Neutrik NA2M-D2B-TX miniature transformer balancing adapter review
I have read the ASR review on the almost same product, with the only difference that it had female XLR and black CINCH, though my adapter has male XLR and red CINCH, otherwise they are same. The review link is:
www.audiosciencereview.com
My opinion how to test transformer adapters was different than the methods used in the review above, so I have bought the adapter and made my own measurements.
Appearance
The product has arrived in a typical blister pack.
It is nicely built, with high quality Neutrik connectors and rugged metal housing, that would withstand severe handling.
Adapter circuit schematics
The adapter consists of input RCA female connector, metal housing, small signal transformer and output XLR male connector. It is intended for SE/balanced signal conversion and circuit separation, in other words a solution of hum in systems with signal ground loops. Its schematics is below
R1 is a primary winding dc resistance (model), L1 is a primary winding inductance, R2 (model) and L2 same meaning at secondary. C1 is a stray capacitance between windings (model). R3 is a real resistor inside the box to flatten HF frequency response.
Specifications
The only available specifications are on the bottom of adapter blister package, saying:
Maximum input level defined at 50Hz and 1% THD is -3dBu (0.548 V). We shall check it.
Measurements
Measured circuit element values are as follows:
R1 = 56.8 ohm
L1 = 1.94 H
R2//R3 = 43.4 ohm
L2 = 1.91 H
Measuring system for frequency response, CMRR and distortion
My measuring system consists of Topping D10s USB DAC, Headamp2 (this is my design of headphone amplifier and is used because of its output impedance Zout = 0.056 ohm and 250 mA drive capability)
and E1DA Cosmos USB ADC switched to 4.5V input with input impedance Zin = 1.66 kohm.
Frequency response
Frequency response, measured at -3dBu, is flat from 40Hz to 40kHz. At 20Hz, there is a -3dB roll-off.
P.S.: With a quick check, there was not so big difference in frequency response when the adapter was driven from 200 ohm impedance. Posted here.
CMRR – common mode rejection ratio
Most important use of these adapters is to break ground loops to fix hum and buzz issues when several class I components are interconnected. CMRR, which shows attenuation of input common mode voltage from input to output, is measured in a circuit shown below:
and this is the result:
It is excellent, superb, 50Hz common voltage is suppressed of 135dB, 1kHz of 107 dB. This is quite impossible to get similar results with electronic preamplifier balanced input.
This is the example of adapter use – the system with Topping DAC, Headamp2 and Cosmos ADC has ground loop issue (if USB isolator is not used) that results in this horrible buzz spectrum:
The same, absolutely same system after insertion of Neutrik NA2M adapter behaves like this:
This is the key use of such adapters, we do not use them to break SINAD barriers, but to break ground loops!
Distortion measurements
THD vs. output voltage
THD vs. output voltage was measured at 50Hz and 1kHz. 1% THD at 50Hz was at 0.6 V, which is slightly better than specified.
THD vs. frequency at -3dBu (as per specs)
THD is acceptable above 100 Hz.
Conclusion
Neutrik NA2M-D2B-T transformer adapter will find its use in the systems with ground loop issues or to separate 2 systems with big voltage differences between 2 grounds. CMRR is excellent and is better than with electronic balanced inputs and the adapter accepts higher CMV voltages. It has to be driven from low impedance, 5 ohm or less at best. When driven from low impedance, it has wide and flat frequency response. It is usable for voltage levels <= 0.5V without audible degradation of the signal. I am voting"not terrible" with respect to higher distortion, changing vote to "fine" with respect to excellent CMRR and built quality.
Comments are welcome and more measurements can be done upon request.
