Radial Engineering ISO Twin (Jensen transformers) technical measurements

Discussion in 'Portable and Other Gear Measurements' started by atomicbob, Oct 30, 2018.

  1. atomicbob

    atomicbob dScope Yoda

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    Radial ISO Twin (Jensen transformers) technical measurements

    If you are unfamiliar with audio measurements please use a search engine with the query:
    "audio measurements" or "audio measurement handbook"
    Look for publications by Richard C. Cabot and also by Bob Metzler, both from Audio Precision. There are other useful publications as well. These will provide basic knowledge.
    Interpretation of the following measurements is beyond the scope of this post.

    The data presented were collected as follows:

    1. PrismSound dScope III, picoscope 5243B, Keysight 34461A DMM
    2. 100K and 10K ohm loads used for measurements
    3. Balanced cables Canare L-4E6S starquad with Neutrik XLR connectors
    4. Vaunix Lab Brick USB hub for measurement equipment
    5. Audioquest Forest and Schiit Pyst USB cables used for measurement equipment
    6. ISO Twin is 1:1 with 0 dB gain @ 0.775 Vrms 0 dBu
    7. 14 and 16 AWG sheilded power cables used

    Reference specification data on two headphones:
    HD 650 impedance 100K, sensitivity 98 dB/mW
    HE-500 impedance 38R, sensitivity 89 dB/mW

    Reference sound levels to consider for headphone usage:
    +9 dBu 100K 16.00 mW - 110 dBSPL @ 98dB/mW
    0 dBu 100K 2.00 mW - 101 dBSPL @ 98dB/mW
    -10 dBu 100K 0.20 mW - 91 dBSPL @ 98dB/mW
    -20 dBu 100K 0.02 mW - 81 dBSPL @ 98dB/mW

    +9 dBu 30R 160.00 mW - 110 dBSPL @ 89dB/mW
    0 dBu 30R 20.00 mW - 102 dBSPL @ 89dB/mW
    -10 dBu 30R 2.00 mW - 92 dBSPL @ 89dB/mW
    -20 dBu 30R 0.20 mW - 82 dBSPL @ 89dB/mW

    Highlights
    Square wave response is excellent.
    Estimated bandwidth is quite high at greather than 5.8 MHz.
    The Radial ISO Twin uses Jensen 1:1 transformers.
    I have little fear of using transformers in audio paths; far less than mediocre active stages. A system optimally gain staged will run approximately 0 dBu average levels throughout. At this signal level the ISO Twin exhibits less than 0.0003% THD+N from 10Hz to 20KHz.

    A system usage of the ISO Twin may be seen here in the very first of the System Synergy Special Sound thread.

    My personal preferences include listening typically at an average of 75 dB SPL. Assuming a typical Peak to Average ratio of 10 dB puts peaks at 85 dB SPL. This suggests the measurements at -20 dBu represent my experience with HD6x0 and HD800 headphones. Auditory experiences for someone listening 10 dB SPL average higher may diverge from my own experiences.

    editorial - I believe there is a tendency to focus excessively on numbers such as THD attempting to reduce a complex topic to a single number representing a sort of goodness rating. Graphs can present far more data conveying a better understanding of the measurement over a range of frequency, levels, etc. Please don't read too much into the numbers presented. Read the tutorial presented here for a good example of why.


    Picture of the Audio Lab setup for ISO Twin measurements
    DSC_0003_small.png.jpg

    ISO Twin measurements part 1 of 4

    ISO Twin THD+N THD nth harmonic distortion (A04) FFT 0dBu 100K load
    20181030 ISO Twin A04 THD+N  THD  nth-HD FFT 100K.png

    ISO Twin THD THD+N vs Freq 0dBu 100K
    20181030 ISO Twin THD THD+N vs Freq 100K.png

    ISO Twin 1 KHz spectrum Left and Right 0dBu 100K load
    20181030 ISO Twin 1 KHz THD+N THD FFT 0dBu 100K.png

