OEP Transformer Max Signal Level (For Mic Pre Output)

[rodabod]

Hi Guys,

I just thought I'd run this one past you to see what your opinions were. I discussed this with Peter (Clintrubber) a while back, but I can't remember a decisive conclusion!

Would the OEP 262A2E 1:2 mic transformer be suitable as a mic pre output transformer?

Rough specs:

Impedance ratio = 600:2.4K
Primary resistance = 2*9.6 = 19.2 Ohms
Secondary resistance = 2*55 = 110 Ohms
"Max Power" = 100mW@300Hz (20dBm), 2.5mW@50Hz (4dBm), 1mW@below 30Hz (0dBm) - for less then 1%THD.

Taken from:

http://www.canford.co.uk/commerce/resources/catdetails/2739.pdf
and http://www.oep.co.uk/

What I was asking myself was, does the power through the transformer not depend on the load at the mic preamp's output? Less current will flow into a 10K input compared to a 600 Ohm input, so therefore less power as I would imagine.

It also boils down to what sort of levels I will be pushing out of the mic circuit. i was planning on using them for an A*PI 312 circuit configured normally as 1:2. Similarly, it also boils down to how much distortion I can tolerate.

Whilst it's always best to try these things in practice, I'd rather not try if someone is of the opinion that this transformer choice is poor. I know that they have been used for this purpose in the past, but I'd like to be more sure.

Cheers,

Roddy

 

[rodabod]

[quote author="kubi"]
Max power is always the same at a certain frequency, just the max voltage changes with the load.
U=sqrt(R*P) (derived from P=U*I and U=R*I)[/quote]

Ok, so for <30Hz @ 10K load, I will have:

V=sqrt(10K*0.001) = 3.33V = 12.6dBu


And for a 600 Ohm load, I will have:

V=sqrt(600*0.001) = 0.775V = 0dBu


So similarly I have more max. ratings, but does anyone have an idea as to how this would perform in practice? I would of course be loading the output with something more in the region of 10K.

Cheers,

Roddy

 

[rodabod]

[quote author="kubi"]
The low DCR (10Ohm) indicates a low number of windings for the primary and slightly more for the secondary (from 55Ohm), thus the inductivity is low as the transformer is meant for lower impedances. Using the transformer within a 10k circuit would worsen the frequency response significantly, especially at the bottom end.[/quote]

Good point Kubi,

So not only might I run into distortion problems, but I may also run into bass loss with the low inductance. Although having said that, those values were for single coils. There will be two wired in series on both primary and secondary.

Maybe I'll need to try this one with a sig. gen. to try it out.

Roddy

 

[Kit]

Would the OEP 262A2E 1:2 mic transformer be suitable as a mic pre output transformer?

Im certainly not an expert on magnetics/inductive components, but isnt the core material of great importance in this situation?

OEP has some interesting products, i dont mean to hijack this thread but has anyone tried this one?

http://www.rsonline.se/cgi-bin/bv/rswww/searchBrowseAction.do?Nr=avl%3ase&N=4294963618&name=SiteStandard&forwardingPage=line&R=2106352&callingPage=/jsp/browse/browse.jsp&BV_SessionID=@@@@0512185519.1169123251@@@@&BV_EngineID=ccdiaddjmdjhhkjcefeceeldgondhgi.0&cacheID=seie

Impressive specs, a little to good to be true perhaps?

 

[recnsci]

[quote author="kubi"]
The low DCR (10Ohm) indicates a low number of windings for the primary and slightly more for the secondary (from 55Ohm), thus the inductivity is low as the transformer is meant for lower impedances. Using the transformer within a 10k circuit would worsen the frequency response significantly, especially at the bottom end.[/quote]

IMHO no.This thing is designed to see 150-600 at primary. Low impedance
drive (like DOA) will drag low end -3dB freq down, not up. Low freq
performance will be determined by DCR+impedance-of-driving-amp and
primary L. One point of concerne here is possible cap coupling of DOA
output and xformer. L_primary and C_couple will form resonant
circuit and thus can cause bumps at low end.
What will be a problem is that if you strap secondaries in series they
will want to see more than 2K. 600 ohm load will shunt some HF
to ground, thus you will loose HF performance.

cheerz
urosh

 

[clintrubber]

[quote author="rodabod"]Would the OEP 262A2E 1:2 mic transformer be suitable as a mic pre output transformer?[/quote]
Nice info above :thumb:

Not a very scientific proof at all, but I guess by now quite a lot of people have used the A262A2E as output-TX for the G1176 & G9 etc.
I also recall an API-like mic-pre with 1731 & the A262A2E as output.
IIRIC Fabio has also some comparisons for various output-TXs on his site.

Cheers,

Peter

 

[gyraf]

Kit:

You can't link to sessions at RS components. They time out.

Jakob E.

 

[dasnevestheo]

Also FETboy preamp uses OEP, anyone heared some ?

 

[ruffrecords]

As a general rule, mic input transformers do not make good output transformers. The normal operating level of a mic input transformer is from -60dBu to about -20dBu. Most often the maximum input level they can take without serious distortion is 0dBu. Out put transformer operating levels are typically between +4dBu and +20dBu so an input transformer used at this level is very likely to saturate.

Cheers

Ian

 

[MagnetoSound]

You can't link to sessions at RS components. They time out.

Especially after eleven years. 

 

[abbey road d enfer]

Ok, so for  <30Hz @ 10K load, I will have:

V=sqrt(10K*0.001) = 3.33V = 12.6dBu

That's not how it works. You have to take intio account the voltage into 600 ohms. Your calculation would be valid if the number of turns was tuned in accordanbce with the actual lod. But no, the actual number of turns is calculated for a 600 ohms load. You have to live with it.


[/quote] And for a 600 Ohm load, I will have:

V=sqrt(600*0.001) = 0.775V = 0dBu
[/quote] This is correct; if you load with 10k (or more) the level will not increase significantly (a little because less resistive loss)