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

[amirm]

This is a review and detailed measurements of the Jensen ISO-MAX CI-1RR isolation transformer usually used to remove ground loops. It was kindly bought and drop shipped to me by the member and costs US $130.

This is a mono device and could not be simpler with just an input and output:

No power is needed.

Basically device takes the typical safety ground referenced RCA signal and delivers a floating signal independent of said ground.

Jensen ISO-MAX CI-1RR Measurements
Our focus in the measurements are to see if there is an loss of fidelity by inserting this device in the audio chain. Let's start with our usual dashboard of 1 KHz tone:

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.

Anyway, the main point of the show is the third harmonic that is around -108 dB. Add some of that mains noise and SINAD becomes 106 dB. At this frequency at least, we are pretty close to transparent but this story is more complicated as you will shortly see.

Frequency response is excellently flat with tiny bit of ringing (into 100 k ohm load):

Naturally there is some phase shift which is load dependent:

We see the true nature of the distortion profile of this transformer when we sweep the frequency:

So the lower the frequency, the more the distortion.
I don't have other references to compare other than a PS Audio PerfectWave DirectStream DAC which uses transformer in its output:

At 20 Hz, the PS Audio DSD DAC distortion rises to 0.1% or -60 dB. So the Jensen ISO-MAX is about 10 dB lower in distortion (assume there were not other distortion factors in the PS Audio DAC).

Transformers also saturate so the higher the voltage, the worse this effect is. Let's sweep the level at multiple frequencies focusing on lower ones:

IMD was not as revealing as I thought given the fact that one of its tones is at 60 Hz:

Conclusions
Average transformer can produce a lot of distortion. Clearly care must have been taken here to use a high quality one -- which is what one expects from Jensen -- to keep distortion in check. And frequency response flat. Distortion in mid frequencies where our hearing is very sensitive is close to threshold of hearing so I don't expect an audible effect. Still no sense in spending $130 if you don't have an audible ground loop.

I am happy to recommend the Jensen ISO-MAX CI-1RR for when you are facing ground loops and nothing else works.

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As always, questions, comments, recommendations, etc. are welcome.

Appreciate any donations using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/

 

[GWolfman]

What's a failproof test to verify that ground loops are actually eliminated? Or was that already proven and I misunderstood something above?

 

[amirm]

Once you insert this device, there is no ground connection anymore to have a loop. So the tests weren't focused on that, but rather what losses you get with it.

 

[dominikz]

We see the true nature of the distortion profile of this transformer when we sweep the frequency:

So the lower the frequency, the more the distortion.
I don't have other references to compare other than a PS Audio PerfectWave DirectStream DAC which uses transformer in its output:

Just to add to this - I've tested several transformers (Jensen, Edcor, Vigortronix...) previously when building some reamp and DI boxes and found the same thing - all of the tested transformers saturated early in low frequencies, with Jensen ones performing much better than the others I tested.

Above is the IMD comparison of passive DIY reamps based on Jensen JT-11P and Edcor WSM-10k/10k transformers, and the commercial unit Little Labs RedEye 3D in passive mode vs soundcard loopback. We can see the Jensen tranformer is close to the soundcard response in LF, while the others exhibit increased LF distortion levels.
When I have some time I can try to re-do and post some measurements in a new thread if there is interest.

 

[milosz]

The test for "does this eliminate the ground loop" is: Listen to your audio system. Do you hear a hum and/or buzz? OK you probably have a ground loop.

Disconnect ALL the inputs to your amp or preamp. The hum/buzz should be gone. Reconnect one of the inputs through this isolation transformer -place this transformer in line with one of the inputs to your amp or preamp. Did the hum or buzz go away? OK you eliminated the ground loop.

Does the humm/buzz come back when you plug the other inputs in? Then EACH ONE could need one of these isolation transformers. Elseways, try to identify the source of that ground loop and eliminate that source.

I found I needed an isolation transformer on the input to my Cable Box from the cable TV company - an RF isolation transformer. Had a nasty ground loop buzz in my A/V system until I put that transformer in there. I used this $15 job from Amazon => https://www.amazon.com/dp/B08FRGH4X2/ref=cm_sw_em_r_mt_dp_WFH7D1T1ANF0WE9BCGE6

 

[abdo123]

A product that does what it says! In this industry! Woaaaaaaaaaaaaaaaaaaah.