    ISO Twin 50 Hz + 7000 Hz spectrum Left and Right 0dBu 100K load
    20181030 ISO Twin 50+7000Hz 0dBu 100K.png

    ISO Twin 600 Hz + 1700 Hz spectrum Left and Right 0dBu 100K load
    20181030 ISO Twin 600+1700Hz 0dBu 100K.png

    ISO Twin IMD spectrum Left and Right -16dBu 100K load
    20181030 ISO Twin 19+20KHz -16dBu 100K.png

    ISO Twin residual noise spectrum Left and Right A=0dB 100K load
    20181030 ISO Twin residual noise A=0dB 100K.png


     
    Last edited: Oct 30, 2018
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  2. atomicbob

    atomicbob dScope Yoda

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    ISO Twin measurements part 2 of 4

    ISO Twin square wave 20 Hz 2 Vpp 10 mS / div 10K load 100 KHz BW
    20181030 SigGen ISO Twin 20 Hz square 2000mVpp 10mS div 100KHz filter 10K.png

    ISO Twin square wave 20 Hz 2 Vpp 10 mS / div 10K load 10 MHz BW
    20181030 SigGen ISO Twin 20 Hz square 2000mVpp 10mS div 5MHz filter 10K.png

    ISO Twin square wave 20 Hz 2 Vpp 10 uS / div 10K load 100 KHz BW
    20181030 SigGen ISO Twin 20 Hz square 2000mVpp 10uS div 100KHz filter 10K.png

    ISO Twin square wave 20 Hz 2 Vpp 10 uS / div 10K load 10 MHz BW
    20181030 SigGen ISO Twin 20 Hz square 2000mVpp 10uS div 5MHz filter 10K.png

    ISO Twin square wave 20 Hz 2 Vpp 20 nS / div 10K load 10 MHz BW
    20181030 SigGen ISO Twin 20 Hz square 2000mVpp 20nS div 10MHz filter 10K - BW calc.png

    Bandwidth estimation: BW (GHz) = 0.35 / RT (nS)
    Where RT = 10 to 90% Rise Time
    0.35 / 60 nS = 5.83 MHz


    ISO Twin amplitude - phase - gain (A01) 100K load

    20181030 ISO Twin A01 amplitude - phase - gain 100K.png

    ISO Twin signal to noise (A07) 100K load
    20181030 ISO Twin A07 SNR 100K.png

    ISO Twin THD+N THD nth harmonic distortion (A04) 100K load
    20181030 ISO Twin A04 THD+N  THD  nth-HD 100K.png

    ISO Twin Crosstalk (A08 A09) 100K load
    20181030 ISO Twin A08 A09 Crosstalk 100K.png



     
    Last edited: Oct 30, 2018
  3. atomicbob

    atomicbob dScope Yoda

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    ISO Twin measurements part 3 of 4

    ISO Twin Frequency Response and Interchannel Phase pg 1/2 100K load
    G2_L1T2_1_A.png

    ISO Twin Frequency Response and Interchannel Phase pg 2/2 100K load
    G2_L1T2_1_B.png

    ISO Twin Gain vs Amplitude Left 100K load
    G2_L1T3_1_A.png

    ISO Twin Gain vs Amplitude Right 100K load
    G2_L1T3_1_B.png

    ISO Twin THD+N vs Frequency Left 100K load
    G2_L1T6_1_A.png

    ISO Twin THD+N vs Frequency Right 100K load
    G2_L1T6_1_B.png

    ISO Twin THD+N vs Amplitude Left 100K load
    G2_L1T7_1_A.png

    ISO Twin THD+N vs Amplitude Right 100K load
    G2_L1T7_1_B.png

    ISO Twin Crosstalk Left to Right vs Frequency 100K load
    G1_L1T11_1.png

    ISO Twin Crosstalk Right to Left vs Frequency 100K load
    G0_L1T12_1.png
     
    Last edited: Oct 30, 2018
  4. atomicbob

    atomicbob dScope Yoda

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    ISO Twin measurements part 4 of 4

