Nagra III Mic Preamplifier circuit

[Fablab]

Hello, some days ago I bought a Nagra mic preamp module from the historical Nagra III recorder

I want to try to use it with a 9 volt battery (although it ask 10,5 Volt). It needs a negative power supply so I think to add a simple circuit with a MAX1044

Someone had experience with this preamp in “standalone” mode?

 

[Fablab]

Here the schematic  eventually someone is interested to build one 

 

[Bo Deadly]

You don't need a supply inverter to run it on a 9V battery. Just connect the + terminal to ground and - to supply.

But I have bad news .... that circuit looks very old (1950's early 60's maybe from looking at all those germanium transistors) and has a lot of electrolytic capacitors. You will need to replace those electrolytics before it will work as designed. It may not work at all. At the very least it will be noisy.

 

[Fablab]

Thank you squarewave, but what happens when I connect the ground of the circuit (with + 9 volt) with the ground of other machines? I

 

[Fuzz Face]

Thank you squarewave, but what happens when I connect the ground of the circuit (with + 9 volt) with the ground of other machines? I

Nothing.

 

[Bo Deadly]

Thank you squarewave, but what happens when I connect the ground of the circuit (with + 9 volt) with the ground of other machines? I

It depends.

If you use a battery, then it will be fine. The ground of your circuit will be connected to + term of the battery and the - term will make -9V. The other "machine" can use negative ground or whatever. It won't matter.

However, if you use a power supply like a guitar pedal power supply that has multiple outputs, the + and - of the outputs are all connected together. So in that case if you connect one circuit ground to + and then another circuit ground to - and then connect the two grounds together, then boom. You will short out the power supply. But if you use a battery, it will be ok. Or buy a supply that makes both + and - voltages (or separate floating outputs).

 

[Fablab]

Great. Thank you