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Xaudia offer microphone re-ribboning and repair services.

2020/06/06

Melodium 42B replacement magnets

Eleven Melodium 42Bs in for service at Xaudia

We now stock magnet assemblies to replace weak or cracked magnets in Melodium 42B ribbon microphones. *

Replacement magnet assembly for Melodium 42B ribbon microphones

The horseshoe type magnets found in some of these mics tend to hold their field well and rarely fail. However, I have occasionally encountered examples where the magnets have cracked and lost some of their strength. This may happen if the mounting screws are overtightened or the microphone has been abused.



Around half of the 42Bs use block magnets with a carrier bar to complete the magnetic loop. These are more prone to losing their field especially if they are removed from the microphone for some reason. It is hard to predict how these will behave. Luckily we can measure them and see if they are up to scratch. A healthy microphone should show above 3000 Gauss in the ribbon gap to give good signal to noise performance.


In this example, the field is down to around 2400 Gauss, which is at about 80% of where it should be. That amounts to 2dB loss of output - not yet a disaster but may be heading that way. With the new assembly in place we measure around 6000 Gauss, which is up + 6dB on a 'good' stock Melodium 42B.

*Magnet failure is rare. A bad ribbon is the most common cause of a weak signal in these microphones, and would be worthwhile testing the ribbon before embarking on any kind of magnet service.

2020/05/30

Sennheiser MD409 foam failure

This seems to be a common issue with old Sennheiser MD409 and similar microphones.

Sennheiser MD409 foam failure


The capsule is held in place by a block of polyurethane foam, which slowly decomposes over the decades, especially if the microphone has been in use in a sweaty rock venue.

Sennheiser MD409 new foam


If left for too long, that capsule will rattle around and there is a risk of more serious damage. the foam can also become sticky and contaminate the capsule diaphragm. If things have not gone too far, it is an easy job to cut some new foam, clean the grills and then the mic is ready for another shift in the studio.

MD409 pair with new foam cleaned and ready to rock

2020/05/23

Lustraphone VR53 upgrade

It has been a long time since my last blog post!

This is mainly because the launch of Extinct Audio took up much more of my time and energy than I had ever imagined. But I have missed this blog and will be posting a bit more often in the coming weeks and months. Thanks for your support.

Lustraphone VR53 ribbon microphone

This week I have been working on a few Lustraphone VR53 ribbon microphones. I have never been very enthusiastic about these mics because generally they have a weak output and can sound dark and flabby. Replacing the ribbons and transformers will get the mic so far, but they never quite get up to the performance of other British ribbon mics like the Reslos and Grampians. Which is a shame because they have a unique vintage design and look as though they should be good!

Part of the problem is the magnetic circuit. The two horseshoe magnets provide the field which is conducted (rather inefficiently) around a steel structure to the ribbon. This gives a field around 1500 to 2000 gauss. (For comparison, the field in a healthy Reslo would typically be around 4000 gauss.)

Milling the pole pieces to make room for new magnets.

The steel pole structure is the limiting factor here and so swapping the horseshoe magnets gives only marginal improvements. For this upgrade I made a decision to mill out the pole pieces and fit some strong magnets right next to the ribbon.



The difference is impressive, bringing the field across the ribbon to 6000 gauss, which should provide about +9 to +12dB increase  in output voltage. With a new ribbon fitted. the output and signal to noise were improved overall by 20dB. Now it can give the other microphones a good run for their money.

Before and after... new magnets and ribbons.

As an aside, the stock 200 ohm transformer in this example is actually pretty good and don't need to be replaced. The 30 ohm and high impedance models are not very well suited to a modern studio and in those cases it is worth swapping them out for a more sensible tranny.

You can read my earlier post about the Lustraphone VR53 microphones here.