    ISO Twin 20 Hz THD+N vs Amplitude 100K load
    20181030 ISO Twin 20 Hz THD+N vs Amplitude 100K - v2.png

    ISO Twin 40 Hz THD+N vs Amplitude 100K load
    20181030 ISO Twin 40 Hz THD+N vs Amplitude 100K - v2.png

    ISO Twin 100 Hz THD+N vs Amplitude 100K load
    20181030 ISO Twin 100 Hz THD+N vs Amplitude 100K - v2.png

    ISO Twin 1000 Hz THD+N vs Amplitude 100K load
    20181030 ISO Twin 1000 Hz THD+N vs Amplitude 100K - v2.png
     
    Last edited: Oct 30, 2018
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  5. atomicbob

    atomicbob dScope Yoda

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    reserved 5/5.
     
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  6. Cspirou

    Cspirou They call me Sparky

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  7. purr1n

    purr1n Finding his inner redneck

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    Might be a good idea to test at 18dBu which seems reasonable given the spec of 21dBu at 1kHz and 1% THD. 1% is usually the knee where things rapidly go south.

    Curious about performance at 50, 30, 20Hz as we go to DC. And also from 16,17, 20dBu. These areas are when "specs" get scary.

    But really not much to fear if a spectrum analysis is done to find max levels per frequency on music or TV broadcast material. Real material doesn't get close to the limits.

    Explosions in Michael Bay movies may be an exception, but there is probably going to be other things to worry about when this happens. Besides, audio engineers should know what they are doing and set reference levels accordingly.
     
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  8. frenchbat

    frenchbat BritishBat's arch enemy - Friend

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    @atomicbob How would things evolve if testing at 150/600 Ohms which are typical for pro-gear ?
     
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  9. purr1n

    purr1n Finding his inner redneck

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    This is a good point, the datasheets of these kinds of transformers usually recommend resistors to bring the load to as close to 600 as possible - although the FR does perfect for 100k loads.
     
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  10. atomicbob

    atomicbob dScope Yoda

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    In this post 4 measurements are presented representing THD+N swept from -60 to +20 dBu, with THD+N in dB on the y-axis and dBu on the x-axis.

    Here is the first one, measured at 20 Hz, repeated with additional annotation:
    20181030 ISO Twin 20 Hz THD+N vs Amplitude 100K - v2 - annotated.png

    This graph shows just under 1% THD+N at +20 dBu at 20 Hz. It also shows approximately 0.056% THD+N at 0 dBu at 20 Hz.

    In post #4 above THD+N vs dBu amplitude is presented for 20 Hz, 40 Hz, 100 Hz and 1000 Hz.

    Please refer to this Sound On Sound article about impedance:
    https://www.soundonsound.com/techniques/understanding-impedance

    While studio oriented, the principles are the same for studio and consumer audio. Pay particular attention to matched vs bridged impedance systems. You will be hard pressed to find matched impedance in use today outside of copper telcom.

    As for choice of test load impedance consider that most audio inputs are designed for 10K to 100K input impedance, both pro and consumer audio. Now consider the reflected transformer impedance, which corresponds to the square of the turns ratio. Brief explanation found here:
    https://electronics.stackexchange.com/questions/80929/reflecting-impedance-in-a-transformer

    Since the ISO Twin is a 1:1 turns ratio transformer, reflected impedance will be roughly the input impedance of the device to which signal is being sent. In most cases this will be between 10K ~ 100K ohms.
     
    Last edited: Oct 31, 2018
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  11. purr1n

    purr1n Finding his inner redneck

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    2OHz: +20dBu at 1% and +0dBu at 0.056%.

    That's actually pretty good and as expected for this part. Amirites would have a conniption.

    I'm pretty sure this is the Jensen version of the Cinemag part I am using. The mumetal can versions even use the same color wire leads.

