This is a review and detailed measurements of the Tripp Lite IS250 Isolation Transformer in the context of audio performance. I purchased it for US $140 with kind donation from a member.
The case is utilitarian but is not meant to be something you look at. Despite the low power rating of 250 Volt-Amp, the little box is quite heavy courtesy of the transformer inside. Back panel provides two outlets which is appreciated:
Notice the UL hologram/safety certification which is quite often lacking in audio tweak products.
Despite the name, please note that the safety earth ground is NOT isolated. Let me repeat: the safety ground pin in your outlet goes right through the device and comes out the same pin in the rear outlets. This is required for safety as otherwise, if the hot wire came loose, it would not trigger your breaker to trip. The isolation therefore is only for the hot and neutral conductors which are coupled magnetically through the transformer. Since unbalanced audio gear almost always connects signal ground and chassis/safety grounds together, this box provides no isolation at all, or any cure for mains/ground loops.
Above should be enough to dissuade anyone from thinking this device helps with mains noise but let's go through our formal testing and measurements.
Tripp Lite IS250 Isolation Transformer Measurements
As usual, let's start with the dashboard of my mains AC (which I call "RAW") this evening:
We have the usual harmonic distortion+noise, delivering us a SINAD of 31.7 dB. Our sine wave is visibly distorted so if this transformer can fix something, the situation is present for it to do so. Here is its dashboard:
Our SINAD remains essentially the same but there is good bit of high frequency filtering. The reason that doesn't impact SINAD is because our biggest issue are the large harmonic spikes and their noise floor which dominates. Indeed our sine wave on top left is still distorted the same way.
We can zoom into to the spectrum with wider bandwidth:
The light blue is raw AC and red is the trip through the transformer. We can clearly see the high frequency noise reduction but there is also some increase in distortion. The transformer is a non-linear device so it creates its own distortion. But again, at high level both waveforms are distorted.
We don't listen to AC mains so let's measure the impact on an audio device, namely the Topping A90 pre-amplifier/headphone amp which is always on my desk. Here is its dashboard with raw AC and XLR input and output:
Superlative performance as always with noise and distortion well below threshold of audibility. Look at what happens though when I turn on the isolation transformer but do NOT use it yet (just showing the FFT)
The transformer is creating a strong magnetic field that is coupling into my system even though I am using XLR cabling! The transformer was about 6 inches away but moving it farther out made no difference. It may actually be leaking into the Audio Precision analyzer itself.
Now let's power the A90 via the transformer:
General performance is identical but we are now saddled with that mains leakage. Mind you, it is harmless at -130 dB but we have caused it by using this "tweak."
For folks who complain that above test is only one frequency, let's do a full frequency sweep with much wider, 90 kHz bandwidth:
THD+N is still below threshold of hearing and no change is seen with the isolation transformer.
Some people think there is magic in "timing domain" so let's run an impulse response with raw AC and through isolation transformer:
We get perfectly matching impulses. So much so that if I turn both graphs on, they land completely on top of each other (inset on the right). The ringing is due to limited sweep bandwidth of 20 kHz.
We could keep running such tests but asking the same question over and over again, just gets you the same answer.
Conclusions
An isolation transformer can be useful in blocking common mode interference. In our scenario though, people buy these boxes with seemingly no audible mains noise so that can't be the reason for purchase. Instead, buyers think something is being isolated so all the bad is left behind the transformer. As I explained, devices like this are not isolating safety ground so whatever remains on that line, gets right through them. That aside, our testing shows that no performance improvement can be had. And you can actually subject your audio system to mains noise due to strong field that the transformer generates.
While I did not show it here, there is some transformer loss as well so you will be wasting power as well.
So while this device is fine, its use for audio performance improvement is not recommended. Save your money for something else.
Edit: video review posted as well:
-----------
As always, questions, comments, recommendations, etc. are welcome.
Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
The case is utilitarian but is not meant to be something you look at. Despite the low power rating of 250 Volt-Amp, the little box is quite heavy courtesy of the transformer inside. Back panel provides two outlets which is appreciated:
Notice the UL hologram/safety certification which is quite often lacking in audio tweak products.
Despite the name, please note that the safety earth ground is NOT isolated. Let me repeat: the safety ground pin in your outlet goes right through the device and comes out the same pin in the rear outlets. This is required for safety as otherwise, if the hot wire came loose, it would not trigger your breaker to trip. The isolation therefore is only for the hot and neutral conductors which are coupled magnetically through the transformer. Since unbalanced audio gear almost always connects signal ground and chassis/safety grounds together, this box provides no isolation at all, or any cure for mains/ground loops.
Above should be enough to dissuade anyone from thinking this device helps with mains noise but let's go through our formal testing and measurements.
Tripp Lite IS250 Isolation Transformer Measurements
As usual, let's start with the dashboard of my mains AC (which I call "RAW") this evening:
We have the usual harmonic distortion+noise, delivering us a SINAD of 31.7 dB. Our sine wave is visibly distorted so if this transformer can fix something, the situation is present for it to do so. Here is its dashboard:
Our SINAD remains essentially the same but there is good bit of high frequency filtering. The reason that doesn't impact SINAD is because our biggest issue are the large harmonic spikes and their noise floor which dominates. Indeed our sine wave on top left is still distorted the same way.
We can zoom into to the spectrum with wider bandwidth:
The light blue is raw AC and red is the trip through the transformer. We can clearly see the high frequency noise reduction but there is also some increase in distortion. The transformer is a non-linear device so it creates its own distortion. But again, at high level both waveforms are distorted.
We don't listen to AC mains so let's measure the impact on an audio device, namely the Topping A90 pre-amplifier/headphone amp which is always on my desk. Here is its dashboard with raw AC and XLR input and output:
Superlative performance as always with noise and distortion well below threshold of audibility. Look at what happens though when I turn on the isolation transformer but do NOT use it yet (just showing the FFT)
The transformer is creating a strong magnetic field that is coupling into my system even though I am using XLR cabling! The transformer was about 6 inches away but moving it farther out made no difference. It may actually be leaking into the Audio Precision analyzer itself.
Now let's power the A90 via the transformer:
General performance is identical but we are now saddled with that mains leakage. Mind you, it is harmless at -130 dB but we have caused it by using this "tweak."
For folks who complain that above test is only one frequency, let's do a full frequency sweep with much wider, 90 kHz bandwidth:
THD+N is still below threshold of hearing and no change is seen with the isolation transformer.
Some people think there is magic in "timing domain" so let's run an impulse response with raw AC and through isolation transformer:
We get perfectly matching impulses. So much so that if I turn both graphs on, they land completely on top of each other (inset on the right). The ringing is due to limited sweep bandwidth of 20 kHz.
We could keep running such tests but asking the same question over and over again, just gets you the same answer.
Conclusions
An isolation transformer can be useful in blocking common mode interference. In our scenario though, people buy these boxes with seemingly no audible mains noise so that can't be the reason for purchase. Instead, buyers think something is being isolated so all the bad is left behind the transformer. As I explained, devices like this are not isolating safety ground so whatever remains on that line, gets right through them. That aside, our testing shows that no performance improvement can be had. And you can actually subject your audio system to mains noise due to strong field that the transformer generates.
While I did not show it here, there is some transformer loss as well so you will be wasting power as well.
So while this device is fine, its use for audio performance improvement is not recommended. Save your money for something else.
Edit: video review posted as well:
-----------
As always, questions, comments, recommendations, etc. are welcome.
Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
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