OEP transformer measurements

Hi!
Did some tests last night, since the OEP A262A2E is a cheap alternative for DIY pre's.
Will do more tests later on too see how the 1:12.9 can be improved.

Best results where when using only one prim / sec windings. See redings with the two sec windings in serie.
Zobel network is a 4k7 resistor in serie with a 3n3 styrol cap over a 3k3 resistor over the secondary winding.
Did a lot of testings with different values for the zobel resistor and cap but this was the best I could get it.

Since some OEP people use to work at Belclere who did transformers for Neve I will do some tests on the Belclere EM20015 / TF10015 to see if they are similare.
The Belclere looks very much like the OEP and was used as input transformer in some versions of Neve's last class A pre 31102. (1978) Also used in the 33609 limiter/compressor

OEP at RS Components 210-6425
OEP at Farnell 149-156

Thanks, Thomas!

Very good and useable info indeed!

I too suspect that the OEP's are underestimated players in our field..

What was your generator impedance? That low-end looks waaay better that the datasheet specs..?

Jakob E.

Did feed it direct from the soundcard (M-Audio Áudiopfile 192) so I guess the impedance is around is below 100ohm.

Since I haven't moved the set-up from a my lab bench i did put in 100ohm in serie with the prime and as you suspected the low-end isn't that good anymore, now it's down 1.5dB at 30Hz and almost 2dB at 20 Hz.
I guess it will work best with a ribbon mic then?

I think you might mean the A262A3E as it is 1+1:6.45+6.45 ratio. As the A262A2E is only 1+1:2+2.

Below are some transient graphs of them compared to original marinair types which might be helpful.



More info on both of these transformers can be found here.

http://www.jlmaudio.com/Neve%20transformer%20info.htm

Joe
www.jlmaudio.com

I too suspect that the OEP's are underestimated players in our field..

Click to expand...

I just like ' em a lot!!

thanks for the data TK!
:thumb:

[quote author="Tekay"] I guess it will work best with a ribbon mic then?[/quote]

No, I don't think they'll be limited to that. Any decent-output-impedance microphone circuit should be able to drive the low end through this quite well.

Jakob E.

Joe! You're right! This is the 1+1:2+2 transformer! Farnell sent me the wrong type and I didn't check it before I put it in the can!

Will order the right type so I can lab a little more later on!

Just curious: has the wild man with hacksaw and welding torch (sorry, CJ !) looked what's inside the OEPs already?

JH.

Nice TK!

When you get the right type, try terminating the transformer like this:

1:6.45 - terminate with a 62k resistor at the secondary, and use 150R in series with he signal, at the primary.

1:12.90 - terminate with a 250k resistor at the secondary and use a 150R in series with the signal, at the primary.

I think this would reflect better how those are used in real world.

For the NEVE test, wire it as 2:3.225, terminate with a 12k at the secondary and use a 120R resistor in series at the input.

Just some thoughts. Let me know if you do not agree...

By the way, What are you using as a tester (analyser)?