    The story goes that back in the day, the Jensen guy asked to look at the Cinemag designs because he was enthralled with the transformers. The Cinemag guy, being the nice guy that he was, showed him everything. Then the Jensen guy started Jensen with the knowledge that he gleaned.

    At least that's the urban legend and why Craig, if he can avoid it, will avoid Jensen. Don't know if there is any truth to this, and in any event, different owners now. That would have been ancient history.
     
    Last edited: Oct 31, 2018
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  12. frenchbat

    frenchbat BritishBat's arch enemy - Friend

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    TY Bob, your answer helps putting things in context for different uses of the isolation trafo box(es), like Marv does when he tests balanced only components, with his single-ended only amplifier.

    That said, and as you put it well in the first post, while being apparently transparent at your low listening level (75dB), it's possibly quite different at highish listening levels.

    IIRC the jensen box was deemed useful, but having a detrimental effect on the sound, when used by multiple users here. I personally think it makes sense to keep using things the way they are intended if possible.

    Edit : I found this article also useful to understand the turn ratio
    https://www.electronics-tutorials.ws/transformer/audio-transformer.html
     
    Last edited: Oct 31, 2018
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  13. purr1n

    purr1n Finding his inner redneck

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    It's the context of usage. I feel that running the balanced outs through the Cinemags to get unbalanced are better (more transparent, less colored) than the unbalanced outputs of the Schiit DACs. For other DACs, the PWD2 for example, I preferred the SE outs instead over running balanced through the same Cinemags to get SE.

    On the Jensen box, the one Bob used is the 1:1 balanced to balanced isolation box and NOT THE SAME thing as the Jensen 4:1 Isobox that many have used here for balanced to unbalanced conversion.
     
  14. frenchbat

    frenchbat BritishBat's arch enemy - Friend

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    Right, I missed that.

    I do get the context, for the Yggdrasil. But as I said elsewhere, I'm hard-pressed to believe there's such a thing as a free lunch.
     
  15. purr1n

    purr1n Finding his inner redneck

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    Never a free lunch!
     
  16. atomicbob

    atomicbob dScope Yoda

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    As mentioned, this is the 1:1 iso, not 4:1. But there is never a free lunch. In the brief guide for Bal to unBal connections the same issue of sound quality degradation was raised. My reply can be found here . It all depends on priorities and preferences. I'll take a slight amount of bass distortion if it renders inaudible hum, which I detest.
     
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  17. purr1n

    purr1n Finding his inner redneck

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    I'd worry about bass distortion at 20Hz with 5.5" woofers more; or unnecessarily putting a cap in the signal path, like for fun, because you know, audiophiles do strange things.
     
    Last edited: Oct 31, 2018
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  18. purr1n

    purr1n Finding his inner redneck

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    Here are some spectrum analyses of real music content. Hopefully, I did these right. Peak (yellow) and mean (green) levels are shown. THE DB SCALE ON THE LEFT REFLECTS x10.

    The recording that gets closest to saturating (NOT REALLY) this line-level transformer is Doin' It Right (second in series) with 38Hz at -5db peak. Dem bass drops ya know - the third one in the series of bass drops. Assuming max output of gear is +22dBu and using Bob's plot, THD would be around 0.05%. That's 65db down.

    We can also see that the recording that doesn't roll massively off below 35Hz is from Alicia Keys Unplugged album. But it still tapers off because that's just the way reality rolls, while also keeping in mind the mastering engineer kept things very bassy for this album.

    a woman's worth.png
    doin it right.png
    get lucky.png
     
    Last edited: Oct 31, 2018
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  19. drgumbybrain

    drgumbybrain Science Nut

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    Dear @atomicbob, congrats for teaching me something about audio tech. May I ask in which system do you use this Radial Iso box?
     
    Last edited: Oct 31, 2018
  20. atomicbob

    atomicbob dScope Yoda

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    My past includes some periods of running live sound and recording live events. Having a number of isolation transformers and DI boxes in the toolkit was often useful. Also handy to have in the audio lab. An example may be found here .
     

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