Transformer Matchbox 50 to 600 ohms

£79.17 (£79.17+VAT)

Transformer box with XLR sockets for connecting vintage microphones to modern preamps. Get the best efficiency and signal-to-noise performance from your ribbon mics.

The standard 50 to 600 ohm model will suit most applications but custom options are available – please ask.


Ribbon microphones often generate a lower output than condenser and dynamic mics. It is important to squeeze every last bit of performance out of the signal chain when recording quieter sound sources, 

Many older ribbon and dynamic microphones  have a 30 ohm or 50 ohm output impedance. However, most modern mics have a higher impedance and consequently many studio preamps give best performance with microphones of 200 to 600 ohms.

The transformer matchbox will connect older 30/50 ohm microphones to modern preamp inputs. It contains a high quality, custom wound Extinct Audio transformer and will give a 12dB increase in level without noise penalty. The transformer is housed in a robust metal enclosure, with gold plated Neutrik XLR connectors.

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

We can also supply custom transformers for microphones with less common impedances.


  • Gold plated Neutrik XLR sockets
  • Rugged aluminium housing
  • 50 ohm input, 600 ohm output impedance.
  • Approximately +12dB increase in output voltage
  • Passive transformer. No active circuitry and no power required.
  • May be placed close to the microphone or close to the preamp.

Suitable for all 30 and 50 ohm microphones including Melodium 42B, STC 4033, Altec and Western Electric 639 birdcage mics,  older STC 4038, and many others.

Please ask about your application.

Some customer feedback on our transformer boxes

“Works beautifully. Transformative on the STC 4021 – the gain is useful, but the flattening of the frequency response makes the biggest difference. Thanks very much!” John Machling, UK

“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

Additional information

Weight0.3 kg

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