Neumann M147 power supply (M147 schem added)

[micolas]

Reviving this thread 15 years later...anybody who saved the schematic would be so kind to share/send it? I have one on the bench that needs repair.
Many thanks
t

Hi @ghiatorino ! Maybe @mikepoole can help you
https://groupdiy.com/threads/neumann-m147-tube-not-6111.79046/post-1073736

 

[mikepoole]

Hi @ghiatorino ! Maybe @mikepoole can help you
https://groupdiy.com/threads/neumann-m147-tube-not-6111.79046/post-1073736

That original link just worked for me: https://groupdiy.com/attachments/image-2-jpeg.90480/

Or here's one I just put up: https://www.dropbox.com/scl/fi/jo46...ey=eh942rv86aaz1pgl473pimefm&st=3gr24aw0&dl=0

 

[ewlewl]

You may want to take care not to reference the ground of the microphone to the shell of the mike and also to the "pin 1" or shield ground of the power supply. In order for this type of output to work correctly, the entire electronics, including the secondary side of the power supply has to have a floating ground reference. This is relatively easy to do with a switching power supply, which is what is used in the original unit. If the microphone output on either pin 2 or 3 is referenced to your shield ground, you will have unmanagable hum problems. The shell of the mike, the shield of the cable and the box of the power supply should be referenced to earth ground, of course.

its grounded to the shell inside mic from center pin on din plug... the sense line inside mic is connected to tube filament supply ..just 2 wires in cable going to thesame filament .i took a 35 volt center tap transformer and off those taps made a half wave rectified voltage for the + - 70 volt lines two 5 watt resistors on each line as a divider to get my +70 - 70 volts. used radio shack 12 volt 2 amp transformer bridge rectifier filtered to a lm 317 regulator ..gonna need bigger heatsink adjusted to +5.2 volts. radio shack 24 volt ac rectified filtered to lm317 regulator adjust to + 32 volts all ground lines inside power supply are tied together

 

[ewlewl]

its grounded to the shell inside mic from center pin on din plug... the sense line inside mic is connected to tube filament supply ..just 2 wires in cable going to thesame filament .i took a 35 volt center tap transformer and off those taps made a half wave rectified voltage for the + - 70 volt lines two 5 watt resistors on each line as a divider to get my +70 - 70 volts. used radio shack 12 volt 2 amp transformer bridge rectifier filtered to a lm 317 regulator ..gonna need bigger heatsink adjusted to +5.2 volts. radio shack 24 volt ac rectified filtered to lm317 regulator adjust to + 32 volts all ground lines inside power supply are tied together

Ground is pin 6 in din plug for 75 to 100 dollars you can build this power supply.it is an 8 conducter cable .hard wired mine to power supply and bought a din plug for mic from TXM Manufacturing... needs at least a 2 amp transformer for filament supply tried a 500 ma but after 10 minutes it started a low hum

 

[ewlewl]

Morning,

I need to build a power supply for a Neumann M147. The only info I can find on the M149A power supply is from this page:
http://www.soundonsound.com/sos/dec00/articles/neumann.htm?print=yes

"... generates ±70V for the valve and capsule biasing as well as +32V and +5V supplies."

I just read Jakob's G7 page and I understand how his capsule is polarized. Would this mic work on the same principle? The front diaphragm at 0V, the center electrode and back diaphragm at say, +70V.

Thanks,
William

its grounded to the shell inside mic from center pin on din plug... the sense line inside mic is connected to tube filament supply ..just 2 wires in cable going to thesame filament .i took a 35 volt center tap transformer and off those taps made a half wave rectified voltage for the + - 70 volt lines two 5 watt resistors on each line as a divider to get my +70 - 70 volts. used radio shack 12 volt 2 amp transformer bridge rectifier filtered to a lm 317 regulator ..gonna need bigger heatsink adjusted to +5.2 volts. radio shack 24 volt ac rectified filtered to lm317 regulator adjust to + 32 volts all ground lines inside power supply are tied together

 

[ewlewl]

I think you are probably going to see 1 - 1.5 ma on the +70 line. The tube plates are driven by a current source. The typical tube preamp stage runs at about a mil. The second stage is an emitter follower. The total current is less than 5.5 ma. Again, there is a current source, so the current will probably be set less than that amount. So you are looking at less than 10ma total on the +32 line. The sense line on the filament input is for long cable runs. If you are using 25 -30 ft. of cable to the power supply, you can ignore the sense. Just make the filament supply variable and set the value to give +5.2 at terminal 2 of the mike connector. The +32v is referenced to ground (and the negative audio output pin). You would not be able to use a split supply unless you went rail to rail and didn't ground the center of the supply, effectively giving a +32 single output supply.

its grounded to the shell inside mic from center pin on din plug... the sense line inside mic is connected to tube filament supply ..just 2 wires in cable going to thesame filament .i took a 35 volt center tap transformer and off those taps made a half wave rectified voltage for the + - 70 volt lines two 5 watt resistors on each line as a divider to get my +70 - 70 volts. used radio shack 12 volt 2 amp transformer bridge rectifier filtered to a lm 317 regulator ..gonna need bigger heatsink adjusted to +5.2 volts. radio shack 24 volt ac rectified filtered to lm317 regulator adjust to + 32 volts all ground lines inside power supply are tied together