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Neutrik NA2M-D2B-Tx balancing transformer adapter review

Rate this adapter

  • Poor

    Votes: 15 22.7%
  • Not terrible

    Votes: 13 19.7%
  • Fine

    Votes: 32 48.5%
  • Excellent

    Votes: 6 9.1%

  • Total voters
    66
I have just made measurements with 200 ohm driving impedance, load impedance remained 1.66 kohm.

Distortion vs. frequency - worse, but not as much as I expected
View attachment 293934


Frequency response, just quick comparison to 0.056 ohm drive (I apologize for not shifting Y scale). Surprisingly still goes down to 40Hz.
View attachment 293927

THD, THD+N at 1kHz/552mV. About 4x more than with 0.056ohm drive.
View attachment 293928



REW and STEPS. REW sometimes goes unstable with my DAC/ADC, so time after time I use STEPS, which is stable and saves my time by no need of repeating of measurements.
I still wonder how much better the LF distortion would be if the receiving impedance was higher, given that most line inputs present a bridging impedance of 10K or more.

Any transformer, however good, will show an increase in distortion at LF due to core saturation driving an impedance lower than it was designed for. A transformer of that size won't be happy into a 1.66k load. My transformers designed for driving a 600 ohm load are several times the size of the one in this adapter.

S.
 
Several scope screenshots with "large" signals

50Hz_saturation_200R.png 50Hz_saturation_0.056R.png 1kHz_big_200R.png 1kHz_big_0.056R.png 1kHz_THD_0.056R.png
 
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I'm strictly a layman when it comes to electronics and I find myself pretty confused when it comes to what the appropriated application of this device is supposed to be. Ashamedly though @pma clearly know what he is talking about, I mostly do not. What I would like is a simple, add-on device that will convert an ordinary audio line-level SE signal to a differential balanced signal with near-zero distortion -- I come away uncertain whether this Neutrix device can effectively do that.

In my observation many preamps and amps don't internally convert SE to differential, hence if you input SE you get, effectively, only SE output regardless of whether XLR output is connected. I have had at least three preamps that apparently operate this way. What exactly is the consequence for downstream amps that are apparently optimized for balance input receive only a "dead" '-' signal? (I think I can guess but I'm not sure.)
 
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I'm strictly a layman when it comes to electronics and I find myself pretty confused when it comes to what the appropriated application of this device is supposed to be. What I would like is simple, add-on device that will convert an ordinary audio line-level SE signal to a differential balanced signal with near-zero distortion -- I come away uncertain whether this Neutrix device can effectively do that.

My observation is that many preamps and amps don't internally convert SE to differential, hence if you input SE you get, effectively, only SE output. I have had at least three preamps that apparently operate this way. What exactly is the consequence for downstream amps that accept the a optimized for balance input receive only a "dead" '-' signal? (I think I can guess but I'm not sure.)
In all cases I think that "near zero" may be difficult to obtain at least for a passive transformer based solution. I'd say those are an industry standard and are well behave with inaudible to me distortion:


1687346656085.png
 
I'm strictly a layman when it comes to electronics and I find myself pretty confused when it comes to what the appropriated application of this device is supposed to be.
Don't worry, practically everyone is confused. Here are the suggestion made by many on what this device and its counterpart, which we are told the same other than a different sex XLR connector. Here are some suggestions I copied from both threads:

  • convert unbalanced outputs to to balanced inputs
  • offer galvanic isolation so that hum is eliminated
  • feed an XLR input from an RCA connector
  • feed an RCA input from an XLR connector
  • ground isolation for microphone level signals, about -30 dBu, for example from a microphone or a direct injection box
  • connect balanced devices to unbalanced inputs at live PA applications
  • connect weird homemade computer thingies some performer have to mixing boards in live events
 
Don't worry, practically everyone is confused. Here are the suggestion made by many on what this device and its counterpart, which we are told the same other than a different sex XLR connector. Here are some suggestions I copied from both threads:

  • convert unbalanced outputs to to balanced inputs
  • offer galvanic isolation so that hum is eliminated
  • feed an XLR input from an RCA connector
  • feed an RCA input from an XLR connector
  • ground isolation for microphone level signals, about -30 dBu, for example from a microphone or a direct injection box
  • connect balanced devices to unbalanced inputs at live PA applications
  • connect weird homemade computer thingies some performer have to mixing boards in live events
May we add this (from the link I posted above),or is irrelevant?


reamp.PNG

All thought the devices it describes has added features,but maybe low cost.
 
Cumulative THD vs. output voltage plots at 50Hz, 100Hz, 1kHz and 5kHz (BW45kHz), top to bottom
NA2M_THDlevel_50Hz-5kHz.png


So yes, best to be used for <= 500mV output voltage.

Interesting feature of audio line transformers is the fact that IMD distortion is much lower than one would expect from THD profiles. This fact is explained in Bill Whitlock book


DIN-IMD_big_0.056R.png


Quote: Unlike that in amplifiers, the distortion mechanism in a transformer is frequency selective. This makes its IM distortion much less than might be
expected. For example, the Jensen JT-10KB-D line input transformer has a THD of about 0.03% for a +26 dBu input at 60 Hz.
But, at an equivalent level, its SMPTE IM distortion is only about 0.01% — about a tenth of what it would be for an amplifier having the same THD.
 