-----------------------
Addendum
Per requests, I have measured the adapter also in the opposite direction, with XLR input and RCA output. I have measured both distortion and frequency response. The results are in both directions almost same, as can be seen from the plots below:
I have read the ASR review on the almost same product, with the only difference that it had female XLR and black CINCH, though my adapter has male XLR and red CINCH, otherwise they are same. The review link is:
Neutrik NA2F-D0B-TX XLR to RCA Adapter Review
This is a review and detailed measurements of the Neutrik NA2F-D0B-TX XLR to RCA (and vice versa) adapter. It is on kind loan from a member and costs US $35. The device feels very solid and oozes quality when you look at the RCA connector: This is a transformer based converter so balanced...
www.audiosciencereview.com
My opinion how to test transformer adapters was different than the methods used in the review above, so I have bought the adapter and made my own measurements.
Appearance
The product has arrived in a typical blister pack.
It is nicely built, with high quality Neutrik connectors and rugged metal housing, that would withstand severe handling.
Adapter circuit schematics
The adapter consists of input RCA female connector, metal housing, small signal transformer and output XLR male connector. It is intended for SE/balanced signal conversion and circuit separation, in other words a solution of hum in systems with signal ground loops. Its schematics is below
R1 is a primary winding dc resistance (model), L1 is a primary winding inductance, R2 (model) and L2 same meaning at secondary. C1 is a stray capacitance between windings (model). R3 is a real resistor inside the box to flatten HF frequency response.
Specifications
The only available specifications are on the bottom of adapter blister package, saying:
Maximum input level defined at 50Hz and 1% THD is -3dBu (0.548 V). We shall check it.
Measurements
Measured circuit element values are as follows:
R1 = 56.8 ohm
L1 = 1.94 H
R2//R3 = 43.4 ohm
L2 = 1.91 H
Measuring system for frequency response, CMRR and distortion
My measuring system consists of Topping D10s USB DAC, Headamp2 (this is my design of headphone amplifier and is used because of its output impedance Zout = 0.056 ohm and 250 mA drive capability)
and E1DA Cosmos USB ADC switched to 4.5V input with input impedance Zin = 1.66 kohm.
Frequency response
Frequency response, measured at -3dBu, is flat from 40Hz to 40kHz. At 20Hz, there is a -3dB roll-off.
P.S.: With a quick check, there was not so big difference in frequency response when the adapter was driven from 200 ohm impedance. Posted here.
CMRR – common mode rejection ratio
Most important use of these adapters is to break ground loops to fix hum and buzz issues when several class I components are interconnected. CMRR, which shows attenuation of input common mode voltage from input to output, is measured in a circuit shown below:
and this is the result:
It is excellent, superb, 50Hz common voltage is suppressed of 135dB, 1kHz of 107 dB. This is quite impossible to get similar results with electronic preamplifier balanced input.
This is the example of adapter use – the system with Topping DAC, Headamp2 and Cosmos ADC has ground loop issue (if USB isolator is not used) that results in this horrible buzz spectrum:
The same, absolutely same system after insertion of Neutrik NA2M adapter behaves like this:
This is the key use of such adapters, we do not use them to break SINAD barriers, but to break ground loops!
Distortion measurements
THD vs. output voltage
THD vs. output voltage was measured at 50Hz and 1kHz. 1% THD at 50Hz was at 0.6 V, which is slightly better than specified.
THD vs. frequency at -3dBu (as per specs)
THD is acceptable above 100 Hz.
Conclusion
Neutrik NA2M-D2B-T transformer adapter will find its use in the systems with ground loop issues or to separate 2 systems with big voltage differences between 2 grounds. CMRR is excellent and is better than with electronic balanced inputs and the adapter accepts higher CMV voltages. It has to be driven from low impedance, 5 ohm or less at best. When driven from low impedance, it has wide and flat frequency response. It is usable for voltage levels <= 0.5V without audible degradation of the signal. I am voting
Comments are welcome and more measurements can be done upon request.
-----------------------
Addendum
Per requests, I have measured the adapter also in the opposite direction, with XLR input and RCA output. I have measured both distortion and frequency response. The results are in both directions almost same, as can be seen from the plots below:
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