Floating Power

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Floating Power

The Jim Henry AMT5000 Project

One of the larger part 15 projects of the season is Jim Henry's construction of HBR (Honey Brook Radio) from an AMT5000 Transmitter 150-feet from his building.

Taking advantage of the AMT5000's Pro Input, a mono balanced +4 dB terminal block (J5), he installed an RDL STA-1 M Line Amp to boost from consumer level (-10 dB) unbalanced up to the balanced Pro level.

The RDL STA-1M describes 3 different ways of wiring the power supply:  1.) Grounded +24 VDC; 2.) Floating +24 VDC; 3.) Bi-Polar +12V/-12VDC.

While we understand both the Grounded and the Bi-Polar arrangements, we do not understand the specifics of a "floating" power supply. (?)


Generally, a floating power supply is one which is not connected to circuit ground.  In modern electronics a "switching supply" is often used where the power input is isolated from the power output by means of a transformer thus it would not be necessary to connect the input to circuit ground.

This may or may not be the case for the specific device cited but it likely is.



Floating Thoughts

Thank you Radio8Z for the comments explaining "floating power", which I can fully understand when talking about AC circuits.

My sticking-point arises over the RDL Line Amp situation is entirely about DC voltage, which cannot be sent across the windings of a transformer so far as I know.

The only way of "floating DC" that I can imagine would be a bi-polar DC supply in which the ground was not connected, but not knowing the details of the RDL power supply it remains unknown whether my guess is right.

Carl Blare

Switching Supply

A switching power supply designed for a DC input uses an oscillator to convert the DC input to AC which is then applied to a transformer which provides for isolation.  After the transformer the AC is rectified by diodes and filtered with capacitors to produce DC on the output.  Multiple output voltages can be produced by using multiple secondary windings on the transformer.

Regulation is usually done by feeding back the voltage output signal through an opto-isolator to the oscillator which provides voltage regulation.  Doing this in this manner results in a high efficiency supply with little heating or wasted power.

An AC line powered switcher operates essentially the same way except the input AC is rectified and filtered before going to the oscillator.  The high efficiency and the output regulation achieved by the opto-isolator feedback means that the input voltage can vary widely while still maintaining the output voltage. This is how many external switchers can operate on either 120 or 240 VAC input without the need to change transformer taps.




Floating and Switching

The discourse on switching power never mentions floating power.

Carl Blare

i think were they are going

i think were they are going with floating is that the power supply DC neg out is not tied to ground. i've seen equipment control consoles (not audio) wired where chassis ground and PSU DC NEG are the same thing. 

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