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isolation transformers

nefilim

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Jon Snow and I have something in common. Amir pointed out my cheapie isolation transformer might not be doing much isolation after all: https://audiosciencereview.com/foru...asurements-of-topping-d50-dac.2403/post-87945

Looking around for modestly priced options I noticed this one:

https://www.amazon.com/dp/B00008YMZO/ref=psdc_10967671_t2_B00007KQKJ

which states "Floating AC output prevents noise coupling" (curiously the 500W model is not explicit about this).

I'm aware of the more traditional "audiophile" options such as Equitech but I'm doubtful the ROI on these are worth it for me.

I'm also using a voltage regulator (https://www.amazon.com/gp/product/B00009RA60) upstream from the transformer, which often indicates overvoltage from the mains.

Power can be a bit spotty here at times with brownouts or brief outages. I believe most of my equipment has decent power supplies so I surmise performance impact/improvement might be minimal here?
Curious if this is worth investing in, both for protecting equipment and any possible performance improvement.
 

amirm

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I am pretty sure all of these Tripp Lite units have shared input and output grounds. The only way to get truly floating ones is to modify them which I do not recommend.

If you need protection, put a whole house surge protection device at the meter. Call your power company and they will install one for reasonably low cost.

There is no reason to use any of this for fidelity.
 

trl

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Hum-X is what you need if you want to safely remove the input ground. It has a powerful bridge regulator inside and couple of optional caps and resistors. The bridge takes care of connecting the Earth-ground again only if the potential between your device's metallic case and the Earth is higher than 1.4V (2 diodes from the bridge). If phase touches the outer case, then your RCBO will trigger.

However, removing the ground will only help you in case you have a really polluted Earth-ground or you got a ground-loop (actually here's where Hum-X excels).

Here's a regular isolation transformer of 250VA (custom-made toroid) with input and output ground connected vs. a mains power outlet:

FUN_max-volume_power-outlet.png

Burson FUN RCA-output max-volume: power outlet
Also tried with and without EMI/RFI filter in front of the power brick, but this makes absolutely no difference, hence no need to upload the graph.

FUN_headphones-max-volume_isolation-transformer.png

Burson FUN RCA-output max-volume: isolation transformer (in & out ground connected)

FUN_max-volume_power-outlet.pngFUN_max-volume_isolation-transformer.png
Same mains vs. isolation transformer, but on the headphones out. as there' absolutely no improvement, I choose the thumbs instead of big pics.


This is the only audio device in my home that show little improvement with the isolation transformer connected; FUN has as 2-pins (no GND) 230V to 12V/6A low-noise SMPS brick. The mains hum is there even if device is powered off, so I assume it's injected somehow from mains to SMPS, probably because the RCA plugs are nearby the DC power switch and the DC cables are like an antenna or something...don't know what to say (top-left from the below pic, there's about one inch between the RCA and the DC switch; there's also the microphone cable in-between...maybe is this one, not sure):

index.php


I've no idea why the isolation transformer removed the mains hum.

My personal thoughts: the device from your link seems a very good isolation transformer, and combined with Hum-X you might lower mains hum or remove ground-loops safely, but without measurements you might not be able to tell a differences.

BTW, I have the exact same relay AVR model APC 1200 VA myself...well, plus two other AVRs with stepper inside. :)

P.S.: Do never remove the safety ground (Earth) by hand, because shock hazard or even death might occur later! Hum-x is tested devices and, if original, it is cheap and safe to go.

P.P.S.: The 50 Hz and its higher harmonic are not audible, even at high listening levels, probably because are below -110dB.
 

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DonH56

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An isolation transformer can (may, insert several caveats here) break a ground loop. Sometimes the hum is from DC, or rectified noise that "looks like" DC, causing transformer hum. The usual fix for that is large series capacitors to block DC with diodes across them to prevent line voltage from appearing across them.

Isolation transformers come in styles from the $20 Radio Shack (which are actually pretty good, with response to about 10 Hz or so for line level signals) to the sweet but pricey ($1200) Jensen models.
 

trl

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I have no DC on my mains, I can show you my 230V/50Hz sine and FFT if you like.

My isolation transformer is having IN GND and OUT GND tied up; there's no switch to remove the GND, by safety reasons.

So this is the only device I've seen that isolation transformer actually does something...even if few dBs, strange thing. :)
 

DonH56

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Agreed... I have seen some isolation transformers that isolate ground as well, sort-of, often with a low-value high-wattage power resistor (UL has a spec for that). Some use an RC circuit, and some go all the way with a cap/bridge like the Hum-X (if I follow what you said). Most, probably the vast majority of the relatively few I have seen and used, do not isolate the safety ground for obvious reasons (cost and safety the biggies).
 

trl

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[...]Most, probably the vast majority of the relatively few I have seen and used, do not isolate the safety ground for obvious reasons (cost and safety the biggies).