May we add this (from the link I posted above),or is irrelevant?


View attachment 293986

All thought the devices it describes has added features,but maybe low cost.
From the link:

Reamping works by converting the balanced line level signal from your audio interface’s output to an unbalanced instrument level signal suitable for guitar gear.

This device does not offer level conversion. Also the low impedance may effect the amplifier sound as it expects a high impedance source.
 
I was asked to show practical use of this adapter. I have showed one, and this is another situation when between source ground (low quality class II sine generator) and PC ground is a voltage difference of 65V/50Hz. It is a „soft“ source, but in case of SE signal link the shield capacitive current totally destroys the usable signal. When I insert the NA2M adapter into the SE link, the 50Hz amplitude is reduced to -95.19dBV, which is an equivalent to 17.399uV. 65V to 17.399uV makes 131.45dB. So the adapter has suppressed the common voltage between grounds by 131.45dB, and made an acceptable THD+N = 0.0063% from the poor instrument. When the PC/ADC is connected to generator directly, we get 50Hz amplitude of -68.42dBV and THD+N = 0.067%, 10x worse.. So, the adapter has reduced the system 50Hz hum of 26.77dB, 21.8x, and this is a considerable improvement, THD+N was improved more than 10x.

With the adapter
NA2M_65Vac_I-O_voltage.png

Without the adapter
Gen-DAC_direct.png
 
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I still wonder how much better the LF distortion would be if the receiving impedance was higher, given that most line inputs present a bridging impedance of 10K or more.

I do not think so. Please have a look at the Bill Whitlock transformer book that I linked here several times.

1687367763967.png


The result, which may surprise some, is that flux density in a transformer is not increased by load current. This also illustrates how load current on the secondary is reflected to the primary.

However, I may measure it with >10k load, but I do not expect improvement in distortion.

But in a real transformer design there is a fixed relationship between signal level, distortion, and source impedance. Since distortion is also a function of magnetic flux density, which increases as frequency decreases, a maximum operating level specification must also specify a frequency. The specified maximum operating level, maximum distortion at a specified low frequency, and maximum allowable source impedance will usually dictate the type of core material which must be used and its physical size. And, of course, cost plays a role, too.
 
I still wonder how much better the LF distortion would be if the receiving impedance was higher, given that most line inputs present a bridging impedance of 10K or more.

Any transformer, however good, will show an increase in distortion at LF due to core saturation driving an impedance lower than it was designed for. A transformer of that size won't be happy into a 1.66k load.

I do not think so. Please have a look at the Bill Whitlock transformer book that I linked here several times.

So - no. :)

I have made measurements with 1.66kohm load and 100kohm load (my SOTA buffer) and there is no difference in distortion.

NA2M_THDfreq_-3dBu_1k66_100k.png


Next time, please, if you do not believe me, which is understandable, do believe the theory and the experts like Bill Whitlock is. To prepare an experiment is quite time consuming, and I knew the result before I started it ;).
Source impedance is important, regarding distortion. Load impedance is not.

P.S.: I am quite happy with consistency of measurements regardless changes in the measurement setup. And conformance of REW x STEPS results.
 
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So - no. :)

I have made measurements with 1.66kohm load and 100kohm load (my SOTA buffer) and there is no difference in distortion.

View attachment 294030

Next time, please, if you do not believe me, which is understandable, do believe the theory and the experts like Bill Whitlock is. To prepare an experiment is quite time consuming, and I knew the result before I started it ;).
Source impedance is important, regarding distortion. Load impedance is not.
Thank you for that. I've learnt something. I wonder then why transformers for 600 ohm loads are so much bigger than those for 10k bridging loads, even when both handle +24dBu at low frequencies.

There's something missing in my knowledge.

S
 
The only notable difference we get with the change of load impedance is frequency response difference at high frequencies above audio band. Below is the measured comparison:

NA2M_FR_-3dBu_1k66_100k_80kHz.png


This shows that at 40kHz there is a FR drop of about 0.3dB with 1.66kohm load compared to 100kohm load. At 80kHz it is -1.1dB. There is absolutely no difference in distortion, of course there is a necessary condition - the generator must be load invariant and must handle both loads with unchanged distortion. And with distortion, including ADC, lower than the adapter has. This is perfectly fulfilled below 1kHz. Above 2kHz, we get the system copy (in distortion).
 
is there a high quality version of this that could be tested to see If a better transformer had lower distortion ? be interesting
 
This is probably good enough for sound reinforcement use - I can't imagine that it would "harm" the audio from the vocal mic of a death metal singer, for example......
 
is there a high quality version of this that could be tested to see If a better transformer had lower distortion ? be interesting

My post here would be of your reference.

If you would be really serious in balanced-->unbalanced or unbalanced-->balanced conversion in HiFi quality, you may better to use such pro converters.
 
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