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Author Topic: Vintage U67 With Euro Power Supply - Suggestions for U.S.?  (Read 836 times)

arch801

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Vintage U67 With Euro Power Supply - Suggestions for U.S.?
« on: September 15, 2021, 03:49:00 PM »

Hi,

I'm hoping you wise wizards can point me in the right direction. I had been looking for an early run u67 for many many years and finally found one I could afford (serial is in the 5000s), but the nu67 is for EU power. I want to be extremely safe with this and not take any risks running improper power to it, so any suggestions any of you may have as far as what my best options are to get this working in the US will be very much welcome.

Thanks!

-Tom
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arch801

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To elaborate, if it's just a matter of getting a robust power transformer that's fine with me,
I just need to know if there are any other concerns I should be aware of, and any suggestions
as far as what kind of power converter to get would be very welcome!

And if converting the power from EU to US would be a bit shaky in general,
I would have no problem selling this EU power supply and buying a US one if that is the best option.

Please let me know your thoughts if you can spare the time. Thanks for any help!
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Kai

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These PSU‘s don‘t need much power, and some voltage variation is allowed.
A normal ca. 100 W step up 110 to 230 (220) V step up transformer is more than sufficient for the job.

If you want to make sure, get an inexpensive voltmeter and measure the step up transformer’s output voltage, e.g. something like this:

VC185-VC185TRMS-DIGITAL-MULTIMETER (URL removed, as only available in Germany. KH)


To do so and avoid any danger:

• Plug a power strip into the output of the unpowered step up transformer.
• Then connect the voltmeter and the switched off PSU to it.
• Use the meters 400 V AC range.
• Power up the step up transformer.
• Voltage should be 210 - 260 V.
• Switch on the PSU.
• Voltage should be 200 - 240 V.
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arch801

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Thank you so much for the reply! That is very informative, and a bit of a relief to know that having a bit of variation won't be a huge problem.

You are a legend sir, your informative posts over the year have really helped me down the path towards professional microphone ownership, and it is very much appreciated! =)
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klaus

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The first question I have: what brand is the "European" power supply?
Because all Neumann supplies I am aware of have multi-taps for the line voltage.
And if it's a budget supply, don't even bother going down that road, because every U67 deserves a well-filtered, well-stabilized high-end supply*

The second issue of concern:
Using a step-up transformer may get you in the neighborhood of 210VDC/6.3VDC, but more than likely the voltages you will find will be off enough that it matters-
for tube life, capsule life, noise floor, distortion.

To correctly dial in the precise voltages, you will need a decent meter and soldering skills,
as high and low voltages are set with dropping resistors that need to be changed (not an issue with the heater voltage on NU67u, which have a trip pot).


* the new NU67V are terrific: they automatically seek the correct voltages, even after a tube change. No more voltage adjustments for life!

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Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

arch801

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Oh wow, okay that is all very interesting.

It's the stock NU67 with a European plug that I have. It's not the re-issue but it is the actual vintage Neumann power supply that came with the mic originally (both are in excellent condition miraculously). I want to extend the life of the original components as much as possible, so what in your opinion would be the most ideal long-lasting solution using the NU67 on a US power outlet?

I am a beginner when it comes to electrical engineering, so while I have soldered a couple of DIY modular synth kits, that's about the extent. I would probably send away for a professional to handle any type of soldering needed, so I would welcome any path that avoids that if possible. I am open to any suggestions you have.

Thank you so much for the advice!
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klaus

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You are already 3/4 there: a Neumann Nu67 power supply already includes the appropriate circuitry to operate with international, including U.S. voltages.

All you need now is a studio tech to properly set the input voltage and calibrate the output voltages (no, I will not recommend to do this yourself, given your marginal knowledge in the field. I have no interest promoting premature death by electrocution).

Have the studio tech call me, and I will advise how to set up your system.
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Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

arch801

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Yes indeed, I will want to outsource that!
Thanks so much for the clarification. I will be checking with some pro-audio friends in California that have dealt with this type of thing.

I also want to have the mic properly checked by someone trustworthy who knows what they are doing. I'll do some research on this forum to see if anyone has been mentioned stateside that could perhaps fill both of these roles. If you have anyone you send this type of business to stateside I'm all ears.

I can send the mic itself for a diagnostic of the component integrity and health, but if they can help calibrate the PSU as well, that would definitely be a bonus. In any case, when I find someone to calibrate the voltage I will point them your way, much obliged!

Thank you again so much for all your help, it is really amazing to have access to such a renown expert on these things.
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uwe ret

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As mentioned earlier in this thread, all original Neumann NU67 versions feature the option to have their transformer configured for either European or American mains (220Vac/50Hz or 110 or 127Vac/60Hz). The attached diagram is of the early version of the NU67.
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