion/ experiences?

For this scenario, I'm assuming a stabilezed and regulated PSU.

 

[neowalla]

I also find this question interesting.

First of all, what can you share for the two microphones without losing quality or getting into problems? (such as increasing crosstalk or the like)

You can of course build two completely separate power supplies in one housing, that will probably work without restrictions.

But what about a sharing a transformer for B+ and heating?

Would a common rectification with separate filtering work for B+ and Filament?

Is it sufficient to separate only the last filter stage, as seen in some stereo equipment?

Or just connect both mics to the corresponding common outputs of one PSU?

Null problemo or what could really go wrong? What's your opinion/ experiences?

For this scenario, I'm assuming a stabilezed and regulated PSU.

Exactly. I know Hamptone offers dual power supplies for tube mics so it is possible but whether they are two discrete supplies in one box, or do they share transformers? Rectification? Filtering? I would think you could power two B+ which seems to be a pretty low current requirement, but what about the heater supply? Lower voltage but more current required. Can you just parallel off the same trans?

 

[TLRT]

Hello my fellow tube addicts, I'm thinking of a pair of U67's for my next project and wondering if it is possible/advisable to build a "dual" power supply for both microphones?

I did that for old Gefell mics, make everything dual- separate transformers and circuits and even mains switch. Then you can use only one without any issues.

 

[C12VR]

you may need a beefier transformer for the heaters. getting DC this way is very wasteful. Haven't run the numbers, but my guess would be you wouldn't have a high enough voltage after rectification.

 

[rock soderstrom]

you may need a beefier transformer for the heaters. getting DC this way is very wasteful. Haven't run the numbers, but my guess would be you wouldn't have a high enough voltage after rectification.

What if you didn't do it like the original?

For this scenario, I'm assuming a stabilezed and regulated PSU.

2xEF86 is an easy load for a LM317 with additional CRCRC filtering for each tube.