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Thanks for all replies... well, I'll leave the Lundahl on the bookshelf then 

Definition of EIN here: https://www.sweetwater.com/insync/ein/ KH

Thanx Klaus, let me try to explain EIN / Equivalent Input Noise more simply:

EIN is the noise of an amplifier looked at, as if all of its noise is an external voltage applied to its input.
This takes the amp’s gain out of the equation, as gain doesn’t change this input signal.


Caused by thermic movement of atoms, even a resistor itself generates noise.
200 Ohm generates 0.26 uV = -129 dBu noise voltage, the lowest EIN possible with a normal dynamic microphone, even if the amp is cooled with helium.

Quadrupling the 200 Ohm resistor doubles the noise.
(Noise adds “geometrically”, not “arithmetically”, as noise is “uncorrelated”).

Unfortunately a transformer transforms:
• the voltage by its ratio,
• but the resistance by the square of it’s input to output ratio.

The Lundahl LL1538 wired 1:5 e.g.:
• Voltage 5 times,
• Resistance 25 times, and therefore noise 11.2 times.

This means, at a close to perfect mic-pre, the transformer does worsen the noise situation.
Only with a bad pre, or a pre not made for mics, the Lundahl transformer has an advantage.


EDIT: Had to correct the noise calculations.

I found a Lundahl LL1538 transformer here and a doubt arose about it. Would there be any way to connect it at the output of a dynamic microphone (such as Shure SM7B, Electrovoice Re20) and thus increase the signal level? I thought of something that was plug'n play using xlr male and female connectors. Has anyone ever tried something like?

Can be done.

• The transformer needs to placed as close as possible to the mic-preamp, with as short cable as possible, or you will get very significant changes in frequency response due to the cable capacitance resonating with the transformer inductance.

• The mic preamp needs to have an input impedance of 6 kOhm when wired for 2.5x-transformation, 25 kOhm when wired for 5x-transformation, to maintain an load impedance of no lower than 1 kOhm to the mic.
This recommendation is way higher than most mic-preamps offer.

Else most mics will sound significantly different.


Probably you will not gain much better S/N ratio in most configurations.
The transformer increases the impedance that shunts the mic-pre’s input by the square of the transformation ratio (x6.25 or x25), increasing the mic-preamp’s EIN.

Additionally, mic-pre‘s typically have lower EIN with higher gain.
So lowering the gain does not proportionally lower the noise.

Definition of EIN here: https://www.sweetwater.com/insync/ein/ KH

For further research on this 1:5 / 1:2.5 transformer and its applications:
http://www.lundahl.se/wp-content/uploads/datasheets/1538_8xl.pdf

I found a Lundahl LL1538 transformer here and a doubt arose about it:

Would there be any way to connect it at the output of a dynamic microphone (such as Shure SM7B, Electrovoice RE20) and thus increase the signal level?

I thought of something that was plug'n play, using XLR male and female connectors. Has anyone ever tried something like this?

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Sold in sets of one male and one female connector.

After 72 hours of leaving the mic uncovered in a well ventilated room, the smell has dissipated. 
I no longer smell anything, so I think it's all good.

I agree in principle, but VM&P vapor near polyester capsule? I see no problem.

Don‘t use any kind of solvents close to the mic capsule.

If you ever watched the diaphragm crinkle and loose tension ONLY FROM THE VAPOR you know what I mean.

A rubber eraser usually removes stuff like the mentioned.

Thanks for the quick reply, Klaus and thanks for the tip on naphtha.
Yes the smell is from the very odius Goo Gone.