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R/E/P => Klaus Heyne's Mic Lab => Topic started by: musicalnyc on February 15, 2018, 11:43:54 pm

Title: Neumann U48 Nuvistor Reversal to VF14
Post by: musicalnyc on February 15, 2018, 11:43:54 pm
I have a Neumann U48 that was converted to Nuvistor long ago via the AR47 plug-in.  I would like to restore it to VF14 specs and I am aware that I need to modify the power supply. 

Is there anything within the microphone itself that needs to be adjusted or modified (besides swapping the AR47 with a VF14) in order to reverse it to stock?

Thanks for your help!
Title: Re: Neumann U48 Nuvistor Reversal
Post by: klaus on February 16, 2018, 01:44:24 am
Hello Peter,
The advantage of the AR-47 Nuvistor plug-in: no additional changes inside the mic are necessary to re-convert to VF14 once the plug-in is removed. The mic will be 100% stock again.

The required higher Nuvistor voltage of 110VDC was obtained by replacing one of the four 1KΩ dropping resistors  in the original NG power supplies with a wire bridge, and placing that resistor in parallel with an existing one.

Once the wire bridge has been removed and the resistor soldered back in its place again (by a qualified technician, of course!) the NG is also back to stock, ready to power a VF14-equipped U47/48.

When it's done, it will look like this:

Title: Re: Neumann U48 Nuvistor Reversal to VF14
Post by: musicalnyc on February 16, 2018, 09:07:05 am
That's great to know.  Thanks, Klaus!