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Breve Tufvassons PFS 250 protective isolation transformer used against audio ground loop issue

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pma

pma

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We used these in my line of work before scopemeters , to use with oscilloscopes that had chassis ground to measure for example across thyristor gates in large drives DC drives . Do not touch the chassi only the plastic knobs on the scope :facepalm: By today's standards this was not very safe behavior :rolleyes: I even recognize the brand .

Yeah, quite familiar with the situation :). The fiber optic transmission systems have been most safe cure by far, I designed my first in 1982.

VHV_lab.JPG
 

amirm

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No one uses a system like that at home. They have no closed loop ADC on their speaker terminal back to their server. By instrumenting the system improperly you created a ground loop.

As I mentioned to you in the other thread, this extremely common but again it is an instrumentation problem. I solve it by using floating input on the analyzer and other techniques to remove the ground loop. Use of an ungrounded transformer is not what I like to do as it creates risk of electrical shock.

Really misleading and disappointing work...
 

tonycollinet

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Interesting test.

It should perhaps be pointed out that in a system, ALL connected equipment should be powered through an (or the same) isolation transformer (or at least all class I). Otherwise it is possible for a fault on a non isolated device to be connected to the metal chassis on all via the interconnect - resulting in a dangerous fault. This would include any powered class I speakers.
 

Lambda

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No one uses a system like that at home.
Right. At home everyone is only connecting individual component to there analyzer...
I solve it by using floating input on the analyzer and other techniques to remove the ground loop. Use of an ungrounded transformer is not what I like to do as it creates risk of electrical shock.
Not everyone has an floating input on there analyzer
And the transformer itself don't needs to be floating only its L and N output wires needs to float.
hb019.jpg

A grounded transformer is even better for noise suppression.

Use of an ungrounded transformer is not what I like to do as it creates risk of electrical shock.
Since most Audio devices are Claas ll anyways in this cases it creates an extra protection against shocks
5.21b.gif



For all Claa I devices PE ground shuld be uninterrupted But this is not the same as transformer output N grounded
But the tripp-lite dose exaclty this and i see no warning abut this in the review?!
1649747760963.png


tripp-lite Transformer as is is not usefull for most and creates risk of electrical shock.
it't output L wire is ground referenced and by would shock you on contact normally an RCD would protect you but with this transformer an RCD
can see the fault!
But not if the Transformer N output is ground:
1649748320589.png


I think this deserves a warning in the review
 

Lambda

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The "analyzer" equivalent for normal people is often an amplifier/preamp/avr. lots of different ground concoct there. not easy to have a floating input on it.
This can be a huge difference as opposed to an controlled lab bench test with only one device.

So assume you have an AVR/pream its ground is connected to many different grounds,potentially noisy. it can’t be "lifted".
Now you connect a unbalance low level analog source to it (Phonon for example) and get noise.
If the Turntable is Class ll (like most of them are) using an isolation transformer (for the turntable) with floating N might fix / improve on the noise level.
 
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pma

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It should perhaps be pointed out that in a system, ALL connected equipment should be powered through an (or the same) isolation transformer (or at least all class I). Otherwise it is possible for a fault on a non isolated device to be connected to the metal chassis on all via the interconnect - resulting in a dangerous fault. This would include any powered class I speakers.

There is no problem if you connect just one equipment to a Class II safety isolation transformer. It is similar and even safer than when you connect a Class I instrument with a Class II instrument via a link signal cable. The leakage current through the safety isolation transformer is much lower than through an internal power transformer inside any Class II instrument. Even if there is a a fault in the instrument supplied from the isolation transformer like a input mains wire fallen on the metal box, you stay safe because the isolation transformer tested does not allow for more than 8.6 uA leakage current. Much less than in case of Class II audio equipment with typical leakage current of 100 - 300 uA. You would need to ban all Class I - Class II connections if you wanted to fulfil what you have said.

Please do not use this thread for semantic and from engineering point stupid discussion. The Spark Lite thread is enough.
 
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pma

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No one uses a system like that at home.

The circuit that I have shown in post #1 (direct, (a)) without the isolation transformer (see below, repeated)

index.php


is exactly the one that people use at home and it results in dozens of complaints on buzz/whistles here at ASR. Of course without a measuring ADC branch which makes no difference in loop currents because of high impedance balanced input. Shall I make a search? Even you have sometimes troubles with loops and mains leakage in your measurements as we can see time after time.

The image below shows again the amplifier output noise floor in both cases (a)-direct and (b)-with isolation and third plot, violet, is added, that shows system noise floor with +IN and -IN measuring wires shorted and connected the Out Lo. It should be noted that this measuring noise floor (violet plot) is independent of (a) or (b), i.e. it does not depend on insertion of the isolation transformer.

classI_vs_isol__system_noise.png



BTW the PFS 250 transformer has IP44 protection so even the dropping water makes no issue. Here we usually have no rain in our living rooms, but yes the garden party situation was probably considered :facepalm::D. Then the audio equipment would be first to be flooded :).
 
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tonycollinet

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There is no problem if you connect just one equipment to a Class II safety isolation transformer. It is similar and even safer than when you connect a Class I instrument with a Class II instrument via a link signal cable. The leakage current through the safety isolation transformer is much lower than through an internal power transformer inside any Class II instrument. Even if there is a a fault in the instrument supplied from the isolation transformer like a input mains wire fallen on the metal box, you stay safe because the isolation transformer tested does not allow for more than 8.6 uA leakage current. Much less than in case of Class II audio equipment with typical leakage current of 100 - 300 uA. You would need to ban all Class I - Class II connections if you wanted to fulfil what you have said.

Please do not use this thread for semantic and from engineering point stupid discussion. The Spark Lite thread is enough.

Is it not the case though that if (for example) you have a class I source, such as a PC, connected via an isolation transformer, that is then connected through a DAC (with a non isolated connection) to a class I amp that is NOT connected via the transformer (so the amp has a connection direct to mains)

Then a fault in the amp connecting mains to the case will connect back through the interconnect screen....

No, I've just realised my mistake. A fault in the non isolated device would (should) simply clear the fuse in that kit/circuit and remove the safety fault.


Please do not use this thread for semantic and from engineering point stupid discussion. The Spark Lite thread is enough.

My (albeit incorrect) point was not related to leakage currents. Surely the point of a forum (and especially this one) is to discuss, and hence clarify technical topics as I have just done above. I'd suggest it is not up to you to state what can and cannot be discussed (particularly topics related to safety). I'd further suggest that in a civilised science/engineering based forum with a bias towards learning, the phrase "stupid discussion" should also be avoided.
 
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Several threads on loop buzz, brief search









 
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BTW with the PFS 250 isolation transformer used we have less than 10uA leakage current under any conditions.

1649763077196.png
 

sq225917

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Thanks Pavel, a perfect example of a class of devices being shown to function as expected when used in the Manor intended. If only all tests on ASR were conducted with such regard for design intent.
 
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