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Blue Jeans Cable Isolation Transformer Review

Rate this isolation transformer:

  • 1. Poor (headless panther)

    Votes: 195 95.6%
  • 2. Not terrible (postman panther)

    Votes: 1 0.5%
  • 3. Fine (happy panther)

    Votes: 1 0.5%
  • 4. Great (golfing panther)

    Votes: 7 3.4%

  • Total voters
    204

amirm

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This is a review and detailed measurements of the Blue Jeans Cable SWT1 Isolation Transformer meant for removal of ground loops. It was kindly sent to me by a member and costs US$50.
Blue Jeans Cable Isolation Transformer SWT1 Review Hum Filter Ground Loop.jpg

As you can see, the box is small which does not bode well for good performance when we think of transformers and low frequencies. The enclosure is plastic which I guess is OK for consumer applications.

Blue Jeans Cable SWT1 Measurements
Even though this is meant for subwoofer use, I thought I start with a 1 kHz tone as to make the results comparable to general purpose isolation transformers:

Blue Jeans Cable Isolation Transformer measurements.png


As expected, we get fair bit of distortion, knocking 50 dB from the performance of my audio analyzer by itself. There is also an 8% drop in level. Before doing more, let's look at the frequency response:
Blue Jeans Cable Isolation Transformer frequency response measurements.png


What the heck is this? Built-in high pass filter?
Edit: This is likely caused by the transformer saturating at lower frequencies. If the drive voltage is lower, then it will do less of this.

Ironically response is flat from 100 Hz up so it is better for your main speakers than subwoofer!

Back to our dashboard, let's put in 40 Hz:
Blue Jeans Cable Isolation Transformer 40 Hz measurements.png


Wow! We have nothing left of our sine wave. Our poor SINAD as a result has dropped to just 5 dB! No wonder there are reports of this box severely distorting subwoofer output. Before you say 2 volts is too much, let's sweep our voltage and frequencies and see what picture emerges:

Blue Jeans Cable Isolation Transformer THD vs Level vs Frequency measurements.png


This could pose as the poster for a horror movie! :) We see the classic rise of distortion inversely proportional to frequency which for subwoofer application, is really bad. The little transformer is saturating and saturating bad. Even at 100 Hz we have clipping at about 1.5 volts out. Optimal output voltage is just 0.1 volt!

No sense in testing more. We know what is going on.

Conclusions
This is a major miss for a company like Blue Jeans Cable which produces very good cables at very reasonable prices. Whoever thought of this product clearly had no understanding of what transformers do to signals other than isolation they provide. It takes a lot to make audible distortion in a subwoofer but the SWT1 gets there with ease. I guess if you have bad hum and you keep levels low the trade off may be worth it. Otherwise I can't figure out a good use for this box.

I can't recommend the Blue Jeans Cable SWT1 Isolation Transformer.

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

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Last edited:
I should add that the high-pass filter is making this much worse as the drive voltage has to be much higher than what comes out of the thing at frequencies < 100 Hz.
 
Blue Jeans cables sell by date has come due. I no longer recommend them for anything. There are better choices and they deserve to disappear.
Why so negative? I think their cables with banana plugs are still the best because they weld the plug to the conductor. Much better then just screw tightening or solder. And those measure well.
 
I should add that the high-pass filter is making this much worse as the drive voltage has to be much higher than what comes out of the thing at frequencies < 100 Hz.
Yes.
This undocumented HPF is really the final touch to a broken design.
 
Most SW inputs are around 0.5V for max. power and thus only when near maximum output the lowest bass will severly suffer.
Still.... this is the stupidest thing to use with subwoofers.
It will have less bass roll-off at lower levels.
This can not be used on the line-outs of DACs etc and should not be used for serious audio and certaily not in the SW path anyway...period.

A solution that creates more (other) problems is not a solution anyway.

I feel sorry for the unsuspecting buyers that assume they bought unusable crap like this.
 
Why so negative? I think their cables with banana plugs are still the best because they weld the plug to the conductor. Much better then just screw tightening or solder. And those measure well.
Better than silver soldered? No. World's Best can provide good components for the same price and don't push BS that Blue Jeans has gotten into of late. Basically you can no longer trust them. They'll sell you stuff like this broken design to accommodate sensibilities of audiophiles that aren't based upon reality.
 
This undocumented HPF is really the final touch to a broken design.
The principal intrinsic HPF is formed by Lp and Rp and it could be measured when using very low drive levels. What we are seing here, though, is that for higher levels and low frequencies, the primary saturates and clips, with Lp going down, creating even more momentary peak current and more saturation (this is positive feedback and creates the nasty "folded over" 40Hz waveform).

In the FR plot, the saturation effects manifest as a hard knee of the roll-off, very similar to what we see with electronics when slew-rate limiting for high frequencies kicks in.

The natural roll-off would a clean 6dB/oct high pass with the associated very rounded knee, sitting at a way lower frequency.

Overall, it's a very questionable product... and some users have already reported severe distortion issues with it...
 
Better than silver soldered? No. World's Best can provide good components for the same price and don't push BS that Blue Jeans has gotten into of late. Basically you can no longer trust them. They'll sell you stuff like this broken design to accommodate sensibilities of audiophiles that aren't based upon reality.
I like World’s Best Cables and own a bunch of their products, but they’re also guilty of spreading audio BS.

IMG_3258.jpeg
 
Stuff like this thing is the reason why every folk with decent gear must have an even basic ADC to measure stuff before even hooking them to rest of the gear.

Thanks Amir!
 
Stuff like this thing is the reason why every folk with decent gear must have an even basic ADC to measure stuff before even hooking them to rest of the gear.

Thanks Amir!
No ADC is required, just common sense takes care of 90%.
We have ASR for the last 10%.
 
Jeez! But positive note is the reduction of a line frequency induced noise at about 3 dB.. Unfortunately also the signal but you win some and lose some..:facepalm:
 
Optimized for subwoofer where the massive distortion is? what??:facepalm:
 
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