I've seen such transformers with a simple switch a big warning label under the switch (similar with big scopes with the GND connector), but if safety ground gets removed non-safely (just by simply disconnecting the ground wire) and house electrical panel is missing the RCBO installed (or directly on the outlet), then if somebody touches the audio device's metallic case might get electrocuted. Of course, this may only happen if inside the audio device there's a current flowing from the phase to the outer case (defects might happen).
 

DonH56

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I've seen such transformers with a simple switch a big warning label under the switch (similar with big scopes with the GND connector), but if safety ground gets removed non-safely (just by simply disconnecting the ground wire) and house electrical panel is missing the RCBO installed (or directly on the outlet), then if somebody touches the audio device's metallic case might get electrocuted. Of course, this may only happen if inside the audio device there's a current flowing from the phase to the outer case (defects might happen).

The only time I've used one of those is on the test bench or as a quick test. I would never install one permanently. I managed to smoke a 2 kVA version on a bad circuit when I was not careful to double-check the wiring... Debugging a PA system, neutral and hot were swapped in the outlet, I did not check first, and was using the transformer because two PA system components were on seperate circuits and I need to isolate them (ground loop between FOH mixer and backstage power amps). The isolation transformer worked as intended, but one of the (bridged) power amps had a short and applied the line across it. Breaker was apparently bad so it stuck on. Burning transformers smell really bad and splatter oily goo that smells for days to come. Not happy.
 
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trl

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So, no thermal fuse was installed inside the transformer? That should trip within minutes. Mine has one, regular, not resettable, but hope will not be needed...never.

BTW, I remember I burned the thermal fuse inside of a transformer from a Pioneer amp (don't remember the model...555 maybe) just by pushing lot of power with the case placed vertically. Transformer was on top of the power transistors...it took less than 1 hour of very loud music program to burn that fuse. I was able to replace it with a simple wire and remember that amps should stay horizontally forever, per manufacturer datasheet. :)
 

DonH56

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So, no thermal fuse was installed inside the transformer? That should trip within minutes. Mine has one, regular, not resettable, but hope will not be needed...never.

BTW, I remember I burned the thermal fuse inside of a transformer from a Pioneer amp (don't remember the model...555 maybe) just by pushing lot of power with the case placed vertically. Transformer was on top of the power transistors...it took less than 1 hour of very loud music program to burn that fuse. I was able to replace it with a simple wire and remember that amps should stay horizontally forever, per manufacturer datasheet. :)

Nope. Very old-school big hulking black behemoth, heaven knows where it came from, had been rattling around the TV/stereo repair shop for ages. It was a serious transformer, wish I still had it!

Only thermal fuses I have blown recently were in the microwave; my wife heating a bunch of popcorn bags years ago for a Cub Scout meeting, and me trying to get leftovers from the freezer to cook right now. Bloody fuses are expensive and getting harder to find, most people just replace things these days.
 

trl

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[...]most people just replace things these days.
This is "helping" the global warming and the pollution also, especially by the partial recycling process and re-manufacture of the new goods. Too bad they don't see that; starting to build repair centres will help a lot our future and our own money. This is like selling electric cars in countries where 1KW of electricity pollutes more (but may cost less) than 1KW of gasoline power. :(
 

restorer-john

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...Bloody fuses are expensive and getting harder to find...

1547079224504.png


No problem getting the little devils here in Australia.

WES (Wagner Electronic Services)

Less fun is digging them out of the primary windings and replacing them, but it's always better than scrapping a TX/former.
 

DonH56

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We have Digikey, Newark, etc. here. You used to be able to go to the corner Radio Shack and get them, or to the local repair shop, those aren't around anymore... :( And I hate paying to overnight a $1 fuse for $10 shipping because we can't live without the microwave. Last time I ordered pack of them to be prepared, then the klystron (or magnetron, I forget) blew about a month later. Taps (may be Last Post for you?)

That old transformer was probably older than me... Definitely no fuse, it didn't just quit, it fried itself.
 

restorer-john

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That old transformer was probably older than me... Definitely no fuse, it didn't just quit, it fried itself.

Properly made transformer it was. They didn't need no stinkin' thermal fuses, they soldiered on until the enameling melted.

I hate thermal fuses. EU directive IIRC. Typical.
 

AnalogSteph

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Replacing a thermal fuse still beats having to rewind (and potentially repot) a transformer by a long shot. If you need to make it more service-friendly, tack on a 70°C device at/near the outside or something., like some restoring folks do around these parts.

Thermal fuses unfortunately weren't a thing in the days of vacuum tube radios. Some of those could really use one!
 
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