Has anyone seen those trafos before ?

[ricothetroll]

Hi,
I bought those two unbranded audio trafos today. The seller told me they're 600:300+300, double mu-metal insulated. He told me the brand is "Neutraf", that were made by/for Neutrik, before the Neutrik branded series.
I will do some simple tests (audio bandwidth and THD vs level) with visual analyser to have a better idea of their performances. I intend to use the as isolation transformers.
Here are some pictures of it :
http://imageshack.us/a/img404/1715/fukq.jpg
http://imageshack.us/a/img266/2162/mz7u.jpg
http://imageshack.us/a/img834/816/ce2f.jpg
Best regards.

 

[andre tchmil]

interesting question, I have a few of these as well.

 

[ricothetroll]

I bought them at Wolec, in Brussels. Quite cheap actually (19€50 ex VAT/p)

 

[ricothetroll]

First measures :
- Primary : L = 5,8H, DCR = 118,5ohm
- 1st sec : L = 1,13H, DCR = 72,9ohm
- 2nd sec : L = 1,15H, DCR = 72,6ohm

First conclusion : the primary inductance looks a little small for being used in a isolation box that should inteface hazardous systems ! The simulation gave me a limit of 600ohm source for a 20Hz cut off frequency. What do you think ?

Best regards.

Eric

 

[ruffrecords]

With those inductances it is more likely intended for a 150 ohm source. 5.8H is 3dB down at 16Hz with a 600 ohm source but that's ignoring the primary dc resistance. Some of the cheaper manufacturers are happy to specify their low end response as the -3dB point. Since most real world sources these days are well below 159 ohms it does not mateer in many situations.

Cheers

Ian

 

[MatthisD]

First measures :
- Primary : L = 5,8H, DCR = 118,5ohm
- 1st sec : L = 1,13H, DCR = 72,9ohm
- 2nd sec : L = 1,15H, DCR = 72,6ohm

First conclusion : the primary inductance looks a little small for being used in a isolation box that should inteface hazardous systems ! The simulation gave me a limit of 600ohm source for a 20Hz cut off frequency. What do you think ?

Best regards.

Eric

Based on those measurements they look more like 1:1 transformers with secondaries in series.

At what frequency is you meter measuring? in any case you can measure another commonly used transformer (if you have one) and compare that to the measured inductance that has been posted in one of the threads as a reference. The DCR seems very high for such low inductance.

 

[ricothetroll]

Thanx for your answers !

At what frequency is you meter measuring? in any case you can measure another commonly used transformer (if you have one) and compare that to the measured inductance that has been posted in one of the threads as a reference. The DCR seems very high for such low inductance.

I don't know at what frequency my meter is performing the measure. It's actually a cheap meter I bought from ebay a few times ago, that I've had the occasion to test on known inductances and that seemed to work well.

Actually, I must admit that I don't understand that dependance of the inductance against frequency : as far as I understand, the inductance value is what allows us to calculate the reactance at a given frequency, X = 2*pi*f*L. How can inductance then itself be dependant of frequancy, and why ? Still a mystery for me. Any explanation would be welcome

I measured the primary inductance of half the primary of a Neutrik NTL1, the meter displayed about 80H. As the whole primary, that was out of range for my meter, is advertised for >150H at 30Hz, my measurement looks OK.

Some other results, with Visual Analyser, RME Multiface interface, output impedance rated 47ohm, input impedance rated >5kohm :
- @20Hz, the max level is 6dBu (THD=1%, rises fast then, @12.5dBu, THD=30%)
- @50Hz, 12,5dBu, THD = 0,5% (max level I can output with my RME Multiface)
- @1kHz, 12,5dBu, THD = 0,007%
- Cutoff frequency, -3dB : 16,5 kHz

Best regards.