Transformer Boxes

Ribbon microphones often have a lower output than condenser and dynamic mics, and so, when recording quieter sound sources, it is important to squeeze every last bit of performance out of the signal chain. Many older ribbon microphones (and some dynamics too) were designed for a 30 ohm or 50 ohm input. However, most modern mics have a higher impedance and consequently most studio preamps give best performance with microphones of 200 to 600 ohms.

So, if you have an old microphone and a modern recording system, you may well need one of our ribbon microphone transformers. This little gadget is designed for interfacing older 30/50 ohm microphones to modern preamp inputs. It contains a high quality custom wound Xaudia transformer and will give a 12dB increase in level without noise penalty. The transformer is housed in a robust metal enclosure, with silver plated Neutrik XLR connectors.

The frequency response is flat from 15Hz to beyond 60KHz, when used into a 2kΩ load.

We can also supply custom transformers for microphones with unusual impedances.

Here are frequency plots for a vintage Reslo RBL microphone connected to an Apogee microphone preamp. The blue line shows the mic connected directly to the preamp, and the red line shows the increase in level with the transformer in-line (click the plot for a higher resolution version).


The measurements show an increase in level of 12dB across the audible range, with no significant change in the frequency response of the microphone.

Melodium 42B (click to enlarge)


Reslo RV microphone (marked “30/50”)


Other very low impedance mics include:
Grampian ribbon mics (including GR1/L and GR2/L)
Cadenza ribbon microphones
RSA & Selmer ribbon mics
STC 4033, and some models of the 4038
Altec and Western Electric ribbon microphones
EMI/HMV ribbon microphones. (20 ohms)

When ordering, please tell us your intended applications so that we can supply the best ratio for your mic.

Some user comments on our transformer boxes
“I’m in the studio, testing the EMI microphone with your transformer and now it’s perfectly usable, even on quiet instruments! Noise floor is sensibly decreased. This is going to make a huge difference for me, thanks a lot!”
Pierluigi Ballarin, Italy

“I am very pleased with your work – the old Zephyr has more gain with the transformer and sounding great.
Luke R Davies, Wangaratta, Australia

“It made a huge difference, I’ve never felt comfortable with the level of hiss I got trying to use the mic with my Euphonix (and it’s a pretty clean sounding desk) but I recorded a great guitar solo, Fender Strat through a Fender Bassman with just the one [30 ohm] STC 4038 about a metre away in a small room.. Delightful. You do good work!”
Chris Porter, UK

“Hugely impressive and ever efficient just like your service. Preamps cruising now.”
Mark Kelly, NI

“It’s nice to have the [extra] gain from the Altecs when the preamp has nothing more to give.”
Matt Howe, UK.

“The impedance matching transformers have been a bit of a revelation too. I can use them with the different 30-50 ohm impedance microphones I have and they really increase the clean gain significantly. and allow me to make a much more versatile use of them. I love the sound of ribbon microphones on soft acoustic instruments like glockenspiel, toy piano, acoustic guitar, mandolin, etc.. and the transformers allow me to do this with less fear of preamp hiss.”
Santiago Calvo Ramos, Otherdays music

“Hey Stewart, great work on the ribbon transformers. I have tried them out on all of my ribbons and they make a huge difference to every one, boosting level and cleaning the signal. My [Grampian] GR2/M blue label sounds fab. The bigger mics, eg the 4038, varacoustic and especially the EMI have all benefitted loads.”
Mark Stevens, UK