Edit: I just noticed Red is stock, blue is transformer.

Why is there a rise in mains hum? shouldn't it be completely the opposite?

 

[Music1969]

In a twist of faith, the addition of ISO-MAX created mains hum where none existed before!

Hmmmm this is the exact opposite of what I expected.

 

[dominikz]

Why is there a rise in mains hum? shouldn't it be completely the opposite?

Hmmmm this is the exact opposite of what I expected.

IMHO this is not completely unexpected - transformers work as they do due to electromagnetic induction, and depending how well the transformer shielding is done, IME it can indeed pick up various electromagnetic noises (including mains hum). Though the Jensen transformers I tested typically have very nice shielding and are quite resistant to mains pickup - so from that sense it is a bit surprising.

 

[TimoJ]

@amirm if possible, please measure frequency response with lower signal levels. i.e. 0.1V, 0.25V, 0.5V, 1V. Is it still flat?

 

[KSTR]

Hmmmm this is the exact opposite of what I expected.

You have to keep in mind the microscopic level, -110dBc. Completely irrelevant.

To "fully eliminate" mains pickup with high impedance line transformers you have to go a very long and expensive way: Humbucking arrangement of two xfomers, double or triple Mu-Metal shields, things like that.

 

[KSTR]

@amirm if possible, please measure frequency response with lower signal levels. i.e. 0.1V, 0.25V, 0.5V, 1V. Is it still flat?

No need to do this. No variation of FR vs lower level. High levels at LF are the problem (some xformers show a chaotic "jump resonance" effect when overdriven, the output waveform goes fully distorted and doesn't return to normal until you back of the volume to 90% or less to where the jump occurred)

 

[KSTR]

LF distortion massively depends on the source impedance, btw. The lower the source impedance, the lower the distortion. Actually the best source impedance is close to the negative value of the xformer's DC resistance, distortion basically vanishes.

HF frequency response is dominated by termination impedance. Most xformer spec sheets state the values of a series RC to be placed across the output for flattest FR at HF. Any additional load that is lower than this damper circuit compromises FR (and phase).

 

[Rja4000]

Interesting

In the past, I measured a Radial DI box (with Jensen transformer)

https://www.audiosciencereview.com/...ave-directstream-dac.9100/page-16#post-233856

 

[TimoJ]

No need to do this. No variation of FR vs lower level. High levels at LF are the problem (some xformers show a chaotic "jump resonance" effect when overdriven, the output waveform goes fully distorted and doesn't return to normal until you back of the volume to 90% or less to where the jump occurred)

I asked because I once had a cheap stereo isolation transformer that certainly didn't have flat response at low levels. Cylinder type with RCA leads coming out from both ends. I'll search if I still have it somewhere and do some measurements.

 

[vkvedam]

Is ground loop hum a big issue in the US Vs UK/EU?

 

[somebodyelse]

What's a failproof test to verify that ground loops are actually eliminated? Or was that already proven and I misunderstood something above?

Jensen's application notes are pretty comprehensive, including systematic methods for finding and fixing ground loops. AN007 covers it in detail IIRC.
https://www.jensen-transformers.com/application-notes/

 

[KxDx]

What's a failproof test to verify that ground loops are actually eliminated? Or was that already proven and I misunderstood something above?

If you don't hear the hum/buzz from your speakers, you're good to go.

 

[KxDx]

I solved the problem by using XLR to RCA cables from my DAC to my amp (parasound NC doesn't have balanced inputs). Buying this transformer would have been the next thing to try, but that did the trick.

 

[TimoJ]

I asked because I once had a cheap stereo isolation transformer that certainly didn't have flat response at low levels. Cylinder type with RCA leads coming out from both ends. I'll search if I still have it somewhere and do some measurements.

Found it, did some measurements:

 

[KSTR]

@TimoJ, that is really rather unusual. I'm sure we won't find this in any quality xformer.
I have some ultra cheap small Triad Magnetics where I could check for this issue.