Radial Engineering ISO Twin (Jensen transformers) technical measurements

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


ISO Twin measurements part 1 of 4

ISO Twin THD+N THD nth harmonic distortion (A04) FFT 0dBu 100K load


ISO Twin THD THD+N vs Freq 0dBu 100K


ISO Twin 1 KHz spectrum Left and Right 0dBu 100K load


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


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


ISO Twin IMD spectrum Left and Right -16dBu 100K load


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

 

ISO Twin measurements part 2 of 4

ISO Twin square wave 20 Hz 2 Vpp 10 mS / div 10K load 100 KHz BW


ISO Twin square wave 20 Hz 2 Vpp 10 mS / div 10K load 10 MHz BW


ISO Twin square wave 20 Hz 2 Vpp 10 uS / div 10K load 100 KHz BW


ISO Twin square wave 20 Hz 2 Vpp 10 uS / div 10K load 10 MHz BW


ISO Twin square wave 20 Hz 2 Vpp 20 nS / div 10K load 10 MHz BW


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


ISO Twin signal to noise (A07) 100K load


ISO Twin THD+N THD nth harmonic distortion (A04) 100K load


ISO Twin Crosstalk (A08 A09) 100K load

 

ISO Twin measurements part 3 of 4

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


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


ISO Twin Gain vs Amplitude Left 100K load


ISO Twin Gain vs Amplitude Right 100K load


ISO Twin THD+N vs Frequency Left 100K load


ISO Twin THD+N vs Frequency Right 100K load


ISO Twin THD+N vs Amplitude Left 100K load


ISO Twin THD+N vs Amplitude Right 100K load


ISO Twin Crosstalk Left to Right vs Frequency 100K load


ISO Twin Crosstalk Right to Left vs Frequency 100K load

 

ISO Twin measurements part 4 of 4

ISO Twin 20 Hz THD+N vs Amplitude 100K load


ISO Twin 40 Hz THD+N vs Amplitude 100K load


ISO Twin 100 Hz THD+N vs Amplitude 100K load


ISO Twin 1000 Hz THD+N vs Amplitude 100K load

 

reserved 5/5.

 

Wow, that 20Hz square wave through a transformer is really good. I would have no issue adding this to the signal path to break ground loops.

Any experience with Neutrik transformers?

http://www.neutrik.us/en-us/accessories/inline-adapters/na2f-d0b-tx

 

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

 

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:


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.

 

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

 

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.

 

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.

 

Dear @atomicbob, congrats for teaching me something about audio tech. May I ask in which system do you use this Radial Iso box?

 

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 .