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Jensen ISO-Max CI-1RR Review (Isolation Transformer)

PeteL

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Yes those devices certainly have their place, yes it feels expensive for such a simple small box, but then you purchase the cheap ones and they are just bad, and you end up buying this anyway. That's one area where price directly correlate unfortunately. Now this specific one is an oddball because they do sell stereo ones for 200$, way more useful, and they advertise a mono one specifically labeled as behing for subwoofer at the same price with better specs in the low end. I fail to find where you would need mono if not for sub.
 

IVX

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actually, E27 $10 600:600 permalloy trafo from Taobao has a similar performance. The distortion at 20Hz is the core saturation effect, so just use a higher cross-section of the permalloy core to keep [email protected] lower.
trafo600600_THD.png
 

IVX

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PeteL, I've bought and measured that trafo 5 years ago or more, tried to find to take pic but without success. The key-words are [permalloy] to keep HF THD lower(nanocrystalline, I believe should be even better due to double saturation flux), and [600:600] which corresponds to load impedance. E27 means EI-shaped core 27mm. Don't worry, any trafo like that will have the same THD level or better if you'll buy a bigger core trafo.
 

PeteL

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PeteL, I've bought and measured that trafo 5 years ago or more, tried to find to take pic but without success. The key-words are [permalloy] to keep HF THD lower(nanocrystalline, I believe should be even better due to double saturation flux), and [600:600] which corresponds to load impedance. E27 means EI-shaped core 27mm. Don't worry, any trafo like that will have the same THD level or better if you'll buy a bigger core trafo.
Ha OK, you have to mount the actual box with connectors and wiring yourself if I get that right.
 

edechamps

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In a twist of faith, the addition of ISO-MAX created mains hum where none existed before! The amount of mains noise induced was location dependent which tells me it is picking it up from its environment. I am not clear on the exact mechanism for this pick up./

Isn't this simply because mains EMI is not drained to safety ground anymore, since, well, the whole point of this device is precisely to isolate from the safety ground? Seems like a "you can't have your cake and eat it too" problem.

Another possibility is that the output impedance of the ISO-Max is higher than your usual source, which makes it easier for mains EMI to induce a voltage in the connection. I measured some isolation transformers years ago and they had an output impedance in the hundreds of ohms - much higher than most line level sources I had lying around.
 

DonH56

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Transformers can pick up and even increase noise within their bandwidth. The better units include better (e.g. mu-metal) shielding and such to reduce hum pickup, but at much higher cost. I have many times had to re-orient transformers in professional sound systems to minimize the hum especially from smaller DI boxes and such. Often you can watch (and hear) the hum change as you move a power cable near and away from the transformer. One of the most painful was a church install (not mine) wherein they mounted several transformers all nice and close on a little wooden shelf below a mixer -- and right below the power supply. Hum galore, and when I propped up the mixer and stood the transformer board on end (90 degrees to the mixer) the hum was essentially gone. They had to rebuild the mixer desk with a new transformer mounting scheme. It was a sweet console, built by one of their church members, who was a great woodworker but not an EE, alas.
 

Helicopter

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Thanks Amir. Looks like a good device for diagnosing as well as solving problems. I wonder how the Boyuu Reisong 2 channel one compares
 

levimax

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Is there any way to measure CMMR for this? That is the one area transformers really shine and would help put it's performance into perspective. I have a DIY tri-amp systems with a computer and unbalanced connections which had ground loop issues (no surprise). I could have converted it all to balanced at great expense in money and time but instead I got a stereo version of an Iso-max and it works perfectly... dead quiet even with my ear next to speakers. Transformers, while old school, still have a place for some applications.
 

pma

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In a twist of faith, the addition of ISO-MAX created mains hum where none existed before! The amount of mains noise induced was location dependent which tells me it is picking it up from its environment. I am not clear on the exact mechanism for this pick up.

This is an error of your arrangement. When you use a signal transformer, the I/O’s must not be floating, otherwise you have the hum components through stray capacitance. Try the grounded source and the problem should disappear. The best result is if both input and output are grounded and the trafo only disconnects the loop.
 

bigLP

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I use a Humdinger by AudioVanAlstine. It did kill the buzz. Pun not intended. I will crack it open later and take a pic to share.
 

H-713

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Is there any way to measure CMMR for this? That is the one area transformers really shine and would help put it's performance into perspective.

Quite easy to measure, but transformers tend to have relatively poor CMRR at high frequencies due to their interwinding capacitances. Then again, the internal compensation of most op-amps means that at higher frequencies, open-loop gain falls, and so does CMRR.

One interesting thing to note is that the distortion from transformers is mostly limited to low frequencies. That's quite the opposite of most solid-state equipment, which has distortion that typically rises with frequency.
 

SIY

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Is there any way to measure CMMR for this? That is the one area transformers really shine and would help put it's performance into perspective. I have a DIY tri-amp systems with a computer and unbalanced connections which had ground loop issues (no surprise). I could have converted it all to balanced at great expense in money and time but instead I got a stereo version of an Iso-max and it works perfectly... dead quiet even with my ear next to speakers. Transformers, while old school, still have a place for some applications.
I don’t have this unit, but I have some JT11 P1 which I think is what they use. If someone else hasn’t, I’ll run a CMR sweep when I get home from work tonight.
 
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This is an error of your arrangement. When you use a signal transformer, the I/O’s must not be floating, otherwise you have the hum components through stray capacitance. Try the grounded source and the problem should disappear. The best result is if both input and output are grounded and the trafo only disconnects the loop.
I tried all that already and it made no difference.
 

KSTR

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Quite easy to measure, but transformers tend to have relatively poor CMRR at high frequencies due to their interwinding capacitances.
Well, most of the better xformers have at least one shield (and preferably a foil shield, not a blind winding), many have two, one for each side. The CMRR-optimized models from Cinemag for example have >90dB CMRR at 20kHz, and dual shields plus extra wire for the can. On the opposite end, their models with extreme interwinding capacitace via their bilifar windings (for maximum bandwidth) still have 60dB at 20kHz.
 

Digital Mastering System

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Jensen says their typical CMRR is north of 80db, which is basically impossible with an opamp arrangement, unless one has 0.001% resistors and an temperature controlled oven to put the circuit into.
Also: Good transformers are full of expensive Nickle, hence are themselves expensive.
 
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