Isolation Transformers

Hi Test Pilot,
The usual thinking is to use isolation transformers, but the owner of Jensen Transformers wrote an article about how this doesn’t really work. Your best safest bet are the semi-active ground lifters, assuming you have any issues at all.

Best,
E

Thanks Eric, could you expand on the semi-active ground lifter comment. 

I'm thinking of this:
https://amzn.to/2Z7qun3

$80 seems pricey though, see if you can find a cheaper version.

But now that I think about it, Jensen Transformers also makes in-line RCA or XLR isolators as well. 
Best,
E

testpilot

258 posts
04-12-2019 7:44am

@jea48 given the choice between the hospital grade Tripp-Lite and the regular Tripp-Lite that you referenced in your post, do you have a preference? I am only concerned with front end equipment isolation i.e. low power requirement.

My Choice?
The regular Trip-lite unit as you call it. The "Grounded Power System", isolation power transformer unit. The grounded isolation transformer still provides isolation from the mains AC power grounded power system.


An Isolated Power System, (IPS).
The secondary winding of the isolation transformer floats above ground. Therefore there is not any reference from the ungrounded legs, leads, of the secondary winding to ground.

For this discussion the IPS is a plug and play unit. It has a 3 wire power cord and grounding type plug. The wall AC power outlet equipment ground is connected to the metal enclosure of the IPS via the equipment grounding conductor of the power cord. The ground contact of the receptacle outlet/s that are connected to the output of the IPS connect to the equipment ground/chassis ground. There’s that AC mains power equipment ground!

Say you connect a CDP to the IPS that requires the use of a safety equipment ground. What happens if there is a wiring fault from the fused conductor to the chassis of the CDP? ....... If the fault is a bolted fault, (an unintentional solid conductor/wire to chassis connection), the conductor becomes a grounded conductor, a neutral. Will anything happen from the electrical fault event? Will the CDP fuse blow? NO..... Nothing will happen. You the user, will not know the internal fault happened.

Worth noting, as long as the ground faulted CDP is plugged into the IPS unit the small slot contact on the receptacle outlet/s (normally the HOT contact) will make that leg, lead, of the secondary winding the grounded conductor, the neutral. (The CDP makes the IPS unit an unintentionally Grounded Power System.) What happen to that total isolation of IPS?

What happens if another piece of audio equipment is connected to the IPS? Say an integrated amp. Will there be any electrical problems because of the ground fault in the CDP? Will any sparks fly? No, as long as there are not any problems with the AC power wiring inside the amp.

When the amp is plugged into an outlet on the IPS unit the normally hot conductor in the power cord becomes the neutral conductor. The normally neutral conductor of the power cord becomes the Hot conductor. (I am not going to address here how reversed AC polarity feeding the primary winding of the power transformer, of a piece of audio equipment, can affect the sound of the system.)

So because of the ground fault condition inside the the CDP the normally Hot contact on the receptacle outlet/s, of the IPS, is now the neutral, the grounded conductor.(If a voltage test is taken you will measure zero volts from the normally Hot contact of the outlet to ground. If you measure for voltage from the normally neutral contact on the outlet to ground you will measure 120Vac nominal. Reversed AC polarity.)

What if the CDP ground fault is after the ON/OFF power switch? When the CDP switch is closed the contact on the outlet of the IPS is grounded. When the power switch on the CDP is open the normally hot wire on the power cord is no longer grounded by the CDP ground fault.

Is the secondary of the IPS floating above ground again? Not 100%. Why? Two things come into play. The primary windings of the two power transformers inside the CDP and amp. And don’t forget the interconnects that connect the CDP to the amp. Now the normally neutral contact on the outlet of the IPS is the neutral, the grounded conductor. Confusing? None of this happens with a "Grounded Power system" .... The HOT conductor is always the Hot conductor and the Neutral conductor, (The Grounded Conductor), is always the Neutral conductor.

I could go on, but this post is long enough!

IPS units should only be used under the direct supervision of qualified trained personnel. They are not Listed/approved for use in a residential dwelling.

Jim.

.

Took some measurements. The voltage in the adjacent socket is 118.8v. With everything plugged into the transformer; streamer, DAC, preamp, and amp, the voltage out of the transformer is 122.4v +/-0.1 volts without anything turned on. With everything turned on the voltage stayed exactly the same with or without music playing even at high volumes. I had seen 124v in the past but I'm guessing it depends on the time of day where the voltage from the wall socket was closer to 120v. So it looks like the difference is roughly around 3.5-4 volts. On surface, the unit (1400VA according to the label) appears to be maintaining the same voltage regardless of the load, at least in my system.  
By the way, this is what TSi Power says on their website:
"An isolation line conditioner can eliminate the need for a dedicated circuit or expensive rewiring. This is particularly helpful when wiring is old or a tenant doesn’t have easy access to distribution panel boards."