1:10 Transformer for simple mic preamp

Hi I've 18 x 1:10 transformer from an old Italian Company Lombardi.
I'm not sure:
primary white blue - 20 ohm with  center tap
secondary red black  - 1500 ohm

It's 1:10?

I want to build simple but good preamp
Suggestions?
Could work on API preamp?
THANKS!!!

isnt ratio 1:8.66 not 1:10?
√(1500/20)

I'm not sure if you can calculate the ratio like that. The dc resistance also depends on the wire thickness, if pri and sec use different wire types your calculation might be off.

Michael

Hi
today Mr Lombardi says me it's 1:10 mic transformer !
It's possible to use them in API or Neve style preamp?

You could just use it with a simple non-inverting gainstage of bifet input opamp (like OPA134/2134) with the gain you need. Simple and good, for higher gain use two in series (look up Jensen´s twin servo to get the idea).

I'm having a 4-channel preamp made using DaviSound MP4s with Jensen JT-115k 1:10 inputs... 1 or 2 MP4 modules and transformer or transformerless output still to be determined; tests in a couple weeks will determine that. Anyhow, simple preamp.

ilfungo said:

Hi I've 18 x 1:10 transformer from an old Italian Company Lombardi.
primary white blue - 20 ohm with  center tap
secondary red black  - 1500 ohm
I want to build simple but good preamp
Suggestions?
Could work on API preamp?

Click to expand...

the numbers you posted appear reasonable for a 1:10.
suggest the API 312  preamp.
simple and time proven.

Thanks for all suggestions!!!
I will try with API 312!!!
Thanks!!!

Wait... I don't know the specs of an original API input transformer, but based on the EA2622 specs., those Lombardi specs are no where near the same! Why sugggest a 312-style preamp for those?

On the Lombardi, using the secondary as the input and primary as the output would typically be appropriate for a preamp based on the specs given.

Recording Engineer said:

Wait... I don't know the specs of an original API input transformer, but based on the EA2622 specs., those Lombardi specs are no where near the same! Why sugggest a 312-style preamp for those?

On the Lombardi, using the secondary as the input and primary as the output would typically be appropriate for a preamp based on the specs given.

Click to expand...

Why do you think this?
Can you explain?
Thanks!

Could go with something like this. I've made a few with Jensen 1:10's and they sound fantastic.

http://www.ka-electronics.com/images/SSL/ssl_82E01.pdf

Well look at the specs of the EA2622:
http://www.capi-gear.com/catalog/images/gallery/2622/2622-specs.pdf

Not remotely the same.

As for my later paragraph, the typical modern mic transformer output is around 150 ohms. The typical modern rule of thumb is a preamp input of about 10X of the mic output, so that's 1500 ohms.... Though modern transformerless mics can be as low as 50 ohms, so they might respond to around 500 ohm preamp input a bit better.

Recording Engineer said:

Well look at the specs of the EA2622:
http://www.capi-gear.com/catalog/images/gallery/2622/2622-specs.pdf

Not remotely the same.

As for my later paragraph, the typical modern mic transformer output is around 150 ohms. The typical modern rule of thumb is a preamp input of about 10X of the mic output, so that's 1500 ohms.... Though modern transformerless mics can be as low as 50 ohms, so they might respond to around 500 ohm preamp input a bit better.

Click to expand...

Ok but
My problem is :
I don't know the impedance of the transformers but only the resistance..
I know they are input mic transformers and the ratio is 1:10 ( from Mr Lombardi).
Thanks!


Thanks signalflow!
Just some Info
It's correct on attacked image?
T1 And T9?
R8 Link?
Thanks!!!

And yes the transformer input SSL preamp certainly seems more appropriate for these... I had a 1983 6048 (all with transformer input preamps). And while I had 24-ch. of outboard pres, including API and Neve, there was occasions when I simply used all onboard preamps and never regretted it; can't say that about the SSL transformerless preamps!

ilfungo said:

I don't know the impedance of the transformers but only the resistance..

Click to expand...

Im a bit confused... I thought you had said 1500 and 20 but not sure. Can you confirm with Mr. Lombardi?

Resistance 1500 and 20 ohm...

Oh I see... in that case, I'd certainly try as much as possible to find out the impedance of the primary and secondary before deciding what to build with them... But so far with the confirmed 1:10 ratio, SSL or some other  or some FET-type or tube-based pre seems way more appropriate than API or Neve.