Positive ground PSU

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MikkelM

Well-known member
Joined
Jun 4, 2004
Messages
90
Location
Denmark
Hi there!

I have just got 2 Nagra E recorders which I want to power up with an PSU.
The machines operates with positive ground...

Can I just use a normal wallwart PSU, or is there something I have to be aware of?

Cheers

Mikkel Meyer
 
Yes you can. Wallwart style psu is usually floating. It doesn't care which pin you use as a "ground".
 
[quote author="audiox"]Yes you can. Wallwart style psu is usually floating. It doesn't care which pin you use as a "ground".[/quote]

The keyword here is "usually". To make sure, measure the resistance between the mains side and the output side, with the power disconnected of course---the R should be very large. If you have a capacitance meter measure the input-to-output capacitance as well, and if it is much more than a couple hundred pF find another adapter.
 
Your Nagra has positive ground (= positive output of the psu is connected to the Nagra's signal ground and chassis). Lets assume that you connect nagra to your mixer. The positive voltage side of psu is now connected to mixers signal ground (which is connected to the safety ground in the mains plug).

A non-floating psu has one of its output leads connected to safety ground in the mains plug (the negative side in practice). It means that the output of psu will be shorted if you connect Nagra to the mixer.

In a floating psu, both output pins are independent of the safety ground (in wall warts there is no safety ground at all, the insulating plastic cover protects you from the mains voltage). For example take a looks at Nordic Power range of wall warts (available from Elfa in Scandinavia).

By the way, there should be a full schematic + some spare parts inside your Nagra E. Have you already opened it?
 
Yep! it has been open, and it looks sweet, but no spareparts or diagrams.
I got the diagrams and manual emailed from Kudelski as an PDF...

I was just curious if I needed to buy an double PSU, delivering +- 18V and then only use - and ground (0).

I am going to build my own single PSU for it. I think thats cheaper, better, and I can control how it works.

Why using positive as ground??

Cheers

Mikkel
 
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